Ultrafast spin-polarization control of Dirac fermions in topological insulators
Sánchez-Barriga, J.; Golias, E.; Varykhalov, A.; Braun, J.; Yashina, L. V.; Schumann, R.; Minár, J.; Ebert, H.; Kornilov, O.; Rader, O.
2016-04-01
Three-dimensional topological insulators (TIs) are characterized by spin-polarized Dirac-cone surface states that are protected from backscattering by time-reversal symmetry. Control of the spin polarization of topological surface states (TSSs) using femtosecond light pulses opens novel perspectives for the generation and manipulation of dissipationless surface spin currents on ultrafast time scales. Using time-, spin-, and angle-resolved spectroscopy, we directly monitor the ultrafast response of the spin polarization of photoexcited TSSs to circularly polarized femtosecond pulses of infrared light. We achieve all-optical switching of the transient out-of-plane spin polarization, which relaxes in about 1.2 ps. Our observations establish the feasibility of ultrafast optical control of spin-polarized Dirac fermions in TIs and pave the way for optospintronic applications at ultimate speeds.
Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs.
Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S; Neupane, Madhab; Chang, Guoqing; Yaji, Koichiro; Yuan, Zhujun; Zhang, Chenglong; Kuroda, Kenta; Bian, Guang; Guo, Cheng; Lu, Hong; Chang, Tay-Rong; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Komori, Fumio; Kondo, Takeshi; Shin, Shik; Lin, Hsin; Jia, Shuang; Hasan, M Zahid
2016-03-04
A Weyl semimetal is a new state of matter that hosts Weyl fermions as quasiparticle excitations. The Weyl fermions at zero energy correspond to points of bulk-band degeneracy, called Weyl nodes, which are separated in momentum space and are connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure the spin polarization of the Fermi arcs in the first experimentally discovered Weyl semimetal TaAs. Our spin data, for the first time, reveal that the Fermi arcs' spin-polarization magnitude is as large as 80% and lies completely in the plane of the surface. Moreover, we demonstrate that the chirality of the Weyl nodes in TaAs cannot be inferred by the spin texture of the Fermi arcs. The observed nondegenerate property of the Fermi arcs is important for establishing its exact topological nature, which reveals that spins on the arc form a novel type of 2D matter. Additionally, the nearly full spin polarization we observed (∼80%) may be useful in spintronic applications.
The polarization function of a finite number of confined spin polarized fermions
Lemmens, Lucien F.; Saeys, Dirk; Brosens, Fons; Devreese, Jozef T.
2001-03-01
The Fourier transform of an inhomogeneous two-point correlation function, in space and Euclidean time, is derived for a limited number of spin polarized fermions in an external potential. The formulation is based on the many-body generalization of the Feynman-Kac functional. Special attention is given to the finite number aspects and the implications thereof for the fugacity. An analysis of the correlation function in terms of single particle propagators is obtained, leading to an occupation function representation. For the harmonic model, the temporal Fourier components of the two-point correlation matrix are worked out in the low temperature limit.
Bulgakov, Evgeny N.; Sadreev, Almas F.
2016-07-01
We consider the trapping of electrons with a definite spin polarization by bound states in the continuum (BSC) in the open Aharonov-Bohm rings in the presence of the Rashba spin-orbit interaction (RSOI). Neglecting the Zeeman term we show the existence of BSCs in the one-dimensional ring when the eigenstates of the closed ring are doubly degenerate. With account of the Zeeman term BSCs occur only at the points of threefold degeneracy. The BSCs are found in the parametric space of flux and RSOI strength in close pairs with opposite spin polarization. Thereby the spin polarization of electrons transmitted through the ring can be altered by minor variation of magnetic or electric field at the vicinity of these pairs. Numerical simulations of the two-dimensional open ring show similar results for the BSCs. Encircling the BSC points in the parametric space of the flux and the RSOI constant gives rise to a geometric phase.
Fermionic bound states in distinct kinklike backgrounds
Energy Technology Data Exchange (ETDEWEB)
Bazeia, D. [Universidade Federal da Paraiba, Departamento de Fisica, Joao Pessoa, Paraiba (Brazil); Mohammadi, A. [Universidade Federal de Campina Grande, Departamento de Fisica, Caixa Postal 10071, Campina Grande, Paraiba (Brazil)
2017-04-15
This work deals with fermions in the background of distinct localized structures in the two-dimensional spacetime. Although the structures have a similar topological character, which is responsible for the appearance of fractionally charged excitations, we want to investigate how the geometric deformations that appear in the localized structures contribute to the change in the physical properties of the fermionic bound states. We investigate the two-kink and compact kinklike backgrounds, and we consider two distinct boson-fermion interactions, one motivated by supersymmetry and the other described by the standard Yukawa coupling. (orig.)
Some Improved Nonperturbative Bounds for Fermionic Expansions
Energy Technology Data Exchange (ETDEWEB)
Lohmann, Martin, E-mail: marlohmann@gmail.com [Universita di Roma Tre, Dipartimento di Matematica (Italy)
2016-06-15
We reconsider the Gram-Hadamard bound as it is used in constructive quantum field theory and many body physics to prove convergence of Fermionic perturbative expansions. Our approach uses a recursion for the amplitudes of the expansion, discovered in a model problem by Djokic (2013). It explains the standard way to bound the expansion from a new point of view, and for some of the amplitudes provides new bounds, which avoid the use of Fourier transform, and are therefore superior to the standard bounds for models like the cold interacting Fermi gas.
Fermion Bound States Around Skyrmions in Doped Antiferromagnets
Institute of Scientific and Technical Information of China (English)
寇谡鹏
2003-01-01
We show the skyrmion effects in doped antiferromagnets for the uniform flux phase. The low-energy effective theory of the t′-J model can be mapped onto the massive quantum electrodynamics. There exist Fermion bound states around skyrmions. For each sublattice, there exist induced fractional fermion numbers around the skyrmions. The total induced fermion number is zero due to the "cancelling effect" between two sublattices with opposite charges.
Relativistic bound-state equations for fermions with instantaneous interactions
Suttorp, L.G.
1979-01-01
Three types of relativistic bound-state equations for a fermion pair with instantaneous interaction are studied, viz., the instantaneous Bethe-Salpeter equation, the quasi-potential equation, and the two-particle Dirac equation. General forms for the equations describing bound states with arbitrary
When measured spin polarization is not spin polarization
Dowben, P. A.; Wu, Ning; Binek, Christian
2011-05-01
Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO2 and Cr2O3 illustrate some of the complications which hinders comparisons of spin polarization values.
Higgs interchange and bound states of superheavy fermions
Indian Academy of Sciences (India)
M De Sanctis
2013-09-01
Hypothetical superheavy fourth-generation fermions with a very small coupling with the rest of the Standard Model can give rise to long enough lived bound states. The production and the detection of these bound states would be experimentally feasible at the LHC. Extending, in the present study, the analysis of other authors, a semirelativistic wave equation is solved using an accurate numerical method to determine the binding energies of these possible superheavy fermion-bound states. The interaction given by the Yukawa potential of the Higgs boson exchange is considered; the corresponding relativistic corrections are calculated by means of a model based on the covariance properties of the Hamiltonian. We study the effects given by the Coulomb force. Moreover, we calculate the contributions given by the Coulombic and confining terms of the strong interaction in the case of superheavy quark bound states. The results of the model are critically analysed.
When measured spin polarization is not spin polarization
Energy Technology Data Exchange (ETDEWEB)
Dowben, P A; Wu Ning; Binek, Christian, E-mail: pdowben@unl.edu [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0299 (United States)
2011-05-04
Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO{sub 2} and Cr{sub 2}O{sub 3} illustrate some of the complications which hinders comparisons of spin polarization values. (viewpoint)
When measured spin polarization is not spin polarization.
Dowben, P A; Wu, Ning; Binek, Christian
2011-05-04
Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO(2) and Cr(2)O(3) illustrate some of the complications which hinders comparisons of spin polarization values. © 2011 IOP Publishing Ltd
Encrypting Majorana fermion qubits as bound states in the continuum
Guessi, L. H.; Dessotti, F. A.; Marques, Y.; Ricco, L. S.; Pereira, G. M.; Menegasso, P.; de Souza, M.; Seridonio, A. C.
2017-07-01
We theoretically investigate a topological Kitaev chain connected to a double quantum-dot (QD) setup hybridized with metallic leads. In this system we observe the emergence of two striking phenomena: (i) a decrypted Majorana fermion (MF) qubit recorded over a single QD, which is detectable by means of conductance measurements due to the asymmetrical MF-qubit leaked state into the QDs; (ii) an encrypted qubit recorded in both QDs when the leakage is symmetrical. In such a regime, we have a cryptographylike manifestation, since the MF qubit becomes bound states in the continuum, which is not detectable in conductance experiments.
Dynamic nuclear spin polarization
Energy Technology Data Exchange (ETDEWEB)
Stuhrmann, H.B. [GKSS-Forschungszentrum Geesthacht GmbH (Germany)
1996-11-01
Polarized neutron scattering from dynamic polarized targets has been applied to various hydrogenous materials at different laboratories. In situ structures of macromolecular components have been determined by nuclear spin contrast variation with an unprecedented precision. The experiments of selective nuclear spin depolarisation not only opened a new dimension to structural studies but also revealed phenomena related to propagation of nuclear spin polarization and the interplay of nuclear polarisation with the electronic spin system. The observation of electron spin label dependent nuclear spin polarisation domains by NMR and polarized neutron scattering opens a way to generalize the method of nuclear spin contrast variation and most importantly it avoids precontrasting by specific deuteration. It also likely might tell us more about the mechanism of dynamic nuclear spin polarisation. (author) 4 figs., refs.
Temperature dependence of the spin polarization in the fractional quantum Hall effects
Murthy, Ganpathy
2000-01-01
Using a Hamiltonian formulation of Composite Fermions that I recently developed with R. Shankar, I compute the dependence of the spin polarization on the temperature for the translationally invariant fractional quantum Hall states at $\
Modulated spin polarization in nanostructures
Energy Technology Data Exchange (ETDEWEB)
Wedekind, Sebastian; Oka, Hirofumi; Rodary, Guillemin; Sander, Dirk; Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)
2009-07-01
Deposition of 0.7 ML Co onto the clean Cu(111) surface at room temperature leads to the formation of triangular two atomic layers high Co islands. We study the electronic properties of these nano islands by scanning tunneling microscopy (STM) and spectroscopy (STS) at 7 K. We observe pronounced spatial modulation patterns in the local density of states (LDOS) within the islands due to electron confinement. We explore the magnetic properties of the very same islands by spin-polarized STM and STS in a magnetic field of up to 4 T. Our spin-polarized measurements in field clearly identify the parallel and anti-parallel spin orientation states of tip and sample. This enables us to measure the spatial distribution of the spin polarization within single Co islands. We find that the spin polarization is spatially modulated. Our results are discussed in view of recent theoretical predictions.
Mass spectrum and bounds on the couplings in Yukawa models with mirror-fermions
Energy Technology Data Exchange (ETDEWEB)
Lin, L.; Muenster, G.; Plagge, M. [Muenster Univ. (Germany). Inst. fuer Theoretische Physik 1; Montvay, I.; Wittig, H. [Deutsches Elektronen-Synchrotron, DESY, Hamburg (Germany); Frick, C.; Trappenberg, T. [HLRZ, Juelich (Germany)
1992-12-01
The SU(2){sub L}xSU(2){sub R} symmetric Yukawa model with mirror-fermions in the limit where the mirror-fermion is decoupled is studied both analytically and numerically. The bare scalar self-coupling {lambda} is fixed at zero and infinity. The phase structure is explored and the relevant phase transition is found to be consistent with a second order one. The fermionic mass spectrum close to that transition is discussed and a first non-perturbative estimate of the influence of fermions on the upper and lower bounds on the renormalized scalar self-coupling is given. Numerical results are confronted with perturbative predictions. (orig.).
Mass Spectrum and Bounds on the Couplings in Yukawa Models With Mirror-Fermions
Lin, L; Plagge, M; Montvay, István; Wittig, H; Frick, C; Trappenberg, T
1993-01-01
The $\\rm SU(2)_L\\otimes SU(2)_R$ symmetric Yukawa model with mirror-fermions in the limit where the mirror-fermion is decoupled is studied both analytically and numerically. The bare scalar self-coupling $\\lambda$ is fixed at zero and infinity. The phase structure is explored and the relevant phase transition is found to be consistent with a second order one. The fermionic mass spectrum close to that transition is discussed and a first non-perturbative estimate of the influence of fermions on the upper and lower bounds on the renormalized scalar self-coupling is given. Numerical results are confronted with perturbative predictions.
Mass spectrum and bounds on the couplings in Yukawa models with mirror-fermions
Energy Technology Data Exchange (ETDEWEB)
Lin, L. (Inst. f. Theor. Physik I, Univ. Muenster (Germany)); Muenster, G. (Inst. f. Theor. Physik I, Univ. Muenster (Germany)); Plagge, M. (Inst. f. Theor. Physik I, Univ. Muenster (Germany)); Montvay, I. (Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany)); Wittig, H. (Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany)); Frick, C. (HLRZ, Juelich (Germany)); Trappenberg, T. (HLRZ, Juelich (Germany))
1993-03-01
The SU(2)[sub L] x SU(2)[sub R] symmetric Yukawa model with mirror-fermions in the limit where the mirror-fermion is decoupled is studied both analytically and numerically. The bare scalar self-coupling [lambda] is fixed at zero and infinity. The phase structure is explored and the relevant phase transition is found to be consistent with a second order one. The fermionic mass spectrum close to that transition is discussed and a first non-perturbative estimate of the influence of fermions on the upper and lower bounds on the renormalized scalar self-coupling is given. Numerical results are confronted with perturbative predictions. (orig.)
Tunable all electric spin polarizer
Bhandari, Nikhil K.
To realize the full potential of spin-based devices, ways must be found to inject, manipulate, and detect the spin of the electron by purely electrical means. Previously, our group has shown that a quantum point contact (QPC) with lateral spin orbit coupling (LSOC) can be used to create a strongly spin-polarized current by purely electrical means. The LSOC results from the lateral in-plane electric field created by the confining potential in QPCs with in-plane side gates (SGs). Strongly spin-polarized currents can be generated by tuning the asymmetric bias voltages on the side gates. A conductance anomaly in the form of a plateau at conductance G ≅ 0.5G0 (where G 0 = 2e2/h) was observed in the ballistic conductance of a QPC based in the absence of magnetic field - which was established to be a signature of complete spin polarization. A Non-Equilibrium Green's Function (NEGF) analysis was used to model a small QPC and three ingredients were found to be essential to generate a strong spin polarization: (1) LSOC, (2) an asymmetric lateral confinement, and (3) a strong electron-electron (e-e) interaction. We have also shown that all-electric control of spin polarization can be achieved for different materials, electron mobility, heterostructure design, QPC dimensions and strength of LSOC. Our previous experimental and theoretical results have also found the presence of other conductance anomalies (i.e., at values different from 0.5 G0 ) and the main reason for these occurrences was shown to be due to the influence of surface roughness scattering. In this thesis, we address the important technological challenge to better control the location of the conductance anomalies in QPCs and create a tunable all-electric spin polarizer based on a QPC with four gates, i.e., with two in-plane SGs in series. Here, the first pair of SGs, near the source, is asymmetrically biased to create spin polarization in the QPC channel. The second set of gates, near the drain, is
Bound states for fermions in the gauge Aharonov-Bohm field
Energy Technology Data Exchange (ETDEWEB)
Voropaev, S.A.; Galtsov, D.V.; Spasov, D.A. (Dept. of Theoretical Physics, Moscow State Univ. (USSR))
1991-09-05
In this paper we discuss some interesting properties of the Aharonov-Bohm interaction for relativistic spin-one-half particles. We will show that the AB potential is powerful enough to create bound states. We will then discuss the wave function, spin-coefficients and the energy level for the bound states of the fermions in the gauge AB field. (orig.).
Spin-polarized spin excitation spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J, E-mail: lothseb@us.ibm.com, E-mail: heinrich@almaden.ibm.com [IBM Research Division, Almaden Research Center, San Jose, CA 95120 (United States)
2010-12-15
We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu{sub 2}N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.
Bound states of massive fermions in Aharonov-Bohm-like fields
Energy Technology Data Exchange (ETDEWEB)
Khalilov, V.R. [Moscow State University, Faculty of Physics, Moscow (Russian Federation)
2014-01-15
Bound states of massive fermions in Aharonov-Bohm (AB)-like fields have analytically been studied. The Hamiltonians with the (AB)-like potentials are essentially singular and therefore require specification of a one-parameter self-adjoint extension. We construct self-adjoint Dirac Hamiltonians with the AB potential in 2+1 dimensions that are specified by boundary conditions at the origin. It is of interest that for some range of the extension parameter the AB potential can bind relativistic charged massive fermions. The bound-state energy is determined by the AB magnetic flux and depends upon the fermion spin and extension parameter; it is a periodical function of the magnetic flux. We also construct self-adjoint Hamiltonians for the so-called Aharonov-Casher (AC) problem, show that nonrelativistic neutral massive fermions can be bound by the (AC) background, determine the range of the extension parameter in which fermion bound states exist, and find their energies as well as wave functions. (orig.)
Melix, Patrick; Rüger, Robert; Heine, Thomas
2016-01-01
We evaluate the performance of spin-polarized DFTB within the SCC-DFTB (also known as DFTB2) model. The method has been implemented in the ADF modeling suite. We briefly review how spin polarization is incorporated into the DFTB2 method and validate the method in terms of structural parameters and energy using the GMTKN30 test set, from which we used 288 spin-polarized systems.
Effects of a potential fourth fermion generation on the Higgs boson mass bounds
Gerhold, P; Kallarackal, J
2010-01-01
We study the effect of a potential fourth fermion generation on the upper and lower Higgs boson mass bounds. This investigation is based on the numerical evaluation of a chirally invariant lattice Higgs-Yukawa model emulating the same Higgs-fermion coupling structure as in the Higgs sector of the electroweak Standard Model. In particular, the considered model obeys a Ginsparg-Wilson version of the underlying $SU(2)_L\\times U(1)_Y$ symmetry, being a global symmetry here due to the neglection of gauge fields in this model. We present our results on the modification of the upper and lower Higgs boson mass bounds induced by the presence of a hypothetical very heavy fourth quark doublet. Finally, we compare these findings to the standard scenario of three fermion generations.
Effects of a potential fourth fermion generation on the upper and lower Higgs boson mass bounds
Gerhold, Philipp; Kallarackal, Jim
2010-01-01
We study the effect of a potential fourth fermion generation on the upper and lower Higgs boson mass bounds. This investigation is based on the numerical evaluation of a chirally invariant lattice Higgs-Yukawa model emulating the same Higgs-fermion coupling structure as in the Higgs sector of the electroweak Standard Model. In particular, the considered model obeys a Ginsparg-Wilson version of the underlying ${SU}(2)_L\\times {U}(1)_Y$ symmetry, being a global symmetry here due to the neglection of gauge fields in this model. We present our results on the modification of the upper and lower Higgs boson mass bounds induced by the presence of a hypothetical very heavy fourth quark doublet. Finally, we compare these findings to the standard scenario of three fermion generations.
Interacting quantum walkers: two-body bosonic and fermionic bound states
Krapivsky, P. L.; Luck, J. M.; Mallick, K.
2015-11-01
We investigate the dynamics of bound states of two interacting particles, either bosons or fermions, performing a continuous-time quantum walk on a one-dimensional lattice. We consider the situation where the distance between both particles has a hard bound, and the richer situation where the particles are bound by a smooth confining potential. The main emphasis is on the velocity characterizing the ballistic spreading of these bound states, and on the structure of the asymptotic distribution profile of their center-of-mass coordinate. The latter profile generically exhibits many internal fronts.
Light Fermion Finite Mass Effects in Non-relativistic Bound States
Eiras, D; Eiras, Dolors; Soto, Joan
2000-01-01
We present analytic expressions for the vacuum polarization effects due to a light fermion with finite mass in the binding energy and in the wave function at the origin of QED and (weak coupling) QCD non-relativistic bound states. Applications to exotic atoms, \\Upsilon (1s) and t\\bar{t} production near threshold are briefly discussed.
Photoassociation of spin polarized Chromium
Rührig, Jahn; Julienne, Paul S; Tiesinga, Eite; Pfau, Tilman
2015-01-01
We report the homonuclear photoassociation (PA) of ultracold ${}^{52}\\mathrm{Cr}$ atoms in an optical dipole trap. This constitutes the first measurement of PA in an element with total electron spin $\\tilde{S}>1$. Although Cr, with its ${}^{7}\\mathrm{S}_{3}$ ground and ${}^{7}\\mathrm{P}_{4,3,2}$ excited states, is expected to have a complicated PA spectrum we show that a spin polarized cloud exhibits a remarkably simple PA spectrum when circularly polarized light is applied. Over a scan range of 20 GHz below the ${}^{7}\\mathrm{P}_{3}$ asymptote we observe two distinct vibrational series each following a LeRoy-Bernstein law for a $C_3 / R^{3}$ potential with excellent agreement. We determine the $C_3$ coefficients of the Hund's case c) relativistic adiabatic potentials to be -1.83$\\pm$0.02 a.u. and -1.46$\\pm$0.01a.u.. Theoretical non-rotating Movre-Pichler calculations enable a first assignment of the series to $\\Omega=6_u$ and $5_g$ potential energy curves. In a different set of experiments we disturb the sel...
Extended bound states and resonances of two fermions on a periodic lattice
Blaer, A S; Chernyshov, O
1997-01-01
The high-$T_c$ cuprates are possible candidates for d-wave superconductivity, with the Cooper pair wave function belonging to a non-trivial irreducible representation of the lattice point group. We argue that this d-wave symmetry is related to a special form of the fermionic kinetic energy and does not require any novel pairing mechanism. In this context, we present a detailed study of the bound states and resonances formed by two lattice fermions interacting via a non-retarded potential that is attractive for nearest neighbors but repulsive for other relative positions. In the case of strong binding, a pair formed by fermions on adjacent lattice sites can have a small effective mass, thereby implying a high condensation temperature. For a weakly bound state, a pair with non-trivial symmetry tends to be smaller in size than an s-wave pair. These and other findings are discussed in connection with the properties of high-$T_c$ cuprate superconductors.
Lorentz violation bounds from torsion trace fermion sector and galaxy M51 data and chiral dynamos
Energy Technology Data Exchange (ETDEWEB)
Garcia de Andrade, L.C. [IF-UERJ, Departamento de Fisica Teorica, Rio de Janeiro, RJ (Brazil)
2017-06-15
Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10{sup -31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10{sup -26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10{sup -24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10{sup -24} and 10{sup -23} Ge
Lorentz violation bounds from torsion trace fermion sector and galaxy M 51 data and chiral dynamos
Garcia de Andrade, L. C.
2017-06-01
Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10^{-31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10^{-26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10^{-24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10^{-24} and 10^{-23} GeV which are not so
Theoretical Bounds on New Four-Fermion Interactions and TeV Scale Physics
Bhattacharya, Tanmoy; Joseph, Anosh; Lin, Huey-Wen; Cohen, Saul D
2012-01-01
The standard model weak interactions can be described by four-fermion V-A operators at low energies. New physics at the TeV scale can, however, generate the other Lorentz structures. In this talk, we review the constraints on such interactions from nuclear and hadronic decays, as well as from collider searches. Currently the most stringent bounds come from the analysis of the 0+ to 0+ nuclear and the pi to e nu gamma radiative pion decays. In the near future, the ultracold neutron beta decay experiments and the direct LHC measurements will compete in setting the most stringent bounds, provided, however, that the neutron-to-proton non-perturbative transition matrix elements can be calculated to a level of 10-20% accuracy.
Determining the spin-orbit coupling via spin-polarized spectroscopy of magnetic impurities
Kaladzhyan, V.; Simon, P.; Bena, C.
2016-10-01
We study the spin-resolved spectral properties of the impurity states associated to the presence of magnetic impurities in two-dimensional as well as one-dimensional systems with Rashba spin-orbit coupling. We focus on Shiba bound states in superconducting materials, as well as on impurity states in metallic systems. Using a combination of a numerical T -matrix approximation and a direct analytical calculation of the bound-state wave function, we compute the local density of states (LDOS) together with its Fourier transform (FT). We find that the FT of the spin-polarized LDOS, a quantity accessible via spin-polarized scanning tunneling microscopy, allows to accurately extract the strength of the spin-orbit coupling. Also, we confirm that the presence of magnetic impurities is strictly necessary for such measurement, and that non-spin-polarized experiments cannot have access to the value of the spin-orbit coupling.
Hsieh, Timothy H; Fu, Liang
2012-03-09
The recently discovered superconductor Cu(x)Bi2Se3 is a candidate for three-dimensional time-reversal-invariant topological superconductors, which are predicted to have robust surface Andreev bound states hosting massless Majorana fermions. In this work, we analytically and numerically find the linearly dispersing Majorana fermions at k=0, which smoothly evolve into a new branch of gapless surface Andreev bound states near the Fermi momentum. The latter is a new type of Andreev bound states resulting from both the nontrivial band structure and the odd-parity pairing symmetry. The tunneling spectra of these surface Andreev bound states agree well with a recent point-contact spectroscopy experiment [S. Sasaki et al., Phys. Rev. Lett. 107, 217001 (2011)] and yield additional predictions for low temperature tunneling and photoemission experiments.
Spin-Polarized States of Nuclear Matter
Institute of Scientific and Technical Information of China (English)
ZUO Wei; U. Lombardo; SHEN Cai-Wan
2003-01-01
The equations of state of spin-polarized nuclear matter and pure neutron matter are studied in theframework of the Brueckner-Hartree-Fock theory including a three-body force. The energy per nucleon E A (δ) calculatedin the full range of spin polarization δ = (ρ↑ - ρ↓)/ρ for symmetric nuclear matter and pure neutron matter fulfills aparabolic law. In both the cases the spin-symmetry energy is calculated as a function of the baryonic density alongwith the related quantities such as the magnetic susceptibility and the Landau parameter Go. The main effect of thethree-body force is to strongly reduce the degenerate Fermi gas magnetic susceptibility even more than the value withonly two-body force. The equation of state is monotonically increasing with the density for all spin-aligned configurationsstudied here so that no any signature is found for a spontaneous transition to a ferromagnetic state.
Aggarwal, Leena; Gayen, Sirshendu; Das, Shekhar; Kumar, Ritesh; Süß, Vicky; Felser, Claudia; Shekhar, Chandra; Sheet, Goutam
2017-01-01
A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics.
Spin polarization dependence of quasiparticle properties in graphene
Qaiumzadeh, Alireza; Jahanbani, Kh.; Asgari, Reza
2012-01-01
We address spin polarization dependence of graphene's Fermi liquid properties quantitatively using a microscopic Random Phase Approximation theory in an interacting spin-polarized Dirac electron system. We show an enhancement of the minority-spin many-body velocity renormalization at fully spin polarization due to reduction in the electron density and consequently increase in the interaction between electrons near the Fermi surface. We also show that the spin dependence of the Fermi velocity ...
Electrically-Generated Spin Polarization in Non-Magnetic Semiconductors
2016-03-31
AFRL-AFOSR-VA-TR-2016-0143 Electrically -generated spin polarization in non-magnetic semiconductors Vanessa Sih UNIVERSITY OF MICHIGAN Final Report 03...SUBTITLE (YIP) - Electrically -generated spin polarization in non-magnetic semiconductors 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-12-1-0258 5c...that produced electrically -generated electron spin polarization in non-magnetic semiconductor heterostructures. Electrically -generated electron spin
Spin Polarization Measurements of Ferromagnetic Atomic Chains on a Supercondcutor: Part II
Jeon, Sangjun; Xie, Yonglong; Drozdov, Ilya K.; Li, Jian; Bernevig, B. Andrei; Yazdani, Ali
A key property of the Majorana fermions edge mode when realized at the edge of a topological superconductor is their spin. Unlike other low energy excitation in a conventional superconductor, which are made up of time-reverse partners of up and down spin, Majorana is expected to have a definite spin orientation. We utilize the technique of spin-polarized STM as described in the last talk to probe the nature of Majorana excitations in chains of Fe atoms on the surface of Pb. Previous effort on this system has detected signature of Majorana as a zero bias peak at end of such chains. While this previous study shows evidence of ferromagnetism and spin-orbit coupling in such atomic chains on Pb, they did not probe the spin properties of the end mode specifically. We describe energy-resolved spin-polarized STM experiments designed to probe whether the previously reported zero energy end modes are spin-polarized or not. Work supported by ONR and the Moore Foundation.
Organic light emitting diodes with spin polarized electrodes
Arisi, E.; Bergenti, I.; Dediu, V.; Loi, M.A.; Muccini, M.; Murgia, M.; Ruani, G.; Taliani, C.; Zamboni, R.
2003-01-01
Electrical and optical properties of Alq3 based organic light emitting diodes with normal and spin polarized electrodes are presented. Epitaxial semitransparent highly spin polarized La0.7Sr0.3MnO3 were used as hole injector, substituting the traditional indium tin oxide electrode. A comparison of e
Spin-Polarization in Quasi-Magnetic Tunnel Junctions
Xie, Zheng-Wei; Li, Ling
2017-05-01
Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.
Detecting Spin-Polarized Currents in Ballistic Nanostructures
DEFF Research Database (Denmark)
Potok, R.; Folk, J.; M. Marcus, C.
2002-01-01
We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in an in-plane magnetic field to be measured. A transverse focusing geometry is used to couple current from an emitter point contact into a collector point contact....
Spin polarization effect for Tc2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying; Zhu Zheng-He
2004-01-01
Density functional method (DFT) (B3p86) of Gaussian98 has been used to optimize the structure of the Tc2 molecule. The result shows that the ground state for Tc2 molecule is an 11-multiple state and its electronic configuration is 11∑- g, which shows the spin polarization effect of Tc2 molecule of a transition metal element for the first time.Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher energy states. So, that the ground state for Tc2 molecule is an 11-multiple state is indicative of the spin polarization effect of Tc2 molecule of a transition metal element: that is, there exist 10 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Tc2 molecule is minimized. It can be concluded that the effect of parallel spin of the Tc2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization.In addition, the Murrell-Sorbie potential functions with the parameters for the ground state 11∑- g and other states of Tc2 molecule are derived. Dissociation energy De for the ground state of Tc2 molecule is 2.266eV, equilibrium bond length Re is 0.2841nm, vibration frequency ωe is 178.52cm-1. Its force constants f2, f3, and f4 are 0.9200aJ.nm-2,-3.5700aJ.nm-3, 11.2748aJ.nm-4 respectively. The other spectroscopic data for the ground state of Tc2 molecule ωexe,Be, αe are 0.5523cm- 1, 0.0426cm- 1, 1.6331 × 10-4cm- 1 respectively.
Spin polarization effect for Cr2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying
2008-01-01
Density functional theory (DFT) (B3P86) of Ganssian 03 has been used to optimize the structure of the Cr2 molecule, a transition metal element molecule. The result shows that the ground state for the Cr2 molecule is a 13-multiple state, indicating that there exists a spin polarization effect in the Cr2 molecule. Meanwhile, we have not found any spin pollution because the wave function of the ground state does not mingle with wave functions of higher-energy states. So the ground state for Cr2 molecule being a 13-multiple state is indicative of spin polarization effect of the Cr2 molecule among transition metal elements, that is, there are 12 parallel spin electrons in the Cr2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Cr2 molecule is minimized. It can be concluded that the effect of parallel spin in the Cr2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition,the Murrell-Sorbie potential functions with the parameters for the ground state and other states of the Cr2 molecule are derived. The dissociation energy De for the ground state of the Cr2 molecule is 0.1034eV, equilibrium bond length Re is 0.3396nm, and vibration frequency ωe is 73.81cm-1. Its force constants f2, f3 and f4 are 0.0835, -0.2831 and 0.3535 aJ·nm-4 respectively. The other spectroscopic data for the ground state of the Cr2 molecule ωeχe, Be and αe are 1.2105, 0.0562 and 7.2938 × 10-4cm-1 respectively.
Spin polarization effect for Fe2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying; Zhu Zheng-He
2006-01-01
This paper uses the density functional theory (DFT)(B3p86) of Gaussian03 to optimize the structure of Fe2 molecule. The result shows that the ground state for Fe2 molecule is a 9-multiple state, which shows spin polarization effect of Fe2 molecule of transition metal elements for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions with higher energy states. So, that the ground state for Fe2 molecule is a 9-multiple state is indicative of the spin polarization effect of Fe2 molecule of transition metal elements. That is, there exist 8 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of the Fe2 molecule is minimized. It can be concluded that the effect of parallel spin of the Fe2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters for the ground state and other states of Fe2 molecule are derived. Dissociation energy De for the ground state of Fe2 molecule is 2.8586ev, equilibrium bond length Re is 0.2124nm, vibration frequency ωe is 336.38 cm-1. Its force constants f2, f3, and f4 are 1.8615aJ·nm-2, -8.6704a J·nm-3, 29.1676aJ·nm-4 respectively. The other spectroscopic data for the ground state of Fe2 moleculeωeχe, Be, αe are 1.5461 cm-1, 0.1339 cm-1, 7.3428×10-4 cm-1 respectively.
Spin polarization effect of Ni2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying; Zhu Zheng-He
2008-01-01
The density functional theory (DFT) method (b3p86) of Gaussian 03 is used to optimize the structure of the Ni2 molecule. The result shows that the ground state for the Ni2 molecule is a 5-multiple state, symbolizing a spin polarization effect existing in the Ni2 molecule, a transition metal molecule, but no spin pollution is found because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Ni2 molecule, which is a 5-multiple state, is indicative of spin polarization effect of the Ni2 molecule, that is, there exist 4 parallel spin electrons in Ni2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Ni2 molecule is minimized. It can be concluded that the effect of parallel spin in the Ni2 molecule is larger than that of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters of the ground state and other states of the Ni2 molecule are derived. The dissociation energy De for the ground state of the Ni2 molecule is 1.835 eV, equilibrium bond length Re is 0.2243 nm, vibration frequency ωe is 262.35 cm-1. Its force constants f2, f3 and f4 are 1.1901 aJ.nm-2, 5.8723 aJ.nm-3, and 21.2505 aJ.nm-4 respectively. The other spectroscopic data for the ground state of the Ni2 molecule ωexe, Be and αe are 1.6315cm-1, 0.1141 cm-1, and 8.0145×10-4 cm-1 respectively.
Spin polarization asymmetry at the surface of chromia
Cao, Shi; Zhang, Xin; Wu, Ning; N'Diaye, A. T.; Chen, G.; Schmid, A. K.; Chen, Xumin; Echtenkamp, W.; Enders, A.; Binek, Ch; Dowben, P. A.
2014-07-01
We demonstrate boundary spin polarization at the surface of a Cr2O3 single crystal using spin-polarized low-energy electron microscopy (SPLEEM), complementing prior spin polarized photoemission, spin polarized inverse photoemission, and x-ray magnetic circular dichroism photoemission electron microscopy measurements. This work shows that placing a Cr2O3 single crystal into a single domain state will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the SPLEEM contrast for the two polarization states may be different, consistent with scanning tunneling microscopy spectroscopy results obtained from ultrathin films of Cr2O3.
Energy Technology Data Exchange (ETDEWEB)
Kawasuso, A., E-mail: kawasuso.atsuo@jaea.go.jp [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Fukaya, Y.; Maekawa, M.; Zhang, H. [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Seki, T.; Yoshino, T.; Saitoh, E.; Takanashi, K. [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)
2013-09-15
Transversely spin-polarized positrons were injected near Pt and Au surfaces under an applied electric current. The three-photon annihilation of spin-triplet positronium, which was emitted from the surfaces into vacuum, was observed. When the positron spin polarization was perpendicular to the current direction, the maximum asymmetry of the three-photon annihilation intensity was observed upon current reversal for the Pt surfaces, whereas it was significantly reduced for the Au surface. The experimental results suggest that electrons near the Pt surfaces were in-plane and transversely spin-polarized with respect to the direction of the electric current. The maximum electron spin polarization was estimated to be more than 0.01 (1%). - Highlights: • Annihilation probability of positronium emitted from the Pt surface into the vacuum under direct current exhibited asymmetry upon current reversal. • The maximum asymmetry appeared when positron spin polarization and the direct current were perpendicular to each other. • Electrons near the Pt surfaces were in-plane and transversely spin-polarized with respect to the direction of the electric current. • Spin-polarized positronium annihilation provides a unique tool for investigating spin polarization on metal surfaces.
Spin polarization effect for Co2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying; Bao Wen-Sheng
2007-01-01
The density functional theory (DFT)(b3p86) of Gaussian 03 has been used to optimize the structure of the Co2molecule, a transition metal element molecule. The result shows that the ground state for the Co2 molecule is a 7-multiple state, indicating a spin polarization effect in the Co2 molecule. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state is not mingled with wavefunctions of higher-energy states. So for the ground state of Co2 molecule to be a 7-multiple state is the indicative of spin polarization effect of the Co2molecule, that is, there exist 6 parallel spin electrons in a Co2 molecule. The number of non-conjugated electrons is the greatest. These electrons occupy different spacial orbitals so that the energy of the Co2 molecule is minimized. It can be concluded that the effect of parallel spin in the Co2 molecule is larger than the effect of the conjugated molecule,which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters for the ground state and the other states of the Co2 molecule are derived. The dissociation energy De for the ground state of Co2 molecule is 4.0489eV, equilibrium bond length Re is 0.2061 nm, and vibration frequency 11.2222 aJ.nm-4respectively(1 a.J=10-18 J). The other spectroscopic data for the ground state of Co2 molecule ωexe,Be, and αe are 0.7202 cm-1, 0.1347 cm-1, and 2.9120× 10-1 cm-1 respectively. And ωexe is the non-syntonic part of frequency, Be is the rotational constant, αe is revised constant of rotational constant for non-rigid part of Co2 molecule.
Spin polarization effect for Mn2 molecule
Institute of Scientific and Technical Information of China (English)
Yan Shi-Ying; Xu Guo-Liang
2007-01-01
The density functional theory method (DFT) (b3p86) of Gaussian 03 has been used to optimize the structure of the Mn2 molecule.The result shows that the ground state of the Mn2 molecule is an 11-multiple state,indicating a spin polarization effect in the Mn2 molecule,a transition metal element molecule.Meanwhile,we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states.So the ground state for Mn2 molecule being of an 11-multiple state is the indicative of spin polarization effect of the Mn2 molecule among those in the transition metal elements:that is,there are 10 parallel spin electrons in a Mn2 molecule.The number of non-conjugated electrons is the greatest.These electrons occupy different spacious orbitals so that the energy of the Mn2 molecule is minimized.It can be concluded that the effect of parallel spin in the Mn2 molecule is larger than the effect of the conjugated molecule,which is obviously related to the effect of electron d delocalization.In addition,the Murrell-Sorbie potential functions with the parameters for the ground state and other states of the Mn2 molecule are derived.The dissociation energy De for the ground state of the Mn2 molecule is 1.4477eV,equilibrium bond length Re is 0.2506 nm,vibration frequency ωe is 211.51 cm-1.Its force constants,f2,f3,and f4 are 0.7240 aJ·nm-2,-3.35574 aJ·nm-3,11.4813 aJ·nm-4 respectively. The other spectroscopic data for the ground state of the Mn2 molecule ωeχe,Be,αe are 1.5301 cm-1,0.0978 cm-1,7.7825×10-4 cm-1 respectively.
Spin polarization effect for molecule Ta2
Institute of Scientific and Technical Information of China (English)
Xie An-Dong
2006-01-01
Density functional theory (DFT) (B3p86) has been used to optimize the structure of the molecule Taa- The result shows that the ground state of molecule Ta,2 is a 7- multiple state and its electronic configuration is 7∑+u which shows the spin polarization effect for molecule Ta2 of transition metal elements for the first time. Meanwhile, spin pollution has not been found because the wavefunction of the ground state does not mix with those of higher states. So, the fact that the ground state of molecule Ta2 is a 7-multiple state indicates a spin polarization effect of molecule Ta2 of the transition metal elements, i.e. there exist 6 parallel spin electrons and the non-conjugated electrons are greatest in number. These electrons occupy different space orbitals so that the energy of molecule Ta2 is minimized. It can be concluded that the effect of parallel spin of the molecule Ta2 is larger than the effect of the conjugated molecule, which is obviously related to the effect of d-electron delocalization. In addition, the Murrell-Sorbie potential functions with parameters for the ground state 7∑+u and other states of the molecule Ta2 are derived. The dissociation energy De, equilibrium bond length Re and vibration frequency ωe for the ground state of molecule Ta2 are 4.5513eV, 0.2433nm and 173.06cm-1, respectively. Its force constants f2,f3 and f4 are 1.5965×l02aJ·nm-2,-6.4722×l03aJ·nm-3 and 29.4851×04aJ·nm-4, respectively. Other spectroscopic data ωe χe, Be and αe for the ground state of Ta2 are 0.2078cm-1, 0.0315cm-1 and 0.7858×104 cm-1, respectively.
Spin polarization effect for Os2 molecule
Institute of Scientific and Technical Information of China (English)
Xie An-Dong; Yan Shi-Ying; Zhu Zheng-He; Fu Yi-Bei
2005-01-01
Density functional Theory (DFT) (B3p86) of Gaussian03 has been used to optimize the structure of Os2 molecule.The result shows that the ground state for Os2 molecule is 9-multiple state and its electronic configuration is 9∑+g,which shows spin polarization effect of Os2 molecule of transition metal elements for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions with higher energy states. So, the fact that the ground state for Os2 molecule is a 9-multiple state is indicative of spin polarization effect of Os2 molecule of transition metal elements. That is, there exist 8 parallel spin electrons.The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Os2 molecule is minimized. It can be concluded that the effect of parallel spin of Os2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters for the ground state 9∑+g and other states of Os2 molecule are derived. Dissociation energy De for the ground state of Os2 molecule is 3.3971eV, equilibrium bond length Re is 0.2403nm, vibration frequency ωe is 235.32cm-1. Its force constants f2, f3, and f4 are 3.1032×102aJ.nm-2,-14.3425×103aJ.nm-3 and 50.5792×104aJ.nm-4 respectively. The other spectroscopic data for the ground state of Os2 molecule ωeχe, Be and αe are 0.4277cm-1, 0.0307cm-1 and 0.6491× 10-4cm-1 respectively.
Energy Technology Data Exchange (ETDEWEB)
Castro, Luis B; Castro, Antonio S de [UNESP-Campus de Guaratingueta, Departamento de Fisica e Quimica, 12516-410 Guaratingueta SP (Brazil)], E-mail: benito@feg.unesp.br, E-mail: castro@pesquisador.cnpq.br
2008-04-15
The Klein-Gordon and the Dirac equations with vector and scalar potentials are investigated under a more general condition, V{sub v}+V{sub s}=constant. These intrinsically relativistic and isospectral problems are solved in the case of squared hyperbolic potential functions and bound states for either particles or antiparticles are found. The eigenvalues and eigenfuntions are discussed in some detail and the effective Compton wavelength is revealed to be an important physical quantity. It is revealed that a boson is better localized than a fermion when they have the same mass and are subjected to the same potentials.
Optical nuclear spin polarization in quantum dots
Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei
2016-10-01
Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time. Project partially supported by the National Natural Science Foundations of China (Grant Nos. 11374039 and 11174042) and the National Basic Research Program of China (Grant Nos. 2011CB922204 and 2013CB632805).
Spin polarization dependence of quasiparticle properties in graphene
Qaiumzadeh, A.; Jahanbani, Kh.; Asgari, Reza
2012-06-01
We address spin polarization dependence of graphene's Fermi liquid properties quantitatively using a microscopic random phase approximation theory in an interacting spin-polarized Dirac electron system. We show an enhancement of the minority-spin many-body velocity renormalization at fully spin polarization due to reduction in the electron density and consequently increase in the interaction between electrons near the Fermi surface. We also show that the spin dependence of the Fermi velocity in the chiral Fermi systems is different than that in a conventional two-dimensional electron liquid. In addition, we show that the ratio of the majority-to-minority-spin lifetime is smaller than unity and related directly to the polarization and electron energy. The spin-polarization dependence of the carrier Fermi velocity is of significance in various spintronic applications.
A frozen spin polarized target for S134
1974-01-01
The CERN-ETH, Zurich-Helsinki-Imperial College-Southampton Collaboration used a frozen spin polarized target together with the ETH spectrometer magnet to study spin effects (S134). Beam was d31 in South Hall
Three-dimensional Majorana fermions in chiral superconductors.
Kozii, Vladyslav; Venderbos, Jörn W F; Fu, Liang
2016-12-01
Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit-coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions.
Direct evidence for ferromagnetic spin polarization in gold nanoparticles
Yamamoto, Y; Miura, T; Teranishi, T.; Miyake, M.; Hori, H.; Suzuki, M.; Kawamura, N.; Miyagawa, H; T. Nakamura; Kobayashi, K
2004-01-01
We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometry. This result is evidence of intrinsic spin polarization in nano-sized gold.
Direct Observation of Ferromagnetic Spin Polarization in Gold Nanoparticles
Yamamoto, Y; Miura, T; Suzuki, M.; Kawamura, N.; Miyagawa, H; T. Nakamura; Kobayashi, K; Teranishi, T.; Hori, H.
2004-01-01
We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using x-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms as estimated by XMCD shows a good agreement with results obtained by conventional magnetometry. This evidences intrinsic spin polarization in nanosized gold.
NLO+NLL Collider Bounds, Dirac Fermion and Scalar Dark Matter in the B-L Model
Klasen, Michael; Queiroz, Farinaldo S
2016-01-01
Baryon and lepton numbers being accidental global symmetries of the Standard Model (SM), it is natural to promote them to local symmetries. However, to preserve anomaly freedom, only combinations of B-L are viable. In this spirit, we investigate possible dark matter realizations in the context of the $U(1)_{B-L}$ model: (i) Dirac fermion with unbroken B-L; (ii) Dirac fermion with broken B-L; (iii) scalar dark matter; (iv) two component dark matter. We compute the relic abundance, direct and indirect detection observables and confront them with recent results from Planck, LUX-2016, and Fermi-LAT and prospects from XENON1T. In addition to the well known LEP bound $M_{Z^{\\prime}}/g_{BL} \\gtrsim 7$ TeV, we include often ignored LHC bounds using 13 TeV dilepton (dimuon+dielectron) data at next-to-leading order plus next-to-leading logarithmic accuracy. We show that, for gauge couplings smaller than $0.4$, the LHC gives rise to the strongest collider limit. In particular, we find $M_{Z^{\\prime}}/g_{BL} > 8.7$ TeV f...
Borromean ground state of fermions in two dimensions
Volosniev, A. G.; Fedorov, D. V.; Jensen, A. S.; Zinner, N. T.
2014-09-01
The study of quantum mechanical bound states is as old as quantum theory itself. Yet, it took many years to realize that three-body Borromean systems that are bound when any two-body subsystem is unbound are abundant in nature. Here we demonstrate the existence of Borromean systems of spin-polarized (spinless) identical fermions in two spatial dimensions. The ground state with zero orbital (planar) angular momentum exists in a Borromean window between critical two- and three-body strengths. The doubly degenerate first excited states of angular momentum one appears only very close to the two-body threshold. They are the lowest in a possible sequence of so-called super-Efimov states. While the observation of the super-Efimov scaling could be very difficult, the Borromean ground state should be observable in cold atomic gases and could be the basis for producing a quantum gas of three-body states in two dimensions.
NLO+NLL collider bounds, Dirac fermion and scalar dark matter in the B-L model
Energy Technology Data Exchange (ETDEWEB)
Klasen, Michael [Westfaelische Wilhelms-Universitaet Muenster, Institut fuer Theoretische Physik, Muenster (Germany); Lyonnet, Florian [Southern Methodist University, Dallas, TX (United States); Queiroz, Farinaldo S. [Max-Planck-Institut fuer Kernphysik, Particle and Astroparticle Physics Division, Heidelberg (Germany)
2017-05-15
Baryon and lepton numbers being accidental global symmetries of the Standard Model (SM), it is natural to promote them to local symmetries. However, to preserve anomaly-freedom, only combinations of B-L are viable. In this spirit, we investigate possible dark matter realizations in the context of the U(1){sub B-L} model: (i) Dirac fermion with unbroken B-L; (ii) Dirac fermion with broken B-L; (iii) scalar dark matter; (iv) two-component dark matter. We compute the relic abundance, direct and indirect detection observables and confront them with recent results from Planck, LUX-2016, and Fermi-LAT and prospects from XENON1T. In addition to the well-known LEP bound M{sub Z}{sup {sub '}}/g{sub BL} >or similar 7 TeV, we include often ignored LHC bounds using 13 TeV dilepton (dimuon + dielectron) data at next-to-leading order plus next-to-leading logarithmic accuracy. We show that, for gauge couplings smaller than 0.4, the LHC gives rise to the strongest collider limit. In particular, we find M{sub Z}{sup {sub '}}/g{sub BL} > 8.7 TeV for g{sub BL} = 0.3. We conclude that the NLO+NLL corrections improve the dilepton bounds on the Z{sup '} mass and that both dark matter candidates are only viable in the Z{sup '} resonance region, with the parameter space for scalar dark matter being fully probed by XENON1T. Lastly, we show that one can successfully have a minimal two-component dark matter model. (orig.)
Spin polarization in high density quark matter
DEFF Research Database (Denmark)
Bohr, Henrik; Panda, Prafulla K.; Providênci, Constanca
2013-01-01
We investigate the occurrence of a ferromagnetic phase transition in high density hadronic matter (e.g., in the interior of a neutron star). This could be induced by a four-fermion interaction analogous to the one which is responsible for chiral symmetry breaking in the Nambu-Jona-Lasinio model......, to which it is related through a Fierz transformation. Flavor SU(2) and flavor SU(3) quark matter are considered. A second-order phase transition is predicted at densities about 5 times the normal nuclear matter density. It is also found that in flavor SU(3) quark matter, a first-order transition from...
Fry, M. P.
2001-01-01
The current status of bounds on and limits of fermion determinants in two, three and four dimensions in QED and QCD is reviewed. A new lower bound on the two-dimensional QED determinant is derived. An outline of the demonstration of the continuity of this determinant at zero mass when the background magnetic field flux is zero is also given.
Approximate energy expression for spin-polarized Fermi liquids
Takano, M; Endo, T; Kimura, R
2003-01-01
An approximate energy expression is proposed for arbitrarily spin-polarized Fermi liquids with central two-body forces. It is explicitly expression as a functional of spin-dependent radial distribution functions and can be used conveniently in the variational method. It includes the potential energies completely and the kinetic energies up to main parts of the three-body cluster terms. This approximation is similar to that used previously for spin-unpolarized and fully polarized matter. A notable feature of this expressed is that it guarantees the necessary conditions on arbitrarily spin-polarized structure functions automatically. The Euler-Lagrange equations are derived from this energy expression and are numerically solved for arbitrarily spin-polarized liquid sup 3 He. The results for liquid sup 3 He with the HFDHE2 potential are consistent with the nearly ferromagnetic property. (author)
Spin polarization transfer by the radical pair mechanism
Energy Technology Data Exchange (ETDEWEB)
Zarea, Mehdi, E-mail: m-zarea@northwestern.edu; Ratner, Mark A.; Wasielewski, Michael R. [Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113 (United States)
2015-08-07
In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies, the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.
Spin-polarized transport in graphene nanoribbon superlattices
Institute of Scientific and Technical Information of China (English)
Yu Xin-Xin; Xie Yue-E; OuYang Tao; Chen Yuan-Ping
2012-01-01
By the Green's function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice (ZGNS) under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy,which leads to spin-polarized transport in structure.Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy.The location and width of the miniband are associated with the geometry of the ZGNS.In the optimal structure,the spin-up and spin-down minibands can be separated completely near the Fermi energy.Therefore,a wide,perfect spin polarization with clear stepwise pattern is observed,i.e.,the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.
SPIN POLARIZED PHOTOELECTRON SPECTROSCOPY AS A PROBE OF MAGNETIC SYSTEMS.
Energy Technology Data Exchange (ETDEWEB)
JOHNSON, P.D.; GUNTHERODT, G.
2006-11-01
Spin-polarized photoelectron spectroscopy has developed into a versatile tool for the study of surface and thin film magnetism. In this chapter, we examine the methodology of the technique and its recent application to a number of different problems. We first examine the photoemission process itself followed by a detailed review of spin-polarization measurement techniques and the related experimental requirements. We review studies of spin polarized surface states, interface states and quantum well states followed by studies of the technologically important oxide systems including half-metallic transition metal oxides, ferromagnet/oxide interfaces and the antiferromagnetic cuprates that exhibit high Tc Superconductivity. We also discuss the application of high-resolution photoemission with spin resolving capabilities to the study of spin dependent self energy effects.
Current-Induced Spin Polarization in Topological Insulator-Graphene Heterostructures.
Vaklinova, Kristina; Hoyer, Alexander; Burghard, Marko; Kern, Klaus
2016-04-13
Further development of the field of all-electric spintronics requires the successful integration of spin transport channels with spin injector/generator elements. While with the advent of graphene and related 2D materials high performance spin channel materials are available, the use of nanostructured spin generators remains a major challenge. Especially promising for the latter purpose are 3D topological insulators, whose 2D surface states host massless Dirac Fermions with spin-momentum locking. Here, we demonstrate injection of spin-polarized current from a topological insulator into graphene, enabled by its intimate coupling to an ultrathin Bi2Te2Se nanoplatelet within a van der Waals epitaxial heterostructure. The spin switching signal, whose magnitude scales inversely with temperature, is detectable up to ∼15 K. Our findings establish topological insulators as prospective future components of spintronic devices wherein spin manipulation is achieved by purely electrical means.
Spin-polarized photoemission from SiGe heterostructures
Energy Technology Data Exchange (ETDEWEB)
Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F. [LNESS-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)
2013-12-04
We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.
Influence of local spin polarization to the Kondo effect
Institute of Scientific and Technical Information of China (English)
LI Huan; GUO Wei
2007-01-01
We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy △= εd↑ - εd↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.
Institute of Scientific and Technical Information of China (English)
Zhang Lei; Deng Ning; Ren Min; Dong Hao; Chen Pei-Yi
2007-01-01
Effective spin-polarized injection from magnetic semiconductor (MS) to nonmagnetic semiconductor (NMS) has been highlighted in recent years. In this paper we study theoretically the dependence of nonequilibrium spin polarization (NESP) in NMS during spin-polarized injection through the magnetic p-n junction. Based on the theory in semiconductor physics, a model is established and the boundary conditions are determined in the case of no external spin-polarized injection and low bias. The control parameters that may influence the NESP in NMS are indicated by calculating the distribution of spin polarization. They are the doping concentrations, the equilibrium spin polarization in MS and the bias. The effective spin-polarized injection can' be realized more easily by optimizing the above parameters.
Contributions in anomalous fermion momenta of neutral vector boson in plane-wave field
Klimenko, E Y
2002-01-01
The contributions of the neutral vector boson to the anomalous magnetic and electric momenta of the polarized fermion moving in the plane-wave electromagnetic field are considered in this paper. The contributions are divided by the fermion spin polarization states, which makes it possible to investigate the important problem on the contributions to the fermion anomalous momenta, coming from the the fermion transition to the intermediate state spin-nonflip or spin flip of fermion
Han, Chengcheng; Matsumoto, Shigeki; Nojiri, Mihoko M; Takeuchi, Michihisa
2016-01-01
A colored heavy particle with sufficiently small width may form non-relativistic bound states when they are produced at the large hadron collider\\,(LHC), and they can annihilate into a diphoton final state. The invariant mass of the diphoton would be around twice of the colored particle mass. In this paper, we study if such bound state can be responsible for the 750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit signal cross section is obtained for the SU(2)$_L$ singlet colored fermion $X$ with $Y_X=4/3$. Having such an exotic hypercharge, the particle is expected to decay through some higher dimensional operators, consistent with the small width assumption. The decay of $X$ may involve a stable particle $\\chi$, if both $X$ and $\\chi$ are odd under some conserved $Z_2$ symmetry. In that case, the particle $X$ suffers from the constraints of jets + missing $E_T$ searches by ATLAS and CMS at 8 TeV and 13 TeV. We found that such a scenario still survives if the mass difference between ...
The double radiative annihilation of the heavy-light fermion bound states
Eeg, Jan O; Picek, I
2001-01-01
We consider the double-radiative decays of heavy-light QED and QCD atoms, $\\mu^+ e^- \\to \\gamma\\gamma$ and $\\bar{B}^{0}_s \\to \\gamma\\gamma$. Especially, we take under scrutiny contributions coming from operators that vanish on the free-quark mass shell. We show that by field redefinitions these operators are converted into contact terms attached to the bound state dynamics. A net off-shell contribution is suppressed with respect to the effect of the well known flavour-changing magnetic-moment operator by the bound-state binding factor. The negligible off-shellness of the weakly bound QED atoms becomes more relevant for strongly bound QCD atoms. We analyze this off-shellness in model-approaches to QCD, one of them enabling us to keep close contact to the related effect in QED. We also comment on the off-shell effect in the corresponding process $\\bar{B}_d \\to K^* \\gamma$, and discuss possible hindering of the claimed beyond-standard-model discovery in this decay mode.
Three-body recombination in spin-polarized atomic hydrogen
Goey, L.P.H. de; Berg, T.H.M. van de; Mulders, N.; Stoof, H.T.C.; Verhaar, B.J.; Glöckle, W.
1986-01-01
In view of the failure of the Kagan dipole mechanism to explain the magnetic field dependence of the H+H+H recombination rate in spin-polarized atomic hydrogen, we consider an additional process, the so-called dipole-exchange mechanism. Two simple approaches to estimate its consequences turn out to
Spin-polarized currents generated by magnetic Fe atomic chains.
Lin, Zheng-Zhe; Chen, Xi
2014-06-13
Fe-based devices are widely used in spintronics because of high spin-polarization and magnetism. In this work, freestanding Fe atomic chains, the thinnest wires, were used to generate spin-polarized currents due to the spin-polarized energy bands. By ab initio calculations, the zigzag structure was found to be more stable than the wide-angle zigzag structure and had a higher ratio of spin-up and spin-down currents. By our theoretical prediction, Fe atomic chains have a sufficiently long thermal lifetime only at T ≦̸ 150 K, while C atomic chains are very stable even at T = 1000 K. This means that the spintronic devices based on Fe chains could work only at low temperatures. A system constructed by a short Fe chain sandwiched between two graphene electrodes could be used as a spin-polarized current generator, while a C chain could not be used in this way. The present work may be instructive and meaningful to further practical applications based on recent technical developments on the preparation of metal atomic chains (Proc. Natl. Acad. Sci. USA 107 9055 (2010)).
Strain effect on spin polarization in a graphene junction
Cao, Zhenzhou; Lu, Ning; Qiu, Xuejun; Wang, Guofei
2017-04-01
We investigate the strain effect on the spin-dependent transport in a graphene junction with spin–orbit coupling and a gate voltage. We find that uniaxial strain along the armchair direction breaks the transmission probability symmetry with respect to the incident angle, reduces the spin-flipped transmission probability, and extends the transmission gap as regard to the Fermi energy, while strain along the zig-zag direction has very little effect on transmission probabilities. We analyze the spin polarization as a function of the strain magnitude, direction, voltage, and area width. Selecting the proper strain direction and magnitude for both the Klein tunneling and classical cases, the direction of the spin-polarization vector can be controlled and its magnitude is dramatically enhanced. Strain will expand the non-zero range of the magnitude of the spin-polarization vector with respect to voltage. Increasing the strain area width over a threshold, keeps the magnitude of the spin-polarization vector stable.
Evolution of electron spin polarization in semiconductor heterostructures
Pershin, Yuriy; Privman, Vladimir
2004-03-01
Last years theoretical and experimental investigations of electron spin-related effects in semiconductor heterostructures have received much consideration because of idea to create a semiconductor device based on the manipulation of electron spin. High degree of electron spin polarization is of crucial importance in operation of spintronic devices. We study possibilities to increase electron spin relaxation time by different means in systems where the D'yakonov-Perel' relaxation mechanism is dominant. Specifically, we show that the electron spin relaxation time in a two-dimensional electron gas with an antidote lattice increases exponentially with antidote radius for certain values of parameters. In another approach, we propose to use electron spin polarization having non-homogeneous direction of spin polarization vector in operation of a spintronic device. It is found that that the electron spin relaxation time essentially depends on the initial spin polarization distribution. This effect has its origin in the coherent spin precession of electrons diffusing in the same direction. We predict a long spin relaxation time of a novel structure: a spin coherence standing wave and discuss its experimental realization.
Experiment on the melting pressure of spin polarized He3
DEFF Research Database (Denmark)
Chapellier, M.; Olsen, M.; Rasmussen, Finn Berg
1981-01-01
In liquid He in a Pomeranchuk cell, the melting curve has been observed to be suppressed, presumably in regions with a strong local spin polarization. In the temperature range 30-50 mK the observed suppression was 60-80 kPa. The corresponding local polarization is estimated, in a crude model, to ...
Spin polarization of electrons with Rashba double-refraction
Energy Technology Data Exchange (ETDEWEB)
Ramaglia, V Marigliano; Bercioux, D; Cataudella, V; De Filippis, G; Perroni, C A [Coherentia-INFM and Dipartimento di Scienze Fisiche Universita degli Studi Federico II, Naples, I-80126 (Italy)
2004-12-22
We demonstrate how the Rashba spin-orbit coupling in semiconductor heterostructures can produce and control a spin-polarized current without ferromagnetic leads. The key idea is to use spin-double refraction of an electronic beam with a nonzero incidence angle. A region where the spin-orbit coupling is present separates the source and the drain without spin-orbit coupling. We show how the transmission and the beam spin polarization critically depend on the incidence angle. The transmission halves when the incidence angle is greater than a limit angle and a significant spin polarization appears. On increasing the spin-orbit coupling one can obtain the modulation of the intensity and of the spin polarization of the output electronic current when the input current is unpolarized. Our analysis shows the possibility of realizing a spin-field-effect transistor based on the propagation of only one mode with the region with spin-orbit coupling, whereas the original Datta and Das device (1990 Appl. Phys. Lett. 56 665) uses the spin precession that originates from the interference between two modes with orthogonal spin.
The surface spin polarization of Co-based Heusler alloys
Energy Technology Data Exchange (ETDEWEB)
Fetzer, Roman; Wuestenberg, Jan-Peter; Neuschwander, Sabine; Aeschlimann, Martin; Cinchetti, Mirko [University of Kaiserslautern (Germany). Department of Physics and Research Center OPTIMAS; Jourdan, Martin; Herbort, Christian; Vilanova Vidal, Enrique; Jakob, Gerhard [University of Mainz (Germany). Institute of Physics
2010-07-01
Co-based Heusler alloys belong mainly to the family of half-metallic ferromagnets (HMFs). The predicted full spin polarization at the Fermi level due to the minority spin band gap makes this class of materials highly interesting for application in the field of spintronics. Thus, the characterization of the surface of Co-based Heusler compounds is extremely relevant for understanding and improving the performance of Heusler-based spintronics devices, like tunnel-magnetoresistance (TMR) junctions. Using Auger electron spectroscopy (AES) and low energy spin polarized electron photoemission, we systematically studied the correlation between chemical composition and spin polarisation of the surface. For various Co-based Heusler alloys, e.g. Co{sub 2}CrAl, Co{sub 2}MnAl and Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5}, we found different degrees of spin-polarization at the very surface region. Reasons for the distinct deviation from the predicted 100% spin polarization and the dependence on the specific surface preparation procedure are discussed.
Universal spin-polarization fluctuations in one-dimensional wires with magnetic impurities
DEFF Research Database (Denmark)
Mortensen, Asger; Egues, J.C.
2002-01-01
-flip suppresses conductance fluctuations while enhancing spin-polarization fluctuations. More importantly, spin-polarization fluctuations attain a universal value 1/3 for large enough spin-flip strengths. This intrinsic spin-polarization fluctuation may pose a severe limiting factor to the realization of steady...
Effect of Electric Field on Spin Polarized Current in Ferromagnetic/ Organic Semiconductor Systems
Institute of Scientific and Technical Information of China (English)
MA Yan-Ni; REN Jun-Feng; ZHANG Yu-Bin; LIU De-Sheng; XIE Shi-Jie
2007-01-01
Considering the special carriers in organic semiconductors, the spin polarized current under electric field in a ferromagnetic/organic semiconductor system is theoretically studied. Based on the spin-diffusion theory, the current spin polarization under the electric field is obtained. It is found that electric field can enhance the current spin polarization.
Probing flavor parameters in the scalar sector and new bounds for the fermion sector
Gaitán, R.; Montes de Oca, J. H.; Orduz-Ducuara, J. A.
2017-07-01
In this paper we study the flavor-changing mediated by the Higgs boson within a Two-Higgs Doublet Model-III context. We explore the parameter space and, considering recent results, find new limits for the model parameters. We also obtain the total Higgs decay width and the branching ratios for different channels taking limits for the t\\to cV and b\\to sγ processes. Considering different constraints, we estimate the branching ratio for h\\to t^* c in the model as well as the bounds for b \\to sγ,h \\to μ\\tau, and h\\to γ Z. Considering the quark top decays to W\\bar{b}, we obtained Br(h \\to Wc\\bar{b})˜10^{-3}.
Effect of Carrier Differences on Spin Polarized Injection into Organic and Inorganic Semiconductors
Institute of Scientific and Technical Information of China (English)
REN Jun-Feng; XIU Ming-Xia
2008-01-01
Spin polarized injection into organic and inorganic semiconductors are studied theoretically from the spin diffusion theory and Ohm's law, and the emphases are placed on the effect of the carrier differences on the current spin polarization. The mobility and the spin-Rip time of carriers in organic and inorganic semiconductors are different. From the calculation, it is found that current spin polarization at a ferromagnetic/organic interface is higher than that at a ferromagnetic/inorganic interface because of different carriers in them. Effects of the conductivity matching, the spin dependent interfacial resistances, and the balk spin polarization of the ferromagnetic layer on the spin polarized injection are also discussed.
Enhancement of spin polarization in transport through protein-like single-helical molecules
Wu, Hai-Na; Wang, Xiao; Zhang, Ya-Jing; Yi, Guang-Yu; Gong, Wei-Jiang
2016-06-01
We investigate the spin-polarized electron transport through the single-helical molecules connected with two normal metallic leads. On the basis of an effective model Hamiltonian, influences of the structural parameters on the conductance and the spin polarization are calculated by using the Landauer-Büttiker formula. The optimal structural parameters for the maximal spin polarization are analyzed. Our results show that the dephasing term is an important factor to enhance the spin polarization, in addition to the intrinsic parameters of the single-helical molecule. This work can be helpful in optimizing the spin polarization in the protein-like single-helical molecules.
Diffusion equation and spin drag in spin-polarized transport
DEFF Research Database (Denmark)
Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger
2001-01-01
We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-spin...... species. This "spin drag" effect enhances the resistivity of the system. The enhancement is stronger the lower the dimension is, and should be measurable in, for example, a two-dimensional electron gas with ferromagnetic contacts. We also include spin-flip scattering, which has two effects......: it equilibrates the spin density imbalance and, provided it has a non-s-wave component, also a current imbalance....
Tilted Foils Nuclear Spin Polarization at REX-ISOLDE
Törnqvist, Hans Toshihide
2013-08-08
This thesis will explain and summarize my work and involvement in experiments aimed at producing nuclear spin polarization of post-accelerated beams of ions with the tilted-foils technique at the REX-ISOLDE linear accelerator at CERN. Polarizing the nuclear spin of radioactive beams in particular may provide access to observables which may be difficult to obtain otherwise. Currently, the techniques commonly employed for nuclear spin polarization are restricted to specific nuclides and experimental measurement techniques. Tilted foils polarization may provide a new tool to extend the range of nuclides that can be polarized and the types of experiments that can be performed. The experiments rely not only on the production but also on the method to measure the degree of attained polarization. Two methods will be treated, based on particle scattering in Coulomb excitation that may be utilized for stable beams, and the $\\beta$-NMR that requires $\\beta$-decaying nuclei. The experimental setups and measurements will...
Collisional properties of cold spin-polarized metastable neon atoms
Spoden, P; Herschbach, N; Van Drunen, W; Ertmer, W; Birkl, G
2005-01-01
We measure the rates of elastic and inelastic two-body collisions of cold spin-polarized neon atoms in the metastable 3P2 state for Ne-20 and Ne-22 by experimental studies of particle loss and rethermalization in a magnetic trap. From particle loss, we determine the loss parameter of inelastic two-body collisions \\beta=6.5(18) 10^{-12} cm^3s^{-1} for Ne-20, and \\beta=1.2(3) 10^{-11} cm^3s^{-1} for Ne-22. This proves the suppression of Penning ionization due to spin polarization. From cross-dimensional relaxation measurements, we obtain elastic scattering lengths of a=-170(40) a_0 for Ne-20 and a=+150(+150/-50) a_0 for Ne-22, where a_0=0.0529 nm.
Collisional properties of cold spin-polarized metastable neon atoms.
Spoden, P; Zinner, M; Herschbach, N; van Drunen, W J; Ertmer, W; Birkl, G
2005-06-10
We measure the rates of elastic and inelastic two-body collisions of cold spin-polarized neon atoms in the metastable 3P2 state for 20Ne and 22Ne in a magnetic trap. From particle loss, we determine the loss parameter of inelastic collisions beta=6.5(18) x 10(-12) cm(3) s(-1) for 20Ne and beta=1.2(3) x 10(-11) cm(3) s(-1) for 22Ne. These losses are caused by ionizing (i.e., Penning) collisions and occur less frequently than for unpolarized atoms. This proves the suppression of Penning ionization due to spin polarization. From cross-dimensional relaxation measurements, we obtain elastic scattering lengths of a=-180(40)a(0) for 20Ne and a = +150(+80)(-50)a(0) for 22Ne, where a(0)=0.0529 nm.
Stability of superfluid phases in the 2D spin-polarized attractive Hubbard model
Kujawa-Cichy, A.; Micnas, R.
2011-08-01
We study the evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (LPs) with increasing attraction, in the presence of the Zeeman magnetic field (h) for d=2, within the spin-polarized attractive Hubbard model. The broken symmetry Hartree approximation as well as the strong coupling expansion are used. We also apply the Kosterlitz-Thouless (KT) scenario to determine the phase coherence temperatures. For spin-independent hopping integrals (t↑=t↓), we find no stable homogeneous polarized superfluid (SCM) state in the ground state for the strong attraction and obtain that for a two-component Fermi system on a 2D lattice with population imbalance, phase separation (PS) is favoured for a fixed particle concentration, even on the LP (BEC) side. We also examine the influence of spin-dependent hopping integrals (mass imbalance) on the stability of the SCM phase. We find a topological quantum phase transition (Lifshitz type) from the unpolarized superfluid phase (SC0) to SCM and tricritical points in the h-|U| and t↑/t↓-|U| ground-state phase diagrams. We also construct the finite temperature phase diagrams for both t↑=t↓ and t↑≠t↓ and analyze the possibility of occurrence of a spin-polarized KT superfluid.
Interacting composite fermions
DEFF Research Database (Denmark)
nrc762, nrc762
2016-01-01
dominates. The interaction between composite fermions in the second Λ level (composite fermion analog of the electronic Landau level) satisfies this property, and recent studies have supported unconventional fractional quantum Hall effect of composite fermions at ν∗=4/3 and 5/3, which manifests...... as fractional quantum Hall effect of electrons at ν=4/11, 4/13, 5/13, and 5/17. I investigate in this article the nature of the fractional quantum Hall states at ν=4/5, 5/7, 6/17, and 6/7, which correspond to composite fermions at ν∗=4/3, 5/3, and 6/5, and find that all these fractional quantum Hall states...... are conventional. The underlying reason is that the interaction between composite fermions depends substantially on both the number and the direction of the vortices attached to the electrons. I also study in detail the states with different spin polarizations at 6/17 and 6/7 and predict the critical Zeeman...
Persson, Daniel; Shevtsov, Oleksii; Löfwander, Tomas; Fogelström, Mikael
2016-10-01
Conventional superconductors disordered by magnetic impurities demonstrate physical properties that are drastically different from their pristine counterparts. In our previous work [D. Persson et al., Phys. Rev. B 92, 245430 (2015), 10.1103/PhysRevB.92.245430], we explored the spectral and thermodynamic properties of such systems for two extreme cases: completely random and ferromagnetically aligned impurity magnetic moments. Here we consider the transport properties of these systems and show that they have a potential to be used in superconducting spintronic devices. Each magnetic impurity contributes a Yu-Shiba-Rusinov (YSR) bound state to the spectrum, residing at subgap energies. Provided the YSR states form metallic bands, we demonstrate that the tunneling current carried by these states can be highly spin polarized when the impurities are ferromagnetically ordered. The spin polarization can be switched by tuning the bias voltage. Moreover, even when the impurity spins are completely uncorrelated, one can still achieve almost 100 % spin polarization of the current, if the tunnel interface is spin active. We compute electric current and noise, varying parameters of the interface between tunneling and fully transparent regimes, and analyze the relative role of single-particle and Andreev reflection processes.
The Rashba effect on a double-barrier spin polarizer
Makler, Sergio S.; Guilherme Zelcovit, João; Boselli, Marco A.; da Cunha Lima, Ivan C.
2004-12-01
The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produces accurate results with little computational effort. In previous articles, we proposed a spin polarizer consisting of a well made of a dilute magnetic semiconductor (DMS) enclosed by two non-magnetic barriers. In the absence of Rashba effect, the magnetization of the well produces totally polarized electronic levels separated by 0.15 eV. The highest steady magnetic field obtained in a laboratory could not produce a Zeeman splitting so big. As a consequence the calculated currents are almost totally polarized. The Rashba spin-orbit Hamiltonian produces a spin flip. Therefore, the levels at the well have not well-defined spin polarization and the currents are less polarized. The device presented here would be useful for spintronics because there are DMS ferromagnetic at room temperature. Our tight-binding Hamiltonian, including the Rashba term, is H=HK+HP+HE+HM+H+H+HR . The first term is the kinetic energy. HP describes the double-barrier profile and the third term represent the electric field due to the applied bias. The magnetic HM, the hole-impurity H and the hole-hole H terms are included in the mean field approximation. The profile and the charge distribution are calculated self-consistently. By using a decimation formalism, all these terms are treated exactly. Finally, the Rashba term HR is very small. Therefore, it is treated using second order perturbation theory. The calculation confirm that the Rashba effect on the currents is of second order. Consequently, the resulting depolarization is very small.
The Rashba effect on a double-barrier spin polarizer
Energy Technology Data Exchange (ETDEWEB)
Makler, Sergio S. [Instituto de Fisica, Universidade Federal Fluminense, Campus da Praia Vermelha, 24210-340 Niteroi-RJ (Brazil)]. E-mail: sergio@if.uff.br; Guilherme Zelcovit, Joao [Instituto de Fisica, Universidade do Estado de Rio de Janeiro, RJ (Brazil); Boselli, Marco A. [Departamento de Fisica, Universidade Federal de Ouro Preto, MG (Brazil); Cunha Lima, Ivan C. da [Instituto de Fisica, Universidade do Estado de Rio de Janeiro, RJ (Brazil)
2004-12-31
The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produces accurate results with little computational effort. In previous articles, we proposed a spin polarizer consisting of a well made of a dilute magnetic semiconductor (DMS) enclosed by two non-magnetic barriers. In the absence of Rashba effect, the magnetization of the well produces totally polarized electronic levels separated by 0.15eV. The highest steady magnetic field obtained in a laboratory could not produce a Zeeman splitting so big. As a consequence the calculated currents are almost totally polarized. The Rashba spin-orbit Hamiltonian produces a spin flip. Therefore, the levels at the well have not well-defined spin polarization and the currents are less polarized. The device presented here would be useful for spintronics because there are DMS ferromagnetic at room temperature. Our tight-binding Hamiltonian, including the Rashba term, isH=HK+HP+HE+HM+Hh-i+Hh-h+HR.The first term is the kinetic energy. HP describes the double-barrier profile and the third term represent the electric field due to the applied bias. The magnetic HM, the hole-impurity Hh-i and the hole-hole Hh-h terms are included in the mean field approximation. The profile and the charge distribution are calculated self-consistently.By using a decimation formalism, all these terms are treated exactly. Finally, the Rashba term HR is very small. Therefore, it is treated using second order perturbation theory. The calculation confirm that the Rashba effect on the currents is of second order. Consequently, the resulting depolarization is very small.
Studies of Unstable Nuclei with Spin-Polarized Proton Target
Sakaguchi, Satoshi; Uesaka, Tomohiro; Wakui, Takashi; Chebotaryov, Sergey; Kawahara, Tomomi; Kawase, Shoichiro; Milman, Evgeniy; Tang, Tsz Leung; Tateishi, Kenichiro; Teranishi, Takashi
2016-02-01
Roles of spin-dependent interactions in unstable nuclei have been investigated via the direct reaction of radioactive ions with a solid spin-polarized proton target. The target has a unique advantage of a high polarization of 20-30% under low magnetic field of 0.1 T and at a high temperature of 100 K, which allow us to detect recoil protons with good angular resolution. Present status of on-going experimental studies at intermediate energies, such as proton elastic scattering and (p, 2p) knockout reaction, and new physics opportunities expected with low-energy RI beams are overviewed.
Spin-polarized transport in Rashba controlled rings
Energy Technology Data Exchange (ETDEWEB)
Romeo, F. [Dipartimento di Fisica ' E. R. Caianiello' and Unita C.N.I.S.M., Universita di Salerno, I-84081 Baronissi (Italy); Citro, R. [Dipartimento di Fisica ' E. R. Caianiello' and Unita C.N.I.S.M., Universita di Salerno, I-84081 Baronissi (Italy)]. E-mail: citro@sa.infn.it
2007-09-15
We study spin-polarized transport in a Rashba one-dimensional ring interrupted by a tunnel barrier placed in one arm and symmetrically coupled to two external leads. By means of the scattering matrix approach, we investigate the effects on the transport properties of both an applied magnetic flux (Aharonov-Bohm flux) and an effective Aharonov-Casher flux induced by the spin-orbit (SO) Rashba interaction. By varying the model parameters we show a spin-filtering effect relevant for the experimental detection of SO interaction in mesoscopic structures.
Energy Technology Data Exchange (ETDEWEB)
An, Xing-Tao, E-mail: anxt2005@163.com [School of Sciences, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018 (China); Mu, Hui-Ying [Department of Chemistry and Environmental Engineering, Hebei Chemical and Pharmaceutical Vocational Technology College, Shijiazhuang, Hebei 050026 (China); Li, Yu-Xian [College of Physical Science and Information Engineering, Hebei Normal University, and Hebei Advanced Thin Films Laboratory, Shijiazhuang, Hebei 050016 (China); Liu, Jian-Jun [College of Physical Science and Information Engineering, Hebei Normal University, and Hebei Advanced Thin Films Laboratory, Shijiazhuang, Hebei 050016 (China); Physics Department, Shijiazhuang University, Shijiazhuang 050035 (China)
2011-10-31
A four-terminal parallel double quantum dots (QDs) device is proposed to generate and detect the spin polarization in QDs. It is found that the spin accumulation in QDs and the spin-polarized currents in the upper and down leads can be generated when a bias voltage is applied between the left and right leads. It is more interesting that the spin polarization in the QDs can be detected using the upper and down leads. Moreover, the direction and magnitude of the spin polarization in the QDs, and in the upper and down leads can be tuned by the energy levels of QDs and the bias. -- Highlights: → The spin polarization in the quantum dots can be generated and controlled. → The spin polarization in quantum dots can be detected by the nonferromagnetic leads. → The system our studied is a discrete level spin Hall system.
Li, C H; van 't Erve, O M J; Robinson, J T; Liu, Y; Li, L; Jonker, B T
2014-03-01
Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators' surface-state spin system and enable utilization of its remarkable properties for future technological applications.
Interplay between spin polarization and color superconductivity in high density quark matter
DEFF Research Database (Denmark)
Tsue, Yasuhiko; da Providência, João; Providência, Constança;
2013-01-01
Here, it is suggested that a four-point interaction of the tensor type may lead to spin polarization in quark matter at high density. It is found that the two-flavor superconducting phase and the spin polarized phase correspond to distinct local minima of a certain generalized thermodynamical...... potential. It follows that a transition from one to the other phase occurs, passing through true minima with both a spin polarization and a color superconducting gap. It is shown that the quark spin polarized phase is realized at rather high density, while the two-flavor color superconducting phase...
Tunable spin polarization and superconductivity in engineered oxide interfaces.
Stornaiuolo, D; Cantoni, C; De Luca, G M; Di Capua, R; Di Gennaro, E; Ghiringhelli, G; Jouault, B; Marrè, D; Massarotti, D; Miletto Granozio, F; Pallecchi, I; Piamonteze, C; Rusponi, S; Tafuri, F; Salluzzo, M
2016-03-01
Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials' engineering tool in today's semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides. Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (TFM = 6-8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin-orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.
Tunable spin polarization and superconductivity in engineered oxide interfaces
Stornaiuolo, D.; Cantoni, C.; de Luca, G. M.; di Capua, R.; di. Gennaro, E.; Ghiringhelli, G.; Jouault, B.; Marrè, D.; Massarotti, D.; Miletto Granozio, F.; Pallecchi, I.; Piamonteze, C.; Rusponi, S.; Tafuri, F.; Salluzzo, M.
2016-03-01
Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials' engineering tool in today's semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides. Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (TFM = 6-8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin-orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.
RKKY interaction for the spin-polarized electron gas
Valizadeh, Mohammad M.; Satpathy, Sashi
2015-11-01
We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky-Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form ℋ = JS1 ṡS2 + D ṡS1 ×S2 + S1 ṡΓ ↔ṡS2. We find that for the spin-polarized electron gas, a nonzero tensor interaction Γ ↔ is present in addition to the scalar RKKY interaction J, while D is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta kF↑ and kF↓, while the R-3 distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.
Rashidian, Zeinab; Rezaeipour, Saeid; Hajati, Yaser; Lorestaniweiss, Zeinab; Ueda, Akiko
2017-02-01
In this work, we study the transport properties of Dirac fermions through the ferromagnetic silicene which is sandwiched between the Graphene leads (G/FS/G). Spin/valley conductance, spin/valley polarization, and also Fano factor are theoretically calculated using the Landauer-Buttiker formula. We find that the fully valley and spin polarized currents through the G/FS/G junction can be obtained by increasing the electric field strength and the length of ferromagnetic silicene region. Moreover, the valley polarization can be tuned from negative to positive values by changing the electric field. We find that the Fano factor also changes with the spin and valley polarization. Our findings of high controllability of the spin and valley transport in such a G/FS/G junction the potential of this junction for spin-valleytronics applications.
Ultracold Dipolar Gas of Fermionic 23Na40 K Molecules in Their Absolute Ground State.
Park, Jee Woo; Will, Sebastian A; Zwierlein, Martin W
2015-05-22
We report on the creation of an ultracold dipolar gas of fermionic 23Na40 K molecules in their absolute rovibrational and hyperfine ground state. Starting from weakly bound Feshbach molecules, we demonstrate hyperfine resolved two-photon transfer into the singlet X 1Σ+|v=0,J=0⟩ ground state, coherently bridging a binding energy difference of 0.65 eV via stimulated rapid adiabatic passage. The spin-polarized, nearly quantum degenerate molecular gas displays a lifetime longer than 2.5 s, highlighting NaK's stability against two-body chemical reactions. A homogeneous electric field is applied to induce a dipole moment of up to 0.8 D. With these advances, the exploration of many-body physics with strongly dipolar Fermi gases of 23Na40K molecules is within experimental reach.
Sample heating system for spin-polarized scanning electron microscopy.
Kohashi, Teruo; Motai, Kumi
2013-08-01
A sample-heating system for spin-polarized scanning electron microscopy (spin SEM) has been developed and used for microscopic magnetization analysis at temperatures up to 500°C. In this system, a compact ceramic heater and a preheating operation keep the ultra-high vacuum conditions while the sample is heated during spin SEM measurement. Moreover, the secondary-electron collector, which is arranged close to the sample, was modified so that it is not damaged at high temperatures. The system was used to heat a Co(1000) single-crystal sample from room temperature up to 500°C, and the magnetic-domain structures were observed. Changes of the domain structures were observed around 220 and 400°C, and these changes are considered to be due to phase transitions of this sample.
Spin-polarizing interferometric beam splitter for free electrons
Dellweg, Matthias M
2016-01-01
A spin-polarizing electron beam splitter is described which relies on an arrangement of linearly polarized laser waves of nonrelativistic intensity. An incident electron beam is first coherently scattered off a bichromatic laser field, splitting the beam into two portions, with electron spin and momentum being entangled. Afterwards, the partial beams are coherently superposed in an interferometric setup formed by standing laser waves. As a result, the outgoing electron beam is separated into its spin components along the laser magnetic field, which is shown by both analytical and numerical solutions of Pauli's equation. The proposed laser field configuration thus exerts the same effect on free electrons like an ordinary Stern-Gerlach magnet does on atoms.
An extended model for electron spin polarization in photosynthetic bacteria
Energy Technology Data Exchange (ETDEWEB)
Morris, A.L.; Norris, J.R. (Argonne National Lab., IL (USA) Chicago Univ., IL (USA). Dept. of Chemistry); Thurnauer, M.C. (Argonne National Lab., IL (USA))
1990-01-01
We have developed a general model for electron spin polarization which includes contributions from both CIDEP (chemically induced dynamic electron polarization) and CRP (correlated radical polarization). In this paper, we apply this model to sequential electron transfer in photosynthetic bacteria. Our model calculates the density matrix for the P{sup +}I{sup {minus}} radical pair and transfers the polarization as it develops to the P{sup +}Q{sup {minus}} radical pair. We illustrate several possible cases. One case is equivalent to CIDEP; no interactions are included on the secondary radical pair, P{sup +}Q{sup {minus}}. Another approximates CRPP by either increasing the transfer rate from P{sup +}I{sup {minus}} to P{sup +}Q{sup {minus}} or restricting interactions to the secondary radical pair, P{sup +}Q{sup {minus}}. Others allow interactions on both the primary and secondary radical pairs with various transfer rates. 15 refs., 4 figs.
Coherent Spin Polarization in an AC-Driven Mesoscopic Device
Directory of Open Access Journals (Sweden)
Asham M. D.
2012-01-01
Full Text Available The spin transport characteristics through a mesoscopic device are investigated under the effect of an AC-field. This device consists of two-diluted magnetic semiconductor (DMS leads and a nonmagnetic semiconducting quantum dot. The conductance for both spin parallel and antiparallel alignment in the two DMS leads is deduced. The corresponding equations for giant magnetoresistance (GMR and spin polarization (SP are also deduced. Calculations show an oscillatory behavior of the present studied pa- rameters. These oscillations are due to the coupling of photon energy and spin-up & spin-down subbands and also due to Fano-resonance. This research work is very im- portant for spintronic devices.
Role of correlations on spin-polarized neutron matter
Vidana, Isaac; Durant, Victoria
2016-01-01
Using the Hellmann--Feynman theorem we analyze the contribution of the different terms of the nucleon-nucleon interaction to the spin symmetry energy of neutron matter. The analysis is performed within the microscopic Brueckner--Hartree--Fock approach using the Argonne V18 realistic potential plus the Urbana IX three-body force. The main contribution to the spin-symmetry energy of neutron matter comes from the S=0 channel, acting only in the non-polarized neutron matter, in particular the $^1S_0$ and the $^1D_2$ partial waves. The importance of correlations in spin-polarized neutron matter is estimated by evaluating the kinetic energy difference between the correlated system and the underlying Fermi sea.
Spin polarization phenomena in dense neutron matter at a strong magnetic field
Isayev, A A
2010-01-01
Spin polarized states in neutron matter at strong magnetic fields up to $10^{18}$ G are considered in the model with the Skyrme effective interaction. Analyzing the self-consistent equations at zero temperature, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter as a function of density corresponds to the negative spin polarization when the majority of neutron spins are oriented oppositely to the direction of the magnetic field. Besides, it is found that in a strong magnetic field the state with the positive spin polarization can be realized as a metastable state at the high density region in neutron matter. At finite temperature, the entropy of the thermodynamically stable branch demonstrates the unusual behavior being larger than that for the nonpolarized state (at vanishing magnetic field) above certain critical density which is caused by the dependence of the entropy on the effective masses of neutrons in a spin polarized state.
MONTE CARLO SIMULATION OF SPIN-POLARIZED SECONDARY ELECTRONS FROM IRON
Institute of Scientific and Technical Information of China (English)
X. Sun; Z.J. Ding; H.M Li; K. Salma; Z.M. Zhang; W.S. Tan
2005-01-01
A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that:(1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27% for Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pb remaining constant at higher kinetic energies;(3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.
Energy Technology Data Exchange (ETDEWEB)
Yu, Dong [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Jiang, Lan, E-mail: jianglan@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Feng; Li, Xin [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Qu, Liangti [Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (China); Lu, Yongfeng [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)
2015-10-23
We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons.
Fong, C. F.; Ota, Y.; Iwamoto, S.; Arakawa, Y.
2017-06-01
Optically induced dynamic nuclear spin polarization (DNP) in a semiconductor quantum dot (QD) requires many cycles of excitation of spin polarized carriers and carrier recombination. As such, the radiative lifetime of the exciton containing the electron becomes one of the limiting factors of DNP. In principle, changing the radiative lifetime of the exciton will affect DNP and thus the nuclear spin polarization. Here, we demonstrate the manipulation of DNP in single QDs through the engineering of the photonic environment using two-dimensional photonic crystals. We find that the achievable degree of nuclear spin polarization can be controlled through the modification of exciton radiative lifetime. Our results show the promise of achieving a higher degree of nuclear spin polarization via photonic environment engineering, with implications on spin-based quantum information processing.
High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb
Sirohi, Anshu; Singh, Chandan K.; Thakur, Gohil S.; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Haque, Zeba; Gupta, L. C.; Kabir, Mukul; Ganguli, Ashok K.; Sheet, Goutam
2016-06-01
CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (˜47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.
Exchange interactions in transition metal oxides: the role of oxygen spin polarization
Logemann, R.; Rudenko, A. N.; Katsnelson, M. I.; Kirilyuk, A.
2017-08-01
Magnetism of transition metal (TM) oxides is usually described in terms of the Heisenberg model, with orientation-independent interactions between the spins. However, the applicability of such a model is not fully justified for TM oxides because spin polarization of oxygen is usually ignored. In the conventional model based on the Anderson principle, oxygen effects are considered as a property of the TM ion and only TM interactions are relevant. Here, we perform a systematic comparison between two approaches for spin polarization on oxygen in typical TM oxides. To this end, we calculate the exchange interactions in NiO, MnO and hematite (Fe2O3) for different magnetic configurations using the magnetic force theorem. We consider the full spin Hamiltonian including oxygen sites, and also derive an effective model where the spin polarization on oxygen renormalizes the exchange interactions between TM sites. Surprisingly, the exchange interactions in NiO depend on the magnetic state if spin polarization on oxygen is neglected, resulting in non-Heisenberg behavior. In contrast, the inclusion of spin polarization in NiO makes the Heisenberg model more applicable. Just the opposite, MnO behaves as a Heisenberg magnet when oxygen spin polarization is neglected, but shows strong non-Heisenberg effects when spin polarization on oxygen is included. In hematite, both models result in non-Heisenberg behavior. The general applicability of the magnetic force theorem as well as the Heisenberg model to TM oxides is discussed.
Polarization Measurement of Spin-Polarized Electrons by Optical Electron Polarimeter
Institute of Scientific and Technical Information of China (English)
DING Hai-Bing; PANG Wen-Ning; LIU Yi-Bao; SHANG Ren-Cheng
2005-01-01
@@ The polarization of spin-polarized electrons, produced from a new GaAs spin-polarized electron source, is determined by an optical electron polarimeter. The He 3 3p → 23S1 (388.9nm) transition is used for the optical electron polarimetry. The structure and performance of the experimental setup of spin-polarized electron source and optical electron polarimeter are described. The result of polarization of 30.8% averaged spin-up and spindown polarized electrons is obtained and presented.
Institute of Scientific and Technical Information of China (English)
Wen Wu
2007-01-01
Spin polarizer is one of the most important devices for the newly developing field of spintronics, which may revolute the popular information techniques. Here we present a phenomenal model for a novel spin polarizer, which utilizes two back to back ferromagnetic metal/semiconductor Schottky barriers to define a semiconductor transport channel whose length is less than the spin decoherence length of the host semiconductor. Along this channel, conducting electrons move diffusively in momentum space while they keep ballistic motion in spin space. Across the channel, electrons suffer a spin dependent tunneling, which establishes spin polarization along the channel.
Spin polarization and color superconductivity in the Nambu-Jona-Lasinio model at finite temperature
Matsuoka, Hiroaki; da Providencia, Joao; Providencia, Constancia; Yamamura, Masatoshi
2016-01-01
We investigate the possible existence of spin polarization and color superconductivity in the Nambu-Jona-Lasinio model with a tensor-type interaction at finite density and temperature. The thermodynamic potential is calculated by the functional integral method. Numerical results indicate that at low temperature and quark chemical potential the chiral condensed phase exists, and at intermediate chemical potential the color superconducting phase appears. In addition, depending on the magnitude of the tensor coupling, at large chemical potential and low temperature, a color superconducting phase and a spin polarized phase may coexist while at intermediate temperatures only the spin polarized phase occurs.
Spin-polarization reversal at the interface between benzene and Fe(100)
Goumri-Said, Souraya
2013-01-03
The spin-polarization at the interface between Fe(100) and a benzene is investigated theoretically using density functional theory for two positions of the organic molecule: planar and perpendicular with respect to the substrate. The electronic and magnetic properties as well as the spin-polarization close to the Fermi level strongly depend on the benzene position on the iron surface. An inversion of the spin-polarization is induced by p-d hybridization and charge transfer from the iron to the carbon sites in both configurations.
Spin Polarization Inversion at Benzene-Absorbed Fe4N Surface
Zhang, Qian
2015-05-27
We report a first-principle study on electronic structure and simulation of the spin-polarized scanning tunneling microscopy graphic of a benzene/Fe4N interface. Fe4N is a compound ferromagnet suitable for many spintronic applications. We found that, depending on the particular termination schemes and interface configurations, the spin polarization on the benzene surface shows a rich variety of properties ranging from cosine-type oscillation to polarization inversion. Spin-polarization inversion above benzene is resulting from the hybridizations between C pz and the out-of-plane d orbitals of Fe atom.
Nuclear reactivity indices in the context of spin polarized density functional theory
Energy Technology Data Exchange (ETDEWEB)
Cardenas, Carlos [Departamento de Quimica, Facultad de Ecologia y Recursos Naturales, Universidad Andres Bello, Republica 275, Santiago (Chile)], E-mail: car.cardenas@uandresbello.edu; Lamsabhi, Al Mokhtar [Departamento de Quimica C-9, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Fuentealba, Patricio [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile)
2006-03-20
In this work, the nuclear reactivity indices of density functional theory have been generalized to the spin polarized case and their relationship to electron spin polarized indices has been established. In particular, the spin polarized version of the nuclear Fukui function has been proposed and a finite difference approximation has been used to evaluate it. Applications to a series of triatomic molecules demonstrate the ability of the new functions to predict the geometrical changes due to a change in the spin multiplicity. The main equations in the different ensembles have also been presented.
Three-body Effect on Equation of State of Spin-polarized Nuclear Matter
Institute of Scientific and Technical Information of China (English)
ZuoWei
2003-01-01
The equation of state (EOS) of spin-polarized nuclear matter has been investigated within the spin-dependent; Brueckner-Hartree-Fock framework by adopting the realistic nucleon-nucleon interaction supplemented with a microscopic three-body force. The three-body force effects have been studied and stressed with a special attention. The calculated results are given in Fig.1. It is seen that; in the Brueckner-Hartree-Fock framework the predicted energy per particle of spin-polarized nuclear matter versus the neutron and proton spin-polarization parameters fulfills a quadratic law in the whole range of spin-polarization. The related physical quantities such as spin the Landau parameters Go in spin channel and G′0 in spin-isospin channel, have been also calculated.
Santhanam, K S V; Chen, Xu; Gupta, S
2014-04-01
Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.
The surface magnetization study of Cr2O3 by spin polarized low energy electron microscopy
Cao, Shi; Wu, Ning; Zhang, Xin; N'diaye, Alpha; Chen, Gong; Schmid, Andreas; Echtenkamp, Will; Lauter, Valeria; Binek, Christian; Dowben, Peter
2014-03-01
The boundary magnetization at the surface of a Cr2O3 single crystal has been demonstrated by using spin-polarized low-energy electron microscopy (SPLEEM), indicating net surface spin polarization. This work shows that the placement of Cr2O3 single crystal in the single domain state, will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the spin-polarized low-energy electron microscopy (SPLEEM) contrast for the two polarizations states is different. In addition, the boundary magnetization protected by the symmetry exists despite of the surface roughness/softness which was studied by the non-spin neutron reflectometry and low energy electron diffraction. Unoccupied surface oxygen sites and chromium sites are possible mechanism contributing to the surface ``softness,'' which will be discussed.
Liu, Qihang; Dessau, D S; Zunger, Alex
2016-01-01
Associated with spin-orbit coupling (SOC) and inversion symmetry breaking, Rashba spin polarization opens a new avenue for spintronic applications that was previously limited to ordinary magnets. However, spin polarization effects in actual Rashba systems are far more complicated than what conventional single-orbital models would suggest. By studying via first-principles DFT and a multi-orbital k.p model a 3D bulk Rashba system (free of complications by surface effects) we find that the physical origin of the leading spin polarization effects is SOC-induced hybridization between spin and multiple orbitals, especially those with nonzero orbital angular momenta. In this framework we establish a general understanding of the orbital mapping, common to the surface of topological insulators and Rashba system. Consequently, the intrinsic mechanism of various spin polarization effects, which pertain to all Rashba systems even those with global inversion symmetry, is understood as a manifestation of the orbital textur...
Hamiltonian description of composite fermions: Magnetoexciton dispersions
Murthy, Ganpathy
1999-11-01
A microscopic Hamiltonian theory of the FQHE, developed by Shankar and myself based on the fermionic Chern-Simons approach, has recently been quite successful in calculating gaps in fractional quantum hall states, and in predicting approximate scaling relations between the gaps of different fractions. I now apply this formalism towards computing magnetoexciton dispersions (including spin-flip dispersions) in the ν=13, 25, and 37 gapped fractions, and find approximate agreement with numerical results. I also analyze the evolution of these dispersions with increasing sample thickness, modelled by a potential soft at high momenta. New results are obtained for instabilities as a function of thickness for 25 and 37, and it is shown that the spin-polarized 25 state, in contrast to the spin-polarized 13 state, cannot be described as a simple quantum ferromagnet.
Fermions as Topological Objects
Directory of Open Access Journals (Sweden)
Yershov V. N.
2006-01-01
Full Text Available A preon-based composite model of the fundamental fermions is discussed, in which the fermions are bound states of smaller entities — primitive charges (preons. The preon is regarded as a dislocation in a dual 3-dimensional manifold — a topological object with no properties, save its unit mass and unit charge. It is shown that the dualism of this manifold gives rise to a hierarchy of complex structures resembling by their properties three families of the fundamental fermions. Although just a scheme for building a model of elementary particles, this description yields a quantitative explanation of many observable particle properties, including their masses.
Spontaneous polarization of composite fermions in the n = 1 Landau level of graphene
Coimbatore Balram, Ajit; Tőke, Csaba; Wójs, Arkadiusz; Jain, Jainendra
Motivated by experiments that reveal expansive fractional quantum Hall states in the n = 1 graphene Landau level and suggest a nontrivial role of the spin degree of freedom [Amet et al., Nat. Commun. 6, 5838 (2014)], we perform accurate quantitative study of the the competition between fractional quantum Hall states with different spin polarizations in the n = 1 graphene Landau level. We find that the fractional quantum Hall effect is well described in terms of composite fermions, but the spin physics is qualitatively different from that in the n = 0 Landau level. In particular, for the states at filling factors ν = s / (2 s +/- 1) , s integer, a combination of exact diagonalization and the composite fermion theory shows that the ground state is fully spin polarized and supports a robust spin wave mode even in the limit of vanishing Zeeman coupling. Thus, even though composite fermions are formed, a mean field description that treats them as weakly interacting particles breaks down, and the exchange interaction between them is strong enough to cause a qualitative change in the behavior by inducing full spin polarization. We also find that the fully spin polarized composite fermion Fermi sea has lower energy than the paired Pfaffian state at the relevant half fillings. Award No. DE-SC0005042 (ACB, JKJ), Hungarian Scientific Research Funds No. K105149 (CT), the Polish NCN Grant 2014/14/A/ST3/00654 and the EU Marie Curie Grant PCIG09-GA-2011-294186 (AW).
Electrical Probing of Inherent Spin Polarization in a Topological Insulator with Electrical Gating
Lee, Joon Sue; Richardella, Anthony; Samarth, Nitin
2015-03-01
The hallmark of a time-reversal symmetry protected three-dimensional topological insulator is the helically spin-textured surface state. Although electrical detection of spin polarization in topological insulators has been demonstrated very recently, there have not been any electrical measurements to demonstrate the entire mapping of the spin polarization throughout the surface state. We report the electrical probing of the spin-polarized surface state using a magnetic tunnel junction as a spin detector while the chemical potential of a topological insulator (Bi,Sb)2Te3 is tuned by back gating. Hysteretic spin signals were observed as the magnetization of the detector ferromagnet (permalloy) switches with in-plane magnetic field. Changing the direction of bias current through the topological insulator channel flips the direction of the spin polarization, resulting in the reverse of sign of the detected spin signals. We demonstrate the control of the Fermi energy, which has importance not only in further understanding of the spin-momentum locking in the surface state but also in possible electrical tuning of the spin polarization for potential spin-based devices. Supported by C-SPIN & DARPA/SRC.
Liu, Qihang; Zhang, Xiuwen; Waugh, J. A.; Dessau, D. S.; Zunger, Alex
2016-09-01
Associated with spin-orbit coupling (SOC) and inversion symmetry breaking, Rashba spin polarization opens an avenue for spintronic applications that was previously limited to ordinary magnets. However, spin-polarization effects in actual Rashba systems are far more complicated than what conventional single-orbital models would suggest. By studying via density functional theory and a multiorbital k .p model a three-dimensional bulk Rashba system (free of complications by surface effects), BiTeI, we find that the physical origin of the leading spin-polarization effects is SOC-induced hybridization between spin and multiple orbitals, especially those with nonzero orbital angular momenta. In this framework we establish a general understanding of the orbital mapping, common to the surface of topological insulators and the Rashba system. Consequently, the intrinsic mechanism of various spin-polarization effects—which pertain to all Rashba systems, even those with global inversion symmetry—is understood as a manifestation of the orbital textures. This finding suggests a route for designing high-spin-polarization materials by considering the atomic-orbital content.
Chirality-induced spin polarization places symmetry constraints on biomolecular interactions
Kumar, Anup; Capua, Eyal; Kesharwani, Manoj K.; Martin, Jan M. L.; Sitbon, Einat; Waldeck, David H.; Naaman, Ron
2017-01-01
Noncovalent interactions between molecules are key for many biological processes. Necessarily, when molecules interact, the electronic charge in each of them is redistributed. Here, we show experimentally that, in chiral molecules, charge redistribution is accompanied by spin polarization. We describe how this spin polarization adds an enantioselective term to the forces, so that homochiral interaction energies differ from heterochiral ones. The spin polarization was measured by using a modified Hall effect device. An electric field that is applied along the molecules causes charge redistribution, and for chiral molecules, a Hall voltage is measured that indicates the spin polarization. Based on this observation, we conjecture that the spin polarization enforces symmetry constraints on the biorecognition process between two chiral molecules, and we describe how these constraints can lead to selectivity in the interaction between enantiomers based on their handedness. Model quantum chemistry calculations that rigorously enforce these constraints show that the interaction energy for methyl groups on homochiral molecules differs significantly from that found for heterochiral molecules at van der Waals contact and shorter (i.e., ∼0.5 kcal/mol at 0.26 nm). PMID:28228525
Spin polarization measurements of ferromagnetic atomic chains on a superconductor: Part I
Xie, Yonglong; Jeon, Sangjun; Drozdov, Ilya; Li, Jian; Bernevig, Andrei; Yazdani, Ali
Introduction of magnetic defects in superconductors gives rise to spin polarized in-gap Shiba states. Recently chains of magnetic atoms, which give rise to a band of Shiba states, have been proposed as a platform for topological superconductivity. Spectroscopic evidence for in-gap Shiba states and Majorana end mode has been reported in previous studies of self-assembled chains of ferromagnetic Fe atoms on the surface of Pb. In this talk, we introduce the technique of spin-polarized scanning tunneling microscopy and spectroscopy (SP-STM) and discuss how we prepare tips that can show spin contrast at zero magnetic field, without disrupting superconductivity on the Pb surface. We use this technique, combined with the use of a vector magnet to orient the tip magnetization to probe the spin polarization of the Shiba states induced by the Fe atomic chains onto the Pb surface. A key to interpreting such experiments with spin-polarized STM tip is to understand the role of spin-polarization in the setpoint effect, which will be discussed in the next talk. Work supported by ONR and Moore Foundation.
Structure-Dependent Spin Polarization in Polymorphic CdS:Y Semiconductor Nanocrystals.
Wang, Pan; Xiao, Bingxin; Zhao, Rui; Ma, Yanzhang; Zhang, Mingzhe
2016-03-01
Searching for the polymorphic semiconductor nanocrystals would provide precise and insightful structure-spin polarization correlations and meaningful guidance for designing and synthesizing high spin-polarized spintronic materials. Herein, the high spin polarization is achieved in polymorphic CdS:Y semiconductor nanocrystals. The high-pressure polymorph of rock-salt CdS:Y nanocrystals has been recovered at ambient conditions synthesized by the wurtzite CdS:Y nanocrystals as starting material under 5.2 GPa and 300 °C conditions. The rock-salt CdS:Y polymorph displays more robust room-temperature ferromagnetism than wurtzite sample, which can reach the ferromagnetic level of conventional semiconductors doped with magnetic transition-metal ions, mainly due to the significantly enhanced spin configuration and defect states. Therefore, crystal structure directly governs the spin configuration, which determines the degree of spin polarization. This work can provide experimental and theoretical methods for designing the high spin-polarized semiconductor nanocrystals, which is important for applications in semiconductor spintronics.
Indian Academy of Sciences (India)
Misra Deepanjali; Tripathy Sukanta Kumar
2016-03-01
A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and magnetic fields. It is found that magnetic impurityincreases the degree of spin polarization irrespective of temperature, while the electron–phonon interaction decreases the degree of spin polarization. Results are found to be in better agreement with experiments.
Rokhinson, Leonid; Kazakov, Aleksandr; Simion, George; Lyanda-Geller, Yuli; Kolkovsky, Valery; Karczewski, Grzegorz; Adamus, Zbigniew; Wojtowicz, Tomasz
2016-10-01
Several experiments in nanowires detected signatures of Majorana fermions, building block for topologicaly protected quantum computer. Now the focus of research is shifting toward systems where non-Abelian statistics of excitations can be demonstrated. To achieve this goal we are developing a new dilute magnetic semiconductor-based platform where non-Abelian excitations can be created and manipulated in a two-dimensional plane, with support for Majorana and higher order non-Abelian excitations. Here we report development of heterostructures where spin polarization of a two-dimensional electron gas in a quantum Hall regime can be controlled locally by electrostatic gating. This is demonstrated via voltage induced shift of quantum Hall ferromagnetic transition in the CdTe quantum wells with engineered placement of paramagnetic Mn impurities. The structures can be used to form helical domain walls in integer quantum Hall regime which, coupled to an s-wave superconductor, are expected to support Majorana zero modes. These heterostructures can be used as a testbed to study gate-reconfigurable domain walls networks.
In situ scanning tunneling microscope tip treatment device for spin polarization imaging
Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN
2008-04-22
A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.
Spin-polarized versus chiral condensate in quark matter at finite temperature and density
DEFF Research Database (Denmark)
Matsuoka, Hiroaki; Tsue, Yasuhiko; da Providencia, Joao
2016-01-01
It is shown that the spin-polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasiniotype model as a low-energy effective theory of quantum chromodynamics. It is indicated within this low-energy ef......It is shown that the spin-polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasiniotype model as a low-energy effective theory of quantum chromodynamics. It is indicated within this low......-energy effective model that the chiral symmetry is broken again by the spin-polarized condensate on increasing the quark number density, while chiral symmetry restoration occurs, in which the chiral condensate disappears at a certain density....
Spin-polarized photoemission of Fe{sub 80}B{sub 20}
Energy Technology Data Exchange (ETDEWEB)
Xu, Y.B.; Walker, C.G.H.; Greig, D. [Department of Physics, University of Leeds, Leeds (United Kingdom); Seddon, E.A.; Kirkman, L.W.; Quinn, F.M. [Daresbury Laboratory, Daresbury, Warrington, Cheshire (United Kingdom); Matthew, J.A.D. [Department of Physics, University of York, Heslington, York (United Kingdom)
1996-03-04
The first spin-resolved photoemission experiment on an iron - boron amorphous alloy using a synchrotron source is presented. The experimental spin polarization of the d band of Fe{sub 80}B{sub 20} has been compared with three theoretical predictions and found to be in best agreement with self-consistent spin-polarized calculations based on a supercell LMTO approach. The observed average spin polarization of the valence band is approximately twice that of 10 eV secondary electrons. Hysteresis loops for Fe{sub 80}B{sub 20} determined from the 1 eV and 20 eV secondary-electron asymmetry are similar to those determined using the magnetooptic Kerr effect, but show a lower coercivity. The differences are attributed to a combination of different sampling depths of the two techniques and to the surface inhomogeneity of the sample. (author)
Spin polarization in high density quark matter under a strong external magnetic field
Tsue, Yasuhiko; Providencia, Constanca; Yamamura, Masatoshi; Bohr, Henrik
2016-01-01
In high density quark matter under a strong external magnetic field, possible phases are investigated by using the Nambu-Jona-Lasinio model with axial vector-type four-point interaction or tensor-type four-point interaction between quarks. In the axial vector-type interaction, it is shown that a quark spin polarized phase is realized in all region of the quark chemical potential under a strong external magnetic field within the lowest Landau level approximation. Each phase is characterized by the chiral condensate or dynamical quark mass. On the other hand, in the tensor-type interaction, it is also shown that the quark spin polarized phase does not appear even if there exists the strong external magnetic field. However, if the anomalous magnetic moment of quark is taken into account, it may be possible to realize the quark spin polarized phase.
High spin polarization in CoFeMnGe equiatomic quaternary Heusler alloy
Energy Technology Data Exchange (ETDEWEB)
Bainsla, Lakhan [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Suresh, K. G., E-mail: suresh@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Nigam, A. K. [Department of Condensed Matter and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005 (India); Manivel Raja, M. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Varaprasad, B. S. D. Ch. S.; Takahashi, Y. K.; Hono, K. [Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan)
2014-11-28
We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO{sub 3} disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for the half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Makarov, Vladimir I., E-mail: vmvimakarov@gmail.com [Department of Physics, University of Puerto Rico, Rio Piedras, PO Box 23343, San Juan, PR 00931-3343 (United States); Khmelinskii, Igor [Universidade do Algarve, FCT, DQF, and CIQA, 8005-139 Faro (Portugal)
2015-04-15
Highlights: • Development of a new spintronics device. • Development of quantum spin polarized filters. • Development of theory of quantum spin polarized filter. - Abstract: Presently we report spin-polarized state transport in semiconductor–dielectric–iron–semiconductor (SDIS) four-nanolayer sandwich devices. The exchange-resonance spectra in such devices are quite specific, differing also from spectra observed earlier in other three-nanolayer devices. The theoretical model developed earlier is extended and used to interpret the available experimental results. A detailed ab initio analysis of the magnetic-field dependence of the output magnetic moment is also performed. The model predicts an exchange spectrum comprising a series of peaks, with the spectral structure determined by several factors, discussed in the paper.
Nuclear spin polarized H and D by means of spin-exchange optical pumping
Stenger, Jörn; Grosshauser, Carsten; Kilian, Wolfgang; Nagengast, Wolfgang; Ranzenberger, Bernd; Rith, Klaus; Schmidt, Frank
1998-01-01
Optically pumped spin-exchange sources for polarized hydrogen and deuterium atoms have been demonstrated to yield high atomic flow and high electron spin polarization. For maximum nuclear polarization the source has to be operated in spin temperature equilibrium, which has already been demonstrated for hydrogen. In spin temperature equilibrium the nuclear spin polarization PI equals the electron spin polarization PS for hydrogen and is even larger than PS for deuterium. We discuss the general properties of spin temperature equilibrium for a sample of deuterium atoms. One result are the equations PI=4PS/(3+PS2) and Pzz=PSṡPI, where Pzz is the nuclear tensor polarization. Furthermore we demonstrate that the deuterium atoms from our source are in spin temperature equilibrium within the experimental accuracy.
Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States
Bentmann, H.; Maaß, H.; Krasovskii, E. E.; Peixoto, T. R. F.; Seibel, C.; Leandersson, M.; Balasubramanian, T.; Reinert, F.
2017-09-01
A comprehensive understanding of spin-polarized photoemission is crucial for accessing the electronic structure of spin-orbit coupled materials. Yet, the impact of the final state in the photoemission process on the photoelectron spin has been difficult to assess in these systems. We present experiments for the spin-orbit split states in a Bi-Ag surface alloy showing that the alteration of the final state with energy may cause a complete reversal of the photoelectron spin polarization. We explain the effect on the basis of ab initio one-step photoemission theory and describe how it originates from linear dichroism in the angular distribution of photoelectrons. Our analysis shows that the modulated photoelectron spin polarization reflects the intrinsic spin density of the surface state being sampled differently depending on the final state, and it indicates linear dichroism as a natural probe of spin-orbit coupling at surfaces.
Electron spin polarization in strong-field ionization of xenon atoms
Hartung, Alexander; Morales, Felipe; Kunitski, Maksim; Henrichs, Kevin; Laucke, Alina; Richter, Martin; Jahnke, Till; Kalinin, Anton; Schöffler, Markus; Schmidt, Lothar Ph. H.; Ivanov, Misha; Smirnova, Olga; Dörner, Reinhard
2016-08-01
As a fundamental property of the electron, the spin plays a decisive role in the electronic structure of matter, from solids to molecules and atoms, for example, by causing magnetism. Yet, despite its importance, the spin dynamics of the electrons released during the interaction of atoms with strong ultrashort laser pulses has remained experimentally unexplored. Here, we report the experimental detection of electron spin polarization by the strong-field ionization of xenon atoms and support our results with theoretical analysis. We found up to 30% spin polarization changing its sign with electron energy. This work opens the new dimension of spin to strong-field physics. It paves the way to the production of sub-femtosecond spin-polarized electron pulses with applications ranging from probing the magnetic properties of matter at ultrafast timescales to testing chiral molecular systems with sub-femtosecond temporal and sub-ångström spatial resolutions.
Spin-Polarized Transport through Parallel Double Quantum Dots Coupled to Ferromagnetic Leads
Institute of Scientific and Technical Information of China (English)
HOU Tao; WU Shao-Quan; BI Ai-Hua; YANG Fu-Bin; SUN Wei-Li
2008-01-01
We theoretically study the spin-polarized transport phenomena of the parallel double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The Hamiltonian is solved by means of the equation-of-motion approach. We analyse the transmission probability of this system in both the equilibrium and nonequilibrium cases, and our results reveal that the transport properties show some noticeable characteristics depending upon both the spin-polarized strength p and the value of the magnetic flux Ф. Moreover, in the parallel configuration, the position of the Kondo peak shifts while it remains unchanged for the antiparallel configuration. These effects might have some potential applications in spintronics.
Peculiarities of spin polarization inversion at a thiophene/cobalt interface
Wang, Xuhui
2013-03-20
We perform ab initio calculations to investigate the spin polarization at the interface between a thiophene molecule and cobalt substrate. We find that the reduced symmetry in the presence of a sulfur atom (in the thiophene molecule) leads to a strong spatial dependence of the spin polarization of the molecule. The two carbon atoms far from the sulfur acquire a polarization opposite to that of the substrate, while the carbon atoms bonded directly to sulfur possess the same polarization as the substrate. We determine the origin of this peculiar spin interface property as well as its impact on the spin transport.
Construction of the spin-polarized slow positron beam with the RI source
Energy Technology Data Exchange (ETDEWEB)
Nakajyo, Terunobu; Tashiro, Mutsumi; Kanazawa, Ikuzo [Tokyo Gakugei Univ., Koganei (Japan); Komori, Fumio; Murata, Yoshimasa; Ito, Yasuo
1997-03-01
The electrostatic slow-positron beam is constructed by using {sup 22}Na source. We design the electrostatic lens, the system of the detector, and the Wien filter for the experiment`s system of the spin-polarized slow positron beam. The reemitted spin-polarized slow-positron spectroscopy is proposed for studying magnetic thin films and magnetic multilayers. We calculated the depolarized positron fractions in the Fe thin film Fe(10nm)/Cu(substrate) and the multilayers Cu(1nm)/Fe(10nm)/Cu(substrate). (author)
Spin-to-Orbital Angular Momentum Conversion and Spin-Polarization Filtering in Electron Beams
Karimi, Ebrahim; Grillo, Vincenzo; Santamato, Enrico; 10.1103/PhysRevLett.108.044801
2012-01-01
We propose the design of a space-variant Wien filter for electron beams that induces a spin half-turn and converts the corresponding spin angular momentum variation into orbital angular momentum of the beam itself by exploiting a geometrical phase arising in the spin manipulation. When applied to a spatially coherent input spin-polarized electron beam, such a device can generate an electron vortex beam, carrying orbital angular momentum. When applied to an unpolarized input beam, the proposed device, in combination with a suitable diffraction element, can act as a very effective spin-polarization filter. The same approach can also be applied to neutron or atom beams.
Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface
DEFF Research Database (Denmark)
Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.;
2003-01-01
Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...
Spin polarization versus color–flavor locking in high-density quark matter
DEFF Research Database (Denmark)
Tsue, Yasuhiko; da Providência, João; Providência, Constança;
2015-01-01
It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of color–flavor locking at high baryon density by using the Nambu–Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between...
Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes
Energy Technology Data Exchange (ETDEWEB)
Yamada, Toyo Kazu, E-mail: toyoyamada@faculty.chiba-u.jp [Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba (Japan); Vazquez de Parga, Amadeo L. [Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia and Dep. Fisica de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain)
2014-11-03
Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.
Tunnel Spin Polarization Versus Energy for Clean and Doped Al2O3 Barriers
Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.
2007-01-01
The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the
Gate control of spin-polarized conductance in alloyed transitional metal nanocontacts
Sivkov, Ilia N.; Brovko, Oleg O.; Rungger, Ivan; Stepanyuk, Valeri S.
2017-03-01
To date, endeavors in nanoscale spintronics are dominated by the use of single-electron or single-spin transistors having at their heart a semiconductor, metallic, or molecular quantum dot whose localized states are non-spin-degenerate and can be controlled by an external bias applied via a gate electrode. Adjusting the bias of the gate one can realign those states with respect to the chemical potentials of the leads and thus tailor the spin-polarized transmission properties of the device. Here we show that similar functionality can be achieved in a purely metallic junction comprised of a metallic magnetic chain attached to metallic paramagnetic leads and biased by a gate electrode. Our ab initio calculations of electron transport through mixed Pt-Fe (Fe-Pd and Fe-Rh) atomic chains suspended between Pt (Pd and Rh) electrodes show that spin-polarized confined states of the chain can be shifted by the gate bias causing a change in the relative contributions of majority and minority channels to the nanocontact's conductance. As a result, we observe strong dependence of conductance spin polarization on the applied gate potential. In some cases the spin polarization of conductance can even be reversed in sign upon gate potential application, which is a remarkable and promising trait for spintronic applications.
Point Contact Andreev Reflection Measurement of the Spin Polarization of Ferromagnetic Alloy NiFeSb
Institute of Scientific and Technical Information of China (English)
李壮志; 陶宏杰; 闻海虎; 张铭; 柳祝红; 崔玉亭; 吴光恒
2002-01-01
We have studied the temperature-dependent and barrier-strength-dependent Andreev reflection tunnelling spectroscopy with point contacts consisting of the newly synthesized half-metallic alloy NiFeSb and a Nb tip. By fitting the data to the generalized Blonder-Tinkham-Klapwijk theory, a spin polarization P ＝ 0.52 has been obtained.
The spin polarized band structure of strained thin films of gadolinium
Energy Technology Data Exchange (ETDEWEB)
Waldfried, C.; Dowben, P.A. [Univ. of Nebraska, Lincoln, NE (United States); Vescovo, E. [Brookhaven National Lab., Upton, NY (United States). National Synchrotron Light Source
1998-12-31
The magnetic properties of strained thin films of gadolinium are characterized by a wave vector and thickness dependence of the exchange splitting. The spin-resolved band structure has been mapped by spin polarized photoemission, and provides considerable insight into the relationship between magnetism of local moment systems, and band structure.
van Gastel, Maurice
2009-09-28
Spin polarization effects play an important role in the theory of isotropic hyperfine interactions for aromatic protons. The spin polarization gives rise to significant isotropic proton hyperfine interactions--spin-dependent one-electron properties--smaller than 0 MHz and the effect has been theoretically described [H. M. McConnell and D. B. J. Chesnut, Chem. Phys. 28, 107 (1958)]. The influence of spin polarization on the zero field splitting parameters, which are spin-dependent two-electron properties, has not been clearly identified yet. A phenomenological equation is proposed here for the contribution of spin polarization to the zero field splitting parameter D in analogy to McConnell's equation for hyperfine interactions. The presence of the effect is demonstrated in a series of calculations on polyacenes in the triplet state and turns out to be responsible for up to 50% of the D parameter in the case of naphthalene! It is found that spin-unrestricted single-determinant methods, including the widely used density functional theory methods, do not accurately reproduce the two-electron reduced electron density required for the evaluation of two-electron spin-dependent properties. For the accurate calculation of zero field splitting parameters by quantum chemical methods, it thus seems necessary to resort to correlated ab initio methods which do not give rise to spin contamination and which do provide an accurate description of the two-electron reduced electron density.
THOLE, BT; VANDERLAAN, G
1991-01-01
Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of
Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts
DEFF Research Database (Denmark)
Hu, C.-M.; Nitta, Junsaku; Jensen, Ane
2001-01-01
Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spin...
Transient charging and discharging of spin-polarized electrons in a quantum dot
DEFF Research Database (Denmark)
De Souza, Fabricio; Leao, S.A.; Gester, R. M.;
2007-01-01
We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leads subjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations, spin accumulation, and tunneling magnetoresistance TMR are calculated using both nonequilibrium Green ...
Biaxial-stress-driven full spin polarization in ferromagnetic hexagonal chromium telluride
Xiao, Xiang-Bo; Li, Jun; Liu, Bang-Gui
2017-03-01
It is important to spintronics to achieve fully-spin-polarized magnetic materials that are stable and can be easily fabricated. Here, through systematical density-functional-theory investigations, we achieve high and even full spin polarization for carriers in the ground-state phase of CrTe by applying tensile biaxial stress. The resulting strain is tensile in the xy plane and compressive in the z axis. With the in-plane tensile strain increasing, the ferromagnetic order is stable against antiferromagnetic fluctuations, and a half-metallic ferromagnetism is achieved at an in-plane strain of 4.8%. With the spin-orbit coupling taken into account, the spin polarization is equivalent to 97% at the electronic transition point, and then becomes 100.0% at the in-plane strain of 6.0%. These make us believe that the full-spin-polarized ferromagnetism in this stable and easily-realizable hexagonal phase could be realized soon, and applied in spintronics.
THOLE, BT; VANDERLAAN, G
1991-01-01
Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of transitio
Atomic origin of the spin-polarization of the Co2FeAl Heusler compound
Liang, Jaw-Yeu; Lam, Tu-Ngoc; Lin, Yan-Cheng; Chang, Shu-Jui; Lin, Hong-Ji; Tseng, Yuan-Chieh
2016-02-01
Using synchrotron x-ray techniques, we studied the Co2FeAl spin-polarization state that generates the half-metallicity of the compound during an A2 (low-spin) → B2 (high-spin) phase transition. Given the advantage of element specificity of x-ray techniques, we could fingerprint the structural and magnetic cross-reactions between Co and Fe within a complex Co2FeAl structure deposited on a MgO (0 0 1) substrate. X-ray diffraction and extended x-ray absorption fine structure investigations determined that the Co atoms preferably populate the (1/4,1/4,1/4) and (3/4,3/4,3/4) sites during the development of the B2 phase. X-ray magnetic spectroscopy showed that although the two magnetic elements were ferromagnetically coupled, they interacted in a competing manner via a charge-transfer effect, which enhanced Co spin polarization at the expense of Fe spin polarization during the phase transition. This means that the spin-polarization of Co2FeAl was electronically dominated by Fe in A2 whereas the charge transfer turned the dominance to Co upon B2 formation. Helicity-dependent x-ray absorption spectra also revealed that only the minority state of Co/Fe was involved in the charge-transfer effect whereas the majority state was independent of it. Despite an overall increase of Co2FeAl magnetization, the charge-transfer effect created an undesired trade-off during the Co-Fe exchange interactions, because of the presence of twice as many X sites (Co) as Y sites (Fe) in the Heusler X 2 YZ formula. This suggests that the spin-polarization of Co2FeAl is unfortunately regulated by compromising the enhanced X (Co) sites and the suppressed Y (Fe) sites, irrespective of the development of the previously known high-spin-polarization phase of B2. This finding provides a possible cause for the limited half-metallicity of Co2FeAl discovered recently. Electronic tuning between the X and Y sites is necessary to further increase the spin-polarization, and likely the half
Ding, Zhichao; Long, Xingwu; Yuan, Jie; Fan, Zhenfang; Luo, Hui
2016-09-01
A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.
Wu, Ying-Hai; Sreejith, G. J.; Jain, Jainendra K.
2012-09-01
The edge of spin-unpolarized or spin-polarized ν=2/3 fractional quantum Hall states is predicted by the effective theory to support a backward-moving neutral mode in addition to a forward-moving charge mode. We study this issue from a microscopic perspective where these states are identified with an effective filling factor of 2 of composite fermions, but with an effective magnetic field that is antiparallel to the external field. A simple counting from the composite fermion description suggests that there might be two backward-moving edge modes, but explicit calculations show that one of these is projected out of the low-energy sector, while the remaining mode provides a good microscopic account of the actual counterpropagating edge mode. The forward-moving modes are identified as “Schur modes,” obtained by multiplying the ground-state wave function by the symmetric Schur polynomials. The edge of the 2/3 spin unpolarized state provides a particularly striking realization of “spin-charge separation” in one-dimensional Tomonaga-Luttinger liquids, with the spin and charge modes moving in opposite directions.
Institute of Scientific and Technical Information of China (English)
Hong Xue-Kun; Yang Xi-Feng; Feng Jin-Fu; Liu Yu-Shen
2013-01-01
We propose a Rashba three-terminal double-quantum-dot device to generate a spin-polarized current and manipulate the electron spin in each quantum dot by utilizing the temperature gradient instead of the electric bias voltage.This device possesses a nonresonant tunneling channel and two resonant tunneling channels.The Keldysh nonequilibrium Green's function techniques are employed to determinate the spin-polarized current flowing from the electrodes and the spin accumulation in each quantum dot.We find that their signs and magnitudes are well controllable by the gate voltage or the temperature gradient.This result is attributed to the change in the slope of the transmission probability at the Fermi levels in the low-temperature region.Importantly,an obviously pure spin current can be injected into or extracted from one of the three electrodes by properly choosing the temperature gradient and the gate voltages.Therefore,the device can be used as an ideal thermal generator to produce a pure spin current and manipulate the electron spin in the quantum dot.
High spin-polarization in ultrathin Co{sub 2}MnSi/CoPd multilayers
Energy Technology Data Exchange (ETDEWEB)
Galanakis, I., E-mail: galanakis@upatras.gr
2015-03-01
Half-metallic Co{sub 2}MnSi finds a broad spectrum of applications in spintronic devices either in the form of thin films or as spacer in multilayers. Using state-of-the-art ab-initio electronic structure calculations we exploit the electronic and magnetic properties of ultrathin Co{sub 2}MnSi/CoPd multilayers. We show that these heterostructures combine high values of spin-polarization at the Co{sub 2}MnSi spacer with the perpendicular magnetic anisotropy of binary compounds such as CoPd. Thus they could find application in spintronic/magnetoelectronic devices. - Highlights: • Ab-initio study of ultrathin Co{sub 2}MnSi/CoPd multilayers. • Large values of spin-polarization at the Fermi are retained. • Route for novel spintronic/magnetoelectronic devices.
Spin Polarized Transport in an AC-Driven Quantum Curved Nanowire
Directory of Open Access Journals (Sweden)
Walid A. Zein
2011-01-01
Full Text Available Using the effective-mass approximation method, and Floquet theory, we study the spin transport characteristics through a curved quantum nanowire. The spin polarization, P, and the tunneling magnetoresistance, TMR, are deduced under the effect of microwave and infrared radiations of wide range of frequencies. The results show an oscillatory behavior of both the spin polarization and the tunneling magnetoresistance. This is due to Fano-type resonance and the interplay between the strength of spin-orbit coupling and the photons in the subbands of the one-dimensional nanowire. The present results show that this investigation is very important, and the present device might be used to be a sensor for small strain in semiconductor nanostructures and photodetector.
Micromagnetism in (001) magnetite by spin-polarized low-energy electron microscopy
Energy Technology Data Exchange (ETDEWEB)
Figuera, Juan de la, E-mail: juan.delafiguera@iqfr.csic.es [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); Vergara, Lucía [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); N' Diaye, Alpha T. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Quesada, Adrian [Instituto de Cerámica y Vidrio, CSIC, Calle Kelsen 5, 28049, Madrid (Spain); Schmid, Andreas K. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
2013-07-15
Spin-polarized low-energy electron microscopy was used to image a magnetite crystal with (001) surface orientation. Sets of spin-dependent images of magnetic domain patterns observed in this surface were used to map the direction of the magnetization vector with high spatial and angular resolution. We find that domains are magnetized along the surface <110> directions, and domain wall structures include 90° and 180° walls. A type of unusually curved domain walls are interpreted as Néel-capped surface terminations of 180° Bloch walls. - Highlights: ► The (001) surface of magnetite is imaged by spin-polarized low-energy electron microscopy. ► The magnetic domain microstructure is resolved. ► Magnetic easy axes in this surface are found to be along <110> directions. ► Magnetic domain wall structures include wide Néel-caps.
Spin polarization in high density quark matter under a strong external magnetic field
DEFF Research Database (Denmark)
Tsue, Yasuhiko; Da Providência, João; Providência, Constança
2016-01-01
In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor......-type interaction under the strong external magnetic field, it is shown that a quark spin polarized phase is realized in all regions of the quark chemical potential under consideration within the lowest Landau level approximation. In the axial-vector-type interaction, it is also shown that the quark spin polarized...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....
Optical spin polarization and Hanle effect in GaAsSb: Temperature dependence
Energy Technology Data Exchange (ETDEWEB)
Qiu, Weiyang; Wang, Xingjun, E-mail: xjwang@mail.sitp.ac.cn, E-mail: luwei@mail.sitp.ac.cn; Chen, Pingping; Li, Ning; Lu, Wei, E-mail: xjwang@mail.sitp.ac.cn, E-mail: luwei@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China)
2014-08-25
Continuous-wave optical orientation spectroscopy and the Hanle effect are used to investigate the optical spin polarization and spin dephasing time (gT{sub s}) in GaAsSb with a Sb concentration of ∼6% as a function of temperature. Optical and spin polarizations up to ∼21% were achieved at ∼120 K, and the scaled spin lifetime gT{sub s} decreased monotonously from ∼1.5 ns at 5 K to ∼20 ps at 200 K. We demonstrate that the spin properties of GaAs could be modified by incorporating a small percentage of Sb into it, as a result of an increase in the spin–orbit interactions.
Generation of a spin-polarized electron beam by multipole magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Karimi, Ebrahim, E-mail: ekarimi@uottawa.ca [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Grillo, Vincenzo [CNR-Istituto Nanoscienze, Centro S3, Via G Campi 213/a, I-41125 Modena (Italy); Boyd, Robert W. [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Institute of Optics, University of Rochester, Rochester, NY 14627 (United States); Santamato, Enrico [Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, 80126 Napoli (Italy); Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Napoli (Italy)
2014-03-01
The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin–magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope. - Highlights: • Theory of generating spin-polarized electron beams. • Interacting electron vortex beams with space-variant magnetic fields. • Bohr–Pauli impossibility of generating spin-polarized free electrons.
Quantum simulation of a spin polarization device in an electron microscope
Grillo, Vincenzo; Marrucci, Lorenzo; Karimi, Ebrahim; Zanella, Riccardo; Santamato, Enrico
2013-09-01
A proposal for an electron-beam device that can act as an efficient spin-polarization filter has been recently put forward (Karimi et al 2012 Phys. Rev. Lett. 108 044801). It is based on combining the recently developed diffraction technology for imposing orbital angular momentum to the beam with a multipolar Wien filter inducing a sort of artificial non-relativistic spin-orbit coupling. Here we reconsider the proposed device with a fully quantum-mechanical simulation of the electron-beam propagation, based on the well-established multi-slice method, supplemented with a Pauli term for taking into account the spin degree of freedom. Using this upgraded numerical tool, we study the feasibility and practical limitations of the proposed method for spin polarizing a free electron beam.
Experimental study on the activation process of GaAs spin-polarized electron source
Institute of Scientific and Technical Information of China (English)
阮存军
2003-01-01
GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is investigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired.
Institute of Scientific and Technical Information of China (English)
Liu Yi-Man; Shao Huai-Hua; Zhou Xiao-Ying; Zhou Guang-Hui
2013-01-01
We study the electronic structure and spin polarization of the surface states of a three-dimensional topological insulator thin film modulated by an electrical potential well.By routinely solving the low-energy surface Dirac equation for the system,we demonstrate that confined surface states exist,in which the electron density is almost localized inside the well and exponentially decayed outside in real space,and that their subband dispersions are quasilinear with respect to the propagating wavevector.Interestingly,the top and bottom surface confined states with the same density distribution have opposite spin polarizations due to the hybridization between the two surfaces.Along with the mathematical analysis,we provide an intuitive,topological understanding of the effect.
Strain-induced phase transition and electron spin-polarization in graphene spirals.
Zhang, Xiaoming; Zhao, Mingwen
2014-07-16
Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices.
Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits.
Pryor, C E; Flatté, M E
2003-12-19
A quantum dot spin light emitting diode provides a test of carrier spin injection into a qubit and a means for analyzing carrier spin injection and local spin polarization. Even with 100% spin-polarized carriers the emitted light may be only partially circularly polarized due to the geometry of the dot. We have calculated carrier polarization-dependent optical matrix elements for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. Calculations for typical SAQD geometries with emission along [110] show light that is only 5% circularly polarized for spin states that are 100% polarized along [110]. Measuring along the growth direction gives near unity conversion of spin to photon polarization and is the least sensitive to uncertainties in SAQD geometry.
Persistent coherence and spin polarization of topological surface states on topological insulators
Pan, Z.-H.; Vescovo, E.; Fedorov, A. V.; Gu, G. D.; Valla, T.
2013-07-01
Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities, which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should remain coherent and significantly spin polarized at ambient temperatures. Here, we studied the coherence and spin structure of the topological states on the surface of a model topological insulator, Bi2Se3, at elevated temperatures in spin- and angle-resolved photoemission spectroscopy. We found an extremely weak broadening and essentially no decay of spin polarization of the topological surface state up to room temperature. Our results demonstrate that the topological states on surfaces of topological insulators could serve as a basis for room-temperature electronic devices.
Spin polarization effects on magnetic dipole moment of 153,155Eu
Hoşgör, Gamze; Yakut, Hakan; Tabar, Emre
2017-02-01
Using the Quasiparticle Phonon Nuclear Model (QPNM) and taking into account the spin-spin interaction the effects of the spin polarization on the intrinsic magnetic moments (gK) of 153-155Eu isotopes have been studied. Our calculations indicated that because of the spin polarization, the spin gyromagnetic factors (gs) of the nucleons in the nucleus reduce noticeable from its free nucleon value and the spin-spin interactions play an important role in the renormalization (gse f f .) of the gs factors. A very good reproduction of the phenomenological quenching of gs factor from its free values (gse f f≅0.6 -0.7 gsf r e e) is obtained. The calculated values of effective gse f f and gK are also in fair agreementwith the experiment data.
Time-dependent tunneling of spin-polarized electrons in coupled quantum wells
Energy Technology Data Exchange (ETDEWEB)
Cruz, H; Luis, D [Departamento de Fisica Basica, Universidad de La Laguna, 38204 La Laguna, Tenerife (Spain)], E-mail: hcruz@ull.es
2008-02-15
We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations.
Energy Technology Data Exchange (ETDEWEB)
Dussaux, A.; Rache Salles, B.; Jenkins, A. S.; Bortolotti, P.; Grollier, J.; Cros, V.; Fert, A. [Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 1 Ave. A. Fresnel, 91767 Palaiseau (France); Grimaldi, E., E-mail: eva.grimaldi@thalesgroup.com [Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 1 Ave. A. Fresnel, 91767 Palaiseau (France); CNES, 1 Avenue Edouard Belin, 31400 Toulouse (France); Khvalkovskiy, A. V. [Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 1 Ave. A. Fresnel, 91767 Palaiseau (France); A.M. Prokhorov General Physics Institute of RAS, Vavilova Str. 38, 119991 Moscow (Russian Federation); Kubota, H.; Fukushima, A.; Yakushiji, K.; Yuasa, S. [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan)
2014-07-14
We investigate the microwave response of a spin transfer vortex based oscillator in a magnetic tunnel junction with an in-plane reference layer combined with a spin valve with an out-of-plane magnetization spin polarizing layer. The main advantage of this perpendicular spin polarizer is to induce a large spin transfer force even at zero magnetic field, thus leading to a record emitted power (up to 0.6 μW) associated to a very narrow spectral linewidth of a few hundreds of kHz. The characteristics of this hybrid vortex based spin transfer nano-oscillator obtained at zero field and room temperature are of great importance for applications based on rf spintronic devices as integrated and tunable microwave source and/or microwave detector.
Spin polarized HSE hybrid functional calculations of VO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Schwingenschloegl, Udo; Wang, Hao [KAUST, PSE Division, Thuwal (Saudi Arabia); Grau-Crespo, Ricardo [University College London, London (United Kingdom)
2013-07-01
We study the rutile (R) and monoclinic (M1) phases of the prototypical compound VO{sub 2} by first principles calculations based on density functional theory, employing the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. Our results show that the HSE lowest-energy solutions for both the low-temperature M1 phase and the high-temperature R phase, which are obtained upon inclusion of spin polarization, are at odds with experimental observations. For the M1 phase the groundstate is (but should not be) magnetic, while the groundstate of the R phase, which is also spin-polarized, is not (but should be) metallic. The energy difference between the low-temperature and high-temperature phases is also in strong discrepancy with the experimental latent heat.
Spin-polarized spin-orbit-split quantum-well states in a metal film
Energy Technology Data Exchange (ETDEWEB)
Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)
2008-07-01
Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.
Directory of Open Access Journals (Sweden)
A. Gover
2006-06-01
Full Text Available The problems of spin-polarized free-electron beam interaction with electromagnetic wave at electron-spin resonance conditions in a magnetic field and of superradiant spin-flip radiative emission are analyzed in the framework of a comprehensive classical model. The spontaneous emission of spin-flip radiation from electron beams is very weak. We show that the detectivity of electron spin resonant spin-flip and combined spin-flip/cyclotron-resonance-emission radiation can be substantially enhanced by operating with ultrashort spin-polarized electron beam bunches under conditions of superradiant (coherent emission. The proposed radiative spin-state modulation and the spin-flip radiative emission schemes can be used for control and noninvasive diagnostics of polarized electron/positron beams. Such schemes are of relevance in important scattering experiments off nucleons in nuclear physics and off magnetic targets in condensed matter physics.
Sławińska, Jagoda; Narayan, Awadhesh; Picozzi, Silvia
2016-12-01
The recent discovery of hidden spin polarization emerging in bulk electronic states of specific nonmagnetic crystals is a fascinating phenomenon, though hardly explored yet. Here, we study from a theoretical perspective nonmagnetic BaNiS2, recently suggested to exhibit a giant Rashba-like spin-orbit splitting of the bulk bands, despite the absence of heavy elements. We employ density functional theory and Green's functions calculations to reveal the exact spin textures of both bulk and surface. We predict unambiguous signatures of spin-polarized electronic states at the surface, which reflect the bulk Rashba splitting and which could be experimentally measured with sufficient resolution: this would constitute a clear report of a bulk-Rashba-induced spin splitting at the surface of centrosymmetric crystals.
Sun, Jia-Tao; Wang, Zhengfei; Meng, S.; Du, Shixuan; Liu, F.; Gao, H.-J.
2016-09-01
Fundamental understanding of two-dimensional materials has spurred a surge in the search for topological quantum phase associated with the valley degree of freedom (VDOF). We discuss a spin-polarized version to the VDOF in which spin degeneracy is broken by the antiferromagnetic exchange coupling (LAFM) between opposite layers of the quasi-two-dimensional silicon nanomembrane (SiNM). Based on first principles calculations, we found that the LAFM state in SiNM can lead to metal-insulator transition (MIT). The broken degeneracy of spin degree of freedom in this insulating state of ultrathin SiNM may differ for different valleys, so that the SiNM can be exploited to produce the spatially separated spin and valley currents. We propose that the tunable spin-polarized valley photocurrents can be generated in an experimentally feasible ellipsometry setup. Our work shows promise for the development of spintronic and valleytronic devices compatible with current silicon industry.
Valley spin polarization by using the extraordinary Rashba effect on silicon.
Sakamoto, Kazuyuki; Kim, Tae-Hwan; Kuzumaki, Takuya; Müller, Beate; Yamamoto, Yuta; Ohtaka, Minoru; Osiecki, Jacek R; Miyamoto, Koji; Takeichi, Yasuo; Harasawa, Ayumi; Stolwijk, Sebastian D; Schmidt, Anke B; Fujii, Jun; Uhrberg, R I G; Donath, Markus; Yeom, Han Woong; Oda, Tatsuki
2013-01-01
The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.
Energy Technology Data Exchange (ETDEWEB)
Seddon, E.A. (SERC, Daresbury Lab., Warrington (United Kingdom)); Hoyland, M.A.; Hughes, H.P. (Cambridge Univ. (United Kingdom). Dept. of Physics); Jordan, R.G. (Florida Atlantic Univ., Boca Raton, FL (United States). Alloy Research Center)
1992-08-01
An apparatus for spin-polarized photoemission experiments upon ferromagnetic materials is described. The instrument incorporates a hemispherical analyzer (with input lens stack) for angle selection ([+-] 3[sup 0] ) and energy discrimination (resolution better than 100 meV), and a high-energy Mott detector for spin analysis. It is designed for use with linearly polarized synchrotron radiation in the energy range 5-85 eV emergent from a toroidal grating monochromator optical system. (orig.).
Effects of pressure and strain on spin polarization of IrMnSb
Tutic, Ibrica; Herran, Juliana; Staten, Bradley; Gray, Paul; Paudel, Tula R.; Sokolov, Andrei; Tsymbal, Evgeny Y.; Lukashev, Pavel V.
2017-02-01
A high degree of spin polarization in electron transport is one of the most sought-after properties of a material which can be used in spintronics—an emerging technology utilizing a spin degree of freedom in electronic devices. An ideal candidate to exhibit highly spin-polarized current would be a room temperature half-metal, a material which behaves as an insulator for one spin channel and as a conductor for the other spin channel. In this paper, we explore a semi-Heusler compound, IrMnSb, which has been reported to exhibit pressure induced half-metallic transition. We confirm that the bulk IrMnSb is a spin-polarized metal, with dominant contribution to electronic states at the Fermi energy from majority-spin electrons. Application of a uniform pressure shifts the Fermi level into the minority-spin energy gap, thus demonstrating pressure induced half-metallic transition. This behavior is explained by the reduction of the exchange splitting of the spin bands consistent with the Stoner model for itinerant magnetism. We find that the half-metallic transition is suppressed when instead of uniform pressure the bulk IrMnSb is exposed to biaxial strain. This suppression of half-metallicity is driven by the epitaxial strain induced tetragonal distortion, which lifts the degeneracy of the Mn 3d t 2g and e g orbitals and reduces the minority-spin band gap under compressive strain, thus preventing half-metallic transition. Our calculations also indicate that in thin film geometry, surface states emerge in the minority-spin band gap, which has detrimental for practical applications impact on the spin polarization of IrMnSb.
Production of a nuclear spin polarized /sup 23/Na-beam by optical pumping
Energy Technology Data Exchange (ETDEWEB)
Dreves, W.; Kamke, W.; Broermann, W.; Fick, D.
1981-11-01
Nuclear spin polarization of an atomic /sup 23/Na-beam was produced by a combination of optical pumping with a dye laser and a sextupole magnet and alternatively, by optical pumping with two dye lasers. The maximum value measured for the vector polarization was P/sub 2/ = 0.86 +- 0.08, using beam foil spectroscopy. Further improvements of polarized ion sources based on this principle are discussed.
Quantifying absolute spin polarization with non-magnetic contacts in FM/ n-GaAs heterostructures
Geppert, Chad; Wienkes, Lee; Christie, Kevin; Patel, Sahil; Palmstrøm, Chris; Crowell, Paul
2014-03-01
We report on a novel method of quantifying spin accumulation in Co2MnSi/ n-GaAs and Fe/ n-GaAs heterostructures using a non-magnetic probe. The presence of a non-equilibrium spin polarization generates a large electrostatic potential shift relative to the equilibrium state. This is due to the combination of (1) the parabolic (non-constant) density of states and (2) the population imbalance between the two spin sub-bands. We observe this shift as a Hanle effect in a non-local, non-magnetic semiconducting contact. Since this signal depends only on experimentally accessible parameters of the bulk semiconductor, its magnitude may be used to quantify the injected spin polarization in absolute terms. By comparison with the (smaller) spin-valve signal observed with a second ferromagnetic contact, we demonstrate that this electrostatic shift scales quadratically with spin polarization, dephases in the presence of both applied and hyperfine fields, and is observable to higher temperatures than traditional non-local measurements. Quantitative modeling allows extraction of absolute polarizations in excess of 50 % at low temperatures, and further indicates that this contribution constitutes a large fraction of the three-terminal signal observed in these devices. Supported by NSF DMR-1104951; by STARnet, a SRC program sponsored by MARCO and DARPA; and by the NSF MRSEC program.
Interpreting current-induced spin polarization in topological insulator surface states
Li, Pengke; Appelbaum, Ian
2016-06-01
Several recent experiments on three-dimensional topological insulators claim to observe a large charge current-induced nonequilibrium ensemble spin polarization of electrons in the helical surface state. We present a comprehensive criticism of such claims, using both theory and experiment: First, we clarify the interpretation of quantities extracted from these measurements by deriving standard expressions from a Boltzmann transport equation approach in the relaxation-time approximation at zero and finite temperature to emphasize our assertion that, despite high in-plane spin projection, obtainable current-induced ensemble spin polarization is minuscule. Second, we use a simple experiment to demonstrate that magnetic field-dependent open-circuit voltage hysteresis (identical to those attributed to current-induced spin polarization in topological insulator surface states) can be generated in analogous devices where current is driven through thin films of a topologically trivial metal. This result ipso facto discredits the naive interpretation of previous experiments with TIs, which were used to claim observation of helicity, i.e., spin-momentum locking in the topologically protected surface state.
Sablikov, Vladimir A.; Shchamkhalova, Bagun S.
2014-05-01
We study the formation of spontaneous spin polarization in inhomogeneous electron systems with pair interaction localized in a small region that is not separated by a barrier from surrounding gas of non-interacting electrons. Such a system is interesting as a minimal model of a quantum point contact in which the electron-electron interaction is strong in a small constriction coupled to electron reservoirs without barriers. Based on the analysis of the grand potential within the self-consistent field approximation, we find that the formation of the polarized state strongly differs from the Bloch or Stoner transition in homogeneous interacting systems. The main difference is that a metastable state appears in the critical point in addition to the globally stable state, so that when the interaction parameter exceeds a critical value, two states coexist. One state has spin polarization and the other is unpolarized. Another feature is that the spin polarization increases continuously with the interaction parameter and has a square-root singularity in the critical point. We study the critical conditions and the grand potentials of the polarized and unpolarized states for one-dimensional and two-dimensional models in the case of extremely small size of the interaction region.
Equation of State of Spin-polarized Neutron Matter and Three-body Effect
Institute of Scientific and Technical Information of China (English)
ZuoWei
2003-01-01
Within the spin-dependent Brueckner-Hartree-Fock (BHF) framework, the equation of state of the spinpolarized neutron matter has been investigated by adopting the realistic nucleon-nucleon interaction supplemented with a microscopic three-body force. The three-body force has been turn out to be crucial for reproducing the empirical saturation properties of nuclear matter in a non-relativistic microscopic approach[2] such as BHF. The related physical quantities such as spin-symmetry energy, magnetic susceptibility, have been extracted. The three-body force effects have been studied and discussed with a special attention. It is found that in the whole range of spin-polarization, the cnergy per particle of spin-polarized neutron matter fulfills a quadratic relation versus the spin-polarization parameter. The calculated spin-symmetry energies as a function of densityare shown in Fig.l, where the solid curve is obtained by using the AVis two-body force plus the three-body force and the dashed curve is the result by adopting the pure AVis two-body force.
Lee, Joon Sue; Richardella, Anthony; Hickey, Danielle Reifsnyder; Mkhoyan, K. Andre; Samarth, Nitin
2015-10-01
We report electrical measurements of the current-induced spin polarization of the surface current in topological insulator devices where contributions from bulk and surface conduction can be disentangled by electrical gating. The devices use a ferromagnetic tunnel junction (permalloy/Al 2O3 ) as a spin detector on a back-gated (Bi,Sb ) 2Te3 channel. We observe hysteretic voltage signals as the magnetization of the detector ferromagnet is switched parallel or antiparallel to the spin polarization of the surface current. The amplitude of the detected voltage change is linearly proportional to the applied dc bias current in the (Bi,Sb ) 2Te3 channel. As the chemical potential is tuned from the bulk bands into the surface state band, we observe an enhancement of the spin-dependent voltages up to 300% within the range of the electrostatic gating. Using a simple model, we extract the spin polarization near charge neutrality (i.e., the Dirac point).
Nonequilibrium spin-polarized thermal transport in ferromagnetic-quantum dot-metal system
Xu, Li; Li, Zhi-Jian; Niu, Pengbin; Nie, Yi-Hang
2016-10-01
We use nonequilibrium Green function to analyze the nonequilibrium spin-polarized thermal transport through the ferromagnetic-quantum dot-metal system, in which a quantum dot (QD) is coupled to the ferromagnetic and metal electrodes with the voltage bias and the temperature shift. The differential thermoelectric conductance L (θ) is always zero and has no relation with the temperature shift when ε is equal to the Fermi level. The positive and negative values of L (θ) manifest the thermoelectric characteristic of electron-like (or hole-like) carrier when the temperature shift is nonzero. The electrostatic potential U becomes spin-dependent, and makes the dot level renormalization when the ferromagnetic-quantum dot-metal system is driven by the voltage bias and the temperature shift. We define that the spin polarization of the currents between the spin current Is and the electric current Ic is denoted as Is /Ic. The spin polarization Is /Ic shows novel and unique physical phenomenon when the voltage bias and the temperature shift are changed in the nonequilibrium state. Another interesting phenomenon is that we can obtain the pure spin current and a zero point of the thermocurrent Ith by adjusting the voltage bias and the temperature shift.
Dreon, Davide; Sidorenkov, Leonid A.; Bouazza, Chayma; Maineult, Wilfried; Dalibard, Jean; Nascimbene, Sylvain
2017-03-01
From the study of long-range-interacting systems to the simulation of gauge fields, open-shell lanthanide atoms with their large magnetic moment and narrow optical transitions open novel directions in the field of ultracold quantum gases. As for other atomic species, the magneto-optical trap (MOT) is the working horse of experiments but its operation is challenging, due to the large electronic spin of the atoms. Here we present an experimental study of narrow-line dysprosium MOTs. We show that the combination of radiation pressure and gravitational forces leads to a spontaneous polarization of the electronic spin. The spin composition is measured using a Stern–Gerlach separation of spin levels, revealing that the gas becomes almost fully spin-polarized for large laser frequency detunings. In this regime, we reach the optimal operation of the MOT, with samples of typically 3× {10}8 atoms at a temperature of 15 μK. The spin polarization reduces the complexity of the radiative cooling description, which allows for a simple model accounting for our measurements. We also measure the rate of density-dependent atom losses, finding good agreement with a model based on light-induced Van der Waals forces. A minimal two-body loss rate β ∼ 2× {10}-11 cm3 s–1 is reached in the spin-polarized regime. Our results constitute a benchmark for the experimental study of ultracold gases of magnetic lanthanide atoms.
Controllable spin polarization and spin filtering in a zigzag silicene nanoribbon
Energy Technology Data Exchange (ETDEWEB)
Farokhnezhad, Mohsen, E-mail: Mohsen-farokhnezhad@physics.iust.ac.ir; Esmaeilzadeh, Mahdi, E-mail: mahdi@iust.ac.ir; Pournaghavi, Nezhat [Department of Physics, Iran University of Science and Technology, Narmak, Tehran 16844 (Iran, Islamic Republic of); Ahmadi, Somaieh [Department of Physics, Imam Khomeini International University, Qazvin (Iran, Islamic Republic of)
2015-05-07
Using non-equilibrium Green's function, we study the spin-dependent electron transport properties in a zigzag silicene nanoribbon. To produce and control spin polarization, it is assumed that two ferromagnetic strips are deposited on the both edges of the silicene nanoribbon and an electric field is perpendicularly applied to the nanoribbon plane. The spin polarization is studied for both parallel and anti-parallel configurations of exchange magnetic fields induced by the ferromagnetic strips. We find that complete spin polarization can take place in the presence of perpendicular electric field for anti-parallel configuration and the nanoribbon can work as a perfect spin filter. The spin direction of transmitted electrons can be easily changed from up to down and vice versa by reversing the electric field direction. For parallel configuration, perfect spin filtering can occur even in the absence of electric field. In this case, the spin direction can be changed by changing the electron energy. Finally, we investigate the effects of nonmagnetic Anderson disorder on spin dependent conductance and find that the perfect spin filtering properties of nanoribbon are destroyed by strong disorder, but the nanoribbon retains these properties in the presence of weak disorder.
Role of spin polarization in FM/Al/FM trilayer film at low temperature
Lu, Ning; Webb, Richard
2014-03-01
Measurements of electronic transport in diffusive FM/normal metal/FM trilayer film are performed at temperature ranging from 2K to 300K to determine the behavior of the spin polarized current in normal metal under the influence of quantum phase coherence and spin-orbital interaction. Ten samples of Hall bar with length of 200 micron and width of 20 micron are fabricated through e-beam lithography followed by e-gun evaporation of Ni0.8Fe0.2, aluminum and Ni0.8Fe0.2 with different thickness (5nm to 45nm) in vacuum. At low temperature of 4.2K, coherent backscattering, Rashba spin-orbital interaction and spin flip scattering of conduction electrons contribute to magnetoresistance at low field. Quantitative analysis of magnetoresistance shows transition between weak localization and weak anti-localization for samples with different thickness ratio, which indicates the spin polarization actually affects the phase coherence length and spin-orbital scattering length. However, at temperature between 50K and 300K, only the spin polarization dominates the magnetoresistance.
Spin polarized PES on interface states of MgO/Fe/GaAs(100)
Energy Technology Data Exchange (ETDEWEB)
Gottlob, Daniel [Experimentelle Physik 1 - Technische Universitaet Dortmund, Otto-Hahn-Str. 4, D-44221 Dortmund (Germany); Institurte of Solid State Research - IFF-9 Electronic Properties - Research Center Juelich, D-52425 Juelich (Germany); Plucinski, Lukasz; Schneider, Claus M. [Institurte of Solid State Research - IFF-9 Electronic Properties - Research Center Juelich, D-52425 Juelich (Germany); Westphal, Carsten [Experimentelle Physik 1 - Technische Universitaet Dortmund, Otto-Hahn-Str. 4, D-44221 Dortmund (Germany)
2010-07-01
Spintronics is an important field of current Solid State Research and Magnetic Tunnel Junctions (MTJ's) now are within our grasp. In MTJ's the nature of the electronic structure at the interface determins the tunneling process, and thereby the magnetoresistive potential of the MTJ. Electronic interface states can have influence on the tunneling process in epitaxial MTJs especially for thinner tunnel barriers. At our ongoing research we will take a closer look at an off-normal surface state of Fe/GaAs(100) and see whether it still exists as an interface state if we cap the Fe by 1-3 monolayers of MgO. We collect spin-polarized spectra to confirm the spin polarization in this band after the evaporation of MgO. The measurements take place at Beamline 5 at DELTA, Dortmund, with a unique detector setup. We can acquire 2-dimensional angle resolved data for band mapping and spin-polarized one-dimensional data quasi-simultaneously. Our samples are prepared in-situ by e-beam evaporation and characterized by LEED and Auger spectroscopy.
Spin Polarization Effects in the Photoluminescence of Polythiophene.
Hess, Bret Clark
peak structure at 310 G. We tentatively attribute the peaks in c-PT to level crossings that occur when electron or hole Zeeman energies are resonant with the quadrupole splittings of iodine nuclei bound to the end of chains. (Abstract shortened with permission of author.) ftn*DOE Report IS -T-1375. This work was performed under contract No. W -7405-Eng-82 with the U.S. Department of Energy.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Qian; Mi, Wenbo, E-mail: miwenbo@tju.edu.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, Faculty of Science, Tianjin University, Tianjin 300072 (China)
2015-09-21
We report the first-principles calculations on the electronic structure and simulation of the spin-polarized scan tunneling microscopy graphic of the small organic molecules (benzene, thiophene, and cyclopentadienyl)/Fe{sub 4}N interfaces. It is found that the plane of benzene and thiophene keeps parallel to Fe{sub 4}N surface, while that of cyclopentadienyl does not. For all the systems, the organic molecules bind strongly with Fe{sub 4}N. Due to the hybridization between molecule p{sub z} orbitals and d orbitals of Fe, i.e., Zener interaction, all the three systems realize the spin-polarization inversion, whereas the spatial spin-polarization inversion distribution shows different intensities influenced by the competition between the spin polarization of C p{sub z} and Fe d states.
Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.
Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A
2012-05-11
Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system.
Fördös, Tibor; Postava, Kamil; Jaffrès, Henri; Pištora, Jaromír
2014-06-01
Spin-polarized light sources such as the spin-polarized light-emitting diodes (spin-LEDs) and spin-polarized lasers (spin-lasers) are prospective devices in which the radiative recombination of spin-polarized carriers results in emission of circularly polarized photons. The main goal of this article is to model emitted radiation and its polarization properties from spin-LED and spin-controlled vertical-cavity surface-emitting laser (spin-VCSEL) solid-state structures. A novel approach based on 4 × 4 transfer matrix formalism is derived for modeling of the interaction of light with matter in active media of resonant multilayer anisotropic structure and enables magneto-optical effects. Quantum transitions, which result in photon emission, are described using general Jones source vectors.
Directory of Open Access Journals (Sweden)
GINDULESCU, A.
2009-03-01
Full Text Available The present paradigm of magnetic data storage is approaching its fundamental limits for areal storage density, as well as for speed in data processing. As a result, several magnetic recording alternatives, such as spin polarized current assisted recording, precessional switching, toggle switching, heat assisted recording are currently under intense research efforts. This article is aimed at providing a pertinent theoretical analysis of the spin polarized current assisted recording, emphasizing its performance with respect to minimum requirements for switching field. The first analytical derivation of the critical field curve in the presence of spin polarized currents is presented and the results are compared to the classical Stoner-Wohlfarth astroid. The analysis is performed under the framework of the Landau-Lifshitz-Gilbert-Slonczewski equation for describing the magnetization dynamics driven by external magnetic fields and spin polarized currents.
Institute of Scientific and Technical Information of China (English)
陈宇光; 郑雁
2011-01-01
In this paper, the arrow - wide - narrow form of the quantum wire is studied by lattice green function method. It was found that spin -orbital coupling can produce not only potential trap, but also bound states, which may result in Fano resonant conductance structure. The spin polarization rate is introduced by Fano resonance or antiresonance. In our model, when the spin - polarized electrons injected from the input lead, the electron spin polarization rate will be as high as the 0.99 in the output lead. And when the system structure parameters change, in the output lead, spin polarization rate will be changed periodically just like the form of sine function.%本文对含Rashba自旋轨道耦合(spin - orbit coupling,SOC)的窄—宽—窄形量子线的电子自旋极化输运性质进行了理论研究.利用晶格格林函数法,计算出该量子线结构和SOC会产生势阱,进而使系统产生束缚态,导致该系统电导呈现Fano共振结构,在相应的自旋极化率中同时也出现了Fano共振或反共振.当自旋向上的电子极化入射时,在出射端会出现高达-0.99,0.99的自旋极化率；当系统结构参数变化时,自旋极化率会出现周期性变化或正弦变化.
Chen, Tsung-Wei; Hsiao, Chin-Lun; Hu, Chong-Der
2016-07-01
We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at the site-I and site-II atoms, and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is {+2, -1, 0} and {-2, +1, 0} for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from +2 to -1 (or -2 to +1), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase.
High spin polarization and spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy
Energy Technology Data Exchange (ETDEWEB)
Bainsla, Lakhan; Mallick, A.I. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Coelho, A.A. [Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas-UNICAMP, SP 6165, Campinas 13 083-859, Sao Paulo (Brazil); Nigam, A.K. [DCMPMS, Tata Institute of Fundamental Research, Mumbai 4000052 (India); Varaprasad, B.S.D.Ch.S.; Takahashi, Y.K. [Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Alam, Aftab [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Suresh, K.G., E-mail: suresh@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Hono, K. [Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan)
2015-11-15
In this paper, we investigate CoFeCrAl alloy by means of ab-initio electronic structure calculations and various experimental techniques. The alloy is found to exist in the B2-type cubic Heusler structure, which is very similar to Y-type (or LiMgPdSn prototype) structure with space group F-43m (#216). Saturation magnetization (M{sub S}) of about 2 µ{sub B}/f.u. is observed at 8 K under ambient pressure, which is in good agreement with the Slater–Pauling rule. M{sub S} values are found to be independent of pressure, which is a prerequisite for half-metals. The ab-initio electronic structure calculations predict half-metallicity for the alloy with a spin slitting energy of 0.31 eV. Importantly, this system shows a high current spin polarization value of 0.67±0.02, as deduced from the point contact Andreev reflection measurements. Linear dependence of electrical resistivity with temperature indicates the possibility of reasonably high spin polarization at elevated temperatures (~150 K) as well. All these suggest that CoFeCrAl is a promising material for the spintronic devices. - Highlights: • The ab-initio calculations predict half-metallic nature for the alloy. • Saturation magnetization (M{sub S}) gives characteristics of half-metallic nature. • Current spin polarization (P) value of 0.67±0.02 is deduced from PCAR measurements. • Deduced P is higher than those obtained for many ternary and/or quaternary alloys. • Resistivity behavior gives signature of high P at elevated temperatures.
Bosonic behavior of entangled fermions
DEFF Research Database (Denmark)
C. Tichy, Malte; Alexander Bouvrie, Peter; Mølmer, Klaus
2012-01-01
Two bound, entangled fermions form a composite boson, which can be treated as an elementary boson as long as the Pauli principle does not affect the behavior of many such composite bosons. The departure of ideal bosonic behavior is quantified by the normalization ratio of multi-composite-boson st......Two bound, entangled fermions form a composite boson, which can be treated as an elementary boson as long as the Pauli principle does not affect the behavior of many such composite bosons. The departure of ideal bosonic behavior is quantified by the normalization ratio of multi...
Effects of a spin-polarized current assisted Ørsted field in magnetization patterning
Energy Technology Data Exchange (ETDEWEB)
Volkov, Oleksii M., E-mail: alexey@volkov.ca; Sheka, Denis D. [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Kravchuk, Volodymyr P.; Gaididei, Yuri [Bogolyubov Institute for Theoretical Physics, 03680 Kiev (Ukraine); Mertens, Franz G. [Physics Institute, University of Bayreuth, 95440 Bayreuth (Germany)
2015-06-07
A spin-polarized electrical current leads to a variety of periodical magnetic structures in nanostripes. In the presence of the Ørsted field, which always assists an electrical current, the basic types of magnetic structures, i.e., a vortex-antivortex crystal and cross-tie domain walls, survive. The Ørsted field prevents saturation of the nanostripe and a longitudinal domain wall appears instead. Possible magnetization structures in stripes with different geometrical and material properties are studied numerically and analytically.
High spin-polarization in ultrathin Co2MnSi/CoPd multilayers
Galanakis, I.
2015-03-01
Half-metallic Co2MnSi finds a broad spectrum of applications in spintronic devices either in the form of thin films or as spacer in multilayers. Using state-of-the-art ab-initio electronic structure calculations we exploit the electronic and magnetic properties of ultrathin Co2MnSi/CoPd multilayers. We show that these heterostructures combine high values of spin-polarization at the Co2MnSi spacer with the perpendicular magnetic anisotropy of binary compounds such as CoPd. Thus they could find application in spintronic/magnetoelectronic devices.
Spin-Polarized Electron Emission from Superlattices with Zero Conduction Band Offset
Energy Technology Data Exchange (ETDEWEB)
Clendenin, James E
1998-11-09
Electron spin polarization as high as 86% has been reproducibly obtained from strained Al{sub x}In{sub y}Ga{sub 1-x-y}As/GaAs superlattice with minimal conduction band offset at the heterointerfaces. The modulation doping of the SL provides high polarization and high quantum yield at the polarization maximum. The position of the maximum can be easily tuned to an excitation wavelength by choice of the SL composition. Further improvement of the emitter parameters can be expected with additional optimization of the SL structure parameters.
Tunnel spin polarization versus energy for clean and doped Al2O3 barriers.
Park, B G; Banerjee, T; Lodder, J C; Jansen, R
2007-11-23
The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the same device. The intrinsic TSP is reduced below the Fermi level, and more strongly so for tunneling into empty states above the Fermi level. For artificially doped barriers, the low bias TMR decreases due to defect-assisted tunneling. Yet, this mechanism becomes ineffective at large bias, where instead inelastic spin scattering causes a strong TMR decay.
Spin-Polarized Electron Injection in Co/Cu/Fe Sandwich Structure
Institute of Scientific and Technical Information of China (English)
WANG Shou-Guo; CHEN Yan-Xue; WANG Zhi-He; CHEN Qiang; XIE Shi-Jie; MEI Liang-Mo
2000-01-01
A material asymmetry Co/Cu/Fe junction structure has been prepared for studying the spin-polarized electron injection at 77K. The sample performance was demonstrated to be analogous to that of a bipolar transistor. The maximal value of the output pulse voltage between Cu and Fe layers could reach the order of severalμV when the bias current between Co and Cu layers was 10μA. The interface roughness, photograph of material, magnetic loop and injection characteristic curves have been measured. Some important points on this topic have been discussed.
Thermonuclear reactivity of D-T fusion plasma with spin-polarized fuel
Energy Technology Data Exchange (ETDEWEB)
Takahashi, Toshiki [Department of Electronic Engineering, Gunma Univ., Kiryu, Gunma (Japan); Nakao, Yasuyuki
1999-04-01
The thermonuclear reactivity of deuterium(D) - tritium(T) fusion plasma with spin-polarized fuel has been studied. Two mechanisms of depolarization, collisions and waves, in the high temperature fusion plasma have been considered. The binary collisions have been found not to change the nuclear spin states. The waves with a frequency of a few GHz, however, changes the spin states appreciably, when {delta}B/B{sub 0} (the ratio of the amplitude of the fluctuating magnetic field to the external field) becomes larger than 10{sup -5}. (author)
Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces
Nanda, B. R. K.; Satpathy, S.
2008-01-01
The formation of a novel spin-polarized 2D electron gas at the LaMnO$_3$ monolayer embedded in SrMnO$_3$ is predicted from the first-principles density-functional calculations. The La (d) electrons become confined in the direction normal to the interface in the potential well of the La layer, serving as a positively-charged layer of electron donors. These electrons mediate a ferromagnetic alignment of the Mn t$_{2g}$ spins near the interface via the Anderson-Hasegawa double exchange and becom...
Three-body non-additive forces between spin-polarized alkali atoms
Soldan, Pavel; Cvitas, Marko T.; Hutson, Jeremy M.
2002-01-01
Three-body non-additive forces in systems of three spin-polarized alkali atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio calculations. The non-additive forces are found to be large, especially near the equilateral equilibrium geometries. For Li, they increase the three-atom potential well depth by a factor of 4 and reduce the equilibrium interatomic distance by 0.9 A. The non-additive forces originate principally from chemical bonding arising from sp mixing effects.
Chen, Ching-Tzu; Liu, Luqiao; Richardella, Anthony; Garate, Ion; Zhu, Yu; Samarth, Nitin
2015-03-01
In this talk, we will demonstrate that the helical spin texture on topological insulator (TI) surfaces can be electrically detected using four-terminal tunnel junction devices with ferromagnetic top electrodes. Consistent results are obtained in both the Edelstein and spin-galvanic effect configurations, allowing a quantitative determination of the charge-spin conversion efficiency in bismuth selenide. By applying finite DC biases at the junction, we further extract the energy dependence of the effective spin polarization in bismuth selenide. The observed temperature stability up to 200K suggests that TIs can be highly promising for room-temperature spintronics applications
A cryostat to hold frozen-spin polarized HD targets in CLAS: HDice-II
Energy Technology Data Exchange (ETDEWEB)
Lowry, M.M., E-mail: mlowry@jlab.org [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Bass, C.D. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); D' Angelo, A. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Universita' di Roma ‘Tor Vergata’, and INFN Sezione di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 1, I-00133 Roma (Italy); Deur, A.; Dezern, G. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Hanretty, C. [University of Virginia, 1400 University Avenue, Charlottesville, VA 22903 (United States); Ho, D. [Carnegie-Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Kageya, T.; Kashy, D. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Khandaker, M. [Norfolk State University, 700 Park Avenue, Norfolk, VA 23504 (United States); Laine, V. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Université Blaise Pascal, 34 Avenue Carnot, 63000 Clermont-Ferrand (France); O' Connell, T. [University of Connecticut, 115 N Eagleville Road, Storrs-Mansfield, CT 06269 (United States); Pastor, O. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Peng, P. [University of Virginia, 1400 University Avenue, Charlottesville, VA 22903 (United States); Sandorfi, A.M. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Sokhan, D. [Institut de Physique Nucleaire, Bat 100 – M053, Orsay 91406 (France); and others
2016-04-11
The design, fabrication, operation, and performance of a {sup 3/4}He dilution refrigerator and superconducting magnet system for holding a frozen-spin polarized hydrogen deuteride target in the Jefferson Laboratory CLAS detector during photon beam running is reported. The device operates both vertically (for target loading) and horizontally (for target bombardment). The device proves capable of maintaining a base temperature of 50 mK and a holding field of 1 T for extended periods. These characteristics enabled multi-month polarization lifetimes for frozen spin HD targets having proton polarization of up to 50% and deuteron up to 27%.
Energy Technology Data Exchange (ETDEWEB)
Chimento, L P; Forte, M [Physics Department, UBA, 1428 Buenos Aires (Argentina); Devecchi, F P; Kremer, G M; Ribas, M O; Samojeden, L L, E-mail: kremer@fisica.ufpr.br, E-mail: devecchi@fisica.ufpr.br, E-mail: chimento@df.uba.ar [Physics Department, UFPR, 81531-990 Curitiba (Brazil)
2011-07-08
In this work we review if fermionic sources could be responsible for accelerated periods during the evolution of a FRW universe. In a first attempt, besides the fermionic source, a matter constituent would answer for the decelerated periods. The coupled differential equations that emerge from the field equations are integrated numerically. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudo-scalar invariants. It is shown that the fermionic field could behave like an inflaton field in the early universe, giving place to a transition to a matter dominated (decelerated) period. In a second formulation we turn our attention to analytical results, specifically using the idea of form-invariance transformations. These transformations can be used for obtaining accelerated cosmologies starting with conventional cosmological models. Here we reconsider the scalar field case and extend the discussion to fermionic fields. Finally we investigate the role of a Dirac field in a Brans-Dicke (BD) context. The results show that this source, in combination with the BD scalar, promote a final eternal accelerated era, after a matter dominated period.
Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.
2016-11-01
We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.
Directory of Open Access Journals (Sweden)
Chao Zhang
2016-11-01
Full Text Available We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.
Shikin, A. M.; Klimovskikh, I. I.; Filyanina, M. V.; Rybkina, A. A.; Pudikov, D. A.; Kokh, K. A.; Tereshchenko, O. E.
2016-08-01
A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi1.5Sb0.5Te1.8Se1.2 and PbBi2Se2Te2) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.
Scale Of Fermion Mass Generation
Niczyporuk, J M
2002-01-01
Unitarity of longitudinal weak vector boson scattering implies an upper bound on the scale of electroweak symmetry breaking, Λ EWSB ≡ 8pv ≈ 1 TeV. Appelquist and Chanowitz have derived an analogous upper bound on the scale of fermion mass generation, proportional to v 2/mf, by considering the scattering of same-helicity fermions into pairs of longitudinal weak vector bosons in a theory without a standard Higgs boson. We show that there is no upper bound, beyond that on the scale of electroweak symmetry breaking, in such a theory. This result is obtained by considering the same process, but with a large number of longitudinal weak vector bosons in the final state. We further argue that there is no scale of (Dirac) fermion mass generation in the standard model. In contrast, there is an upper bound on the scale of Majorana-neutrino mass generation, given by ΛMaj ≡ 4πv2/m ν. In general, the upper bound on the scale of fermion mass generation depend...
Go, Gyungchoon; Lee, Kyung-Jin; Kim, Young Keun
2017-04-01
Recently, the switching of a perpendicularly magnetized ferromagnet (FM) by injecting an in-plane current into an attached non-magnet (NM) has become of emerging technological interest. This magnetization switching is attributed to the spin-orbit torque (SOT) originating from the strong spin-orbit coupling of the NM layer. However, the switching efficiency of the NM/FM structure itself may be insufficient for practical use, as for example, in spin transfer torque (STT)-based magnetic random access memory (MRAM) devices. Here we investigate spin torque in an NM/FM structure with an additional spin polarizer (SP) layer abutted to the NM layer. In addition to the SOT contribution, a spin-polarized current from the SP layer creates an extra spin chemical potential difference at the NM/FM interface and gives rise to a STT on the FM layer. We show that, using typical parameters including device width, thickness, spin diffusion length, and the spin Hall angle, the spin torque from the SP layer can be much larger than that from the spin Hall effect (SHE) of the NM.
Electron spin coherence and effect of spin polarization on electron relaxation dynamics in GaAs
Teng, Lihua; Wang, Xia; Ge, Weikun; Lai, Tianshu
2011-09-01
Time-resolved circularly and linearly polarized pump-probe spectroscopy is used to study the evolution of the electron spin coherence and electron relaxation dynamics in bulk GaAs at 9.6 K. In particular, their dependence on photon energy (or electron excess energy) is carefully investigated. The absorption quantum beats which are observed in circularly polarized pump-probe spectroscopy are obtained, reflecting the dephasing of the electron spin coherence. A circularly dichromatic pump-probe model is developed with both the spin-polarization-dependent band-filling and band-gap renormalization effects being taken into account. The model is used to simulate the differential transmission spectra for the collinearly polarized, co-helicity circularly polarized and cross-helicity circularly polarized pump-probe configurations, respectively. It is found that the model simulates well the features of the absorption quantum beats for a spin-dependent thermalized distribution of the photocreated carriers by a circularly polarized pump pulse, such as the variation of the oscillatory amplitude and phase reversal of the absorption quantum beats with photon energy increase. The simulation is in good agreement with our experimental results and reveals the effect of spin polarization on electron relaxation dynamics.
Nishizawa, N; Munekata, H
2016-01-01
We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: firstly, the stripe-laser-like structure that helps intensifying the EL light at the cleaved side walls below the spin injector Fe slab, and secondly, the crystalline AlOx spin tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region, whereas it increases steeply and reaches close to the pure CP when J = 100 A/cm2. There, either right- or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-polarized-current induced birefringence and optical spin-axis conversion are suggested to account for the observed experimental results.
Energy Technology Data Exchange (ETDEWEB)
Guo, Junji; Liao, Wenhu, E-mail: whliao2007@aliyun.com; Zhao, Heping [College of Physics, Mechanical and Electrical Engineering, Jishou University, Jishou 416000 (China); Zhou, Guanghui [Department of Physics and Key Laboratory for Low-Dimensional Quantum Structures and Manipulation (Ministry of Education), Hunan Normal University, Changsha 410081 (China)
2014-01-14
We theoretically investigate the electrically controllable spin polarization and selective efficiency of the edge state Dirac electron in a two-dimensional topological insulator (TI) sandwiched between ferromagnetic (FM) electrodes by using the method of Keldysh nonequilibrium Green's function. A nearly full spin polarization of the topological edge state with giant inversion of ∼80% is observed, which is much higher than the value previously reported. Moreover, the selective efficiency for spin-up electrons under the modulation of the parallel configuration of FM electrodes has been demonstrated to be larger than 95% for the first time, while that for spin-down electrons in the antiparallel case is higher than 90% in a wide energy range, owing to the inter-edge spin tunneling induced backscattering and spin dephasing effect. The obtained results may provide a deeper understanding of the TI edge states and a valuable guidance to design spin switch and filter with high on-off speed and selective efficiency based on TIs.
Liu, Luqiao
2016-10-01
Spin orbit interactions give rise to interesting physics phenomena in solid state materials such as the spin Hall effect (SHE) and topological insulator surface states. Those effects have been extensively studied using various electrical detection methods. However, to date most experiments focus only on characterizing electrons near the Fermi surface, while spin-orbit interaction is expected to be energy dependent. Here we developed a tunneling spectroscopy technique to measure spin Hall materials and topological insulators under finite bias voltages. By electrically injecting spin polarized electrons into spin Hall metals or topological insulators using tunnel junctions and measuring the induced transverse voltage, we are able to study SHE in typical 5d transition metals and the spin momentum locking in topological insulators. For spin Hall effect metals, the magnitude of the spin Hall angle has been a highly controversial topic in previous studies. Results obtained from various techniques can differ by more than an order of magnitude. Our results from this transport measurement turned out to be consistent with the values obtained from spin Hall torque measurements, which can help to address the long debating issue. Besides the magnitude, the voltage dependent spectra from our experiment also provide useful information in distinguishing between different potential mechanisms. Finally, because of the impedance matching capability of tunnel junctions, the spin polarized tunneling technique can also be used as a powerful tool to measure resistive materials such as the topological insulators. Orders of magnitude improvement in the effective spin Hall angle was demonstrated through our measurement
Current-induced magnetization switching with a spin-polarized scanning tunneling microscope
Krause, Stefan
2008-03-01
In present data storage applications magnetic nanostructures are switched by external magnetic fields. Due to their non-local character, however, cross-talk between adjacent nanomagnets may occur. An elegant method to circumvent this problem is magnetization switching by spin-polarized currents, as observed in GMR,1] as well as in TMR,2] studies. However, the layered structures of these devices do not provide any insight to the details of the spatial distribution of the switching processes. Spin-polarized scanning tunneling microscopy (SP-STM) is a well-established tool to reveal the magnetic structure of surfaces at spatial resolution down to the atomic scale. Besides, SP-STM takes advantage of a perfect TMR junction consisting of an isolating vacuum barrier separating two magnetic electrodes, which are represented by the foremost tip atom and the sample. Our experiments demonstrate that SP-STM serves as a tool to manipulate the switching behavior of uniaxial superparamagnetic nanoislands,3]. Furthermore, we show how SP-STM can be used to switch the magnetization of quasistable magnetic nanoislands at low temperature (T=31,). Besides its scientific relevance to investigate the details of current-induced magnetization switching (CIMS), this technique opens perspectives for future data storage technologies based on SP-STM. [1] J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000). [2] Y. Liu et al., Appl. Phys. Lett. 82, 2871 (2003). [3] S. Krause et al., Science 317, 1537 (2007).
Magnetic properties and spin polarization of Ru doped half metallic CrO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
West, Kevin G.; Dao, Nam N. H.; Lu, Jiwei, E-mail: jl5tk@virginia.edu [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Osofsky, Michael; Mazin, I. I. [Naval Research Laboratory, Washington, DC 20375 (United States); Wolf, Stuart A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States)
2015-07-06
Chromium dioxide (CrO{sub 2}) is a half metal that is of interest for spintronic devices. It has not been synthesized through traditional physical vapor deposition (PVD) techniques because of its thermodynamic instability in low oxygen pressures. Epitaxial thin films of Ru doped tetragonal rutile CrO{sub 2} were synthesized by a PVD technique. The as-deposited Ru{sub x}Cr{sub 1−x}O{sub 2} was ferrimagnetic with the saturation magnetization moment showing a strong dependence on the Ru concentration. Curie temperature as high as 241 K has been obtained for ∼23 at. % Ru. The Ru substitution increased the electrical conductivity by increasing the minority spin concentration. The spin polarization was found to be as high as 70% for 9 at. % Ru and decreased to ∼60% with Ru concentrations up to ∼44 at. %, which is determined by the Fermi velocities of the majority and minority spins. First principle calculations were performed to understand the effect of Ru content on the properties of CrO{sub 2}. The PVD processes of Ru doped CrO{sub 2} could lead to the practical applications of the high spin polarization of CrO{sub 2} in spintronic devices.
Spatial distribution of spin polarization in a channel on the surface of a topological insulator.
Zhou, Xiaoying; Shao, Huaihua; Liu, Yiman; Tang, Dongsheng; Zhou, Guanghui
2012-05-09
We study the spatial distribution of electron spin polarization for a gate-controlled T-shaped channel on the surface of a three-dimensional topological insulator (3D TI). We demonstrate that an energy gap depending on channel geometry parameters is definitely opened due to the spatial confinement. Spin surface locking in momentum space for a uniform wide channel with Hamiltonian linearity in the wavevector is still kept, but it is broken with Hamiltonian nonlinearity in the wavevector, like that for two-dimensional surface states widely studied in the literature. However, the spin surface locking for a T-shaped channel is broken even with Hamiltonian linearity in the wavevector. Interestingly, the magnitude and direction of the in-plane spin polarization are spatially dependent in all regions due to the breaking of translational symmetry of the T-shaped channel system. These interesting findings for an electrically controlled nanostructure based on the 3D TI surface may be testable with the present experimental technique, and may provide further understanding the nature of 3D TI surface states.
First-principle calculation of spin polarization in Cu{sub 3}N{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Ghoohestani, Marzieh [Department of Physics, Vali-E-Asr University of Rafsanjan, 77139-36417 Rafsanjan (Iran, Islamic Republic of); Karimipour, Masoud, E-mail: masoud.karimipour@gmail.com [Department of Physics, Vali-E-Asr University of Rafsanjan, 77139-36417 Rafsanjan (Iran, Islamic Republic of); Allah Badehian, Hojat [Condensed Matter Lab, Department of Physics, Shahid Chamran University, Ahvaz (Iran, Islamic Republic of); Javad Hashemifar, Seyed [Department of Physics, Isfahan University of Technology, 84156-83111 Isfahan (Iran, Islamic Republic of)
2013-10-15
We have studied intercalation of nitrogen atom into the cubic Cu{sub 3}N structure by performing accurate total energy calculations in the framework of density functional theory by using the full-potential linearized augmented plane wave method. The spin polarized Perdew–Burke–Ernzerhof (PBE) and modified Becke–Johnson (mBJ) parameterizations of the generalized gradient approximation were employed to obtain the structural and electronic properties of Cu{sub 3}N and Cu{sub 3}N{sub 2} structures. It is found that nitrogen intercalation into Cu{sub 3}N is an endothermic process which significantly influences the structural, electronic, and magnetic properties of the system. This process, within PBE, gives rise to a nearly half metallic behavior, while mBJ favors semiconductor ferromagnetism in the intercalated Cu{sub 3}N{sub 2} system. The 2p orbital of the intercalated nitrogen atom shows significant contribution to the spin polarization of the system. - Highlights: • Cu{sub 3}N{sub 2} structure is thermodynamically stable in an anti-ReO{sub 3} type cell. • The compound is half metal with an indirect band gap of 2.5 eV and 0.2 eV for spin up and spin down states, respectively. • 2p orbitals of N intercalated atoms show significant contribution to the system polarization. • The net magnetic moment in ground state is 2.30 μB/cell.
All-electrical generation of spin-polarized currents in quantum spin Hall insulators
Tao, L. L.; Cheung, K. T.; Zhang, L.; Wang, J.
2017-03-01
The control and generation of spin-polarized current (SPC) without magnetic materials and an external magnetic field is a big challenge in spintronics and normally requires a spin-flip mechanism. In this Rapid Communication, we show the theoretical discovery of all-electrical generation of SPC without relying on spin-flip spin-orbit coupling (SOC). We find that the SPC can be produced as long as an energy-dependent phase difference between the spin up and down electrons can be established. We verify this through quantum transport calculations on a gated stanene zigzag nanoribbon, which is a quantum spin Hall (QSH) insulator. Our calculations indicate that the transient current as well as ac conductance are significantly spin polarized, which results from the genetic phase difference between spin up and down electrons after traversing the system. Our results are robust against edge imperfections and generally valid for other QSH insulators, such as silicene and germanene, etc. These findings establish a different route for generating SPCs by purely electrical means and open the door for interesting applications of semiconductor spintronics.
Optical cooling and trapping highly magnetic atoms: The benefits of a spontaneous spin polarization
Dreon, Davide; Bouazza, Chayma; Maineult, Wilfried; Dalibard, Jean; Nascimbene, Sylvain
2016-01-01
From the study of long-range-interacting systems to the simulation of gauge fields, open-shell Lanthanide atoms with their large magnetic moment and narrow optical transitions open novel directions in the field of ultracold quantum gases. As for other atomic species, the magneto-optical trap (MOT) is the working horse of experiments but its operation is challenging, due to the large electronic spin of the atoms. Here we present an experimental study of narrow-line Dysprosium MOTs. We show that the combination of radiation pressure and gravitational forces leads to a spontaneous polarization of the electronic spin. The spin composition is measured using a Stern-Gerlach separation of spin levels, revealing that the gas becomes almost fully spin-polarized for large laser frequency detunings. In this regime, we reach the optimal operation of the MOT, with samples of typically $3\\times 10^8$ atoms at a temperature of 20$\\,\\mu$K. The spin polarization reduces the complexity of the radiative cooling description, whi...
Agrawal, Jyoti; Frampton, Paul H.; Jack Ng, Y.; Nishino, Hitoshi; Yasuda, Osamu
1991-03-01
An extension of the standard model is proposed. The gauge group is SU(2) X ⊗ SU(3) C ⊗ SU(2) S ⊗ U(1) Q, where all gauge symmetries are unbroken. The colour and electric charge are combined with SU(2) S which becomes strongly coupled at approximately 500 GeV and binds preons to form fermionic and vector bound states. The usual quarks and leptons are singlets under SU(2) X but additional fermions, called sarks. transform under it and the electroweak group. The present model explains why no more than three light quark-lepton families can exist. Neutral sark baryons, called narks, are candidates for the cosmological dark matter having the characteristics designed for WIMPS. Further phenomenological implications of sarks are analyzed i including electron-positron annihilation. Z 0 decay, flavor-changing neutral currents. baryon-number non-conservation, sarkonium and the neutron electric dipole moment.
Wu, Qing; Liu, Yu; Wang, Hailong; Li, Yuan; Huang, Wei; Zhao, Jianhua; Chen, Yonghai
2017-01-01
In the absent of magnetic field, we have observed the anisotropic spin polarization degree of photoconduction (SPD-PC) in (Ga,Mn)As/GaAs heterojunction. We think three kinds of mechanisms contribute to the magnetic related signal, (i) (Ga,Mn)As self-producing due to the valence band polarization, (ii) unequal intensity of left and right circularly polarized light reaching to GaAs layer to excite unequal spin polarized carriers in GaAs layer, and (iii) (Ga,Mn)As as the spin filter layer for spin transport from GaAs to (Ga,Mn)As. Different from the previous experiments, the influence coming from the Zeeman splitting induced by an external magnetic field can be avoided here. While temperature dependence experiment indicates that the SPD-PC is mixed with the magnetic uncorrelated signals, which may come from current induced spin polarization. PMID:28084437
Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8 +δ
Fanciulli, Mauro; Muff, Stefan; Weber, Andrew P.; Dil, J. Hugo
2017-06-01
Photoelectrons produced from the excitation of spin-degenerate states in solids can have a sizable spin polarization, which is related to the phase of interfering channels in the photoemission matrix elements. Such spin polarization can be measured by spin-resolved photoemission spectroscopy to gain information about the transitions and the Wigner time delay of the process. Incorporating strongly correlated electron systems into this paradigm could yield a novel means of extracting phase information crucial to understanding the mechanism of their emergent behavior. In this work, we present, as a case study, experimental measurements of the cuprate superconductor Bi2Sr2CaCu2O8 +δ by spin-resolved photoemission while maintaining full angular and energy resolution. A spin polarization of at least 10 % is observed, which is related to the phase of the photoelectron wave function.
Yamada, T K; Heijnen, G M M; Kempen, H V; Mizoguchi, T
2003-01-01
Normalized differential tunneling conductivities obtained with Fe-coated W tips show a spin-polarized peak around +0.8 V on ultrathin bct Mn films grown on Fe(001)-whiskers. This spin-polarized peak results in a clear magnetic contrast in spectroscopic images. Our normalization removes the influence of the tunneling probability and makes the spectroscopic curves most reliable for a derivation of the spin-resolved sample density of states (DOS) at positive voltages. From this analysis we conclude that the magnetic contrast in our spectroscopic maps is caused by a highly polarized DOS. Furthermore, a tip polarization of about 15% is found. (author)
Measurement of Integrated Stokes Parameters for He 3 3p State Excited by Spin-Polarized Electrons
Institute of Scientific and Technical Information of China (English)
DING Hai-Bing; PANG Wen-Ning; LIU Yi-Bao; SHANG Ren-Cheng
2005-01-01
@@ Integrated Stokes parameters Pi (i = 1, 2, 3) for the He 3 3p → 2 3S1 (388.9nm) transition after excitation from the ground state to the 3 3 P state by a transversely spin-polarized electron beam are measured in near threshold energy region. The experimental results are presented. The linear-polarization P2 are consistent with zero over the incident energy range, providing evidence for the LS coupling mechanism of the 3 3P state. The measured circular polarization P3 are non-zero, indicating strong electron-electron exchange effects in the spin-polarized electron-atom collision process.
Kokado, Satoshi; Sakuraba, Yuya; Tsunoda, Masakiyo
2016-10-01
We derive a simple relational expression between the spin polarization ratio of resistivity, Pρ, and the anisotropic magnetoresistance ratio Δρ/ρ, and that between the spin polarization ratio of the density of states at the Fermi energy, PDOS, and Δρ/ρ for nearly half-metallic ferromagnets. We find that Pρ and PDOS increase with increasing |Δρ/ρ| from 0 to a maximum value. In addition, we roughly estimate Pρ and PDOS for a Co2FeGa0.5Ge0.5 Heusler alloy by substituting its experimentally observed Δρ/ρ into the respective expressions.
Chantis, Athanasios N; Belashchenko, Kirill D.; Smith, Darryl L.; Tsymbal, Evgeny Y.; van Schilfgaarde, Mark; Albers, Robert C
2007-01-01
A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to reverse the spin polarization with voltage bias of electrons transmitted across this interface. Using a Green's function approach within the local spin density approximation we calculate spin-dependent current in a Fe/GaAs/Cu tunnel junction as a function of applied bias voltage. We find a change in sign of the spin polarization of tunneling electrons with bias voltage due to the interface minority-spin resonance. Th...
Rincón, Elizabeth; Pérez, Patricia; Chamorro, Eduardo
2007-11-01
The local reactivity proclivities in a series of simple substituted nitrenes (N-X) and phosphinidenes (P-X) have been explored for the lowest-lying singlet and triplet electronic states within the framework of spin-polarized density functional theory (SP-DFT). Linear correlations have been found between both the global and local philicities for spin polarization and the vertical singlet-triplet energy gaps. The accumulation and depletion of the electron or spin density can be directly related to the electronegativity of the substituent atoms. The local analysis has been achieved on the basis of a recent implementation of condensed-to-site SP-DFT Fukui functions.
Light Front Fermion Model Propagation
Institute of Scientific and Technical Information of China (English)
Jorge Henrique Sales; Alfredo Takashi Suzuki
2013-01-01
In this work we consider the propagation of two fermion fields interacting with each other by the exchange of intermediate scalar bosons in the light front.We obtain the corrections up to fourth order in the coupling constant using hierarchical equations in order to obtain the bound state equation (Bethe-Salpeter equation).
Indian Academy of Sciences (India)
Sudhanshu S Jha; S D Mahanti
2007-05-01
We use different determinantal Hartree–Fock (HF) wave functions to calculate true variational upper bounds for the ground state energy of spin-half fermions in volume 0, with mass , electric charge zero, and magnetic moment , interacting through magnetic dipole–dipole interaction. We ﬁnd that at high densities when the average interparticle distance 0 becomes small compared to the magnetic length m ≡ 22/ħ2, a ferromagnetic state with spheroidal occupation function ↑ $(\\vec{k})$, involving quadrupolar deformation, gives a lower upper bound compared to the variational energy for the uniform paramagnetic state or for the state with dipolar deformation. This system is unstable towards inﬁnite density collapse, but we show explicitly that a suitable short-range repulsive (hard core) interaction of strength 0 and range a can stop this collapse. The existence of a stable equilibrium high density ferromagnetic state with spheroidal occupation function is possible as long as the ratio of coupling constants cm ≡ (03/2) is not very smallcompared to 1.
Towards Quantum Turbulence in Cold Atomic Fermionic Superfluids
Bulgac, Aurel; Wlazłowski, Gabriel
2016-01-01
Fermionic superfluids provide a new realization of quantum turbulence, accessible to both experiment and theory, yet relevant to both cold atoms and nuclear astrophysics. In particular, the strongly interacting Fermi gas realized in cold-atom experiments is closely related to dilute neutron matter in the neutron star crust. Unlike the liquid superfluids 4He (bosons) and 3He (fermions), where quantum turbulence has been studied in laboratory for decades, quantum gases, and in particular superfluid Fermi gases stand apart for a number of reasons. Fermi gases admit a rather reliable microscopic description based on density functional theory which describes both static and dynamical phenomena. Cold atom experiments demonstrate exquisite control over particle number, spin polarization, density, temperature, and interacting strength. Topological defects such as domain walls and quantized vortices, which lie at the heart of quantum turbulence, can be created and manipulated with time-dependent external potentials, a...
Wang, Xin; deGroot, F.M.F.; Cramer, SP
1997-01-01
This paper demonstrates that spin-polarized x-ray-excitation spectra can be obtained using K alpha emission as well as K beta lines. A spin-polarized analysis of K alpha x-ray emission and the excitation spectra by K alpha detection on a Ni compound is reported. A systematic analysis of the first-ro
Wang, Xin; deGroot, F.M.F.; Cramer, SP
1997-01-01
This paper demonstrates that spin-polarized x-ray-excitation spectra can be obtained using K alpha emission as well as K beta lines. A spin-polarized analysis of K alpha x-ray emission and the excitation spectra by K alpha detection on a Ni compound is reported. A systematic analysis of the
Suppression of Penning ionization in a spin-polarized mixture of rubidium and He*
Byron, L. J.; Dall, R. G.; Rugway, Wu; Truscott, A. G.
2010-01-01
This paper presents the first study of the collision dynamics of an ultra-cold spin-polarized mixture of rubidium and metastable helium (He*) atoms. Our experiment monitors ion production from the mixture for both magnetically polarized and unpolarized cases. In the unpolarized case, we observe an increase in our background ion rate. However, in the completely polarized sample the ion production is below the sensitivity of our experiment. Nonetheless, we determine an upper limit of 5×10-12 cm3 s-1 for the polarized rate constant (βRb-He*), which is two orders of magnitude below the unpolarized rate constant. Such a suppression of the He*-87Rb polarized rate was not apparent a priori and opens the intriguing possibility of creating a dual Bose-Einstein condensate comprising an alkali ground-state atom and an excited-state noble-gas atom.
Gerhardt, N. C.; Li, M.; Jaehme, H.; Soldat, H.; Hofmann, M. R.; Ackemann, T.
2010-02-01
Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications.
Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie
2017-02-01
We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications
Anisotropic Heisenberg form of RKKY interaction in the one-dimensional spin-polarized electron gas
Valizadeh, M. M.
2016-09-01
We study the indirect exchange interaction between two localized magnetic moments, known as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, in a one-dimensional (1D) spin-polarized electron gas. We find explicit expressions for each term of this interaction, study their oscillatory behaviors as a function of the distance between two magnetic moments, R, and compare them with the known results for RKKY interaction in the case of 1D standard electron gas. We show this interaction can be written in an anisotropic Heisenberg form, E(R) = λ2χ xx(S1xS2x + S1yS2y) + λ2χ zzS1zS2z, coming from broken time-reversal symmetry of the host material.
Heuristic model of chemically induced electron spin polarization in two dimensions
Adrian, Frank J.
2010-11-01
A heuristic model of chemically induced electron spin polarization (CIDEP) that breaks the polarization mechanism into its component steps, with each step governed by an appropriate solution of the diffusion equation, is extended from a three to a two-dimensional system. The required solution of the 2D diffusion equation is provided by a relatively simple analytic approximation to the usual infinite series solution. The model yields the polarization and its time development for weak to strong singlet-triplet mixing in the radical pairs, whereas previous models are limited to very weak or very strong mixing. Its results agree with a variational solution of an integral equation of Monchick and are encouraging for observation of CIDEP in dimensionally restricted systems. The method also may be applicable to other diffusion-controlled, spin-dependent chemistry in spatially restricted environments.
Spin polarized surface resonance bands in single layer Bi on Ge(1 1 1)
Bottegoni, F.; Calloni, A.; Bussetti, G.; Camera, A.; Zucchetti, C.; Finazzi, M.; Duò, L.; Ciccacci, F.
2016-05-01
The spin features of surface resonance bands in single layer Bi on Ge(1 1 1) are studied by means of spin- and angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy. We characterize the occupied and empty surface states of Ge(1 1 1) and show that the deposition of one monolayer of Bi on Ge(1 1 1) leads to the appearance of spin-polarized surface resonance bands. In particular, the C 3v symmetry, which Bi adatoms adopt on Ge(1 1 1), allows for the presence of Rashba-like occupied and unoccupied electronic states around the \\overline{\\text{M}} point of the Bi surface Brillouin zone with a giant spin-orbit constant |{α\\text{R}}| =≤ft(1.4+/- 0.1\\right) eV · Å.
Spin-polarized Voltages on a 2D Self-assembled Plasmonic Crystal
Proscia, Nicholas V; Chang, Roger; Kretzschmar, Ilona; Menon, Vinod M; Vuong, Luat T
2015-01-01
The Photon Drag Effect (PDE) is a nonlinear process akin to optical rectification in which the momentum of light is transferred to charged carriers and converted to a DC voltage. Here, we experimentally demonstrate the spin-polarized voltage, associated with the transference of light's spin angular momenta to the linear momenta of charges, with visible-light illumination on a nanovoid self-assembled plasmonic crystal surface. Numerical calculations show that the gradient force, generally considered independent of polarization, is responsible for the majority of the momentum transfer. The PDE in this achiral system represents a distinct spin-orbit interaction that produces asymmetric hotspots whose locations change with circular polarization handedness. Our results significantly advance our understanding of the PDE and demonstrate realistic potential for scalable plasmonic materials that utilize PDE.
Excitation of plasmons in Ag/Fe/W structure by spin-polarized electrons
Energy Technology Data Exchange (ETDEWEB)
Samarin, Sergey N.; Kostylev, Mikhail; Williams, J. F. [School of Physics, The University of Western Australia, Perth WA 6009 (Australia); Artamonov, Oleg M.; Baraban, Alexander P. [St. Petersburg State University, Faculty of Physics, St. Petersburg 199034 (Russian Federation); Guagliardo, Paul [Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth WA 6009 (Australia)
2015-09-07
Using Spin-polarized Electron-Energy Loss Spectroscopy (SPEELS), the plasmon excitations were probed in a few atomic layers thick Ag film deposited on an Fe layer or on a single crystal of W(110). The measurements were performed at two specular geometries with either a 25° or 72° angle of incidence. On a clean Fe layer (10 atomic layers thick), Stoner excitation asymmetry was observed, as expected. Deposition of a silver film on top of the Fe layer dramatically changed the asymmetry of the SPEELS spectra. The spin-effect depends on the kinematics of the scattering: angles of incidence and detection. The spin-dependence of the plasmon excitations in the silver film on the W(110) surface and on the ferromagnetic Fe film is suggested to arise from the spin-active Ag/W or Ag/Fe interfaces.
Anisotropic tunneling between spin-polarized tips and substrate with strong spin-orbit coupling
Xie, Yonglong; Jeon, Sangjun; Drozdov, Ilya; Li, Jian; Bernevig, Andrei; Yazdani, Ali
2015-03-01
The ability to measure spin structure on the nanometer scale has attracted substantial interest for a long time. Spin-polarized scanning tunneling microscopy (SP-STM) is an excellent tool for studying fundamental aspect of magnetism at atomic scale. We combine a low temperature STM equipped with a vector magnet and a spin-polarizable tip, to probe superconductors with strong spin-orbit coupling such as Pb, which is emerging as a platform for engineering topological superconductivity. We observe anisotropic tunneling conductance between tip and substrate as a function of the angle of applied in-plane magnetic field. This finding suggests that SP-STM may provide a tool to locally measure spin-orbit coupling, even in non-magnetic substrates.
Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction
Institute of Scientific and Technical Information of China (English)
Tian Hong-Yu; Wang Jun
2012-01-01
We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions.The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon.It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived,the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG,while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect,in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations.Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices.
Spin-polarized electronic properties of NiHe0.25 under pressure
Institute of Scientific and Technical Information of China (English)
San Xiao-Jiao; Liu Zhi-Ming; Ma Yan-Ming; Cui Tian; Liu Bing-Bing; Zou Guang-Tian
2009-01-01
This paper studies the effects of He atom on the spin-polarized electronic properties of nickel under pressures using ab initio pseudopotential plan-wave method. Under high pressures, the compound of NiHeo.25 can exist and helium-bubble can not create in Ni. A pressure-induced ferromagnetic to paramagnetic phase transition has been predicted in NiHe0.25 at about 218 GPa. It is found that under pressures, the magnetic property of Ni atoms is more strongly affected by He atom than by H atom and that the behaviour of He atom in Ni are completely different from that of H atom, like the bonding characteristics and the electron transfer.
Spin-polarized quantum transport through an Aharonov-Bohm quantum-dot-ring
Institute of Scientific and Technical Information of China (English)
Wang Jian-Ming; Wang Rui; Liang Jiu-Qing
2007-01-01
In this paper the quantum transport through an Aharonov-Bohm (AB) quantum-dot-ring with two dot-array arms described by a single-band tight-binding Hamiltonian is investigated in the presence of additional magnetic fields applied to the dot-array arms to produce spin flip of electrons. A far richer interference pattern than that in the charge transport alone is found. Besides the usual AB oscillation the tunable spin polarization of the current by the magnetic flux is a new observation and is seen to be particularly useful in technical applications. The spectrum of transmission probability is modulated by the quantum dot numbers on the up-arc and down-arc of the ring, which, however, does not affect the period of the AB oscillation.
Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature
Directory of Open Access Journals (Sweden)
Si-Da Li
2013-01-01
Full Text Available We predict through our first-principles calculations that four double perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs are half-metallic ferrimagnets. Our calculated results shows that the four optimized structures have negative formation energy, from -0.42 to -0.26 eV per formula unit, which implies that they could probably be realized. In the case of Bi2FeMoO6, the half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and 650 K, respectively, which indicates that high spin polarization could be kept at high temperatures far beyond room temperature. It is believed that some of them could be synthesized soon and would prove useful for spintronic applications.
Spin-orbit-induced longitudinal spin-polarized currents in nonmagnetic solids
Wimmer, S.; Seemann, M.; Chadova, K.; Ködderitzsch, D.; Ebert, H.
2015-07-01
For certain nonmagnetic solids with low symmetry the occurrence of spin-polarized longitudinal currents is predicted. These arise due to an interplay of spin-orbit interaction and the particular crystal symmetry. This result is derived using a group-theoretical scheme that allows investigating the symmetry properties of any linear response tensor relevant to the field of spintronics. For the spin conductivity tensor it is shown that only the magnetic Laue group has to be considered in this context. Within the introduced general scheme also the spin Hall and additional related transverse effects emerge without making reference to the two-current model. Numerical studies confirm these findings and demonstrate for (Au1-xPtx)4Sc that the longitudinal spin conductivity may be on the same order of magnitude as the conventional transverse one. The presented formalism only relies on the magnetic space group and therefore is universally applicable to any type of magnetic order.
Mieville, Laurent; Worledge, Daniel; Geballe, Theodore H.; Char, Kookrin
1998-03-01
The recently reported "colossal" magnetoresistance (CMR) effect in (La_1-xA_x)MnO3 (where A stands for alkaline earth element) has shed new light on the magnetic properties exhibited by some members of the perovskite family with the generic formula ABO_3. We have studied the interface resistance between metals (Al, Nb and Pd) and magnetic perovskites ((La_0.66Sr_0.34)MnO_3, SrRuO3 and (La_0.5Sr_0.5)CoO_3) thin films grown by pulsed laser deposition. Low temperature measurements of tunnel junctions which aim to measure directly the amount of spin polarized carriers present in these perovskites will be also reviewed.
TOPICAL REVIEW: Highly spin-polarized materials and devices for spintronics
Directory of Open Access Journals (Sweden)
Koichiro Inomata et al.
2008-01-01
Full Text Available The performance of spintronics depends on the spin polarization of the current. In this study half-metallic Co-based full-Heusler alloys and a spin filtering device (SFD using a ferromagnetic barrier have been investigated as highly spin-polarized current sources. The multilayers were prepared by magnetron sputtering in an ultrahigh vacuum and microfabricated using photolithography and Ar ion etching. We investigated two systems of Co-based full-Heusler alloys, Co2Cr1 ? xFexAl (CCFA(x and Co2FeSi1 ? xAlx (CFSA(x and revealed the structure and magnetic and transport properties. We demonstrated giant tunnel magnetoresistance (TMR of up to 220% at room temperature and 390% at 5 K for the magnetic tunnel junctions (MTJs using Co2FeSi0.5Al0.5 (CFSA(0.5 Heusler alloy electrodes. The 390% TMR corresponds to 0.81 spin polarization for CFSA(0.5 at 5 K. We also investigated the crystalline structure and local structure around Co atoms by x-ray diffraction (XRD and nuclear magnetic resonance (NMR analyses, respectively, for CFSA films sputtered on a Cr-buffered MgO (001 substrate followed by post-annealing at various temperatures in an ultrahigh vacuum. The disordered structures in CFSA films were clarified by NMR measurements and the relationship between TMR and the disordered structure was discussed. We clarified that the TMR of the MTJs with CFSA(0.5 electrodes depends on the structure, and is significantly higher for L21 than B2 in the crystalline structure. The second part of this paper is devoted to a SFD using a ferromagnetic barrier. The Co ferrite is investigated as a ferromagnetic barrier because of its high Curie temperature and high resistivity. We demonstrate the strong spin filtering effect through an ultrathin insulating ferrimagnetic Co-ferrite barrier at a low temperature. The barrier was prepared by the surface plasma oxidization of a CoFe2 film deposited on a MgO (001 single crystal substrate, wherein the spinel structure of CoFe2O4 (CFO
Robust spin-polarized midgap states at step edges of topological crystalline insulators
Sessi, Paolo; Di Sante, Domenico; Szczerbakow, Andrzej; Glott, Florian; Wilfert, Stefan; Schmidt, Henrik; Bathon, Thomas; Dziawa, Piotr; Greiter, Martin; Neupert, Titus; Sangiovanni, Giorgio; Story, Tomasz; Thomale, Ronny; Bode, Matthias
2016-12-01
Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three-dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight-binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This nontrivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature.
Spin-polarized transport through a laterally coupled Aharonov-Bohm ring with two magnetic impurities
Cattapan, G.; Lotti, P.
2012-04-01
We consider spin-polarized electron transport through an Aharonov-Bohm ring threaded by magnetic flux, side coupled to a quantum waveguide. The ring contains two magnetic defects symmetrically placed with respect to the stub. In the framework of the quantum-waveguide approach, we treat the transport process as a multi-channel scattering problem, the possible spin channels being degenerate in energy. We study both the phase coherence of the electron's wave function, and the entanglement formation between the impurities spins due to the scattering process, in correspondence to various initial spin configurations. To this end, we consider both a suitable spin-flip parameter, and the transmission concurrencies for the outgoing state. In particular, we find that phase coherence is preserved in correspondence to the maximally entangled singlet state of the impurities, in close analogy to what has been found in the literature for a serially coupled ring.
Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets
Energy Technology Data Exchange (ETDEWEB)
Menchero, Jose Gabriel [Univ. of California, Berkeley, CA (United States). Dept. of Physics
1997-05-01
In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.
Energy Technology Data Exchange (ETDEWEB)
Chopdekar, Rajesh V.; Arenholz, Elke; Suzuki, Y.
2008-08-18
We have probed the nature of magnetism at the surface of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films. The spin polarization of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films is not intrinsically suppressed at all surfaces and interfaces but is highly sensitive to both the epitaxial strain state as well as the substrate orientation. Through the use of soft x-ray spectroscopy, the magnetic properties of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces have been investigated and compared to bulk magnetometry and resistivity measurements. The magnetization of (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces are more bulk-like as a function of thickness whereas the magnetization at the (001)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interface is suppressed significantly below a layer thickness of 20 nm. Such findings are correlated with the biaxial strain state of the La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films; for a given film thickness it is the tetragonal distortion of (001) La{sub 0.7}Sr{sub 0.3}MnO{sub 3} that severely impacts the magnetization, whereas the trigonal distortion for (111)-oriented films and monoclinic distortion for (110)-oriented films have less of an impact. These observations provide evidence that surface magnetization and thus spin polarization depends strongly on the crystal surface orientation as well as epitaxial strain.
Eschrig, Matthias
2010-03-01
Interfaces between solids with different ordering phenomena have become a focus of research in recent years. One reason is that new and unexpected phases that are not stable in either of the adjacent materials can appear in the interface regions. The mechanism for creating such phases is due to induced symmetry breaking, as opposed to spontaneous symmetry breaking in the bulk materials. As a prominent example I discuss interface-induced exotic superconductivity in heterostructures composed of conventional singlet superconductors and strongly spin-polarized ferromagnets. I present new intriguing effects, such as a tunable pure spin-supercurrent in a strongly spin-polarized ferromagnet contacted with only one superconducting electrode, and a difference in the critical currents for positive and negative bias in a high transmission ferromagnetic Josephson junction [1]. The latter, rather surprising effect has a physical explanation in terms of a new ``crossed Cooper pair transmission'' process. In this process two singlet Cooper pairs are coherently decomposed into two equal-spin triplet pairs, which are respectively transmitted via different spin bands in the ferromagnet, after which they again recombine into two singlet pairs. This effect is analogous to the well-known crossed Andreev reflection process, which however is strongly suppressed in this particular case. Furthermore, I discuss how the manipulation of interface spins can be used to pump triplet pairs. This opens an avenue for new types of superconducting quantum devices and new ways to test properties of exotic superconducting phases in experiment. [1] R. Grein, M. Eschrig, G. Metalidis, and G. Sch"on, Phys. Rev. Lett. 102, 227005 (2009).
Fermions on one or fewer Kinks
Chu, Yi-Zen
2007-01-01
We find the full spectrum of fermion bound states on a Z_2 kink. In addition to the zero mode, there are int[2 m_f/m_s] bound states, where m_f is the fermion and m_s the scalar mass. We also study fermion modes on the background of a well-separated kink-antikink pair. Using a variational argument, we prove that there is at least one bound state in this background, and that the energy of this bound state goes to zero with increasing kink-antikink separation, 2L, and faster than e^{-a2L} where a = min(m_s, 2 m_f). By numerical evaluation, we find some of the low lying bound states explicitly.
Wang, Zhijun; Alexandradinata, A.; Cava, Robert J.; Bernevig, B. Andrei
Spatial symmetries in crystals are distinguished by whether they preserve the spatial origin. We show how this basic geometric property gives rise to a new topology in band insulators. We study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these nonsymmorphic symmetries protect a novel surface fermion whose dispersion is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These exotic fermions are materialized in the large-gap insulators: KHg X (X = As,Sb,Bi), which we propose as the first material class whose topology relies on nonsymmorphic symmetries. Beside the hourglass fermion, a different surface of KHg X manifests a 3D generalization of the quantum spin Hall effect. To describe the bulk topology of nonsymmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our nontrivial topology originates not from an inversion of the parity quantum numbers, but rather of the rotational quantum numbers, which we propose as a fruitful in the search for topological materials. Finally, KHg X uniquely exemplifies a cohomological insulator, a concept that we will introduce in a companion work.
Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals
Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.
2016-06-01
Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.
Band renormalization and spin polarization of MoS{sub 2} in graphene/MoS{sub 2} heterostructures
Energy Technology Data Exchange (ETDEWEB)
Coy-Diaz, Horacio; Batzill, Matthias [Department of Physics, University of South Florida, Tampa, FL (United States); Bertran, Francois; Chen, Chaoyu; Avila, Jose; Rault, Julien; Le Fevre, Patrick; Asensio, Maria C. [Synchrotron SOLEIL, L' Orme des Merisiers, Gif sur Yvette (France)
2015-12-15
Transition metal dichalcogenides exhibit spin-orbit split bands at the K-point that become spin polarized for broken crystal inversion symmetry. This enables simultaneous manipulation of valley and spin degrees of freedom. While the inversion symmetry is broken for monolayers, we show here that spin polarization of the MoS{sub 2} surface may also be obtained by interfacing it with graphene, which induces a space charge region in the surface of MoS{sub 2}. Polarization induced symmetry breaking in the potential gradient of the space charge is considered to be responsible for the observed spin polarization. In addition to spin polarization we also observe a renormalization of the valence band maximum (VBM) upon interfacing of MoS{sub 2} with graphene. The energy difference between the VBM at the Γ-point and K-point shifts by ∝150 meV between the clean and graphene covered surface. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Fong, C. F.; Ota, Y.; Harbord, E.; Iwamoto, S.; Arakawa, Y.
2016-03-01
Repeated injection of spin-polarized carriers in a quantum dot (QD) leads to the polarization of nuclear spins, a process known as dynamic nuclear spin polarization (DNP). Here, we report the observation of p-shell carrier assisted DNP in single QDs at zero external magnetic field. The nuclear field—measured by using the Overhauser shift of the singly charged exciton state of the QDs—continues to increase, even after the carrier population in the s-shell saturates. This is also accompanied by an abrupt increase in nuclear spin buildup time as p-shell emission overtakes that of the s shell. We attribute the observation to p-shell electrons strongly altering the nuclear spin dynamics in the QD, supported by numerical simulation results based on a rate equation model of coupling between electron and nuclear spin system. Dynamic nuclear spin polarization with p-shell carriers could open up avenues for further control to increase the degree of nuclear spin polarization in QDs.
Energy Technology Data Exchange (ETDEWEB)
Ueda, K.; Koyama, T.; Hiramatsu, R.; Kobayashi, K.; Ono, T. [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Chiba, D. [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 322-0012 (Japan); Fukami, S. [Green Innovation Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan); Center for Spintronics Integrated Systems, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Tanigawa, H.; Suzuki, T. [RENESAS Electronics Corporation, Sagamihara, Kanagawa 252-5298 (Japan); Ohshima, N. [NEC Energy Device Ltd., 1120 Shimokuzawa, Chuo-ku, Sagamihara, Kanagawa 252-5298 (Japan); Ishiwata, N. [Green Innovation Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan); Nakatani, Y. [University of Electro-communications, Chofu, Tokyo 182-8585 (Japan)
2012-05-14
We have investigated the temperature dependence of the current-induced magnetic domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire at various temperatures and with various applied currents. The carrier spin polarization was estimated from the measured domain wall velocity. We found that it decreased more with increasing temperature from 100 K to 530 K than the saturation magnetization did.
Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals.
Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M
2016-06-01
Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.
Energy Technology Data Exchange (ETDEWEB)
Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
2016-02-08
Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.
Wilson Fermions with Four Fermion Interactions
Rantaharju, Jarno; Pica, Claudio; Sannino, Francesco
2016-01-01
Four fermion interactions appear in many models of Beyond Standard Model physics. In Technicolour and composite Higgs models Standard Model fermion masses can be generated by four fermion terms. They are also expected to modify the dynamics of the new strongly interacting sector. In particular in technicolour models it has been suggested that they can be used to break infrared conformality and produce a walking theory with a large mass anomalous dimension. We study the SU(2) gauge theory with 2 adjoint fermions and a chirally symmetric four fermion term. We demonstrate chiral symmetry breaking at large four fermion coupling and study the phase diagram of the model.
Wilson Fermions with Four Fermion Interactions
DEFF Research Database (Denmark)
Rantaharju, Jarno; Drach, Vincent; Hietanen, Ari;
2015-01-01
We present a lattice study of a four fermion theory, known as Nambu Jona-Lasinio (NJL) theory, via Wilson fermions. Four fermion interactions naturally occur in several extensions of the Standard Model as a low energy parameterisation of a more fundamental theory. In models of dynamical electrowe...
Institute of Scientific and Technical Information of China (English)
Wang Yu-Mei; Ren Jun-Feng; Yuan Xiao-Bo; Dou Zhao-Tao; Hu Gui-Chao
2012-01-01
From experimental results of spin polarized injection and transport in organic semiconductors (OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic (FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm's law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.
Tsuda, Shibun; Nguyen, Minh-Hai; Terasawa, Daiju; Fukuda, Akira; Sawada, Anju
2016-03-01
We investigate the huge longitudinal resistance (HLR) at which the magnetoresistance of the ν =2/3 fractional quantum Hall state (QHS) is increased with dynamic nuclear spin polarization. We measure the magnetoresistance temperature dependence in the resistively saturated HLR by increasing the temperature of the sample rapidly in order to prevent relaxation of the nuclear spin polarization. The obtained results indicate that the magnetoresistance decreases as the temperature increases. The Hall resistance in the HLR is also measured and found to exhibit a plateau close to a quantized value. We discuss the negative magnetoresistance temperature dependence with a stripe-shaped domain state deformed by the nuclear spin polarization.
Stability and bifurcation analysis of spin-polarized vertical-cavity surface-emitting lasers
Li, Nianqiang; Susanto, H.; Cemlyn, B. R.; Henning, I. D.; Adams, M. J.
2017-07-01
A detailed stability and bifurcation analysis of spin-polarized vertical-cavity surface-emitting lasers (VCSELs) is presented. We consider both steady-state and dynamical regimes. In the case of steady-state operation, we carry out a small-signal (asymptotic) stability analysis of the steady-state solutions for a representative set of spin-VCSEL parameters. Compared with full numerical simulation, we show this produces surprisingly accurate results over the whole range of pump ellipticity, and spin-VCSEL bias up to 1.5 times the threshold. We then combine direct numerical integration of the extended spin-flip model and standard continuation technique to examine the underlying dynamics. We find that the spin VCSEL undergoes a period-doubling or quasiperiodic route to chaos as either the pump magnitude or polarization ellipticity is varied. Moreover, we find that different dynamical states can coexist in a finite interval of pump intensity, and observe a hysteresis loop whose width is tunable via the pump polarization. Finally we report a comparison of stability maps in the plane of the pump polarization against pump magnitude produced by categorizing the dynamic output of a spin VCSEL from time-domain simulations, against supercritical bifurcation curves obtained by the standard continuation package auto. This helps us better understand the underlying dynamics of the spin VCSELs.
Zhou, Guoqing; Tang, Guoqiang; Li, Tian; Pan, Guoxing; Deng, Zanhong; Zhang, Fapei
2017-03-01
The ferromagnetic electrode on which a clean high-quality electrode/interlayer interface is formed, is critical to achieve efficient injection of spin-dependent electrons in spintronic devices. In this work, we report on the preparation of graphene-passivated cobalt electrodes for application in vertical spin valves (SVs). In this strategy, high-quality monolayer and bi-layer graphene sheets have been grown directly on the crystal Co film substrates in a controllable process by chemical vapor deposition. The electrode is oxidation resistant and ensures a clean crystalline graphene/Co interface. The AlO x -based magnetic junction devices using such bottom electrodes, exhibit a negative tunnel magneto-resistance (TMR) of ca. 1.0% in the range of 5 K–300 K. Furthermore, we have also fabricated organic-based SVs employing a thin layer of fullerene C60 or an N-type polymeric semiconductor as the interlayer. The devices of both materials show a tunneling behavior of spin-polarized electron transport as well as appreciable TMR effect, demonstrating the high potential of such graphene-coated Co electrodes for organic-based spintronics.
Spin-polarized transport through single-molecule magnet Mn6 complexes
Cremades, Eduard
2013-01-01
The coherent transport properties of a device, constructed by sandwiching a Mn6 single-molecule magnet between two gold surfaces, are studied theoretically by using the non-equilibrium Green\\'s function approach combined with density functional theory. Two spin states of such Mn6 complexes are explored, namely the ferromagnetically coupled configuration of the six MnIII cations, leading to the S = 12 ground state, and the low S = 4 spin state. For voltages up to 1 volt the S = 12 ground state shows a current one order of magnitude larger than that of the S = 4 state. Furthermore this is almost completely spin-polarized, since the Mn6 frontier molecular orbitals for S = 12 belong to the same spin manifold. As such the high-anisotropy Mn6 molecule appears as a promising candidate for implementing, at the single molecular level, both spin-switches and low-temperature spin-valves. © 2013 The Royal Society of Chemistry.
Chen, M. N.; Su, W.; Deng, M. X.; Ruan, Jiawei; Luo, W.; Shao, D. X.; Sheng, L.; Xing, D. Y.
2016-11-01
A great deal of attention has been paid to the topological phases engineered by photonics over the past few years. Here, we propose a topological quantum phase transition to a quantum anomalous Hall (QAH) phase induced by off-resonant circularly polarized light in a two-dimensional system that is initially in a quantum spin Hall phase or a trivial insulator phase. This provides an alternative method to realize the QAH effect, other than magnetic doping. The circularly polarized light effectively creates a Zeeman exchange field and a renormalized Dirac mass, which are tunable by varying the intensity of the light and drive the quantum phase transition. Both the transverse and longitudinal Hall conductivities are studied, and the former is consistent with the topological phase transition when the Fermi level lies in the band gap. A highly controllable spin-polarized longitudinal electrical current can be generated when the Fermi level is in the conduction band, which may be useful for designing topological spintronics.
Studies of magnetostriction and spin polarized band structures of rare earth intermetallics
Wallace, W. E.
1979-01-01
Anisotropic magnetostriction measurements of R6Fe23, R = (Tb, Dy, Ho, and Er) were carried out from 77 K to room temperature. Magnetic fields up to 2.1 Tesla were applied. All the compounds exhibited large magnetostrictions at 77 K, the largest effect being obtained for Tb6Fe23. Saturation magnetostriction values for the compounds were also determined for 77 K and room temperature. Results of the temperature dependence of magnetostriction for Er6Fe23 are in good agreement with Callen and Callen's single ion theory. Therefore, the main sources of magnetostriction in this compound is the Er ion. The spin-up and spin-down electronic energy bands, the density of states and the magnetic moments of YCo5, SmCo5, and GdCo5 were calculated by the spin polarized augmented plane wave technique. The calculations obtained show the origin of the moment, provide good estimates of its magnitude and variation, and the reasons for those variations. They also show the important role of partial charge transfer and of d-d electronic coupling. Calculations for LaNi5 and GdNi5 systems are discussed.
Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene
Huang, Chunli; Chong, Y. D.; Cazalilla, Miguel A.
2016-08-01
Spintronics—the all-electrical control of the electron spin for quantum or classical information storage and processing—is one of the most promising applications of the two-dimensional material graphene. Although pristine graphene has negligible spin-orbit coupling (SOC), both theory and experiment suggest that SOC in graphene can be enhanced by extrinsic means, such as functionalization by adatom impurities. We present a theory of transport in graphene that accounts for the spin-coherent dynamics of the carriers, including hitherto-neglected spin precession processes taking place during resonant scattering in the dilute impurity limit. We uncover an "anisotropic spin precession" (ASP) scattering process in graphene, which contributes a large current-induced spin polarization and modifies the standard spin Hall effect. ASP scattering arises from two dimensionality and extrinsic SOC, and apart from graphene, it can be present in other 2D materials or in the surface states of 3D materials with a fluctuating SOC. Our theory also yields a comprehensive description of the spin relaxation mechanisms present in adatom-decorated graphene, including Elliot-Yafet and D'yakonov-Perel relaxation rates, the latter of which can become an amplification process in a certain parameter regime of the SOC disorder potential. Our work provides theoretical foundations for designing future graphene-based integrated spintronic devices.
Seo, Dong-Kyun
2007-11-14
We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.
Spin-polarized exciton quantum beating in hybrid organic-inorganic perovskites
Odenthal, Patrick; Talmadge, William; Gundlach, Nathan; Wang, Ruizhi; Zhang, Chuang; Sun, Dali; Yu, Zhi-Gang; Valy Vardeny, Z.; Li, Yan S.
2017-09-01
Hybrid organic-inorganic perovskites have emerged as a new class of semiconductors that exhibit excellent performance as active layers in photovoltaic solar cells. These compounds are also highly promising materials for the field of spintronics due to their large and tunable spin-orbit coupling, spin-dependent optical selection rules, and their predicted electrically tunable Rashba spin splitting. Here we demonstrate the optical orientation of excitons and optical detection of spin-polarized exciton quantum beating in polycrystalline films of the hybrid perovskite CH3NH3PbClxI3-x. Time-resolved Faraday rotation measurement in zero magnetic field reveals unexpectedly long spin lifetimes exceeding 1 ns at 4 K, despite the large spin-orbit couplings of the heavy lead and iodine atoms. The quantum beating of exciton states in transverse magnetic fields shows two distinct frequencies, corresponding to two g-factors of 2.63 and -0.33, which we assign to electrons and holes, respectively. These results provide a basic picture of the exciton states in hybrid perovskites, and suggest they hold potential for spintronic applications.
Spin-polarized photoemission study on the temperature dependence of the exchange splitting of Ni
Raue, R.; Hopster, H.; Clauberg, R.
1984-06-01
Using spin-polarized photoemission with high energy- and angle resolution (Δ E=100 meV, ΔΘ=±3°) we have investigated the temperature dependence of the exchange splitting of Ni in the temperature range 0.5≦ T/T c≦0.94. At room temperature we find Δ ex=0.18 eV for the exchange splitting of the S 4 band at the X point of the Brillouin zone. With increasing temperature the total (spin-averaged) energy distribution shows a narrowing and merges into one peak. The spin-resolved energy distribution curves approach each other and are strongly broadened. A discussion of the data within current theories of itinerant electron magnetism is given. The spectra indicate that neither the pure Stoner model nor the prediction of local band theory, assuming a temperature independent exchange splitting are justified for Ni. We conclude that the exchange splitting decreases with increasing temperature and that transverse as well as longitudinal spin fluctuations are responsible for the broadening of the spin-resoived energy distribution curves.
Energy Technology Data Exchange (ETDEWEB)
Schenck, A.; Gygax, F.N. [Institute for Particle Physics of ETH Zuerich, Villigen (Switzerland); McEwen, K.A. [Department of Physics and Astronomy, University College London, London (United Kingdom)
2002-05-06
We have measured the Knight shift and inhomogeneous line broadening of positive muons implanted in monocrystalline UPd{sub 3} from 2 K up to 300 K. We find two components in the transverse-field (H{sub ext}=0.6 T) precession signal with amplitude ratio 2:1, which is independent of temperature up to 300 K. The two signals are associated with two different muon sites with axial symmetry. Both the Knight shifts and the relaxation rates show pronounced anomalies at the critical temperatures of T{sub 2}{approx_equal}4.4 K, believed to reflect, inter alia, a magnetic transition, T{sub 1}{approx_equal}6.8 K and T{sub 0}{approx_equal}7.6 K, originating from antiferroquadrupolar ordering. Details depend on sample orientation and signal component. It is argued that the particular temperature dependence of both the Knight shift and the inhomogeneous line broadening of the stronger component below 10 K is associated with the contact hyperfine contribution to the Knight shift and reflects an inhomogeneous conduction electron spin polarization caused by the antiferroquadrupolar order. Additional zero-field {mu}SR measurements yield a very small temperature-independent relaxation rate consistent with the field inhomogeneity arising from the Pd nuclear dipole fields. In particular, below 4.5 K there is no evidence for additional static fields due to a magnetically ordered state. (author)
Self-sustained spin-polarized current oscillations in multiquantum well structures
Energy Technology Data Exchange (ETDEWEB)
Escobedo, Ramon [Departamento de Matematica Aplicada y Ciencias de la Computacion, Universidad de Cantabria, 39005 Santander (Spain); Carretero, Manuel; Bonilla, Luis L [G. Millan Institute, Fluid Dynamics, Nanoscience and Industrial Mathematics, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Platero, Gloria [Instituto de Ciencia de Materiales, CSIC, 28049 Cantoblanco (Spain)], E-mail: escobedo@unican.es, E-mail: manuel.carretero@uc3m.es, E-mail: bonilla@ing.uc3m.es, E-mail: gplatero@icmm.csic.es
2009-01-15
Nonlinear transport through diluted magnetic semiconductor nanostructures is investigated. We have considered a II-VI multiquantum well nanostructure whose wells are selectively doped with Mn. The response to a dc voltage bias may be either a stationary or an oscillatory current. We have studied the transition from stationary to time-dependent current as a function of the doping density and the number of quantum wells. Analysis and numerical solution of a nonlinear spin transport model shows that the current in a structure without magnetic impurities is stationary, whereas current oscillations may appear if at least one well contains magnetic impurities. For long structures having two wells with magnetic impurities, a detailed analysis of nucleation of charge dipole domains shows that self-sustained current oscillations are caused by repeated triggering of dipole domains at the magnetic wells and motion towards the collector. Depending on the location of the magnetic wells and the voltage, dipole domains may be triggered at both wells or at only one. In the latter case, the well closer to the collector may inhibit domain motion between the first and the second well inside the structure. Our study could allow design of oscillatory spin-polarized current injectors.
Magnetic properties of f-electron systems in spin-polarized relativistic density functional theory
Yamagami, H.; Mavromaras, A.; Kübler, J.
1997-12-01
The magnetic ground state of the series of lanthanide and actinide trivalent ions is investigated by means of spin-polarized relativistic spin-density functional theory. In the local density functional approximation (LDA) an internal effective magnetic field due to exchange and correlation couples to the spin degrees of freedom. The resulting set of coupled Dirac equations yields ground-state multiplets that obey the well-known Hund's rules. This remarkable result comes about by the coupling of the j = l + 1/2 with the j = l - 1/2 states due to the exchange - correlation potential that is, as usual, the functional derivative of the exchange - correlation energy with respect to the spin magnetic moment. The effect of the coupling is shown to depend on the varying relative strengths of spin - orbit coupling and exchange splitting within the f series. Since in the f levels the internal exchange splitting dominates rather than the spin - orbit splitting, the energy level scheme is that of the Paschen - Back effect, and thus features of the Russell - Saunders coupling persist in spite of relativistic effects.
Spin-polarized supercurrents for spintronics: a review of current progress.
Eschrig, Matthias
2015-10-01
During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both by offering the possibility of long-range spin-polarized supercurrents. Such supercurrents constitute a fruitful basis for the study of fundamental physics as they combine macroscopic quantum coherence with microscopic exchange interactions, spin selectivity, and spin transport. This report follows recent developments in the controlled creation of long-range equal-spin triplet supercurrents in ferromagnets and its contribution to spintronics. The mutual proximity-induced modification of order in superconductor-ferromagnet hybrid structures introduces in a natural way such evasive phenomena as triplet superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov pairing, long-range equal-spin supercurrents, [Formula: see text]-Josephson junctions, as well as long-range magnetic proximity effects. All these effects were rather exotic before 2000, when improvements in nanofabrication and materials control allowed for a new quality of hybrid structures. Guided by pioneering theoretical studies, experimental progress evolved rapidly, and since 2010 triplet supercurrents are routinely produced and observed. We have entered a new stage of studying new phases of matter previously out of our reach, and of merging the hitherto disparate fields of superconductivity and spintronics to a new research direction: super-spintronics.
Potential spin-polarized transport in gold-doped armchair graphene nanoribbons
Energy Technology Data Exchange (ETDEWEB)
Srivastava, Pankaj, E-mail: pankajs@iiitm.ac.in [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Dhar, Subhra [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Jaiswal, Neeraj K. [Discipline of Physics, PDPM-Indian Institute of Information Technology, Design and Manufacturing (IIITDM), Jabalpur 482005 (India)
2015-04-17
Based on NEGF-DFT computations, systematic investigation of electronic, magnetic and transport properties of AGNRs are done by employing Au through different doping mechanisms. Remarkable Au–AGNR bonding is observed in case of substitution due to the presence of impurity at the edges. Both substitution and adsorption of Au on AGNR surface induce significant changes in the electronic spin transport of the sp{sup 2} hybridized carbon sheets. AGNRs are semiconducting with lower total energy for the FM configuration, and the I–V characteristics reveal semiconductor to metal transition of Au-doped AGNR. The spin injection is voltage controlled in all the investigated Au-doped AGNRs. - Highlights: • Edge Au-substitution promotes semiconductor–metal transition in AGNR. • NDR due to bias-dependent transmission in Au-substituted AGNRs. • Voltage controlled spin injection in all investigated Au-doped AGNRs. • Strong spin polarization occurs at 0.5 V in Au-hole adsorbed AGNRs.
Origin and enhancement of spin polarized current in diluted magnetic oxides by oxygen vacancies
Energy Technology Data Exchange (ETDEWEB)
Chou, Hsiung, E-mail: hchou@mail.nsysu.edu.tw; Yang, Kung-Shang; Tsao, Yao-Chung; Dwivedi, G. D.; Lin, Cheng-Pang [Department of Physics, National Sun Yat-Sen University, 70, Lienhai Road, Gushan District, Kaohsiung 804, Taiwan (China); Sun, Shih-Jye [Department of Applied Physics, National Kaohsiung University, 700, Gaoxiongdaxue Rd., Nanzi District, Kaohsiung 811, Taiwan (China); Lin, L. K.; Lee, S. F. [Institute of Physics, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115, Taiwan (China)
2016-04-04
Spin polarized current (SPC) is a crucial characteristic of diluted magnetic oxides due to the potential application of oxides in spintronic devices. However, most research has been focused on ferromagnetic properties rather than polarization of electric current, because direct measurements are difficult and the origin of SPC has yet to be fully understood. The method to increase the SPC percentage is beyond practical consideration at present. To address this problem, we focus on the role of oxygen vacancies (V{sub O}) on SPC, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1%–30%)H{sub 2}]. We found that the conductivity increases with an increase of V{sub O} via two independent channels: the variable range hopping (VRH) within localized states and the itinerant transport in the conduction band. The point contact Andreev reflection measurements at 4.2 K, where the electric conduction is governed only by the VRH mechanism, prove that the current flowing in the VRH hopping channel is SPC. The percentage of SPC increases with the introduction of V{sub O} and increase in its concentration. The transport measurement shows that by manipulating V{sub O}, one can control the percentage of VRH hopping conduction such that it can even dominate room temperature conduction. The highest achieved SPC ratio at room temperature was 80%.
Spin-polarized current injection induced magnetic reconstruction at oxide interface
Fang, F.; Yin, Y. W.; Li, Qi; Lüpke, G.
2017-01-01
Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications. PMID:28051142
Precision measurement of the positron asymmetry of laser-cooled, spin-polarized 37K
Melconian, Dan; Fenker, B.; Behr, J. A.; Anholm, M.; Ashery, D.; Behling, R. S.; Cohen, I.; Craiciu, I.; Gorelov, A.; Gwinner, G.; McNeil, J.; Mehlman, M.; Smale, S.; Warner, C. L.
2017-01-01
Precision low-energy measurements in nuclear β decay can be used to provide constraints on possible physics beyond the standard model, complementing searches at high-energy colliders. The short-lived isotope 37K was produced at ISAC-TRIUMF and confined in an alternating magneto-optical trap before being spin-polarized to 99.13(9)% via optical pumping. Our system allows for an exceptionally open geometry with the decay products escaping with their momenta unperturbed by the shallow trapping potential. The emitted positrons are detected in a pair of symmetric detectors placed along the polarization axis to measure the β asymmetry. The analysis was performed blind and considers β-scattering as well as other systematic effects. The results place limits on the mass of a hypothetical W boson coupling to right-handed neutrinos as well as contribute to an independent determination of the Vud element of the CKM matrix. The β asymmetry result as well as improvements and future plans will be described. This work is supported in part by the U.S. Department of Energy, the Natural Sciences and Engineering Research Council of Canada, and the Israel Science Foundation.
Spin-polarized wide electron slabs in functionally graded polar oxide heterostructures.
Ye, Jiandong; Ter Lim, Sze; Bosman, Michel; Gu, Shulin; Zheng, Youdou; Tan, Hark Hoe; Jagadish, Chennupati; Sun, Xiaowei; Teo, Kie Leong
2012-01-01
We report on the high mobility wide electron slabs with enhanced correlation effects by tailoring the polarization effects in a functionally graded ZnMgO/ZnO heterostructures. The characteristics of three-dimensional (3D) spreading electrons are evidenced by the capacitance-voltage profiling and the quantization of 3D Fermi surface in magneto-transport measurements. Despite the weak spin-orbit interaction, such electron slabs are spin-polarized with a large zero-field spin splitting energy, which is induced by the carrier-mediated ferromagnetism. Our results suggest that the vast majority of electrons are localized at the surface magnetic moment which does not allow spin manipulations, and only in the region visited by the itinerant carriers that the ferromagnetic exchange interactions via coupling to the surface local moments contribute to the spin transport. The host ferromagnetism is likely due to the formation of Zn cation vacancies on the surface regime induced by the stabilization mechanism and strain-relaxation in ZnMgO polar ionic surface.
Dual of QCD with One Adjoint Fermion
Mojaza, Matin; Pica, Claudio; Sannino, Francesco
2011-01-01
We construct the magnetic dual of QCD with one adjoint Weyl fermion. The dual is a consistent solution of the 't Hooft anomaly matching conditions, allows for flavor decoupling and remarkably constitutes the first nonsupersymmetric dual valid for any number of colors. The dual allows to bound the anomalous dimension of the Dirac fermion mass operator to be less than one in the conformal window.
Energy Technology Data Exchange (ETDEWEB)
Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Kushnir, Mykola Ya. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine); Morales-Meza, Mishel [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Sukhov, Alexander [Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany); Rusyn, Volodymyr [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine)
2016-04-01
We report on complex magnetization dynamics in a forced spin valve oscillator subjected to a varying magnetic field and a constant spin-polarized current. The transition from periodic to chaotic magnetic motion was illustrated with bifurcation diagrams and Hausdorff dimension – the methods developed for dissipative self-organizing systems. It was shown that bifurcation cascades can be obtained either by tuning the injected spin-polarized current or by changing the magnitude of applied magnetic field. The order–chaos transition in magnetization dynamics can be also directly observed from the hysteresis curves. The resulting complex oscillations are useful for development of spin-valve devices operating in harmonic and chaotic modes.
Rezania, Hamed; Abdi, Ameneh
2017-04-01
We study the behaviors of both Hartree and correlation energies of undoped gapped armchair graphene nanoribbon using random phase approximation in the context of Hubbard model Hamiltonian. Specially, the effects of spin polarization and gap parameter on electron density dependence of Hartree and correlation energies of armchair graphene nanoribbon has been addressed. Our results show the variation of gap parameter leads to considerable effect on correlation and Hartree energy behavior of spin unpolarized gapped graphene in the middle electron density region. However local Hubbard interaction parameter affects the behaviors of Hartree and correlation energy on the whole range of electron density in zero magnetization case. We also show that a considerable reduction has been observed for density dependence of Hartree and correlation energies of spin polarized gapped graphene nanoribbon.
Energy Technology Data Exchange (ETDEWEB)
Chaves-O' Flynn, Gabriel D., E-mail: gdc229@nyu.edu; Wolf, Georg; Pinna, Daniele; Kent, Andrew D. [Department of Physics, New York University, New York, New York 10003 (United States)
2015-05-07
We present the results of zero temperature macrospin and micromagnetic simulations of spin transfer switching of thin film nanomagnets in the shape of an ellipse with a spin-polarization tilted out of the layer plane. The perpendicular component of the spin-polarization is shown to increase the reversal speed, leading to a lower current for switching in a given time. However, for tilt angles larger than a critical angle, the layer magnetization starts to precess about an out-of-plane axis, which leads to a final magnetization state that is very sensitive to simulation conditions. As the ellipse lateral size increases, this out-of-plane precession is suppressed, due to the excitation of spatially non-uniform magnetization modes.
Bhat, Tahir Mohiuddin; Gupta, Dinesh C.
2017-08-01
The structural, electronic, magnetic and transport properties of a new quaternary Heusler alloy CoMnVAs have been investigated by employing generalized gradient approximation (GGA), modified Becke-Johnson (mBJ) and GGA with Hubbard U correction (GGA + U). The alloy is energetically more stable in ferromagnetic Y1 type structure. Elastic parameters reveal high anisotropy and ductile nature of the material. CoMnVAs shows half-metallic ferromagnet character with 100% spin polarization at Fermi level with band gap of 0.55 eV in the minority spin state. The alloy also possesses high electrical conductivity and Seebeck coefficients with 15 μVK-1 at room temperature, achieving a figure of merit of 0.65 at high temperatures. The high degree of ductility, 100% spin polarization and large Seebeck coefficient, makes it an attractive candidate to be used in spin voltage generators and thermoelectric materials.
Energy Technology Data Exchange (ETDEWEB)
Kuzubov, Alexander A. [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Kovaleva, Evgenia A., E-mail: kovaleva.evgeniya1991@mail.ru [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Tomilin, Felix N.; Mikhaleva, Natalya S.; Kuklin, Artem V. [Siberian Federal University, 79 Svobodny Prospect, 660041 Krasnoyarsk (Russian Federation); Kirensky Institute of Physics, 50 Akademgorodok, 660036 Krasnoyarsk (Russian Federation)
2015-12-15
The interaction between armchair carbon and boron nitride nanotubes (NT) with ferromagnetic transition metal (TM) surfaces, namely, Ni(111) and Co(0001), was studied by means of density functional theory. Different configurations of composite compartments mutual arrangement were considered. Partial densities of states and spin density spatial distribution of optimized structures were investigated. Influence of ferromagnetic substrate on nanotubes’ electronic properties was discussed. The values of spin polarization magnitude at the Fermi level are also presented and confirm the patterns of spin density spatial distribution. - Highlights: • Interaction of armchair nanotubes with ferromagnetic metal surfaces was investigated. • Different configurations of nanotube's location were considered. • For all nanotubes the energy difference between configurations is negligible. • Nanotubes were found to be more or less spin-polarized regarding to the configuration. • BN nanotubes demonstrate vanishing of the band gap and contact-induced conductivity.
von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland
2014-10-01
The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications.
Ballistic and diffusive current spin polarization in L1{sub o}-ordered FePt and FePd
Energy Technology Data Exchange (ETDEWEB)
Seemann, Klaus M.; Baltz, Vincent; Hickey, Mark C.; Marrows, Christopher H.; Hickey, Bryan J. [E.C. Stoner Laboratory, School of Physics and Astronomy, University of Leeds, Leeds (United Kingdom); MacKenzie, Maureen; Chapman, John N. [Department of Physics and Astronomy, University of Glasgow, Glasgow (United Kingdom); Miguel, Jorge; Kuch, Wolfgang [Institut fuer Experimentalphysik, Freie Universitaet Berlin, Berlin (Germany); Kronast, Florian [BESSY, Albert-Einstein-Strasse 15, Berlin (Germany)
2008-07-01
We report on the discrepancy of the current spin polarization in the ballistic and diffusive electron transport regime in L1{sub o}-ordered epitaxial FePt and FePd layers. The films studied displayed a chemical long range order parameter of 0.4spin polarization of 50%.
Energy Technology Data Exchange (ETDEWEB)
Chen, Shujun; Zhang, Senfu; Zhu, Qiyuan; Liu, Xianyin; Jin, Chendong; Wang, Jianbo; Liu, Qingfang, E-mail: liuqf@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China)
2015-05-07
By micromagnetic simulation, we investigated the dynamic of magnetic vortex driven by spin-polarized current in Permalloy nanodisks in the presence of interfacial/superficial Dzyaloshinskii-Moriya interactions (DMI). It is found that spin-polarized current can drive the vortex precession. In the presence of DMI, the oscillation frequency of the vortex is about 3 times higher than that of without DMI for the same nanodisk. Moreover, the linewidth is more narrow than that of without DMI when the radius of nanodisk is 50 nm. In addition, the vortex can support a higher current density than that of without DMI. Introduction of DMI in this system can provide a new way to design magnetic vortex oscillator.
Energy Technology Data Exchange (ETDEWEB)
Liu, X. H.; Luo, H.; Qu, T. L., E-mail: qutianliang@nudt.edu.cn; Yang, K. Y.; Ding, Z. C. [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)
2015-10-15
We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of {sup 87}Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the {sup 87}Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the {sup 87}Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.
Spin polarization driven by a charge-density wave in monolayer 1T−TaS2
Zhang, Qingyun
2014-08-06
Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics. © 2014 American Physical Society.
Directory of Open Access Journals (Sweden)
X. H. Liu
2015-10-01
Full Text Available We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of 87Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the 87Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the 87Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.
Bhandari, Nikhil; Charles, James; Dutta, Maitreya; Das, Partha; Cahay, Marc; Newrock, Richard; Herbert, Steven
2013-03-01
We report the first experimental investigation of a device consisting of a quantum point contact (QPC) with four gates - two in-plane side gates in series. The first set of gates (nearest the source contact) is asymmetrically biased to create spin polarization in the channel of the QPC. A symmetric bias is then applied on the second set of side gates (nearest the drain) and varied to tune the location of a conductance anomaly near 0.5 (x2e2/h). The experimental results compare well with simulations of the four-gate QPC devices using a Non-Equilibrium Green's Function formalism. The device is shown to be a tunable all-electric spin polarizer. The range of common-mode bias on the first set of gates over which maximum spin polarization can be achieved is much broader for the four-gate structure compared with the case of a QPC with a single pair of in-plane side gates. This work is supported by NSF under Award 1028483.
Gómez, Guillermina; Belelli, Patricia G.; Cabeza, Gabriela F.; Castellani, Norberto J.
2010-12-01
The adsorption of 1,3-butadiene (BD) on the Pd/Ni(1 1 1) multilayers has been studied using the VASP method in the framework of the density functional theory (DFT). The adsorption on two different configurations of the Pd n/Ni m(1 1 1) systems were considered. The most stable adsorption sites are dependent on the substrate composition and on the inclusion or not of spin polarization. On Pd 1Ni 3(1 1 1) surface, di-π-cis and 1,2,3,4-tetra-σ adsorption structures are the most stable for non-spin polarized (NSP) and spin polarized (SP) levels of calculation, respectively. Conversely, on Pd 3Ni 1(1 1 1) surface, the 1,2,3,4-tetra-σ adsorption structure is the most stable for both NSP and SP levels, respectively. The magnetization of the Pd atoms strongly modifies the adsorption energy of BD and its most stable adsorption mode. On the other hand, as a consequence of BD adsorption, the Pd magnetization decreases. The smaller adsorption energies of BD and 1-butene on the Pd 1Ni 3(1 1 1) surface than on Pd(1 1 1) can be associated to the strained Pd overlayer deposited on Ni(1 1 1).
Giant photoinduced Faraday rotation due to the spin-polarized electron gas in an n-GaAs microcavity
Giri, R.; Cronenberger, S.; Vladimirova, M.; Scalbert, D.; Kavokin, K. V.; Glazov, M. M.; Nawrocki, M.; Lemaître, A.; Bloch, J.
2012-05-01
Faraday rotation up to 19∘ in the absence of an external magnetic field is demonstrated in an n-type bulk GaAs microcavity under circularly polarized optical excitation. This strong effect is achieved because (i) the spin-polarized electron gas is an efficient Faraday rotator and (ii) the light wave makes multiple round trips in the cavity. We introduce a concept of Faraday rotation cross section as a proportionality coefficient between the rotation angle, electron spin density and optical path and calculate this cross section for our system. From independent measurements of photoinduced Faraday rotation and electron spin polarization we obtain quantitatively the cross section of the Faraday rotation induced by free electron spin polarization σFexp=-(2.5±0.6)×10-15 rad×cm2 for photon energy 18 meV below the band gap of GaAs, and electron concentration 2×1016 cm-3. It appears to exceed the theoretical value σFth=-0.7×10-15 rad×cm2, calculated without fitting parameters. We also demonstrate the proof-of-principle of a fast optically controlled Faraday rotator.
Observation of spin-wave Doppler shift in Co90Fe10/Ru micro-strips for evaluating spin polarization
Sugimoto, Satoshi; Rosamond, Mark C.; Linfield, Edmund H.; Marrows, Christopher H.
2016-09-01
The current-induced spin-wave Doppler shift has been investigated for Co90Fe10 films, with and without under- and overlayers of Ru, aiming to obtain quantitative insights into the value of spin polarization of the diffusive electrical currents flowing in this material. This extends the use of spin-wave Doppler shift spectroscopy beyond the study of permalloy to other soft magnetic materials suitable for use in spintronic applications such as racetrack memories. The Damon-Eshbach spin-wave mode was employed, and a control experiment of permalloy yielded a value of spin polarization of P = 0.44 ± 0.03 for that material. An extended method to properly evaluate spin-wave Doppler shifts is developed that takes account of the non-negligible Oersted fields that are generated by the current density asymmetry caused by conducting under- or overlayers. The values of spin polarization for various Co90Fe10-based structures are found to lie in the range of 0.3-0.35, only slightly less than in permalloy.
Fabrication of highly spin-polarized Co2FeAl0.5Si0.5 thin-films
Directory of Open Access Journals (Sweden)
M. Vahidi
2014-04-01
Full Text Available Ferromagnetic Heusler Co2FeAl0.5Si0.5 epitaxial thin-films have been fabricated in the L21 structure with saturation magnetizations over 1200 emu/cm3. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100 substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.
Institute of Scientific and Technical Information of China (English)
GAO Ying-Fang; ZHANG Yong-Ping; LIANG Jiu-Qing
2004-01-01
@@ We study the transport of spin-polarized current induced by the Aharonov-Bohm and Aharonov-Casher phases in a mesoscopic ring with two leads in the presence of a cylindrically symmetric electric field and the magnetic flux at the centre of the same ring. An exact solution for the quantum transport is obtained. It is shown that the transport spin-polarized current and its polarizability can be controlled by the electric field and the magnetic flux as well.
EDITORIAL: New materials with high spin polarization: half-metallic Heusler compounds
Felser, Claudia; Hillebrands, Burkard
2007-03-01
The development of magnetic Heusler compounds, specifically designed as materials for spintronic applications, has made tremendous progress in the very recent past [1-21]. Heusler compounds can be made as half-metals, showing a high spin polarization of the conduction electrons of up to 100% [1]. These materials are exceptionally well suited for applications in magnetic tunnel junctions acting, for example, as sensors for magnetic fields. The tunnelling magneto-resistance (TMR) effect is the relative change in the electrical resistance upon application of a small magnetic field. Tunnel junctions with a TMR effect of 580% at 4 K were reported by the group of Miyazaki and Ando [1], consisting of two Co2MnSi Heusler electrodes. High Curie temperatures were found in Co2 Heusler compounds with values up to 1120 K in Co2FeSi [2]. The latest results are for a TMR device made from the Co2FeAl0.5Si0.5 Heusler compound and working at room temperature with a TMR effect of 174% [3]. The first significant magneto-resistance effect was discovered in Co2Cr0.6Fe0.4Al (CCFA) in Mainz [4]. With the classical Heusler compound CCFA as one electrode, the record TMR effect at 4 K is 240% [5]. Positive and negative TMR values at room temperature utilizing magnetic tunnel junctions with one Heusler compound electrode render magnetic logic possible [6]. Research efforts exist, in particular, in Japan and in Germany. The status of research as of winter 2005 was compiled in a recent special volume of Journal of Physics D: Applied Physics [7-20]. Since then specific progress has been made on the issues of (i) new advanced Heusler materials, (ii) advanced characterization, and (iii) advanced devices using the new materials. In Germany, the Mainz and Kaiserslautern based Research Unit 559 `New Materials with High Spin Polarization', funded since 2004 by the Deutsche Forschungsgemeinschaft, is a basic science approach to Heusler compounds, and it addresses the first two topics in particular
Malladi, Machara Krishna Girish
, where the inhomogeneity is the least in these samples measured. Such magnetoresistance has been attributed to the spin-dependent of splitting of the bands in the presence of magnetic nanoparticles with large moments and Schottky junction properties. A large spin-splitting (on the order of 100-150 meV in p-Si and 65-80 meV in n-Si) has been estimated along with large g-factor of 87 (p-Si) and 40 (n-Si). The spin polarization values based on these measurements has been estimated to be 99.6% in p-Si and 95.70% in n-Si at room temperature. Such large spin polarization values show a great promise for this material system to be the base material for the demonstration of a Si-based room temperature spintronic device.
Yang, Kung-Shang; Huang, Tzu-Yu; Dwivedi, G. D.; Lin, Lu-Kuei; Lee, Shang-Fan; Sun, Shih-Jye; Chou, Hsiung
2017-07-01
Oxygen vacancy induced ferromagnetic coupling in diluted magnetic oxide (DMO) semiconductors have been reported in several studies, but technologically more crucial spin-polarized current (SPC) is still under-developed in DMOs. Few studies have claimed that VRH mechanism can originate the SPC, but, how VRH mechanism associated with percolation path, is not clearly understood. We used Point-contact Andreev reflection (PCAR) technique to probe the SPC in Co-doped ZnO (CZO) films. Since the high resistance samples cause broadening in conductance(G)-voltage(V) curves, which may result in an unreliable evaluation of spin polarization, we include two extra parameters, (i) effective temperature and (ii) spreading resistance, for the simulation to avoid the uncertainty in extracting spin polarization. The effective G-V curves and higher spin polarization can be obtained above a certain oxygen vacancy concentration. The number of completed and fragmentary percolation paths is proportional to the concentration of oxygen vacancies. For low oxygen vacancy samples, the Pb-tip has a higher probability of covering fragmentary percolation paths than the complete ones, due to its small contact size. The completed paths may remain independent of one another and get polarized in different directions, resulting in lower spin-polarization value. High oxygen vacancy samples provide a high density of completed path, most of them link to one another by crossing over, and gives rise to high spin-polarization value.
NMR investigations of surfaces and interfaces using spin-polarized xenon
Energy Technology Data Exchange (ETDEWEB)
Gaede, Holly Caroline [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
1995-07-01
^{129}Xe NMR is potentially useful for the investigation of material surfaces, but has been limited to high surface area samples in which sufficient xenon can be loaded to achieve acceptable signal to noise ratios. In Chapter 2 conventional ^{129}Xe NMR is used to study a high surface area polymer, a catalyst, and a confined liquid crystal to determine the topology of these systems. Further information about the spatial proximity of different sites of the catalyst and liquid crystal systems is determined through two dimensional exchange NMR in Chapter 3. Lower surface area systems may be investigated with spin-polarized xenon, which may be achieved through optical pumping and spin exchange. Optically polarized xenon can be up to 10^{5}times more sensitive than thermally polarized xenon. In Chapter 4 highly polarized xenon is used to examine the surface of poly(acrylonitrile) and the formation of xenon clathrate hydrates. An attractive use of polarized xenon is as a magnetization source in cross polarization experiments. Cross polarization from adsorbed polarized xenon may allow detection of surface nuclei with drastic enhancements. A non-selective low field thermal mixing technique is used to enhance the ^{13}C signal of CO_{2} of xenon occluded in solid CO_{2} by a factor of 200. High-field cross polarization from xenon to proton on the surface of high surface area polymers has enabled signal enhancements of ~1,000. These studies, together with investigations of the efficiency of the cross polarization process from polarized xenon, are discussed in Chapter 5. Another use of polarized xenon is as an imaging contrast agent in systems that are not compatible with traditional contrast agents. The resolution attainable with this method is determined through images of structured phantoms in Chapter 6.
Tunable topological insulators with a single spin-polarized surface Dirac cone
Hsieh, David
2010-03-01
The topological insulator is a fundamentally new time-reversal-invariant topologically ordered phase of matter, which exhibits exotic quantum-Hall-like behavior even in the absence of an applied magnetic field. These materials are characterized by a spin-orbit coupling induced bulk energy gap and an odd number of spin-polarized Dirac cones localized on their surfaces. In this talk, I will review the first experimental realization of the topological insulator in Bi1-xSbx [1,2], and then report our recent experimental discovery and findings of a new generation of topological insulators with order-of-magnitude larger bulk band gaps and a single spin-helical surface Dirac cone [3,4]. I will also discuss a novel `effective gating' technique that can be used to optimize the insulating properties of the bulk, and to tune the Dirac carrier density on the surfaces of these new topological insulators [5]. These experiments pave the way for future transport based studies of topological insulator devices, and offer the potential for a graphene-like revolution to take place for topological insulators. [1] ``A topological Dirac insulator in a quantum spin Hall phase'', D. Hsieh et al., Nature 452, 970 (2008). [2] ``Observation of unconventional quantum spin textures in topological insulators'', D. Hsieh et al., Science 323, 919 (2009). [3] ``Observation of a large-gap topological-insulator class with a single Dirac cone on the surface'', Y. Xia et al., Nature Phys. 5, 398 (2009). [4] ``Observation of time-reversal-protected single-Dirac-cone topological-insulator states in Bi2Te3 and Sb2Te3'', D. Hsieh et al., Phys. Rev. Lett., 103, 146401 (2009). [5] ``A tunable topological insulator in the spin helical Dirac transport regime'', D. Hsieh et al., Nature 460, 1101 (2009).
Generation of spin polarized currents with coherent trapping in magnetic semiconductors
Pereira, Pedro H.; Bezerra, Anibal T.; Farinas, Paulo F.; Maialle, Marcelo Z.; Degani, Marcos H.; Studart, Nelson
2017-04-01
A semiconductor heterostructure consisting of two quantum wells, one of them magnetically doped, is proposed for the generation of spin currents by two lasers tuned at the resonances formed between two lowest energy states (1 and 2) and the continuum (3), which are set by design to be in a Λ like configuration. By numerically simulating the proposed structure under the action of the laser fields, we are able to observe the formation of a quasi-dark state near the resonance. The structure’s design has been idealized as to place state 2 in the magnetically doped quantum-well, where a constant magnetic field breaks the electronic spin degeneracy, leading to the giant Zeeman splitting. This ensures that only one of the electronic spins is driven into a dark resonance, thus blocking it from escaping the system. The other spin is free to escape, so that a spin polarized photocurrent is generated. The polarization can be switched by changing the frequency of the controlling laser. Since this kind of trapping is based on quantum interference, the switching times are expected to be fast. In our simulation, we do not simplify the structure down to level modeling, rather we simulate the full structure under time dependent oscillating laser fields and then identify the signatures that indicate a three-level like behavior. We based our search for the structure on real doping parameters found in real materials used in the literature, however the idea relies on the potential profiles studied, and the presence of the giant splitting, regardless of the underlying material that may be used.
Liu, Jianbin; Zheng, Huaibin; Chen, Hui; Li, Fu-li; Xu, Zhuo
2016-01-01
Ghost imaging with thermal fermions is calculated based on two-particle interference in Feynman's path integral theory. It is found that ghost imaging with thermal fermions can be simulated by ghost imaging with thermal bosons and classical particles. Photons in pseudothermal light are employed to experimentally study fermionic ghost imaging. Ghost imaging with thermal bosons and fermions is discussed based on the point-to-point (spot) correlation between the object and image planes. The employed method offers an efficient guidance for future ghost imaging with real thermal fermions, which may also be generalized to study other second-order interference phenomena with fermions.
Energy Technology Data Exchange (ETDEWEB)
Guessi, L.H.; Leandro, S.C.; Seridonio, A.C.; Siqueira, E.C. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Ilha Solteira, SP (Brazil). Dept. de Fisico Quimica; Souza, F.M.; Vernek, E. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica; Yoshida, M. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Rio Claro, SP (Brazil); Figueira, M.S. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica
2012-07-01
Full text: In this work, we report a theoretical description of the differential conductance in the low bias regime, for a normal scanning tunneling microscope (STM) probe in the presence of ferromagnetic (FM) hosts with impurities. The hosts are treated as a spin-polarized electron gas hybridized to a pair of side-coupled impurities. Two setups of different dimensionalities are considered, a quantum wire (QW) and a metallic surface (MS). In order to deal with the non-interacting and the Coulomb blockade regimes of these systems, the analysis is done in the framework of the two-impurity Anderson model (TIAM) in combination with the equation of motion (EOM) approach for the Hamiltonian Green functions (GFs). The Fano effect appears in such setups, due to the quantum interference between the transport channels composed by the spin-polarized conduction bands and the electron tunneling into (or out of) the impurities. Thus the conductance of the STM reveals as a function of the probe position, a Fano interference strong dependent on the host dimensionality. It leads to the emergence of spin-polarized quantum beats in the Friedel oscillations for the conductance signal, which are uniform in the QW system in opposite to those found in the MS case, characterized by a long-range damped behavior. We remark that, the energy levels of the impurities and the Coulomb repulsion, modulate these beats. As a result, they establish a scenario where the interplay between the Coulomb blockade and the ferromagnetism of a metallic environment, can be useful for future quantum computation devices. (author)
Constraints on dark matter annihilation to fermions and a photon
Chowdhury, Debtosh; Laha, Ranjan
2016-01-01
We consider Majorana dark matter annihilation to fermion - anti-fermion pair and a photon in the effective field theory paradigm, by introducing dimension 6 and dimension 8 operators in the Lagrangian. For a given value of the cut-off scale, the latter dominates the annihilation process for heavier dark matter masses. We find a cancellation in the dark matter annihilation to a fermion - anti-fermion pair when considering the interference of the dimension 6 and the dimension 8 operators. Constraints on the effective scale cut-off is derived while considering indirect detection experiments and the relic density requirements and then comparing them to the bound coming from collider experiments.
Institute of Scientific and Technical Information of China (English)
LI Yu-Xian
2008-01-01
Spin-dependent Andreev reflection and spin polarization through a diluted magnetic semiconductor quantum wire coupled to normal metallic and superconductor electrodes are investigated using scattering theory. When the spin-orbit coupling is considered, more Andreev conductance steps appear at the same Fermi energy. Magnetic semiconductor quantum wire separates the spin-up and spin-down electrons. The Fermi energy, at which different-spin-state electrons begin to separate, becomes lower due to the effect of the spin-orbit interaction. The spin filter effect can be measured more easily by investigating the Andreev conductance than by investigating the normal conductance.
Spin-Polarized Intergrain Tunneling in La2/3Sr1/3MnO3
Hwang, H. Y.; Cheong, S.-W.; Ong, N. P.; Batlogg, B.
1996-09-01
The magnetoresistance (MR) and the field dependent magnetization have been systematically examined in the low temperature ferromagnetic metallic state of single crystal and polycrystalline La2/3Sr1/3MnO3. We find that the intrinsic negative MR in single crystal is due to the suppression of spin fluctuations, and magnetic domain boundaries do not dominate the scattering process. In contrast, we demonstrate that the MR in the polycrystalline samples exhibits two distinct regions: large MR at low fields dominated by spin-polarized tunneling between grains and high field MR which is remarkably temperature independent from 5 to 280 K.
Design and fabrication of nano-ring MRAM demo devices based on spin-polarized current driving
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Nano-ring-type magnetic tunnel junctions(NR-MTJ)were nano-fabricated.The tunneling magnetoresistance(TMR)versus current(Ⅰ)loops of the NR-MTJs for a spin-polarized current switching were measured and the TMR ratio of around 20%～50% with a Al-O barrier at room temperature were observed.The critical value of switching current for the free Co_(60)Fe_(20)B_(20) layer between parallel and anti-parallel magnetization states is smaller than 650μA.The NR-MTJs arrays were also integrated above the transistors in ...
Indian Academy of Sciences (India)
AHMED GUEDDOUH; BACHIR BENTRIA; IBN KHALDOUN LEFKAIER; YAHIA BOUROUROU
2016-10-01
In this paper, spin and non-spin polarization (SP, NSP) are performed to study structural properties and bond hardness of Fe$_x$B ($x = 1, 2, 3$) compounds using density functional theory (DFT) within generalized gradientapproximation (GGA) to evaluate the effect of spin polarization on these properties. The non-spin-polarization results show that the non-magnetic state (NM) is less stable thermodynamically for Fe$_x$B compounds than spinpolarization by the calculated cohesive energy and formation enthalpy. Spin-polarization calculations show that ferromagnetic state (FM) is stable for FexB structures and carry magnetic moment of 1.12, 1.83 and 2.03 $\\mu$B inFeB, Fe$_2$B and Fe$_3$B, respectively. The calculated lattice parameters, bulk modulus and magnetic moments agree well with experimental and other theoretical results. Significant differences in volume and in bulk modulus werefound between the ferromagnetic and non-magnetic cases, i.e., 6.8, 32.8, respectively.We predict the critical pressure between ferromagnetic and non-magnetic phases. The model for hardness calculation using Mulliken population coupled to semi-empirical hardness theory proved effective in hardness prediction for the metal borides which agree well with the experimental values. These results would help to gain insight into the spin-polarized effect on the structural and bond hardness.
Dual of QCD with One Adjoint Fermion
DEFF Research Database (Denmark)
Mojaza, Matin; Nardecchia, Marco; Pica, Claudio;
2011-01-01
We construct the magnetic dual of QCD with one adjoint Weyl fermion. The dual is a consistent solution of the 't Hooft anomaly matching conditions, allows for flavor decoupling and remarkably constitutes the first nonsupersymmetric dual valid for any number of colors. The dual allows to bound the...
Spin polarization and magnetic characteristics at C6H6/Co2MnSi(001) spinterface
Sun, Meifang; Wang, Xiaocha; Mi, Wenbo
2017-09-01
Organic materials with mechanical flexibility, low cost, chemical engineering, and long spin lifetime attract considerable attention for building spintronic devices. Here, a C6H6/Co2MnSi(001) spinterface is investigated by first-principles calculations and spin-polarized scanning tunneling microscopy simulations. Several high symmetry adsorption sites are discussed, together with two possible surface terminations of Co2MnSi(001). An inversion of the spin polarization is induced near EF even in the case of an external electric field, indicating that C6H6 can act as a spin filter to exploit the spin injection efficiency in organic spintronic devices. Unlike previous studies on molecule/ferromagnet interfaces, this inversion is closely related to the electronic structure of the atoms in the subsurface layer of Co2MnSi according to the orbital symmetry analysis. Furthermore, the magnetic moment and magnetic anisotropic energy (MAE) in the outermost Co2MnSi layer are studied. Particularly, in the most stable configuration, the sign of MAE is inversed due to hybridization between C p and Co dz2 orbitals, which suggests that a greater modification on MAE can be achieved by the use of a highly chemically reactive organic molecule. These findings improve the study on the engineering of magnetic properties at molecule/ferromagnetic interfaces through a single π-conjugated organic molecule.
Wang, Hao
2014-07-01
The metal-insulator transition of VO2 so far has evaded an accurate description by density functional theory. The screened hybrid functional of Heyd, Scuseria and Ernzerhof leads to reasonable solutions for both the low-temperature monoclinic and high-temperature rutile phases only if spin polarization is excluded from the calculations. We explore whether a satisfactory agreement with experiment can be achieved by tuning the fraction of Hartree Fock exchange (α) in the density functional. It is found that two branches of locally stable solutions exist for the rutile phase for 12.5%≤α≤20%. One is metallic and has the correct stability as compared to the monoclinic phase, the other is insulating with lower energy than the metallic branch. We discuss these observations based on the V 3d orbital occupations and conclude that α=10% is the best possible choice for spin-polarized VO2 calculations. © 2014 Elsevier B.V. All rights reserved.
Unusually large spin polarization and magnetoresistance in a FeMg8-FeMg8 superatomic dimer
Zhu, Lin; Qian, Meichun; Khanna, Shiv N.
2013-08-01
Electronic transport across a FeMg8 magnetic superatom and its dimer has been investigated using a density functional theory combined with Keldysh nonequilibrium Green's-function formalism. For a single cluster, our studies for the cluster supported in various orientations on a Au(100) surface show that the transport is sensitive to the contact geometry. Investigations covering the cases where the axes of Mg square antiprism are 45°, perpendicular, and parallel to the transport direction, show that the equilibrium conductance, transferred charge, and current polarizations can all change significantly with orientation. Our studies on the transport across a magnetic superatom dimer FeMg8-FeMg8 focus on the effect of electrode contact distance and the support. The calculated I-V curves show negative differential resistance behavior at larger electrode-cluster contact distances. Further, the equilibrium conductance in ferromagnetic state shows an unusually high spin polarization that is about 81.48% for specific contact distance, and a large magnetoresistance ratio exceeding 500% is also found. The results show that the superatom assemblies can provide unusual transport characteristics, and that the spin polarization and magnetoresistance can be controlled via the contact geometry.
Temperature insensitivity of the spin-polarization in Co2MnSi films on GaAs (001)
Branford, W. R.; Singh, L. J.; Barber, Z. H.; Kohn, A.; Petford-Long, A. K.; Van Roy, W.; Magnus, F.; Morrison, K.; Clowes, S. K.; Bugoslavsky, Y. V.; Cohen, L. F.
2007-02-01
The Heusler alloys Co2MnSi and NiMnSb are predicted to be 100% spin-polarized and are leading candidate materials for spin-injection and detection in hybrid spintronic devices. Co2MnSi is lattice matched with GaAs, whereas NiMnSb is strongly mismatched to GaAs. Here, we study the temperature and thickness dependence of the anomalous Hall (AH) effect in a series of textured, predominantly (001) oriented, sputter deposited Co2MnSi thin films on GaAs, and compare the behaviour to that of a molecular beam epitaxy (MBE) grown NiMnSb film on GaAs (001) with low antisite disorder. We show that the Co2MnSi films have temperature independent AH conductivity, even for the thinnest films with strongly temperature dependent saturation magnetization. We discuss whether a temperature insensitive AH conductivity necessarily indicates that the spin-polarization of charge carriers is also temperature independent.
The Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature
Beyer, J.; Buyanova, I. A.; Suraprapapich, S.; Tu, C. W.; Chen, W. M.
2012-04-01
The Hanle effect in InAs/GaAs quantum dots (QDs) is studied under optical orientation as a function of temperature over the range of 150-300 K, with the aim of understanding the physical mechanism responsible for the observed sharp increase of electron spin polarization with increasing temperature. The deduced spin lifetime Ts of positive trions in the QDs is found to be independent of temperature, and is also insensitive to excitation energy and density. It is argued that the measured Ts is mainly determined by the longitudinal spin-flip time (T1) and the spin dephasing time ({T}_{2}^{\\ast }) of the studied QD ensemble, of which both are temperature independent over the studied temperature range and the latter makes a larger contribution. The observed sharply rising QD spin polarization degree with increasing temperature, on the other hand, is shown to be induced by an increase in spin injection efficiency from the barrier/wetting layer and also by a moderate increase in spin detection efficiency of the QD.
Yin, Li; Mi, Wenbo; Wang, Xiaocha
2016-12-01
The tetragonal Fe4N /BiFeO3(001 ) heterostructures aimed at simultaneously gaining the perpendicular magnetic anisotropy (PMA) and high spin polarization have been investigated by the first-principles method. It is found that Fe4N with FeAFeB termination is better for achieving interfacial and inner PMA simultaneously than (FeB)2N termination. When the positions of interfacial FeA and FeB relative to Fe in BiFeO3 are changed, the PMA in Fe4N transforms into the in-plane magnetic anisotropy. Especially, PMA in Fe4N near the heterointerfaces depends on the direction of ferroelectric polarization in BiFeO3 . Finally, the interfacial and inner PMA of Fe4N along with high spin polarization appear in the stable FeAFeB/Fe -O2 case owing to the 3 d -3 d orbital hybridization. These results provide the opportunities for developing multifunctional spintronic devices.
Composite-fermionization of the mixture composed of Tonks gas and Fermi gas
Institute of Scientific and Technical Information of China (English)
Hao Ya-Jiang
2011-01-01
This paper investigates the ground-state properties of the mixture composed of the strongly interacting TonksGirardeau gas and spin polarized Fermi gas confined in one-dimensional harmonic traps, where the interaction between the Bose atoms and Fermi atoms is tunable. With a generalized Bose-Fermi transformation the mixture is mapped into a two-component Fermi gas. The homogeneous Fermi gas is exactly solvable by the Bethe-ansatz method and the ground state energy density can be obtained. Combining the ground-state energy function of the homogeneous system with local density approximation it obtains the ground-state density distributions of inhomogeneous mixture. It is shown that with the increase in boson-fermion interaction, the system exhibits composite-fermionization crossover.
Yang, Shi-Peng; Lu, Mao-Wang; Huang, Xin-Hong; Tang, Qiang; Zhou, Yong-Long
2017-04-01
A theoretical study has been carried out on the spin-dependent electron transport in a hybrid magnetic-electric barrier nanostructure with both Rashba and Dresselhaus spin-orbit couplings, which can be experimentally realized by depositing a ferromagnetic strip and a Schottky metal strip on top of a semiconductor heterostructure. The spin-orbit coupling-dependent transmission coefficient, conductance, and spin polarization are calculated by solving the Schrödinger equation exactly with the help of the transfer-matrix method. We find that both the magnitude and sign of the electron spin polarization vary strongly with the spin-orbit coupling strength. Thus, the degree of electron spin polarization can be manipulated by properly adjusting the spin-orbit coupling strength, and such a nanosystem can be employed as a controllable spin filter for spintronics applications.
Ito, Yosuke; Sato, Daichi; Kamada, Keigo; Kobayashi, Tetsuo
2016-07-11
An optically pumped K-Rb hybrid atomic magnetometer can be a useful tool for biomagnetic measurements due to the high spatial homogeneity of its sensor property inside a cell. However, because the property varies depending on the densities of potassium and rubidium atoms, optimization of the densities is essential. In this study, by using the Bloch equations of K and Rb and considering the spatial distribution of the spin polarization, we confirmed that the calculation results of spin polarization behavior are in good agreement with the experimental data. Using our model, we calculated the spatial distribution of the spin polarization and found that the optimal density of K atoms is 3 × 1019 m-3 and the optimal density ratio is nK/nRb ~ 400 to maximize the output signal and enhance spatial homogeneity of the sensor property.
Wu, Qiang; Altman, M S
2013-07-01
Spin polarized low energy electron microscopy has been used to investigate the quantum size effect (QSE) in electron reflectivity from Fe films grown on a pseudomorphic Cu layer on a W(110) surface. Intensity oscillations caused by the QSE as functions of Fe film thickness and incident electron energy identify quantum well resonance conditions in the film. Evaluation of these intensity oscillations using the phase accumulation model provides information on the unoccupied spin polarized band structure in the Fe film above the vacuum level. We also find evidence that the presence of the non-magnetic Cu layer shifts spin polarized quantum well resonances in the Fe layer uniformly downward in energy by 1.1eV compared to Fe/W(110) films without an interface Cu layer, suggesting that the Cu layer gives a small degree of control over the quantum well resonances.
Fermion Dipole Moment and Holography
Kulaxizi, Manuela
2015-01-01
In the background of a charged AdS black hole, we consider a Dirac particle endowed with an arbitrary magnetic dipole moment. For non-zero charge and dipole coupling of the bulk fermion, we find that the dual boundary theory can be plagued with superluminal modes. Requiring consistency of the dual CFT amounts to constraining the strength of the dipole coupling by an upper bound. We briefly discuss the implications of our results for the physics of holographic non-Fermi liquids.
Wilson Fermions with Four Fermion Interactions
Rantaharju, Jarno; Hietanen, Ari; Pica, Claudio; Sannino, Francesco
2015-01-01
We present a lattice study of a four fermion theory, known as Nambu Jona-Lasinio (NJL) theory, via Wilson fermions. Four fermion interactions naturally occur in several extensions of the Standard Model as a low energy parameterisation of a more fundamental theory. In models of dynamical electroweak symmetry breaking these operators, at an effective level, are used to endow the Standard Model fermions with masses. Furthermore these operators, when sufficiently strong, can drastically modify the fundamental composite dynamics by, for example, turning a strongly coupled infrared conformal theory into a (near) conformal one with desirable features for model building. As first step, we study spontaneous chiral symmetry breaking for the lattice version of the NJL model.
Mass Spectrum of Fermion on Bloch Branes with New Scalar-fermion Coupling
Xie, Qun-Ying; Zhao, Zhen-Hua; Du, Yun-Zhi; Zhang, Yu-Peng
2015-01-01
In order to localize a left- or right-handed fermion zero mode on a thick brane, one usually introduces the Yukawa coupling $\\eta \\bar{\\Psi} F(\\chi) \\Psi$ between a bulk fermion and the background scalar field $\\chi$. However, the Yukawa coupling will do not work if the background scalar is an even function of the extra dimension. Recently, Ref. [Phy. Rev. \\textbf{D} 89 (2014) 086001] has presented a new scalar-fermion coupling form $\\lambda \\bar \\Psi \\Gamma^M \\partial_M F(\\chi) \\gamma^5 \\Psi$ in order to deal with this problem. In this paper, we investigate the localization and mass spectrum of fermion on the Bloch brane by using the new scalar-fermion coupling with $F(\\chi)=\\chi^n$. It is found that the effective potentials have rich structure and may be volcano-like, finite square well-like, and infinite potentials, which depend on the parameter $n$. As a result, there may appear some resonant KK fermions, finite or infinite numbers of bound KK fermions.
Staggered domain wall fermions
Hoelbling, Christian
2016-01-01
We construct domain wall fermions with a staggered kernel and investigate their spectral and chiral properties numerically in the Schwinger model. In some relevant cases we see an improvement of chirality by more than an order of magnitude as compared to usual domain wall fermions. Moreover, we present first results for four-dimensional quantum chromodynamics, where we also observe significant reductions of chiral symmetry violations for staggered domain wall fermions.
Fermion field renormalization prescriptions
Zhou, Yong
2005-01-01
We discuss all possible fermion field renormalization prescriptions in conventional field renormalization meaning and mainly pay attention to the imaginary part of unstable fermion Field Renormalization Constants (FRC). We find that introducing the off-diagonal fermion FRC leads to the decay widths of physical processes $t\\to c Z$ and $b\\to s \\gamma$ gauge-parameter dependent. We also discuss the necessity of renormalizing the bare fields in conventional quantum field theory.
Fermions as topological objects
Yershov, V N
2002-01-01
A conceptual preon-based model of fermions is discussed. The preon is regarded as a topological object with three degrees of freedom in a dual three-dimensional manifold. It is shown that properties of this manifold give rise to a set of preon structures, which resemble three families of fermions. The number of preons in each structure is easily associated with the mass of a fermion. Being just a kind of zero-approximation to a theory of particles and interactions below the quark scale, our model however predicts masses of fermions with an accuracy of about 0.0002% without using any experimental input parameters.
Tran, M; Jaffrès, H; Deranlot, C; George, J-M; Fert, A; Miard, A; Lemaître, A
2009-01-23
We report on spin injection experiments at a Co/Al2O3/GaAs interface with electrical detection. The application of a transverse magnetic field induces a large voltage drop DeltaV at the interface as high as 1.2 mV for a current density of 0.34 nA.microm(-2). This represents a dramatic increase of the spin accumulation signal, well above the theoretical predictions for spin injection through a ferromagnet/semiconductor interface. Such an enhancement is consistent with a sequential tunneling process via localized states located in the vicinity of the Al2O3/GaAs interface. For spin-polarized carriers these states act as an accumulation layer where the spin lifetime is large. A model taking into account the spin lifetime and the escape tunneling time for carriers traveling back into the ferromagnetic contact reproduces accurately the experimental results.
Magnetism of epitaxial Tb films on W(110) studied by spin-polarized low-energy electron microscopy
Prieto, J. E.; Chen, Gong; Schmid, A. K.; de la Figuera, J.
2016-11-01
Thin epitaxial films of Tb metal were grown on a clean W(110) substrate in ultrahigh vacuum and studied in situ by low-energy electron microscopy. Annealed films present magnetic contrast in spin-polarized low-energy electron microscopy. The energy dependence of the electron reflectivity was determined and a maximum value of its spin asymmetry of about 1% was measured. The magnetization direction of the Tb films is in-plane. Upon raising the temperature, no change in the domain distribution is observed, while the asymmetry in the electron reflectivity decreases when approaching the critical temperature, following a power law ˜(1-T /TC) β with a critical exponent β of 0.39.
Li, Shiqi; Sarachik, M. P.
2017-01-01
The resistivities of the dilute, strongly interacting two-dimensional electron systems in the insulating phase of a silicon MOSFET are the same for unpolarized electrons in the absence of magnetic field and for electrons that are fully spin polarized by the presence of an in-plane magnetic field. In both cases the resistivity obeys Efros-Shklovskii variable range hopping ρ (T ) =ρ0exp[(TES/T ) 1 /2] , with TE S and 1 /ρ0 mapping onto each other if one applies a shift of the critical density nc reported earlier. With and without magnetic field, the parameters TE S and 1 /ρ0=σ0 exhibit scaling consistent with critical behavior approaching a metal-insulator transition.
Vuichoud, Basile; Milani, Jonas; Chappuis, Quentin; Bornet, Aurélien; Bodenhausen, Geoffrey; Jannin, Sami
2015-11-01
Dynamic nuclear polarization at 1.2 K and 6.7 T allows one to achieve spin temperatures on the order of a few millikelvin, so that the high-temperature approximation (Δ E spy'), provided perturbations due to second-order (strong coupling) effects are properly taken into account. If spin S is suitably discreet and does not affect the relaxation of spin I, this provides an elegant way of measuring spin polarizations 'on the fly' in a broad range of molecules, thus obviating the need for laborious measurements of signal intensities at thermal equilibrium. The method, dubbed Spin PolarimetrY Magnetic Resonance (SPY-MR), is illustrated for various pairs of 13 C spins (I, S) in acetate and pyruvate.
Institute of Scientific and Technical Information of China (English)
Ding Xiu-Huan; Zhang Cun-Xi; Wang Rui; Zhou Yun-Qing; Kong Ling-Min
2012-01-01
We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling.The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron.The splitting of the Fano-type resonance induces the spin-polarization dependent electron current.The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron,the oscillation frequency,and the amplitude of the external field.These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.
Magnetic damping and spin polarization of highly ordered B2 Co{sub 2}FeAl thin films
Energy Technology Data Exchange (ETDEWEB)
Cui, Yishen [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Lu, Jiwei, E-mail: jl5tk@virginia.edu [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Schäfer, Sebastian; Khodadadi, Behrouz; Mewes, Tim [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Osofsky, Mike [Naval Research Laboratory, Washington, DC 20375 (United States); Wolf, Stuart A. [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)
2014-08-21
Epitaxial Co{sub 2}FeAl films were synthesized using the Biased Target Ion Beam Deposition technique. Post annealing yielded Co{sub 2}FeAl films with an improved B2 chemical ordering. Both the magnetization and the Gilbert damping parameter were reduced with increased B2 ordering. A low damping parameter, ∼0.002, was attained in B2 ordered Co{sub 2}FeAl films without the presence of the L2{sub 1} Heusler phase, which suggests that the B2 structure is sufficient for providing low damping in Co{sub 2}FeAl. The spin polarization was ∼53% and was insensitive to the chemical ordering.
Maslova, N. S.; Mantsevich, V. N.; Arseyev, P. I.
2017-02-01
We perform theoretical investigation of the localized state dynamics in the presence of interaction with the reservoir and Coulomb correlations. We analyze kinetic equations for electron occupation numbers with different spins taking into account high order correlation functions for the localized electrons. We reveal that in the stationary state electron occupation numbers with the opposite spins always have the same value - the stationary state is a "paramagnetic" one. "Magnetic" properties can appear only in the non-stationary characteristics of the single-impurity Anderson model and in the dynamics of the localized electrons second order correlation functions. We found, that for deep energy levels and strong Coulomb correlations, relaxation time for initial "magnetic" state can be several orders larger than for "paramagnetic" one. So, long-living "magnetic" moment can exist in the system. We also found non-stationary spin polarized currents flowing in opposite directions for the different spins in the particular time interval.
Directory of Open Access Journals (Sweden)
D. H. Berman
2014-03-01
Full Text Available Resonant behavior involving spin-orbit entangled states occurs for spin transport along a narrow channel defined in a two-dimensional electron gas, including an apparent rapid relaxation of the spin polarization for special values of the channel width and applied magnetic field (so-called ballistic spin resonance. A fully quantum-mechanical theory for transport using multiple subbands of the one-dimensional system provides the dependence of the spin density on the applied magnetic field and channel width and position along the channel. We show how the spatially nonoscillating part of the spin density vanishes when the Zeeman energy matches the subband energy splittings. The resonance phenomenon persists in the presence of disorder.
Lu, Yi-Lin; Dong, Shengjie; Zhou, Baozeng; Sun, Lili; Zhao, Hui; Wu, Ping
2017-09-01
The effects of 3d transition metals doping on the structural, electronic, and magnetic properties of aluminum hydride were investigated based on spin-polarized first-principles calculations. The studies indicated that V, Cr, Mn, and Fe doping could produce polarization of high-spin state, while Co and Ni doping would induce polarization of low-spin state. It was found that the magnetic ground state depended on the distance between two substitutions and the long-range ferromagnetic coupling was achieved upon doping V, Mn, and Fe. The present work indicated that the introduced 3d-block dopants could tailor aluminum hydride into either a potential half-metallic or n-type magnetic semiconductor by tuning the valence electrons of the impurities. The main findings of this work pointed out the possibilities of the applications of hydrides in future hydride electronics and spintronics.
Energy Technology Data Exchange (ETDEWEB)
Sun, X. [Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Wang, B. [Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Pratt, A. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Department of Physics, University of York, York YO10 5DD (United Kingdom); Yamauchi, Y. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan)
2014-07-21
The geometric, electronic, and magnetic structures of a manganese phthalocyanine (MnPc) molecule on an antiferromagnetic IrMn(100) surface are studied by density functional theory calculations. Two kinds of orientation of the adsorbed MnPc molecule are predicted to coexist due to molecular self-assembly on the surface—a top-site geometry with the Mn–N bonds aligned along the 〈100〉 direction, and a hollow-site orientation in which the Mn–N bonds are parallel to the 〈110〉 direction. The MnPc molecule is antiferromagnetically coupled to the substrate at the top site with a slight reduction in the magnetic moment of the Mn atom of the MnPc molecule (Mn{sub mol}). In contrast, the magnetic moment of the Mn{sub mol} is enhanced to 4.28 μB at the hollow site, a value larger than that in the free MnPc molecule (3.51 μB). Molecular distortion induced by adsorption is revealed to be responsible for the enhancement of the magnetic moment. Furthermore, the spin polarization of the Mn{sub mol} atom at around the Fermi level is found to change from negative to positive through an elongation of the Mn–N bonds of the MnPc. We propose that a reversible switch of the low/high magnetic moment and negative/positive spin polarization might be realized through some mechanical engineering methods.
Spin Polarization of 2D Electrons in GaAs Quantum Wells at ν=1/2 from Gallium NMR Measurements
Freytag, N.; Horvatić, M.; Berthier, C.; Lévy, L.-P.; Melinte, S.; Bayot, V.; Shayegan, M.
2000-03-01
The spin polarization (\\cal P) of a two-dimensional electron gas (2DEG) in two GaAs/AlGaAs multiple-quantum-well heterostructures was probed by measurements of magnetic hyperfine shifts of gallium nuclei located in the quantum wells. The low temperature (50 mK Shankar(R. Shankar, cond-mat/9911288.).
Institute of Scientific and Technical Information of China (English)
Wu Li-Jun; Han Yu
2013-01-01
The spin-polarized linear conductance spectrum and current-voltage characteristics in a four-quantum-dot ring embodied into Aharonov-Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin-orbit interaction.It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π,and that Hubbard U cannot influence the electron transport properties in this case.When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength,the electronic spin polarization can reach a maximum value.Furthermore,by adjusting the bias voltages applied to the leads,the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations.Based on the numerical results,such a model can be applied to the design of a spin filter device.
Fasshauer, Elke
2015-01-01
We report on an implementation of the multiconfigurational time-dependent Hartree method (MCTDH) for spin-polarized fermions (MCTDHF). Our approach is based on a mapping for opera- tors in Fock space that allows a compact and efficient application of the Hamiltonian and solution of the MCTDHF equations of motion. Our implementation extends, builds on and exploits the recursive implementation of MCTDH for bosons (R-MCTDHB) package. Together with R-MCTDHB, the present implementation of MCTDHF forms the MCTDH-X package. We benchmark the accuracy of the algorithm with the harmonic interaction model and a time-dependent generalization thereof. These models consider parabolically trapped particles that interact through a harmonic interaction potential. We demonstrate, that MCTDHF is capable of solving the time-dependent many-fermion Schr\\"odinger equation to an in principle arbitrary degree of precision and can hence yield numerically exact results even in the case of Hamiltonians with time-dependent one-body and t...
Experimental Signatures of Split Fermions in Extra Dimensions
Grossman, Yuval
2000-01-01
The smallness and hierarchy of the fermion parameters could be explained in theories with extra dimensions where doublets and singlets are localized at slightly separated points. Scattering cross sections for collisions of such fermions vanish exponentially at energies high enough to probe the separation distance. This is because the separation puts a lower bound on the attainable impact parameter in the collision. The NLC, and in particular the combination of the e^+e^- and e^-e^- modes, can...
The Friedrichs-Model with fermion-boson couplings II
Civitarese, O; Pronko, G P
2007-01-01
In this work we present a formal solution of the extended version of the Friedrichs Model. The Hamiltonian consists of discrete and continuum bosonic states, which are coupled to fermions. The simultaneous treatment of the couplings of the fermions with the discrete and continuous sectors of the bosonic degrees of freedom leads to a system of coupled equations, whose solutions are found by applying standard methods of representation of bound and resonant states.
Fermion dispersion in axion medium
Mikheev, N. V.; Narynskaya, E. N.
2008-01-01
The interaction of a fermion with the dense axion medium is investigated for the purpose of finding an axion medium effect on the fermion dispersion. It is shown that axion medium influence on the fermion dispersion under astrophysical conditions is negligible small if the correct Lagrangian of the axion-fermion interaction is used.
Complex fermion coherent states
Tyc, T; Sanders, B C; Oliver, W D; Tyc, Tomas; Hamilton, Brett; Sanders, Barry C.; Oliver, William D.
2005-01-01
Whereas boson coherent states provide an elegant, intuitive and useful representation, we show that the desirable features of boson coherent states do not carry over very well to fermion fields unless one is prepared to use exotic approaches such as Grassmann fields. Specifically, we identify four appealing properties of boson coherent states (eigenstate of annihilation operator, displaced vacuum state, preservation of product states under linear coupling, and factorization of correlators) and show that fermion coherent states, and approximations to fermion coherent states, defined over the complex field, do not behave well for any of these four criteria.
Fermion Superfluidity And Confining Interactions
Galal, A A
2004-01-01
We study the pairing of Fermi systems with long-range, confining interparticle interactions. We solve the Cooper problem for a pair of fermions interacting via a regularized harmonic oscillator potential and determine the s-wave spectrum of bound states. Using a model of two interacting species of fermions, we calculate the ground state energy of the normal phase in the Hartree-Fock approximation and find that it is infrared (IR) divergent, due to a combination of the sharpness of the Fermi sea and the long-range nature of the interaction. We calculate the correlation energy in the normal phase using the random phase approximation (RPA) and demonstrate the cancellation of infrared divergences between the Hartree-Fock and RPA contributions. Introducing a variational wavefunction to study the superfluid phase, we solve the BCS equations using a Hartree-Fock-Bogoliubov (HFB) analysis to determine the wave-function, excitation gap, and other parameters of the superfluid phase. We show that the system crosses over...
Semiclassical Theory of Fermions
Florentino Ribeiro, Raphael
2016-01-01
A blend of non-perturbative semiclassical techniques is employed to systematically construct approximations to noninteracting many-fermion systems (coupled to some external potential mimicking the Kohn-Sham potential of density functional theory). In particular, uniform asymptotic approximations are obtained for the particle and kinetic energy density in terms of the external potential acting on the fermions and the Fermi energy. Dominant corrections to the classical limit of quantum mechanic...
Top Quark, Heavy Fermions and the Composite Higgs Boson
Institute of Scientific and Technical Information of China (English)
ZHANG Bin; ZHENG Han-Qing
2001-01-01
We study the properties of heavy fermions in the vector-like representation of the electroweak gauge group SU(2)w × U(1)y with Yukawa couplings to the standard model Higgs boson. Applying the renormalization group analysis,we discuss the effects of heavy fermions to the vacuum stability bound and the triviality bound on the mass of the Higgs boson. We also discuss the interesting possibility that the Higgs particle is composed of the top quark and heavy fermions.The bound on the composite Higgs mass is estimated using the method of Bardeen, Hill and Lindner (Phys. Rev. D41 (1990) 1647), 150 GeV≤ mH ≤450 GeV.
Spin currents injected electrically and thermally from highly spin polarized Co{sub 2}MnSi
Energy Technology Data Exchange (ETDEWEB)
Pfeiffer, Alexander; Reeve, Robert M.; Kronenberg, Alexander; Jourdan, Martin; Kläui, Mathias, E-mail: klaeui@uni-mainz.de [Institut für Physik, Johannes Gutenberg-Universität Mainz, 55099 Mainz (Germany); Hu, Shaojie [Research Center for Quantum Nano-Spin Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Kimura, Takashi [Research Center for Quantum Nano-Spin Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan)
2015-08-24
We demonstrate the injection and detection of electrically and thermally generated spin currents probed in Co{sub 2}MnSi/Cu lateral spin valves. Devices with different electrode separations are patterned to measure the non-local signal as a function of the electrode spacing and we determine a relatively high effective spin polarization α of Co{sub 2}MnSi to be 0.63 and the spin diffusion length of Cu to be 500 nm at room temperature. The electrically generated non-local signal is measured as a function of temperature and a maximum signal is observed for a temperature of 80 K. The thermally generated non-local signal is measured as a function of current density and temperature in a second harmonic measurement detection scheme. We find different temperature dependences for the electrically and thermally generated non-local signals, which allows us to conclude that the temperature dependence of the signals is not just dominated by the transport in the Cu wire, but there is a crucial contribution from the different generation mechanisms, which has been largely disregarded till date.
Energy Technology Data Exchange (ETDEWEB)
Roy, Urmimala; Dey, Rik; Pramanik, Tanmoy; Ghosh, Bahniman; Register, Leonard F.; Banerjee, Sanjay K. [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States)
2015-04-28
We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory.
Roy, Urmimala; Dey, Rik; Pramanik, Tanmoy; Ghosh, Bahniman; Register, Leonard F.; Banerjee, Sanjay K.
2015-04-01
We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory.
Pincelli, T.; Petrov, V. N.; Brajnik, G.; Ciprian, R.; Lollobrigida, V.; Torelli, P.; Krizmancic, D.; Salvador, F.; De Luisa, A.; Sergo, R.; Gubertini, A.; Cautero, G.; Carrato, S.; Rossi, G.; Panaccione, G.
2016-03-01
ULTRASPIN is an apparatus devoted to the measurement of the spin polarization (SP) of electrons ejected from solid surfaces in a UHV environment. It is designed to exploit ultrafast light sources (free electron laser or laser high harmonic generation) and to perform (photo)electron spin analysis by an arrangement of Mott scattering polarimeters that measure the full SP vector. The system consists of two interconnected UHV vessels: one for surface science sample cleaning treatments, e-beam deposition of ultrathin films, and low energy electron diffraction/AES characterization. The sample environment in the polarimeter allows for cryogenic cooling and in-operando application of electric and magnetic fields. The photoelectrons are collected by an electrostatic accelerator and transport lens that form a periaxial beam that is subsequently directed by a Y-shaped electrostatic deflector to either one of the two orthogonal Mott polarimeters. The apparatus has been designed to operate in the extreme conditions of ultraintense single-X-ray pulses as originated by free electron lasers (up to 1 kHz), but it allows also for the single electron counting mode suitable when using statistical sources such as synchrotron radiation, cw-laser, or e-gun beams (up to 150 kcps).
Directory of Open Access Journals (Sweden)
J. Sánchez-Barriga
2014-03-01
Full Text Available Topological insulators are characterized by Dirac-cone surface states with electron spins locked perpendicular to their linear momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy. We solve this puzzle and show that vacuum ultraviolet photons (50–70 eV with linear or circular polarization indeed probe the initial-state spin texture of Bi_{2}Se_{3} while circularly polarized 6-eV low-energy photons flip the electron spins out of plane and reverse their spin polarization, with its sign determined by the light helicity. Our photoemission calculations, taking into account the interplay between the varying probing depth, dipole-selection rules, and spin-dependent scattering effects involving initial and final states, explain these findings and reveal proper conditions for light-induced spin manipulation. Our results pave the way for future applications of topological insulators in optospintronic devices.
Mulhollan, Gregory A; Brachmann, Axel; Clendenin, James E; Garwin, Edward; Kirby, Robert; Luh Dah An; Maruyama, Takashi; Prepost, Richard
2005-01-01
Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile Preliminary measurements have been carried out on bulk GaAs. As expected, the yield change far from the bandgap is quite large. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. For a bias which enhances emission, the yield nearly doubles. For a bias which diminishes emission, the yield is a...
García-Fuente, A; Gallego, L J; Vega, A
2016-08-10
We present a systematic theoretical study of the electronic transport in hydrogen passivated zigzag graphene and silicene nanoribbons with between zero and four neighboring H atoms on one edge replaced by magnetic transition metals (Fe, Co, and Ni). The calculations were performed using equilibrium transport and density-functional theory with the generalized gradient approximation to exchange and correlation. We considered the magnetic moments of the two edges aligned both ferromagnetically (Ferro-F form) and antiferromagnetically (Ferro-A form). The Ferro-A graphene-based ribbons were all semiconducting and would support moderate spin-polarized currents of either sign by applying positive or negative gate voltages. The Ferro-F graphene-based ribbons were all metallic; the most interesting for possible spintronic applications being that with a single Ni atom, in which strong spin-filtering at low bias resulted from a deep trough in the transmission of one spin component around the Fermi level. By contrast, in the Si-based analog this trough was split, partially eliminating the polarization of the current. This splitting was found to be related to the buckled structure of the Si-based nanoribbon, which has its origin in its preference for sp(3)-like hybridization.
Fenker, Benjamin Brown
Precise low-energy measurements in nuclear beta-decay provide constraints on possible physics beyond the standard model complementary to high-energy collider experiments. This thesis describes the most precise measurement of the positron asymmetry from a polarized nucleus to date. At the TRIUMF Neutral Atom Trap, atoms of the positron emitter 37K are confined in an alternating-current magneto-optical trap and spin-polarized to 99.13(9)% via optical pumping. The use of atom-trapping techniques allow for an exceptionally open geometry with the decay products escaping the trapping region unperturbed by the trapping potential. The emitted positrons are detected in a pair of symmetric detectors placed along the polarization axis to measure the asymmetry. The analysis was performed blind and considers beta-scattering and other systematic effects. The result, Abeta (0) = -0.5707 +/- 0.0018, places limits on the mass of a hypothetical W boson coupling to right-handed neutrinos to be > 300GeV/c 2 at zero-mixing as well as contributes to an independent determination of the Vud element of the CKM matrix.
Energy Technology Data Exchange (ETDEWEB)
Pincelli, T., E-mail: pincelli@iom.cnr.it; Rossi, G. [Dipartimento di Fisica, Università degli studi di Milano, Via Celoria 16, 20133 Milano (Italy); Laboratorio TASC, IOM-CNR, S.S. 14 km 163.5, Basovizza, 34149 Trieste (Italy); Petrov, V. N. [Saint Petersburg State Polytechnical University, Politechnicheskaya Street 29, 195251 Saint Petersburg (Russian Federation); Brajnik, G.; Carrato, S. [Università degli Studi di Trieste, Piazzale Europa 1, 34127 Trieste (Italy); Ciprian, R.; Torelli, P.; Krizmancic, D.; Salvador, F.; De Luisa, A.; Panaccione, G. [Laboratorio TASC, IOM-CNR, S.S. 14 km 163.5, Basovizza, 34149 Trieste (Italy); Lollobrigida, V. [Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Sergo, R.; Gubertini, A.; Cautero, G. [Sincrotrone Trieste S.C.p.A, Strada Statale 14-km 163.5 in AREA Science Park, Basovizza, 34149 Trieste (Italy)
2016-03-15
ULTRASPIN is an apparatus devoted to the measurement of the spin polarization (SP) of electrons ejected from solid surfaces in a UHV environment. It is designed to exploit ultrafast light sources (free electron laser or laser high harmonic generation) and to perform (photo)electron spin analysis by an arrangement of Mott scattering polarimeters that measure the full SP vector. The system consists of two interconnected UHV vessels: one for surface science sample cleaning treatments, e-beam deposition of ultrathin films, and low energy electron diffraction/AES characterization. The sample environment in the polarimeter allows for cryogenic cooling and in-operando application of electric and magnetic fields. The photoelectrons are collected by an electrostatic accelerator and transport lens that form a periaxial beam that is subsequently directed by a Y-shaped electrostatic deflector to either one of the two orthogonal Mott polarimeters. The apparatus has been designed to operate in the extreme conditions of ultraintense single-X-ray pulses as originated by free electron lasers (up to 1 kHz), but it allows also for the single electron counting mode suitable when using statistical sources such as synchrotron radiation, cw-laser, or e-gun beams (up to 150 kcps).
Indian Academy of Sciences (India)
R C Patnaik; R K Das; R L Hota; G S Tripathi
2001-10-01
We present theoretical analyses of anisotropic lattice diamagnetism, magnetization due to magnetic ions and carrier spin-polarization in the diluted magnetic semiconductor, Pb1-EuTe. The lattice diamagnetism results from orbital susceptibility due to inter band effects and spin-orbit contributions. The spin-orbit contribution is found to be dominant. However, both the contributions show pronounced anisotropy. With increase inx, the diamagnetism decreases. We consider contributions from randomly distributed isolated magnetic ions and clusters of pairs and triads for the local moment magnetization. The isolated magnetic-ion contribution is the dominant one. We calculate the magnetization for two typical magnetic ion concentrations: = 0.03 and = 0.06. Temperature dependence of the magnetization is also considered. Apart from lattice and localized magnetic ions, the carrier contribution to the spin-density is also calculated for a carrier density of = 1018 cm-3. The relative spin-density of carriers increases with increase in the magnetic ﬁeld strength and magnetic ion concentration. The agreement with experiment where available is reasonably good.
Divergence of the axial current and fermion density in Gross-Neveu models
Karbstein, Felix
2007-01-01
The divergence of the axial current is used to relate the spatial derivative of the fermion density to the bare fermion mass and scalar/pseudoscalar condensates in 1+1 dimensional Gross-Neveu models. This serves as a novel test of known results, to explain simple features of the continuous chiral model and to resolve a conflict concerning the assignment of baryon number to certain multi-fermion bound states.
Spin-polarized electron gas in Co2MSi/SrTiO3(M= Ti, V, Cr, Mn, and Fe) heterostructures
Nazir, S.
2016-06-08
Spin-polarized density functional theory is used to study the TiO2 terminated interfaces between the magnetic Heusler alloys Co2Si (M = Ti, V, Cr, Mn, and Fe) and the non-polar band insulator SrTiO3. The structural relaxation at the interface turns out to depend systematically on the lattice mis- match. Charge transfer from the Heusler alloys (mainly the M 3d orbitals) to the Ti dxy orbitals of the TiO2 interface layer is found to gradually grow from M = Ti to Fe, resulting in an electron gas with increasing density of spin-polarized charge carriers. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Energy Technology Data Exchange (ETDEWEB)
Mitsuoka, Shin-ichi [Osaka Univ., Ibaraki (Japan). Research Center for Nuclear Physics; Shimoda, Tadashi; Miyatake, Hiroari [and others
1996-05-01
To study mechanisms of the ({sup 14}N, {sup 12}B) reactions at intermediate energies, double differential cross section and nuclear spin-polarization of the {sup 12}B projectile-like fragments have been measured as a function of longitudinal momentum in the angular range of 0deg - 9deg. Large spin-polarization of the reaction products {sup 12}B has been observed in the {sup 9}Be({sup 14}N, {sup 12}B) reaction at 39.3 MeV/u. The momentum distributions at forward angles exhibit characteristic features which can not be understood by the current projectile fragmentation picture. It is shown that by assuming the existence of direct two-proton transfer process in addition to the fragmentation process, both the cross section and polarization of {sup 12}B fragments are successfully explained. The target and incident energy dependence of the momentum distribution are also explained reasonably. (author)
Bigi, Chiara; Vobornik, Ivana; Das, Pranab K; Benedetti, Davide; Salvador, Federico; Panaccione, Giancarlo; Rossi, Giorgio
2016-01-01
Complete Photoemission Experiments, enabling to measure the full quantum set of the photoelectron final state, are in high demand for the study of materials and nanostructures whose properties are determined by strong electron and spin correlations. We report here on the implementation of the new spin polarimeter VESPA (Very Efficient Spin Polarization Analysis) at the APE-NFFA Beamline at Elettra that is based on the exchange coupling between the photoelectron spin and a ferromagnetic surface in a reflectometry setup. The system was designed to be integrated with a dedicated Scienta-Omicron DA30 electron energy analyser allowing for two simultaneous reflectometry measurements, along perpendicular axes, that, after magnetization switching of the two targets allow to perform the 3D vectorial reconstruction of the spin polarization while operating the DA30 in high resolution mode. VESPA represents the very first installation for spin-resolved ARPES (SP-ARPES) at the Elettra synchrotron in Trieste, and is being ...
Ouassou, Jabir Ali; Pal, Avradeep; Blamire, Mark; Eschrig, Matthias; Linder, Jacob
2017-05-16
Interfacing superconductors with strongly spin-polarized magnetic materials opens the possibility to discover new spintronic devices in which spin-triplet Cooper pairs play a key role. Motivated by the recent derivation of spin-polarized quasiclassical boundary conditions capable of describing such a scenario in the diffusive limit, we consider the emergent physics in hybrid structures comprised of a conventional s-wave superconductor (e.g. Nb, Al) and either strongly spin-polarized ferromagnetic insulators (e.g. EuO, GdN) or halfmetallic ferromagnets (e.g. CrO2, LCMO). In contrast to most previous works, we focus on how the superconductor itself is influenced by the proximity effect, and how the generated triplet Cooper pairs manifest themselves in the self-consistently computed density of states (DOS) and the superconducting critical temperature T c . We provide a comprehensive treatment of how the superconductor and its properties are affected by the triplet pairs, demonstrating that our theory can reproduce the recent observation of an unusually large zero-energy peak in a superconductor interfaced with a half-metal, which even exceeds the normal-state DOS. We also discuss the recent observation of a large superconducting spin-valve effect with a T c change ~1 K in superconductor/half-metal structures, in which case our results indicate that the experiment cannot be explained fully by a long-ranged triplet proximity effect.
Energy Technology Data Exchange (ETDEWEB)
Seemann, K M; Hickey, M C; Baltz, V; Hickey, B J; Marrows, C H [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)], E-mail: k.seemann@fz-juelich.de, E-mail: c.h.marrows@leeds.ac.uk
2010-03-15
We report magnetic domain wall (DW) resistance in epitaxial films of FePd. When equal numbers of Fe and Pd atoms are present, this material forms an ordered structure with alternating crystal planes of Fe and Pd. We prepared films enriched with Pd to varying degrees, gradually degrading this structure. As might be expected, this increased the electrical resistivity of the films by introducing extra defects that can scatter electrons. However, unexpectedly, the additional resistance arising from the {approx}10 nm thick DWs rose as a proportion of the overall resistivity, roughly doubling when halving the degree of chemical ordering-as determined from x-ray diffraction measurements-within the films. These data can be used to infer a rise in the spin polarization of the current flowing in the layers when extra Pd atoms are introduced. On the other hand, a separate measurement of spin polarization using a superconducting point contact technique that is insensitive to electron scattering revealed no changes as extra Pd was introduced. We conclude that Pd atoms scatter electrons of one spin far more strongly than the other, suggesting a possible means of producing highly spin-polarized currents for use in spintronic devices.
Thurber, Kent R; Tycko, Robert
2014-05-14
We report solid state (13)C and (1)H nuclear magnetic resonance (NMR) experiments with magic-angle spinning (MAS) on frozen solutions containing nitroxide-based paramagnetic dopants that indicate significant perturbations of nuclear spin polarizations without microwave irradiation. At temperatures near 25 K, (1)H and cross-polarized (13)C NMR signals from (15)N,(13)C-labeled L-alanine in trinitroxide-doped glycerol/water are reduced by factors as large as six compared to signals from samples without nitroxide doping. Without MAS or at temperatures near 100 K, differences between signals with and without nitroxide doping are much smaller. We attribute most of the reduction of NMR signals under MAS near 25 K to nuclear spin depolarization through the cross-effect dynamic nuclear polarization mechanism, in which three-spin flips drive nuclear polarizations toward equilibrium with spin polarization differences between electron pairs. When T1e is sufficiently long relative to the MAS rotation period, the distribution of electron spin polarization across the nitroxide electron paramagnetic resonance lineshape can be very different from the corresponding distribution in a static sample at thermal equilibrium, leading to the observed effects. We describe three-spin and 3000-spin calculations that qualitatively reproduce the experimental observations.
Flavor Constraints on Split Fermion Models
Energy Technology Data Exchange (ETDEWEB)
Lillie, Ben
2003-06-26
We examine the contributions to rare processes that arise in models where the Standard Model fermions are localized at distinct points in compact extra dimensions. Tree-level flavor changing neutral current interactions for the Kaluza-Klein (KK) gauge field excitations are induced in such models, and hence strong constraints are thought to exist on the size of the additional dimensions. We find a general parameterization of the model which does not depend on any specific fermion geography and show that typical values of the parameters can reproduce the fermion hierarchy pattern. Using this parameterization, we reexamine the contributions to neutral meson mixing, rare meson decays, and single top-quark production in e{sup +}e{sup -} collisions. We find that is it possible to evade the stringent bounds for natural regions of the parameters, while retaining finite separations between the fermion fields and without introducing a new hierarchy. The resulting limits on the size of the compact dimension can be as low as TeV{sup -1}.
Flavor Constraints on Split Fermion Models
Lillie, Benjamin Huntington; Lillie, Ben; Hewett, JoAnne
2003-01-01
We examine the contributions to rare processes that arise in models where the Standard Model fermions are localized at distinct points in compact extra dimensions. Tree-level flavor changing neutral current interactions for the Kaluza-Klein (KK) gauge field excitations are induced in such models, and hence strong constraints are thought to exist on the size of the additional dimensions. We find a general parameterization of the model which does not depend on any specific fermion geography and show that typical values of the parameters can reproduce the fermion hierarchy pattern. Using this parameterization, we reexamine the contributions to neutral meson mixing, rare meson decays, and single top-quark production in $e^+e^-$ collisions. We find that is it possible to evade the stringent bounds for natural regions of the parameters, while retaining finite separations between the fermion fields and without introducing a new hierarchy. The resulting limits on the size of the compact dimension can be as low as TeV...
Spin polarization of the Ar* 2p{sup -1}{sub 1/2} 4s and 2p{sup -1}{sub 1/2} 3d resonant Auger decay
Energy Technology Data Exchange (ETDEWEB)
Turri, G [Department of Physics, Western Michigan University, Kalamazoo, MI 49008 (United States); Lohmann, B [Institut fuer Theoretische Physik, Westfaelische Wilhelms-Universitaet Muenster, Wilhelm-Klemm-Strasse 9, D-48149 Muenster (Germany); Langer, B [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, D-12489 Berlin (Germany); Snell, G [Department of Physics, Western Michigan University, Kalamazoo, MI 49008 (United States); Becker, U [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin/Dahlem (Germany); Berrah, N [Department of Physics, Western Michigan University, Kalamazoo, MI 49008 (United States)
2007-09-14
The spin-resolved Auger decay of the Ar 2p{sup -1}{sub 1/2} 3d state was measured at moderate energy resolution and compared with the decay of the 2p{sup -1}{sub 1/2} 4s. The former shows a lower transferred spin polarization and a similar, if not higher, dynamical spin polarization, supporting the statement that a fully resolved spectrum is not a necessary condition for observing dynamical spin polarization. An interpretation of the spin polarization as configuration interaction induced effect in the final ionic state leads to partial agreement with our relativistic distorted wave calculation utilizing a 36 configuration state function basis set. Comparison of the experimental and numerical results leads to ambiguities for at least one Auger line. A hypothetical, qualitative interpretation is discussed.
Composite gauge-bosons made of fermions
Suzuki, Mahiko
2016-07-01
We construct a class of Abelian and non-Abelian local gauge theories that consist only of matter fields of fermions. The Lagrangian is local and does not contain an auxiliary vector field nor a subsidiary condition on the matter fields. It does not involve an extra dimension nor supersymmetry. This Lagrangian can be extended to non-Abelian gauge symmetry only in the case of SU(2) doublet matter fields. We carry out an explicit diagrammatic computation in the leading 1 /N order to show that massless spin-one bound states appear with the correct gauge coupling. Our diagram calculation exposes the dynamical features that cannot be seen in the formal auxiliary vector-field method. For instance, it shows that the s -wave fermion-antifermion interaction in the 3S1 channel (ψ ¯ γμψ ) alone cannot form the bound gauge bosons; the fermion-antifermion pairs must couple to the d -wave state too. One feature common to our class of Lagrangian is that the Noether current does not exist. Therefore it evades possible conflict with the no-go theorem of Weinberg and Witten on the formation of the non-Abelian gauge bosons.
Composite gauge-bosons made of fermions
Suzuki, Mahiko
2016-01-01
We construct a class of Abelian and non-Abelian local gauge theories that consist only of matter fields of fermions. The Lagrangian is compact and local without containing an auxiliary vector field nor a subsidiary condition on the matter fields. Because of the special structure, this Lagrangian can be extended to non-Abelian gauge symmetry only in the case of SU(2) doublet matter fields. We carry out explicit dynamical computation in the leading 1/N order to show that massless spin-one bound states appear with the correct gauge coupling. Our diagram calculation exposes the dynamical features that cannot be explored in the formal auxiliary vector-field trick. For instance, it shows that the s-wave fermion-antifermion interaction alone cannot form the bound gauge-bosons; the fermion-antifermion pairs must couple to the d-wave state too. Since our models are unrenormalizable in the world of (3+1) dimension, they can be phenomenologically relevant, if at all, only when momentum cutoff is introduced.
Constraints on a system of two neutral fermions from cosmology
Energy Technology Data Exchange (ETDEWEB)
Binetruy, P.; Girardi, G.; Salati, P.
1984-05-14
Using the standard model of cosmology we study the evolution of the population of a coupled system of two neutral fermions in which the lighter one is stable. During the expansion their population can be frozen at a certain level which makes them contribute to the mass density of the universe. The details of the freezing depend crucially on the couplings and on the masses of these two fermions, so that, comparison with the measured mass density in the universe gives constraints on the parameters of the physical system we examine. We discuss in detail different configurations for the coupling among these fermions; in particular in the case of large mixing we obtain restrictive bounds on both masses. Our study is relevant to supersymmetric grand unified models which predict the occurrence of light interacting neutral fermions, particularly higgsinos.
Fermion masses from dimensional reduction
Energy Technology Data Exchange (ETDEWEB)
Kapetanakis, D. (National Research Centre for the Physical Sciences Democritos, Athens (Greece)); Zoupanos, G. (European Organization for Nuclear Research, Geneva (Switzerland))
1990-10-11
We consider the fermion masses in gauge theories obtained from ten dimensions through dimensional reduction on coset spaces. We calculate the general fermion mass matrix and we apply the mass formula in illustrative examples. (orig.).
Kamleh, W; Williams, A G; Kamleh, Waseem; Leinweber, Derek B.; Williams, Anthony G.; 10.1016/j.nuclphysbps.2003.12.058
2004-01-01
The use of APE smearing or other blocking techniques in fermion actions can provide many advantages. There are many variants of these fat link actions in lattice QCD currently, such as FLIC fermions. Frequently, fat link actions make use of the APE blocking technique in combination with a projection of the blocked links back into the special unitary group. This reunitarisation is often performed using an iterative maximisation of a gauge invariant measure. This technique is not differentiable with respect to the gauge field and thus prevents the use of standard Hybrid Monte Carlo simulation algorithms. The use of an alternative projection technique circumvents this difficulty and allows the simulation of dynamical fat link fermions with standard HMC and its variants.
Cold asymmetrical fermion superfluids
Energy Technology Data Exchange (ETDEWEB)
Caldas, Heron
2003-12-19
The recent experimental advances in cold atomic traps have induced a great amount of interest in fields from condensed matter to particle physics, including approaches and prospects from the theoretical point of view. In this work we investigate the general properties and the ground state of an asymmetrical dilute gas of cold fermionic atoms, formed by two particle species having different densities. We have show in a recent paper, that a mixed phase composed of normal and superfluid components is the energetically favored ground state of such a cold fermionic system. Here we extend the analysis and verify that in fact, the mixed phase is the preferred ground state of an asymmetrical superfluid in various situations. We predict that the mixed phase can serve as a way of detecting superfluidity and estimating the magnitude of the gap parameter in asymmetrical fermionic systems.
Magnetic Dirac fermions and Chern insulator supported on pristine silicon surface
Fu, Huixia; Liu, Zheng; Lian, Chao; Zhang, Jin; Li, Hui; Sun, Jia-Tao; Meng, Sheng
2016-07-01
Emergence of ferromagnetism in nonmagnetic semiconductors is strongly desirable, especially in topological materials because of the possibility of achieving the quantum anomalous Hall effect. Based on first-principles calculations, we propose that for Si thin film grown on metal substrate, the pristine Si(111)-√{3 }×√{3 } surface with a spontaneous weak reconstruction has a strong tendency toward ferromagnetism and nontrivial topological properties, characterized by spin-polarized Dirac-fermion surface states. In contrast to conventional routes relying on introduction of alien charge carriers or specially patterned substrates, the spontaneous magnetic order and spin-orbit coupling on the pristine silicon surface together give rise to the quantized anomalous Hall effect with a finite Chern number C =-1 . This work suggests opportunities in silicon-based spintronics and quantum computing free from alien dopants or proximity effects.
Tsekov, R
2016-01-01
Thermodynamically, bosons and fermions differ by their statistics only. A general entropy functional is proposed by superposition of entropic terms, typical for different quantum gases. The statistical properties of the corresponding Janus particles are derived by variation of the weight of the boson/fermion fraction. It is shown that di-bosons and anti-fermions separate in gas and liquid phases, while three-phase equilibrium appears for poly-boson/fermion Janus particles.
Grand Unification and Exotic Fermions
Feger, Robert P
2015-01-01
We exploit the recently developed software package LieART to show that SU(N) grand unified theories with chiral fermions in mixed tensor irreducible representations can lead to standard model chiral fermions without additional light exotic chiral fermions, i.e., only standard model fermions are light in these models. Results are tabulated which may be of use to model builders in the future. An SU(6) toy model is given and model searches are discussed.
Unification with mirror fermions
Directory of Open Access Journals (Sweden)
Triantaphyllou George
2014-04-01
Full Text Available We present a new framework unifying interactions in nature by introducing mirror fermions, explaining the hierarchy between the weak scale and the coupling unification scale, which is found to lie close to Planck energies. A novel process leading to the emergence of symmetry is proposed, which not only reduces the arbitrariness of the scenario proposed but is also followed by significant cosmological implications. Phenomenology includes the probability of detection of mirror fermions via the corresponding composite bosonic states and the relevant quantum corrections at the LHC.
Fermions from classical statistics
2010-01-01
We describe fermions in terms of a classical statistical ensemble. The states $\\tau$ of this ensemble are characterized by a sequence of values one or zero or a corresponding set of two-level observables. Every classical probability distribution can be associated to a quantum state for fermions. If the time evolution of the classical probabilities $p_\\tau$ amounts to a rotation of the wave function $q_\\tau(t)=\\pm \\sqrt{p_\\tau(t)}$, we infer the unitary time evolution of a quantum system of fe...
Bipartite Composite Fermion States
Sreejith, G. J.; Tőke, C.; Wójs, A.; Jain, J. K.
2011-08-01
We study a class of ansatz wave functions in which composite fermions form two correlated “partitions.” These “bipartite” composite fermion states are demonstrated to be very accurate for electrons in a strong magnetic field interacting via a short-range 3-body interaction potential over a broad range of filling factors. Furthermore, this approach gives accurate approximations for the exact Coulomb ground state at 2+3/5 and 2+4/7 and is thus a promising candidate for the observed fractional quantum Hall states at the hole conjugate fractions at 2+2/5 and 2+3/7.
Chiral fermions on the lattice
Jahn, O; Jahn, Oliver; Pawlowski, Jan M.
2002-01-01
We discuss topological obstructions to putting chiral fermions on an even dimensional lattice. The setting includes Ginsparg-Wilson fermions, but is more general. We prove a theorem which relates the total chirality to the difference of generalised winding numbers of chiral projection operators. For an odd number of Weyl fermions this implies that particles and anti-particles live in topologically different spaces.
Topological susceptibility from overlap fermion
Institute of Scientific and Technical Information of China (English)
应和平; 张剑波
2003-01-01
We numerically calculate the topological charge of the gauge configurations on a finite lattice by the fermionic method with overlap fermions. By using the lattice index theorem, we identify the index of the massless overlap fermion operator to the topological charge of the background gauge configuration. The resulting topological susceptibility X is in good agreement with the anticipation made by Witten and Veneziano.
Catalysis of Electroweak Baryogenesis via Fermionic Higgs Portal Dark Matter
Chao, Wei
2015-01-01
We investigate catalysis of electroweak baryogenesis by fermionic Higgs portal dark matter using a two Higgs doublet model augmented by vector-like fermions. The lightest neutral fermion mass eigenstate provides a viable dark matter candidate in the presence of a stabilizing symmetry Z_2 or gauged U(1)_D symmetry. Allowing for a non-vanishing CP-violating phase in the lowest-dimension Higgs portal dark matter interactions allows generation of the observed dark matter relic density while evading direct detection bounds. The same phase provides a source for electroweak baryogenesis. We show that it is possible to obtain the observed abundances of visible and dark matter while satisfying present bounds from electric dipole moment (EDM) searches and direct detection experiments. Improving the present electron (neutron) EDM sensitivity by one (two) orders of magnitude would provide a conclusive test of this scenario.
Combescure, Monique; Robert, Didier
2012-06-01
The aim of this paper is to give a self-contained and unified presentation of a fermionic coherent state theory with the necessary mathematical details, discussing their definition, properties and some applications. After defining Grassmann algebras, it is possible to get a classical analog for the fermionic degrees of freedom in a quantum system. Following the basic work of Berezin (1966 The Method of Second Quantization (New York: Academic); 1987 Introduction to Superanalysis (Dordrecht: Reidel Publishing Company)), we show that we can compute with Grassmann numbers as we do with complex numbers: derivation, integration, Fourier transform. After that we show that we have quantization formulas for fermionic observables. In particular, there exists a Moyal product formula. As an application, we consider explicit computations for propagators with quadratic Hamiltonians in annihilation and creation operators. We prove a Mehler formula for the propagator and Mehlig-Wilkinson-type formulas for the covariant and contravariant symbols of ‘metaplectic’ transformations for fermionic states. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Coherent states: mathematical and physical aspects’.
Phantom cosmologies and fermions
Chimento, Luis P; Forte, Monica; Kremer, Gilberto M
2007-01-01
Form invariance transformations can be used for constructing phantom cosmologies starting with conventional cosmological models. In this work we reconsider the scalar field case and extend the discussion to fermionic fields, where the "phantomization" process exhibits a new class of possible accelerated regimes.
Cabra, D C; Cabra, Daniel C; Rossini, Gerardo L
1996-01-01
We give an explicit holomorphic factorization of SU(N)_1 WZW primaries in terms of gauge invariant composite fermions. In the N=2 case, we show that these composites realize the spinon algebra. Both in this and in the general case, the underlying Yangian symmetry implies that these operators span the whole Fock space.
Fermions, wigs, and attractors
Energy Technology Data Exchange (ETDEWEB)
Gentile, L.G.C., E-mail: lgentile@pd.infn.it [DISIT, Università del Piemonte Orientale, via T. Michel, 11, Alessandria 15120 (Italy); Dipartimento di Fisica “Galileo Galilei”, Università di Padova, via Marzolo 8, 35131 Padova (Italy); INFN, Sezione di Padova, via Marzolo 8, 35131 Padova (Italy); Grassi, P.A., E-mail: pgrassi@mfn.unipmn.it [DISIT, Università del Piemonte Orientale, via T. Michel, 11, Alessandria 15120 (Italy); INFN, Gruppo Collegato di Alessandria, Sezione di Torino (Italy); Marrani, A., E-mail: alessio.marrani@fys.kuleuven.be [ITF KU Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Mezzalira, A., E-mail: andrea.mezzalira@ulb.ac.be [Physique Théorique et Mathématique Université Libre de Bruxelles, C.P. 231, 1050 Bruxelles (Belgium)
2014-05-01
We compute the modifications to the attractor mechanism due to fermionic corrections. In N=2,D=4 supergravity, at the fourth order, we find terms giving rise to new contributions to the horizon values of the scalar fields of the vector multiplets.
Renormalization of fermion mixing
Energy Technology Data Exchange (ETDEWEB)
Schiopu, R.
2007-05-11
Precision measurements of phenomena related to fermion mixing require the inclusion of higher order corrections in the calculation of corresponding theoretical predictions. For this, a complete renormalization scheme for models that allow for fermion mixing is highly required. The correct treatment of unstable particles makes this task difficult and yet, no satisfactory and general solution can be found in the literature. In the present work, we study the renormalization of the fermion Lagrange density with Dirac and Majorana particles in models that involve mixing. The first part of the thesis provides a general renormalization prescription for the Lagrangian, while the second one is an application to specific models. In a general framework, using the on-shell renormalization scheme, we identify the physical mass and the decay width of a fermion from its full propagator. The so-called wave function renormalization constants are determined such that the subtracted propagator is diagonal on-shell. As a consequence of absorptive parts in the self-energy, the constants that are supposed to renormalize the incoming fermion and the outgoing antifermion are different from the ones that should renormalize the outgoing fermion and the incoming antifermion and not related by hermiticity, as desired. Instead of defining field renormalization constants identical to the wave function renormalization ones, we differentiate the two by a set of finite constants. Using the additional freedom offered by this finite difference, we investigate the possibility of defining field renormalization constants related by hermiticity. We show that for Dirac fermions, unless the model has very special features, the hermiticity condition leads to ill-defined matrix elements due to self-energy corrections of external legs. In the case of Majorana fermions, the constraints for the model are less restrictive. Here one might have a better chance to define field renormalization constants related by
Towards quantum turbulence in cold atomic fermionic superfluids
Bulgac, Aurel; McNeil Forbes, Michael; Wlazłowski, Gabriel
2017-01-01
Fermionic superfluids provide a new realization of quantum turbulence, accessible to both experiment and theory, yet relevant to phenomena from both cold atoms to nuclear astrophysics. In particular, the strongly interacting Fermi gas realized in cold-atom experiments is closely related to dilute neutron matter in neutron star crusts. Unlike the liquid superfluids 4He (bosons) and 3He (fermions), where quantum turbulence has been studied in laboratory for decades, superfluid Fermi gases stand apart for a number of reasons. They admit a rather reliable theoretical description based on density functional theory called the time-dependent superfluid local density approximation that describes both static and dynamic phenomena. Cold atom experiments demonstrate exquisite control over particle number, spin polarization, density, temperature, and interaction strength. Topological defects such as domain walls and quantized vortices, which lie at the heart of quantum turbulence, can be created and manipulated with time-dependent external potentials, and agree with the time-dependent theoretical techniques. While similar experimental and theoretical control exists for weakly interacting Bose gases, the unitary Fermi gas is strongly interacting. The resulting vortex line density is extremely high, and quantum turbulence may thus be realized in small systems where classical turbulence is suppressed. Fermi gases also permit the study of exotic superfluid phenomena such as the Larkin-Ovchinnikov-Fulde-Ferrell pairing mechanism for polarized superfluids which may give rise to 3D supersolids, and a pseudo-gap at finite temperatures that might affect the regime of classical turbulence. The dynamics associated with these phenomena has only started to be explored. Finally, superfluid mixtures have recently been realized, providing experimental access to phenomena like Andreev-Bashkin entrainment predicted decades ago. Superfluid Fermi gases thus provide a rich forum for addressing
Al-Hashimi, M H; Wiese, U -J
2016-01-01
Majorana fermion dynamics may arise at the edge of Kitaev wires or superconductors. Alternatively, it can be engineered by using trapped ions or ultracold atoms in an optical lattice as quantum simulators. This motivates the theoretical study of Majorana fermions confined to a finite volume, whose boundary conditions are characterized by self-adjoint extension parameters. While the boundary conditions for Dirac fermions in $(1+1)$-d are characterized by a 1-parameter family, $\\lambda = - \\lambda^*$, of self-adjoint extensions, for Majorana fermions $\\lambda$ is restricted to $\\pm i$. Based on this result, we compute the frequency spectrum of Majorana fermions confined to a 1-d interval. The boundary conditions for Dirac fermions confined to a 3-d region of space are characterized by a 4-parameter family of self-adjoint extensions, which is reduced to two distinct 1-parameter families for Majorana fermions. We also consider the problems related to the quantum mechanical interpretation of the Majorana equation ...
Schweidenback, Lars
In this thesis we describe two spectroscopic projects project on semiconductor heterostructures, as well as putting together and testing a micro-photoluminescence/7 tesla magnet system for the study of micron size two-dimensional crystals. Below we discuss the three parts in more detail. i) MnAs-based spin light emitting diodes. We have studied the injection of spin-polarized electrons from a ferromagnetic MnAs contact into an AlGaAs(n)/GaAs(i)/AlGaAs(p) n-i-p light emitting diode. We have recorder the emitted electroluminescence as function of magnetic field applied at right angles to the device plane in the 7-300 K temperature range. It was found that at 7 Kelvin the emitted light is circularly polarized with a polarization that is proportional to the MnAs contact magnetization with a saturation value of 26% for B > 1.25 tesla. The polarization persists up to room temperature with a saturation value of 6%. ii) Optical Aharonov-Bohm effect in InGaAs quantum wells. The excitonic photoluminescence intensity from InGaAs quantum wells as function of magnetic field exhibits two local maxima superimposed on a decreasing background. The maxima are attributed to the optical Aharonov-Bohm effect of electrons orbiting around a hole localized at the center of an Indium rich InGaAs islands detected by cross sectional scanning tunneling microscopy. Analysis of the position of the maxima yields a value of the electron orbit radius. iii) Micro-Photoluminescence. We have put together a micro-photoluminescence /7 tesla system for the study of two dimensional crystals. The samples are placed inside a continuous flow cryostat whose tail is positioned in the bore of the 7 tesla magnet. A microscope objective is used to focus the exciting laser light and collect the emitted photoluminescence. The system was tested by recording the photoluminescence spectra of WS2 and WSe 2 monolayers at T = 77 K.
Fermionic T-duality in fermionic double space
Nikolic, Bojan
2016-01-01
In this article we offer the interpretation of the fermionic T-duality of the type II superstring theory in double space. We generalize the idea of double space doubling the fermionic sector of the superspace. In such doubled space fermionic T-duality is repersented as permutation of the fermionic coordinates $\\theta^\\alpha$ and $\\bar\\theta^\\alpha$ with the corresponding fermionic T-dual ones, $\\vartheta_\\alpha$ and $\\bar\\vartheta_\\alpha$, respectively. Demanding that T-dual transformation law has the same form as inital one, we obtain the known form of the fermionic T-dual NS-R i R-R background fields. Fermionic T-dual NS-NS background fields are obtained under some assumptions. We conclude that only symmetric part of R-R field strength and symmetric part of its fermionic T-dual contribute to the fermionic T-duality transformation of dilaton field and analyze the dilaton field in fermionic double space. As a model we use the ghost free action of type II superstring in pure spinor formulation in approximation...
Fermionic T-duality in fermionic double space
Nikolić, B.; Sazdović, B.
2017-04-01
In this article we offer the interpretation of the fermionic T-duality of the type II superstring theory in double space. We generalize the idea of double space doubling the fermionic sector of the superspace. In such doubled space fermionic T-duality is represented as permutation of the fermionic coordinates θα and θbarα with the corresponding fermionic T-dual ones, ϑα and ϑbarα, respectively. Demanding that T-dual transformation law has the same form as initial one, we obtain the known form of the fermionic T-dual NS-R and R-R background fields. Fermionic T-dual NS-NS background fields are obtained under some assumptions. We conclude that only symmetric part of R-R field strength and symmetric part of its fermionic T-dual contribute to the fermionic T-duality transformation of dilaton field and analyze the dilaton field in fermionic double space. As a model we use the ghost free action of type II superstring in pure spinor formulation in approximation of constant background fields up to the quadratic terms.
Energy Technology Data Exchange (ETDEWEB)
Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Saini, Hardev S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Reshak, Ali H. [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)
2014-12-15
We report full potential treatment of electronic and magnetic properties of Cr{sub 2−x}Fe{sub x}CoZ (Z=Al, Si) Heusler alloys where x=0.0, 0.25, 0.5, 0.75 and 1.0, based on density functional theory (DFT). Both parent alloys (Cr{sub 2}CoAl and Cr{sub 2}CoSi) are not half-metallic frromagnets. The gradual replacement of one Cr sublattice with Fe induces the half-metallicity in these systems, resulting maximum spin polarization. The half-metallicity starts to appear in Cr{sub 2−x}Fe{sub x}CoAl and Cr{sub 2−x}Fe{sub x}CoSi with x=0.50 and x=0.25, respectively, and the values of minority-spin gap and half-metallic gap or spin-flip gap increase with further increase of x. These gaps are found to be maximum for x=1.0 for both cases. An excellent agreement between the structural properties of CoFeCrAl with available experimental study is obtained. The Fermi level tuning by Fe-doping makes these alloys highly spin polarized and thus these can be used as promising candidates for spin valves and magnetic tunnelling junction applications. - Highlights: • Tuning of E{sub F} in Cr{sub 2}CoZ (Z=Al, Si) has been demonstrated via Fe doping. • Effect of Fe doping on half-metallicity and magnetism have been discussed. • The new alloys have a potential of being used as spin polarized electrodes.
Mironov, A. E.; Hewitt, J. D.; Eden, J. G.
2017-03-01
We report the selective population of Rb or Cs n p P2 3/2 (n =5 , 6; F =4 , 5) hyperfine states by the photodissociation of a transient, alkali-rare gas diatomic molecule. Circularly polarized (σ-), amplified spontaneous emission (ASE) on the D2 line of Rb or Cs (780.0 and 852.1 nm, respectively) is generated when Rb-Xe or Cs-Xe ground state collision pairs are photoexcited by a σ+-polarized optical field having a wavelength within the D2 blue satellite continuum, associated with the B Σ2 1/2 +←X Σ2 1/2 + (free←free ) transition of the diatomic molecule. The degree of spin polarization of Cs (6 p P3/2 2 ), specifically, is found to be dependent on the interatomic distance (R ) at which the excited complex is born, a result attributed to the structure of the B Σ2 1/2 + state. For Cs-Xe atomic pairs, tuning the wavelength of the optical field from 843 to 848 nm varies the degree of circular polarization of the ASE from 63% to almost unity because of the perturbation, in the 5 ≤R ≤6 Å interval, of the Σ2 1/2 + potential by a d σ molecular orbital associated with a higher Λ 2 electronic state. Monitoring only the Cs 6 p P3/2 2 spin polarization reveals a previously unobserved interaction of CsXe (B Σ2 1/2 + ) with the lowest vibrational levels of a Λ 2 state derived from Cs (5 d )+Xe . By inserting a molecular intermediate into the alkali atom excitation mechanism, these experiments realize electronic spin polarization through populating no more than two n p P2 3/2 hyperfine states, and demonstrate a sensitive spectroscopic probe of R -dependent state-state interactions and their impact on interatomic potentials.
Andreev reflection and spin polarization of SrRuO{sub 3} thin films on SrTiO{sub 3} (111)
Energy Technology Data Exchange (ETDEWEB)
Foerster, M; Rigato, F; Fontcuberta, J [Institut de Ciencia de Materials de Barcelona - CSIC, E-08193 Bellaterra (Spain); Piano, S; Mellor, C J, E-mail: mfoerster@icmab.es [School of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham (United Kingdom)
2011-07-06
Epitaxial SrRuO{sub 3} thin films with an extremely flat surface morphology suitable for the use in thin film heterostructures have been grown on SrTiO{sub 3} (111) substrates. The transport spin polarization was measured by point contact spectroscopy for SrRuO{sub 3} films on SrTiO{sub 3} (111) and comparable samples on SrTiO{sub 3} (001). The measured polarization for both types of samples is slightly smaller than previously measured by the same technique. Possible reasons for this difference are discussed.
Nedelkoski, Zlatko; Sanchez, Ana M.; Ghasemi, Arsham; Hamaya, Kohei; Evans, Richard F. L.; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.
2016-11-01
Atomic resolution scanning transmission electron microscopy reveals the presence of an antiphase boundary in the half-metallic Co2Fe(Al,Si) full Heusler alloy. By employing the density functional theory calculations, we show that this defect leads to reversal of the sign of the spin-polarization in the vicinity of the defect. In addition, we show that this defect reduces the strength of the exchange interactions, without changing the ferromagnetic ordering across the boundary. Atomistic spin calculations predict that this effect reduces the width of the magnetic domain wall compared to that in the bulk.
Akabori, M; Yamada, S.
2004-01-01
We investigated the transport properties of ferromagnetic/semiconductor hybrid structures utilizing an InAs/In_Al_As modulation-doped heterostructures formed on a GaAs (001) substrate with In_xAl_As step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured magneto-transport properties of the samples with current flow between...
Energy Technology Data Exchange (ETDEWEB)
Kortright, Jeffrey B; Kortright, Jeffrey B; Lincoln, Derek M; Edelstein, Ruth Shima; Epstein, Arthur J
2008-05-20
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the V L2,3 and C and N K edges reveal bonding/backbonding interactions in films of the 400 K magnetic semiconductor V[TCNE]x~;;2. In V spectra, dxy-like orbitals are modeled assuming V2+ in an octahedral ligand field, while dz2 and dx2-y2 orbitals involved in strong covalent bonding cannot be modeled by atomic calculations. C and N MCD, and differences in XAS from neutral TCNE molecules, reveal spin-polarized molecular orbitals in V[TCNE]x~;;2 associated with backbonding interactions that yield its novel properties.
2007-10-08
Melkov,3 Vasil Tiberkevich,4 and Andrei N. Slavin4 1Dipartimento di Fisica della Materia e Tecnologie Fisiche Avanzate, University of Messina...nanocontact. In Eq. 1, the unit vector p defining the spin-polarization direction is parallel to the direction ez of the in-plane external magnetic field...linear theory,3 the propagating spin- wave mode excited at the threshold is a cylindrical spin- wave with the wave vector kL=1.2/Rc and frequency L
Dimensional Hierarchy of Fermionic Interacting Topological Phases
Queiroz, Raquel; Khalaf, Eslam; Stern, Ady
2016-11-01
We present a dimensional reduction argument to derive the classification reduction of fermionic symmetry protected topological phases in the presence of interactions. The dimensional reduction proceeds by relating the topological character of a d -dimensional system to the number of zero-energy bound states localized at zero-dimensional topological defects present at its surface. This correspondence leads to a general condition for symmetry preserving interactions that render the system topologically trivial, and allows us to explicitly write a quartic interaction to this end. Our reduction shows that all phases with topological invariant smaller than n are topologically distinct, thereby reducing the noninteracting Z classification to Zn.
Dimensional Hierarchy of Fermionic Interacting Topological Phases.
Queiroz, Raquel; Khalaf, Eslam; Stern, Ady
2016-11-11
We present a dimensional reduction argument to derive the classification reduction of fermionic symmetry protected topological phases in the presence of interactions. The dimensional reduction proceeds by relating the topological character of a d-dimensional system to the number of zero-energy bound states localized at zero-dimensional topological defects present at its surface. This correspondence leads to a general condition for symmetry preserving interactions that render the system topologically trivial, and allows us to explicitly write a quartic interaction to this end. Our reduction shows that all phases with topological invariant smaller than n are topologically distinct, thereby reducing the noninteracting Z classification to Z_{n}.
Holomorphic Symplectic Fermions
Davydov, Alexei
2016-01-01
Let V be the even part of the vertex operator super-algebra of r pairs of symplectic fermions. Up to two conjectures, we show that V admits a unique holomorphic extension if r is a multiple of 8, and no holomorphic extension otherwise. This is implied by two results obtained in this paper: 1) If r is a multiple of 8, one possible holomorphic extension is given by the lattice vertex operator algebra for the even self dual lattice $D_r^+$ with shifted stress tensor. 2) We classify Lagrangian algebras in SF(h), a ribbon category associated to symplectic fermions. The classification of holomorphic extensions of V follows from 1) and 2) if one assumes that SF(h) is ribbon equivalent to Rep(V), and that simple modules of extensions of V are in one-to-one relation with simple local modules of the corresponding commutative algebra in SF(h).
Leptogenesis from split fermions
Energy Technology Data Exchange (ETDEWEB)
Nagatani, Yukinori; Perez, Gilad
2004-01-11
We present a new type of leptogenesis mechanism based on a two-scalar split-fermions framework. At high temperatures the bulk scalar vacuum expectation values (VEVs) vanish and lepton number is strongly violated. Below some temperature, T{sub c}, the scalars develop extra dimension dependent VEVs. This transition is assumed to proceed via a first order phase transition. In the broken phase the fermions are localized and lepton number violation is negligible. The lepton-bulk scalar Yukawa couplings contain sizable CP phases which induce lepton production near the interface between the two phases. We provide a qualitative estimation of the resultant baryon asymmetry which agrees with current observation. The neutrino flavor parameters are accounted for by the above model with an additional approximate U(1) symmetry.
Chavanis, Pierre-Henri; Méhats, Florian
2014-01-01
We study the fermionic King model which may provide a relevant model of dark matter halos. The exclusion constraint can be due to quantum mechanics (for fermions such as massive neutrinos) or to Lynden-Bell's statistics (for collisionless systems undergoing violent relaxation). This model has a finite mass. Furthermore, a statistical equilibrium state exists for all accessible values of energy. Dwarf and intermediate size halos are degenerate quantum objects stabilized against gravitational collapse by the Pauli exclusion principle. Large halos at sufficiently high energies are in a gaseous phase where quantum effects are negligible. They are stabilized by thermal motion. Below a critical energy they undergo gravitational collapse (gravothermal catastrophe). This may lead to the formation of a central black hole that does not affect the structure of the halo. This may also lead to the formation of a compact degenerate object surrounded by a hot massive atmosphere extending at large distances. We argue that la...
Lin, De-Hone
2015-01-01
This paper is concerned with the application of a spacetime structure to a three-dimensional quantum system. There are three components. First, the main part of this paper presents the constraint conditions which build the relation of a spacetime structure and a form invariance solution to the covariant Dirac equation. The second is to devise a spacetime cage for fermions with chosen constraints. The third part discusses the feasibility of the cage with an experiment.
Tripartite composite fermion states
Sreejith, G. J.; Wu, Ying-Hai; Wójs, A.; Jain, J. K.
2013-06-01
The Read-Rezayi wave function is one of the candidates for the fractional quantum Hall effect at filling fraction ν=2+⅗, and thereby also its hole conjugate at 2+⅖. We study a general class of tripartite composite fermion wave functions, which reduce to the Rezayi-Read ground state and quasiholes for appropriate quantum numbers, but also allow a construction of wave functions for quasiparticles and neutral excitations by analogy to the standard composite fermion theory. We present numerical evidence in finite systems that these trial wave functions capture well the low energy physics of a four-body model interaction. We also compare the tripartite composite fermion wave functions with the exact Coulomb eigenstates at 2+⅗, and find reasonably good agreement. The ground state as well as several excited states of the four-body interaction are seen to evolve adiabatically into the corresponding Coulomb states for N=15 particles. These results support the plausibility of the Read-Rezayi proposal for the 2+⅖ and 2+⅗ fractional quantum Hall effect. However, certain other proposals also remain viable, and further study of excitations and edge states will be necessary for a decisive establishment of the physical mechanism of these fractional quantum Hall states.
Topology and Fermionic Condensate
Kulikov, I.; Pronin, P.
The purpose of this paper is to investigate an influence of a space-time topology on the formation of fermionic condensate in the model with four-fermion interaction ()2. The value for the space-time with topology of R1 × R1 × S1 is found. Moreover a relation of the value of fermionic condensate to a periodic length is studied. In this connection the possibility of a relation of the topologic deposits to structure of hadrons is discussed.Translated AbstractTopologie und FermikondensatEs wird der Einfluß einer Raum-Zeittopologie auf die Bildung des Fermikondensats in einem Modell mit Vierfermionenwechselwirkung ()2 untersucht. Für eine Raum-Zeit mit der Topologie R1 × R2 × S1 werden die Parameter gegeben. Weiterhin wird die Relation der Größe des Fermikondensats zu einer periodischen Länge untersucht. In diesem Zusammenhang wird die Verbindung des topologischen Depots zur Struktur der Hadronen diskutiert.
Avramov, Paul; Kuzubov, Alexander A; Kuklin, Artem V; Lee, Hyosun; Kovaleva, Evgenia A; Sakai, Seiji; Entani, Shiro; Naramoto, Hiroshi; Sorokin, Pavel B
2017-01-26
The structure of the interfaces and the mechanisms of induced spin polarization of 1D infinite and finite narrow graphene- and h-BN zigzag nanoribbons placed on a SrO-terminated La1-xSrxMnO3 (LSMO) (001) surface were studied using density functional theory (DFT) electronic structure calculations. It was found that the π-conjugated nanofragments are bonded to the LSMO(001) surface by weak disperse interactions. The types of coordination of the fragments, the strength of bonding, and the rate of spin polarization depend upon the nature of the fragments. Infinite and finite graphene narrow zigzag nanoribbons are characterized by the lift of the spin degeneracy and strong spin polarization caused by interface-induced structural asymmetry and oxygen-mediated indirect exchange interactions with Mn ions of LSMO support. Spin polarization changes the semiconducting nature of infinite graphene nanoribbons to half-metallic state with visible spin-up density of states at the Fermi level. The h-BN nanoribbon binding energy is weaker than graphene nanoribbon ones with noticeably shorter interlayer distance. The asymmetry effect and indirect exchange interactions cause spin polarization of h-BN nanoribbon as well with formation of embedded states inside the band gap. The results show a possibility to use one-atom thick nanofragments to design LSMO-based heterostructures for spintronic nanodevices with h-BN as an inert spacer to develop different potential barriers.
Hadron Properties with FLIC Fermions
Energy Technology Data Exchange (ETDEWEB)
James Zanotti; Wolodymyr Melnitchouk; Anthony Williams; J Zhang
2003-07-01
The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a)-improvement in lattice fermion actions offering near continuum results at finite lattice spacing. It provides computationally inexpensive access to the light quark mass regime of QCD where chiral nonanalytic behavior associated with Goldstone bosons is revealed. The motivation and formulation of FLIC fermions, its excellent scaling properties and its low-lying hadron mass phenomenology are presented.
Super Efimov effect of resonantly interacting fermions in two dimensions.
Nishida, Yusuke; Moroz, Sergej; Son, Dam Thanh
2013-06-07
We study a system of spinless fermions in two dimensions with a short-range interaction fine-tuned to a p-wave resonance. We show that three such fermions form an infinite tower of bound states of orbital angular momentum ℓ=±1 and their binding energies obey a universal doubly exponential scaling E(3)((n))∝exp(-2e(3πn/4+θ)) at large n. This "super Efimov effect" is found by a renormalization group analysis and confirmed by solving the bound state problem. We also provide an indication that there are ℓ=±2 four-body resonances associated with every three-body bound state at E(4)((n))∝exp(-2e(3πn/4+θ-0.188)). These universal few-body states may be observed in ultracold atom experiments and should be taken into account in future many-body studies of the system.
Abes, M.; Atkinson, D.; Tanner, B. K.; Charlton, T. R.; Langridge, Sean; Hase, T. P. A.; Ali, M.; Marrows, C. H.; Hickey, B. J.; Neudert, A.; Hicken, R. J.; Arena, D.; Wilkins, S. B.; Mirone, A.; Lebègue, S.
2010-11-01
Using the surface, interface, and element specificity of x-ray resonant magnetic scattering in combination with x-ray magnetic circular dichroism, we have spatially resolved the magnetic spin polarization, and the associated interface proximity effect, in a Mn-based high-susceptibility material close to a ferromagnetic Co layer. We have measured the magnetic polarization of Mn and Cu3d electrons in paramagnetic CuMn alloy layers in [Co/Cu(x)/CuMn/Cu(x)]20 multilayer samples with varying copper layer thicknesses from x=0 to 25Å . The size of the Mn and CuL2,3 edge dichroism shows a decrease in the Mn-induced polarization for increasing copper thickness indicating the dominant interfacial nature of the Cu and Mn spin polarization. The Mn polarization is much higher than that of Cu. Evidently, the Mn moment is a useful probe of the local spin density. Mn atoms appear to be coupled antiferromagnetically with the Co layer below x=10Å and ferromagnetically coupled above. In contrast, the interfacial Cu atoms remain ferromagnetically aligned to the Co layer for all thicknesses studied.
Indian Academy of Sciences (India)
B Pintér; F De Proft; T Veszprémi; P Geerlings
2005-09-01
Regioselectivity of the photochemical [2 + 2] cyclo-addition of triplet carbonyl compounds with a series of ground state electron-rich and electron-poor alkenes, the Paterno-Büchi reaction, is studied. Activation barriers for the first step of the triplet reaction are computed in the case of the O-attack. Next, the observed regioselectivity is explained using a series of DFT-based reactivity indices. In the first step, we use the local softness and the local HSAB principle within a softness matching approach, and explain the relative activation barriers of the addition step. In the final step, the regioselectivity is assessed within the framework of spin-polarized conceptual density functional theory, considering response functions of the system's external potential , number of electrons and spin number , being the difference between the number of and electrons in the spin-polarized system. Although the concept of local spin philicity, introduced recently within this theory, appears less suited to predict the regioselectivity in this reaction, the correct regioselectivity emerges from considering an interaction between the largest values of the generalized Fukui functions ss on both interacting molecules.
Betancourt, J.; Paudel, T. R.; Tsymbal, E. Y.; Velev, J. P.
2017-07-01
Two-dimensional electron gases (2DEGs) at oxide interfaces have been a topic of intensive research due to their high carrier mobility and strong confinement. Additionally, strong correlations in the oxide materials can give rise to new and interesting physics, such as magnetism and metal-insulator transitions at the interface. Using first-principles calculations based on density functional theory, we demonstrate the presence of a highly spin-polarized 2DEG at the interface between the Mott insulator GdTi O3 and a band insulator SrTi O3 . The strong correlations in the dopant cause ferromagnetic alignment of the interface Ti atoms and result in a fully spin-polarized 2DEG. The 2DEG consists of two types of carriers distinguished by their orbital character. The majority of the interface charge is strongly localized on the Ti dx y orbitals at the interface and a smaller fraction resides on the delocalized Ti dx z ,y z states.
Tian, Jifa; Miotkowski, Ireneusz; Hong, Seokmin; Datta, Supriyo; Chen, Yong
Topological insulators (TIs) possess nontrivial spin-momentum-locked topological surface states (TSS). Real TI can also host trivial surface 2DEG with strong Rashba spin-orbit coupling derived from the bulk states. Both TSS and Rashba 2DEG can generate current induced spin polarization, although the dominant helicities of their spin-momentum locking (SML) are expected to be opposite. Here, we report spin potentiometric measurements in exfoliated bulk-insulating Bi2Te2Se and bulk-metallic Bi2Se3 thin flakes. In both materials, the voltage measured by a FM electrode shows a hysteretic step-like change when the FM magnetization is switched by an in-plane magnetic field. The trend of the voltage change can be reversed by reversing the direction of the dc current, and the amplitude of the spin signal increases linearly with increasing bias current. Such a spin signal is consistent with a current induced spin polarization arising from a helical SML. However, the observed trend of the voltage change is opposite between Bi2Te2Se and Bi2Se3, suggesting opposite signs of dominant spin helicity that we attribute to TSS and Rashba 2DEG respectively.
On free fermions and plane partitions
Foda, O; Zuparic, M
2008-01-01
We use free fermion methods to re-derive a result of Okounkov and Reshetikhin relating charged fermions to random plane partitions, and to extend it to relate neutral fermions to strict plane partitions.
Energy Technology Data Exchange (ETDEWEB)
Bataille, A.M. [DRECAM/SPCSI, CEA Saclay, 91191 Gif-sur-Yvette (France)]. E-mail: alexandre.bataille@cea.fr; Mattana, R. [Unite Mixte de Physique CNRS/Thales, 91767 Palaiseau Cedex, France and Universite Paris-Sud, 91405 Orsay (France); Seneor, P. [Unite Mixte de Physique CNRS/Thales, 91767 Palaiseau Cedex, France and Universite Paris-Sud, 91405 Orsay (France); Tagliaferri, A. [INFM, dipartimento di fisica del politecnico, 20133 Milan (Italy); Gota, S. [DRECAM/SPCSI, CEA Saclay, 91191 Gif-sur-Yvette (France); Bouzehouane, K. [Unite Mixte de Physique CNRS/Thales, 91767 Palaiseau Cedex, France and Universite Paris-Sud, 91405 Orsay (France); Deranlot, C. [Unite Mixte de Physique CNRS/Thales, 91767 Palaiseau Cedex, France and Universite Paris-Sud, 91405 Orsay (France); Guittet, M.-J. [DRECAM/SPCSI, CEA Saclay, 91191 Gif-sur-Yvette (France); Moussy, J.-B. [DRECAM/SPCSI, CEA Saclay, 91191 Gif-sur-Yvette (France); De Nadai, C. [ESRF, BP 220, 38043 Grenoble Cedex (France); Brookes, N.B. [ESRF, BP 220, 38043 Grenoble Cedex (France); Petroff, F. [Unite Mixte de Physique CNRS/Thales, 91767 Palaiseau Cedex, France and Universite Paris-Sud, 91405 Orsay (France); Gautier-Soyer, M. [DRECAM/SPCSI, CEA Saclay, 91191 Gif-sur-Yvette (France)
2007-09-15
We report on two independent measurements of the spin polarization at the Fe{sub 3}O{sub 4}/{gamma}-Al{sub 2}O{sub 3} interface. Fe{sub 3}O{sub 4}/{gamma}-Al{sub 2}O{sub 3} (111) bilayers have been epitaxially grown by oxygen-assisted molecular beam epitaxy onto {alpha}-Al{sub 2}O{sub 3} (0001) substrates and some were covered ex situ by a cobalt electrode. Spin resolved photoemission yield to a negative spin polarization ({approx}-40 %) while transport measurements on Fe{sub 3}O{sub 4}/{gamma}-Al{sub 2}O{sub 3}/Co magnetic tunnel junctions show a positive TMR, which suggest that the tunnel spin polarization at the Fe{sub 3}O{sub 4}/{gamma}-Al{sub 2}O{sub 3} interface is positive.
On Fermionic Entangled State Representation and Fermionic Entangled Wigner Operator
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
By analogy with the bosonic bipartite entangled state we construct fermionic entangled state with the Grassmann numbers. The Wigner operator in the fermionic entangled state representation is introduced, whose marginal distributions are understood in an entangled way. The technique of integration within an ordered product (IWOP) of Fermi operators is used in our discussion.
Supersymmetry for Fermion Masses
Institute of Scientific and Technical Information of China (English)
LIU Chun
2007-01-01
It is proposed that supersymmetry (SUSY) may be used to understand fermion mass hierarchies. A family symmetry Z3L is introduced, which is the cyclic symmetry among the three generation SU(2) doublets. SUSY breaks at a high energy scale ～ 1011 GeV. The electroweak energy scale ～ 100 GeV is unnaturally small. No additional global symmetry, like the R-parity, is imposed. The Yukawa couplings and R-parity violating couplings all take their natural values, which are (&)(100 ～ 10-2). Under the family symmetry, only the third generation charged fermions get their masses. This family symmetry is broken in the soft SUSY breaking terms, which result in a hierarchical pattern of the fermion masses. It turns out that for the charged leptons, the τ mass is fromthe Higgs vacuum expectation value (VEV)and the sneutrino VEVs, the muon mass is due to the sneutrino VEVs, and the electron gains its mass due to both Z3L and SUSY breaking. The large neutrino mixing are produced with neutralinos playing the partial role of right-handed neutrinos. |Ve3|, which is for ve-vτ mixing, is expected to be about 0.1. For the quarks, the third generation masses are from the Higgs VEVs, the second generation masses are from quantum corrections, and the down quark mass due to the sneutrino VEVs. It explains mc/ms, ms/me, md ＞ mu, and so on. Other aspects of the model are discussed.
Recent advances in description of few two-component fermions
Kartavtsev, O I
2012-01-01
Overview of the recent advances in description of the few two-component fermions is presented. The zero-range interaction limit is generally considered to discuss the principal aspects of the few-body dynamics. Significant attention is paid to detailed description of two identical fermions of mass $m$ and a distinct particle of mass $m_1$; two universal $L^P = 1^-$ bound states arise for mass ratio $m/m_1$ increasing up to the critical value $\\mu_c \\approx 13.607$, beyond which the Efimov effect takes place. The topics considered include rigorous treatment of the few-fermion problem in the zero-range interaction limit, low-dimensional results, the four-body energy spectrum, crossover of the energy spectra for $m/m_1$ near the critical value $\\mu_c $, and properties of potential-dependent states. At last, enlisted are the problems, whose solution is in due course.
Landau Levels of Majorana Fermions in a Spin Liquid.
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
2016-04-22
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.
Crossover from Bosonic to Fermionic features in Composite Boson Systems
Thilagam, A
2013-01-01
We study the quantum dynamics of conversion of composite bosons into fermionic fragment species with increasing densities of bound fermion pairs using the open quantum system approach. The Hilbert space of $N$-state-function is decomposed into a composite boson subspace and an orthogonal fragment subspace of quasi-free fermions that enlarges as the composite boson constituents deviate from ideal boson commutation relations. The tunneling dynamics of coupled composite boson states in confined systems is examined, and the appearance of exceptional points under experimentally testable conditions (densities, lattice temperatures) is highlighted. The theory is extended to examine the energy transfer between macroscopically coherent systems such as multichromophoric macromolecules (MCMMs) in photosynthetic light harvesting complexes.
Heavy fermion superconductivity
Brison, Jean-Pascal; Glémot, Loı̈c; Suderow, Hermann; Huxley, Andrew; Kambe, Shinsaku; Flouquet, Jacques
2000-05-01
The quest for a precise identification of the symmetry of the order parameter in heavy fermion systems has really started with the discovery of the complex superconducting phase diagram in UPt 3. About 10 years latter, despite numerous experiments and theoretical efforts, this is still not achieved, and we will quickly review the present status of knowledge and the main open question. Actually, the more forsaken issue of the nature of the pairing mechanism has been recently tackled by different groups with macroscopic or microscopic measurement, and significant progress have been obtained. We will discuss the results emerging from these recent studies which all support non-phonon-mediated mechanisms.
Phenomenology of high colour fermions
Energy Technology Data Exchange (ETDEWEB)
Lust, D.; Streng, K.H.; Papantonopoulos, E.; Zoupanos, G.
1986-04-28
We present the phenomenological consequences of a dynamical scenario for electroweak symmetry breaking and generation of fermion masses, involving the presence of fermions which transform under high colour representations. Particular emphasis is given to the predictions for rare processes and to the possible signals in present and future machines. (orig.).
Espin, Johnny
2015-01-01
It has been proposed several times in the past that one can obtain an equivalent, but in many aspects simpler description of fermions by first reformulating their first-order (Dirac) Lagrangian in terms of two-component spinors, and then integrating out the spinors of one chirality ($e.g.$ primed or dotted). The resulting new Lagrangian is second-order in derivatives, and contains two-component spinors of only one chirality. The new second-order formulation simplifies the fermion Feynman rules of the theory considerably, $e.g.$ the propagator becomes a multiple of an identity matrix in the field space. The aim of this thesis is to work out the details of this formulation for theories such as Quantum Electrodynamics, and the Standard Model of elementary particles. After having developed the tools necessary to establish the second-order formalism as an equivalent approach to spinor field theories, we proceed with some important consistency checks that the new formulation is required to pass, namely the presence...
Feldman, Benjamin E.; Drozdov, Ilya K.; Randeria, Mallika T.; Li, Jian; Bernevig, B. Andrei; Yazdani, Ali
2015-03-01
Recently, it was shown that Majorana fermions can be realized by depositing chains of magnetic atoms on a superconductor if the spins are non-collinear or if they are ferromagnetic and subject to large spin-orbit coupling. Scanning tunneling microscopy (STM) studies of Fe chains on a Pb(110) surface revealed zero-energy states localized to the ends, and a spin-polarized tip was used to show ferromagnetism in the chains as well as spin-orbit coupling on the Pb surface, providing strong evidence for Majorana fermions. These measurements were performed at 1.4 K, and the width of the zero-energy mode was limited by thermal broadening. In this talk, I will present subsequent measurements in which we extend these results to temperatures below 250 mK using a dilution refrigerator STM. The low temperature allows us to obtain significantly higher energy resolution, and I will discuss our results in the context of Majorana fermions.
Radiative neutrino masses in the singlet-doublet fermion dark matter model with scalar singlets
Restrepo, Diego; Sánchez-Peláez, Marta; Zapata, Oscar; Tangarife, Walter
2015-01-01
When the singlet-doublet fermion dark matter model is extended with additional $Z_2$--odd real singlet scalars, neutrino masses and mixings can be generated at one-loop level. In this work, we discuss the salient features arising from the combination of the two resulting simplified dark matter models. When the $Z_2$-lightest odd particle is a scalar singlet, $\\operatorname{Br}(\\mu\\to e \\gamma)$ could be measurable provided that the singlet-doublet fermion mixing is small enough. In this scenario, also the new decay channels of vector-like fermions into scalars can generate interesting leptonic plus missing transverse energy signals at the LHC. On the other hand, in the case of doublet-like fermion dark matter, scalar coannihilations lead to an increase in the relic density which allow to lower the bound of doublet-like fermion dark matter.
Holographic fermions in asymptotically scaling geometries with hyperscaling violation
Fan, Zhongying
2013-01-01
We investigate holographic fermions in general asymptotically scaling geometries with hyperscaling violation exponent $\\theta$, which is a natural generalization of fermions in Lifshitz spacetime. We prove that the retarded Green functions in this background satisfy the ARPES (angle-resolved photoemission spectroscopy) sum rules by introducing a dynamical source on a UV brane for zero density fermionic systems. The big difference from the Lifshitz case is that the mass of probe fermions decoupled from the UV theory and thus has no longer been restricted by unitarity bound. We also study finite density fermions at finite temperature, with dynamical exponent $z=2$. We find that the dispersion relation is linear but the logarithm of the spectral function is not linearly related to the logarithm of $k_\\bot =k-k_F$, independent of charge $q$ and $\\theta$. Furthermore, we show that with the increasing of charge, new branches of Fermi surfaces emerge and tend to gathering together to form a shell-like structure when...
Collisional properties of weakly bound heteronuclear dimers
Marcelis, B.; Kokkelmans, S.J.J.M.F.; Shlyapnikov, G.V.; Petrov, D.S.
2008-01-01
We consider collisional properties of weakly bound heteronuclear molecules (dimers) formed in a two-species mixture of atoms with a large mass difference. We focus on dimers containing light fermionic atoms as they manifest collisional stability due to an effective dimer-dimer repulsion originating
Nishibata, H.; Shimoda, T.; Odahara, A.; Morimoto, S.; Kanaya, S.; Yagi, A.; Kanaoka, H.; Pearson, M. R.; Levy, C. D. P.; Kimura, M.
2017-04-01
The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the "island of inversion" associated with the neutron magic number N = 20, is studied by β-γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ = 1 /2+ and 1 /2- are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.
Nazir, Safdar
2013-04-11
The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.
Mukadam, M. D.; Roy, Syamashree; Meena, S. S.; Bhatt, Pramod; Yusuf, S. M.
2016-12-01
The electronic structure and magnetism of the quaternary Heusler alloy NiFeMnSn are studied using the full-potential linearized augmented plane-wave (FPLAPW) method. The calculation for the perfectly LiMgPdSn-type ordered crystal structure (type I) of NiFeMnSn shows a high spin polarization (˜76 %) with a ferromagnetic ground state. The total spin magnetic moment is in good agreement with the Slater-Pauling rule. The structural investigations using neutron diffraction at 500 K, and Mössbauer spectroscopy at 300 K on the NiFeMnSn alloy, prepared using an arc melting, show the presence of atomic site disorder. The electronic structure calculation for the disordered structure shows that the site disorder destroys the nearly half-metallic nature of this alloy. The magnetization measurements indicate that the Curie temperature is well above room temperature (˜405 K) as desired for the spintronics application.
Study of Ru{sub 2}VGe and Ru{sub 2}VSb: High-spin polarized and half-metallic Heusler alloys
Energy Technology Data Exchange (ETDEWEB)
Bhat, Idris Hamid; Gupta, Dinesh C. [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior – 474011 (India)
2015-06-24
Electronic and magnetic properties of Ru{sub 2}VGe and Ru{sub 2}VSb have been investigated by ab-initio. The optimized equilibrium lattice parameters were found to be 6.032 Å for Ru{sub 2}VGe and 6.272 Å for Ru{sub 2}VSb. Both the materials have ferromagnetic ground states and V mainly contributes to the magnetic properties in these materials. The highly spin-polarized half-metallic materials have integral magnetic moments of 1.0 µ{sub B} for Ru{sub 2}VGe and 2.0 µ{sub B} for Ru{sub 2}VSb with an energy gap of 0.095 eV for Ru2VGe and 0.186 eV for Ru{sub 2}VSb in the spin-down channel.
Boosting equal time bound states
Dietrich, Dennis D; Jarvinen, Matti
2012-01-01
We present an explicit and exact boost of a relativistic bound state defined at equal time of the constituents in the Born approximation (lowest order in hbar). To this end, we construct the Poincar\\'e generators of QED and QCD in D=1+1 dimensions, using Gauss' law to express A^0 in terms of the fermion fields in A^1=0 gauge. We determine the fermion-antifermion bound states in the Born approximation as eigenstates of the time and space translation generators P^0 and P^1. The boost operator is combined with a gauge transformation so as to maintain the gauge condition A^1=0 in the new frame. We verify that the boosted state remains an eigenstate of P^0 and P^1 with appropriately transformed eigenvalues and determine the transformation law of the equal-time, relativistic wave function. The shape of the wave function is independent of the CM momentum when expressed in terms of a variable, which is quadratically related to the distance x between the fermions. As a consequence, the Lorentz contraction of the wave ...
Energy Technology Data Exchange (ETDEWEB)
Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)
2015-01-15
Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.
Mass Ansatze for the standard model fermions from a composite perspective
Fariborz, Amir H; Nasri, Salah
2016-01-01
We consider a composite model in which the standard model fermions are bound states of elementary spin $\\frac{1}{2}$ particles, the preons, situated in the conjugate product representation of the color group. In this framework we propose and analyze two mass Ansatze one for the leptons, the other one for the quarks, based on mass formulae of the Gell-Mann Okubo type. We find that these mass Ansatze can give an adequate description of the known standard model fermion masses.
The noncommutative effects on the dipole moments of fermions in the standard model
Iltan, E.
2003-01-01
We study the dipole moments, electric dipole moment, weak electric dipole moment, anomalous magnetic moment, anomalous weak magnetic moment, of fermions in the noncommutative extension of the SM. We observe that the noncommutative effects are among the possible candidates to explain the electric and weak electric dipole moment of fermions. Furthermore, the upper bounds for the parameters which carry space-time and space-space noncommutativity can be obtained by using the theoretical and exper...
Fermionic dark matter in a simple t-channel model
Energy Technology Data Exchange (ETDEWEB)
Goyal, Ashok; Kumar, Mukesh [National Institute for Theoretical Physics, School of Physics and Mandelstam Institute for Theoretical Physics, University of the Witwatersrand, Johannesburg, Wits 2050 (South Africa)
2016-11-02
We consider a fermionic dark matter (DM) particle in renormalizable Standard Model (SM) gauge interactions in a simple t-channel model. The DM particle interactions with SM fermions is through the exchange of scalar and vector mediators which carry colour or lepton number. In the case of coloured mediators considered in this study, we find that if the DM is thermally produced and accounts for the observed relic density almost the entire parameter space is ruled out by the direct detection observations. The bounds from the monojet plus missing energy searches at the Large Hadron Collider are less stringent in this case. In contrast for the case of Majorana DM, we obtain strong bounds from the monojet searches which rule out DM particles of mass less than about a few hundred GeV for both the scalar and vector mediators.
Anomalies of magnetoresistance in Ce-based heavy fermion compounds
Sluchanko, N. E.; Bogach, A. V.; Anisimov, M. A.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Chistyakov, O. D.; Burkhanov, G. S.; Gabani, S.; Flachbart, K.
2015-12-01
Magnetoresistance Δρ(H,T) of several heavy-fermion compounds, CeAl2, CeAl3 and CeCu6, substitutional solid solutions with quantum critical behavior CeCu6-xAux (x = 0.1, 0.2) and alloys with magnetic ground state Ce(Al1-xMx)2 (M = Co, Ni, x ≤ 0.8) was studied in a wide range of temperatures (1.8-40 K) in magnetic fields up to 80 kOe. It was shown that a consistent interpretation of the field dependences of the resistance for both non-magnetic and magnetically ordered cerium-based intermetallic compounds with strong electron correlations can be achieved within the framework of an approach that accounts for scattering of charge carriers by localized magnetic moments in a metal matrix. Within this approach, three different components of the magnetoresistance of cerium intermetallic compounds were identified: the negative Brillouin contribution proportional to the local magnetization ( -Δρ/ρ˜Mloc2 ), the alternating linear contribution ( Δρ/ρ˜H ) and the magnetic component, saturating in magnetic fields below 15 kOe. In the framework of the Yosida model for the cerium alloys under study, estimates of the local magnetic susceptibility χloc(H, T0) were obtained from the magnetoresistance data. Numerical differentiation of the magnetoresistance with respect to the magnetic field and analysis of the obtained d (Δρ/ρ)/d H =f (H ,T ) dependences allowed us to reconstruct the H-T magnetic phase diagrams of the strongly correlated electron systems under study as well as to examine the effects of spin polarization and renormalization of the electronic states on charge transport both in the regime of quantum critical behavior and in the magnetically ordered state.
Tomographic probability representation for quantum fermion fields
Andreev, V A; Man'ko, V I; Son, Nguyen Hung; Thanh, Nguyen Cong; Timofeev, Yu P; Zakharov, S D
2009-01-01
Tomographic probability representation is introduced for fermion fields. The states of the fermions are mapped onto probability distribution of discrete random variables (spin projections). The operators acting on the fermion states are described by fermionic tomographic symbols. The product of the operators acting on the fermion states is mapped onto star-product of the fermionic symbols. The kernel of the star-product is obtained. The antisymmetry of the fermion states is formulated as the specific symmetry property of the tomographic joint probability distribution associated with the states.
Bound entanglement and entanglement bounds
Energy Technology Data Exchange (ETDEWEB)
Sauer, Simeon [Physikalisch-Astronomische Fakultaet, Friedrich-Schiller-Univesitaet Jena (Germany)]|[Physikalisches Institut, Albert-Ludwigs-Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany); Melo, Fernando de; Mintert, Florian; Buchleitner, Andreas [Physikalisches Institut, Albert-Ludwigs-Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany)]|[Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str.38, D-01187 Dresden (Germany); Bae, Joonwoo [School of Computational Sciences, Korea Institute for Advanced Study, Seoul 130-012 (Korea); Hiesmayr, Beatrix [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria)
2008-07-01
We investigate the separability of Bell-diagonal states of two qutrits. By using lower bounds to algebraically estimate concurrence, we find convex regions of bound entangled states. Some of these regions exactly coincide with the obtained results when employing optimal entanglement witnesses, what shows that the lower bound can serve as a precise detector of entanglement. Some hitherto unknown regions of bound entangled states were discovered with this approach, and delimited efficiently.
Entanglement in fermionic Fock space
Sárosi, Gábor
2013-01-01
We propose a generalization of the usual SLOCC and LU classification of entangled pure state fermionic systems based on the Spin group. Our generalization uses the fact that there is a representation of this group acting on the fermionic Fock space which when restricted to fixed particle number subspaces recovers naturally the usual SLOCC transformations. The new ingredient is the occurrence of Bogoliubov transformations of the whole Fock space changing the particle number. The classification scheme built on the Spin group prohibits naturally entanglement between states containing even and odd number of fermions. In our scheme the problem of classification of entanglement types boils down to the classification of spinors where totally separable states are represented by so called pure spinors. We construct the basic invariants of the Spin group and show how some of the known SLOCC invariants are just their special cases. As an example we present the classification of fermionic systems with a Fock space based ...
Saxena, Pooja
2016-01-01
A search for high mass Higgs boson of the MSSM decaying into two fermions using the first 2015 data at 13 TeV is presented. The four final decay channels of mu \\tau_h, e \\tau_h, \\tau_h \\tau_h and e mu is used. The limits on production cross section times branching ratio has been set.Other results from Run1 and different searches and measurements involving Higgs decays fermions will also be reviewed.
Fermions as generalized Ising models
Wetterich, C.
2017-04-01
We establish a general map between Grassmann functionals for fermions and probability or weight distributions for Ising spins. The equivalence between the two formulations is based on identical transfer matrices and expectation values of products of observables. The map preserves locality properties and can be realized for arbitrary dimensions. We present a simple example where a quantum field theory for free massless Dirac fermions in two-dimensional Minkowski space is represented by an asymmetric Ising model on a euclidean square lattice.
Integrable Gross-Neveu models with fermion-fermion and fermion-antifermion pairing
Thies, Michael
2014-01-01
The massless Gross-Neveu and chiral Gross-Neveu models are well known examples of integrable quantum field theories in 1+1 dimensions. We address the question whether integrability is preserved if one either replaces the four-fermion interaction in fermion-antifermion channels by a dual interaction in fermion-fermion channels, or if one adds such a dual interaction to an existing integrable model. The relativistic Hartree-Fock-Bogoliubov approach is adequate to deal with the large N limit of such models. In this way, we construct and solve three integrable models with Cooper pairing. We also identify a candidate for a fourth integrable model with maximal kinematic symmetry, the "perfect" Gross-Neveu model. This type of field theories can serve as exactly solvable toy models for color superconductivity in quantum chromodynamics.
Studying fermionic ghost imaging with independent photons
Liu, Jianbin; Zhou, Yu; Zheng, Huaibin; Chen, Hui; Li, Fu-li; Xu, Zhuo
2016-12-01
Ghost imaging with thermal fermions is calculated based on two-particle interference in Feynman's path integral theory. It is found that ghost imaging with thermal fermions can be simulated by ghost imaging with thermal bosons and classical particles. Photons in pseudothermal light are employed to experimentally study fermionic ghost imaging. Ghost imaging with thermal bosons and fermions is discussed based on the point-to-point (spot) correlation between the object and image planes. The employed method offers an efficient guidance for future ghost imaging with real thermal fermions, which may also be generalized to study other second-order interference phenomena with fermions.
Energy Technology Data Exchange (ETDEWEB)
Hearne, G.R., E-mail: grhearne@uj.ac.za [Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park, 2006 Johannesburg (South Africa); Diguet, G. [Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park, 2006 Johannesburg (South Africa); Baudelet, F.; Itié, J.-P. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Manyala, N. [Department of Physics and Institute of Applied Materials, University of Pretoria, Private Bag X20, Hatfield, 0028 Pretoria (South Africa)
2015-04-01
Both Fe and Co K-edge x-ray magnetic circular dichroism (XMCD) have been employed as element-specific probes of the magnetic moments in the composition series of the disordered ferromagnet Fe{sub 1−x}Co{sub x}Si (for x=0.2, 0.3, 0.4, 0.5). A definitive single peaked XMCD profile occurs for all compositions at both Fe and Co K-edges. The Fe 4p orbital moment, deduced from the integral of the XMCD signal, has a steep dependence on x at low doping levels and evolves to a different (weaker) dependence at x≥0.3, similar to the behavior of the magnetization in the Co composition range studied here. It is systematically higher, by at least a factor of two, than the corresponding Co orbital moment for most of the composition series. Fine structure beyond the K-edge absorption (limited range EXAFS) suggests that the local order (atomic environment) is very similar across the series, from the perspective of both the Fe and Co absorbing atom. The variation in the XMCD integral across the Co composition range has two regimes, that which occurs below x=0.3 and then evolves to different behavior at higher doping levels. This is more conspicuously present in the Fe contribution. This is rationalized as the evolution from a half-metallic ferromagnet at low Co doping to that of a strong ferromagnet at x>0.3 and as such, spin polarization crossover occurs. The Fermi level is tuned from the majority spin band for x<0.3 where a strongly polarized majority spin electron gas prevails, to a regime where minority spin carriers dominate at higher doping. The evolution of the Fe-derived spin polarized (3d) bands, indirectly probed here via the 4p states, is the primary determinant of the doping dependence of the magnetism in this alloy series. - Highlights: • Element-specific probing of the electronic structure of the Fe{sub 1−x}Co{sub x}Si series. • XMCD at the level of 10{sup −4} at the K-edge in such low-moment systems. • Element-specific probing of magnetic contributions
Energy Technology Data Exchange (ETDEWEB)
Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)
2014-04-15
Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without
Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R
2014-04-01
Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without
Fermions on the electroweak string
Moreno, J M; Quirós, Mariano; Moreno, J M; Oaknin, D H; Quiros, M
1995-01-01
We construct a simple class of exact solutions of the electroweak theory including the naked Z--string and fermion fields. It consists in the Z--string configuration (\\phi,Z_\\theta), the {\\it time} and z components of the neutral gauge bosons (Z_{0,3},A_{0,3}) and a fermion condensate (lepton or quark) zero mode. The Z--string is not altered (no feed back from the rest of fields on the Z--string) while fermion condensates are zero modes of the Dirac equation in the presence of the Z--string background (no feed back from the {\\it time} and z components of the neutral gauge bosons on the fermion fields). For the case of the n--vortex Z--string the number of zero modes found for charged leptons and quarks is (according to previous results by Jackiw and Rossi) equal to |n|, while for (massless) neutrinos is |n|-1. The presence of fermion fields in its core make the obtained configuration a superconducting string, but their presence (as well as that of Z_{0,3},A_{0,3}) does not enhance the stability of the Z--stri...
Bootstrap bound for conformal multi-flavor QCD on lattice
Nakayama, Yu
2016-01-01
The recent work by Iha et al shows an upper bound on mass anomalous dimension $\\gamma_m$ of multi-flavor massless QCD at the renormalization group fixed point from the conformal bootstrap in $SU(N_F)_V$ symmetric conformal field theories under the assumption that the fixed point is realizable with the lattice regularization based on staggered fermions. We show that the almost identical but slightly stronger bound applies to the regularization based on Wilson fermions (or domain wall fermions) by studying the conformal bootstrap in $SU(N_f)_L \\times SU(N_f)_R$ symmetric conformal field theories. For $N_f=8$, our bound implies $\\gamma_m < 1.31$ to avoid dangerously irrelevant operators that are not compatible with the lattice symmetry.
Bootstrap bound for conformal multi-flavor QCD on lattice
Energy Technology Data Exchange (ETDEWEB)
Nakayama, Yu [Department of Physics, Rikkyo University,Toshima, Tokyo 171-8501 (Japan); Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo,5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)
2016-07-08
The recent work by Iha et al. shows an upper bound on mass anomalous dimension γ{sub m} of multi-flavor massless QCD at the renormalization group fixed point from the conformal bootstrap in SU(N{sub F}){sub V} symmetric conformal field theories under the assumption that the fixed point is realizable with the lattice regularization based on staggered fermions. We show that the almost identical but slightly stronger bound applies to the regularization based on Wilson fermions (or domain wall fermions) by studying the conformal bootstrap in SU(N{sub f}){sub L}×SU(N{sub f}){sub R} symmetric conformal field theories. For N{sub f}=8, our bound implies γ{sub m}<1.31 to avoid dangerously irrelevant operators that are not compatible with the lattice symmetry.
Imaging electrostatically confined Dirac fermions in graphene quantum dots
Lee, Juwon; Wong, Dillon; Velasco, Jairo, Jr.; Rodriguez-Nieva, Joaquin F.; Kahn, Salman; Tsai, Hsin-Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid S.; Crommie, Michael F.
2016-11-01
Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.
Scalar Resonance at 750 GeV as Composite of Heavy Vector-Like Fermions
Liao, Wei; Zheng, Han-Qing
2016-08-01
We study a model of scalars which includes both the SM Higgs and a scalar singlet as composites of heavy vector-like fermions. The vector-like fermions are bounded by the super-strong four-fermion interactions. The scalar singlet decays to SM vector bosons through loop of heavy vector-like fermions. We show that the surprisingly large production cross section of di-photon events at 750 GeV resonance and the odd decay properties can all be explained. This model serves as a good model for both SM Higgs and a scalar resonance at 750 GeV. Supported by National Natural Science Foundation of China (NSFC) under Grant Nos. 11135009, 11375065 and 10925522
Fermion production during and after axion inflation
Energy Technology Data Exchange (ETDEWEB)
Adshead, Peter; Sfakianakis, Evangelos I. [Department of Physics, University of Illinois at Urbana-Champaign,Urbana, Illinois 61801 (United States)
2015-11-11
We study derivatively coupled fermions in axion-driven inflation, specifically m{sub ϕ}{sup 2}ϕ{sup 2} and monodromy inflation, and calculate particle production during the inflationary epoch and the post-inflationary axion oscillations. During inflation, the rolling axion acts as an effective chemical potential for helicity which biases the gravitational production of one fermion helicity over the other. This mechanism allows for efficient gravitational production of heavy fermion states that would otherwise be highly suppressed. Following inflation, the axion oscillates and fermions with both helicities are produced as the effective frequency of the fermion field changes non-adiabatically. For certain values of the fermion mass and axion-fermion coupling strength, the two helicity states are produced asymmetrically, resulting in unequal number-densities of left- and right-helicity fermions.
Acoustoelectric current for composite fermions
Bergli, J.; Galperin, Y. M.
2001-07-01
The acoustoelectric current for composite fermions in a two-dimensional electron gas (2DEG) close to the half-filled Landau level is calculated in the random phase approximation. The Boltzmann equation is used to find the nonequilibrium distribution of composite fermions to second order in the acoustic field. It is shown that the oscillating Chern-Simons field created by the induced density fluctuations in the 2DEG is important for the acoustoelectric current. This leads to a violation of the Weinreich relation between the acoustoelectric current and acoustic intensity. The deviations from the Weinreich relation can be detected by measuring the angle between the longitudinal and the Hall components of the acoustoelectric current. This departure from the Weinreich relation gives additional information on the properties of the composite fermion fluid.
Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoT e2
Sakano, M.; Bahramy, M. S.; Tsuji, H.; Araya, I.; Ikeura, K.; Sakai, H.; Ishiwata, S.; Yaji, K.; Kuroda, K.; Harasawa, A.; Shin, S.; Ishizaka, K.
2017-03-01
We investigate the surface electronic structures of polar 1 T'-MoT e2 , the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain dependences, indicating the opposite bulk polarity. For both domains, some segmentlike band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side.
Cossu, Fabrizio
2014-07-28
By first-principles calculations we investigate the structural, electronic, and magnetic properties of the (LaMnO
Gupta, Dinesh C.; Bhat, Idris H.
2015-01-01
Electronic and magnetic properties of Ru2VGe and Ru2VSb have been calculated using full potential linearized augmented plane wane method. The optimized equilibrium lattice constants in stable Fm-3m configuration were found to be 6.032 Å for Ru2VGe and 6.272 Å for Ru2VSb. Spin-resolved calculations show that V mainly contributes to the magnetic properties in these materials. The materials follow the Slater-Pauling rule and hence have integral magnetic moments which is due to 100% spin polarization at Fermi energy. The calculated total magnetic moments per unit cell were found to be 1.0 μB for Ru2VGe and 2.0 μB for Ru2VSb. Both the materials having ferromagnetic ground state, exhibit half-metallicity with an energy gap in the spin-down channel of 0.095 eV for Ru2VGe and 0.186 eV for Ru2VSb.
Tashiro, Motomichi
2007-01-01
The spin-exchange effect in spin-polarized electron collisions with unpolarized open-shell molecules, O$_2$, B$_2$, S$_2$ and Si$_2$, has been studied by the R-matrix method with the fixed-bond approximation. All of these molecules have ${}^3 \\Sigma_{g}^{-}$ symmetry in their ground states. Usual integrated cross sections with unpolarized electrons has also been studied. We used the complete active space self consistent field orbitals and put more than 10 target electronic states in the R-matrix models. In electron O$_2$ elastic collisions, calculated polarization fractions agree well with the experimental results, especially around the ${}^4 \\Sigma_u^-$ resonance. In e-B$_2$, S$_2$ and Si$_2$ elastic collisions, larger spin-exchange effect is observed compared to the e-O$_2$ elastic collisions. In all four cases, spin-exchange effect becomes prominent near resonances. This association of resonance and magnitude of the spin-exchange effect was studied by explicitly removing the resonance configurations from t...
Garcia-Diaz, Reyes; Cocoletzi, Gregorio H.; Mandru, Andrada-Oana; Wang, Kangkang; Smith, Arthur R.; Takeuchi, Noboru
2017-10-01
Using first principles total energy calculations within the periodic spin polarized density functional theory, we have investigated the structural, electronic, and magnetic properties of manganese gallium (MnGa) alloys. Specifically, we explore the MnGa(111)-1 × 2 and 2 × 2 reconstructions. The surface formation energies reveal that selected substitutions occur under Mn (Ga) rich growth conditions. Structures with top layers missing all Mn (Ga) atoms and two layers deep substitutions are also investigated. However, the formation energy shows that these structures are less favorable. For the stable structures, the magnetic properties per layer are proportional to the Mn:Ga ratio. Also, the density of states shows that the MnGa surfaces are metallic. The projected density of states shows that the electronic states in the vicinity of the Fermi level are due mainly to the manganese 3d orbitals. However charge density plots reveal that Mn 3d electrons are closer to the nucleus than Ga sp electrons. Consequently, experimental scanning tunneling microscopy images reveal periodically-arranged bright features, corresponding to the Ga atoms.
Sakai, Osamu; Suzuki, Taku T.
2017-06-01
The scattering of the electron-spin-polarized 4He+ beam on paramagnetic materials has an anomalously large asymmetric scattering component (ASC) around 5%, which is 104 of that expected from the spin-orbit coupling (SOC) for the potential of the target nucleus. In addition, the ASC of some materials (for example, Au and Pt) changes sign near the scattering angle (θ) of 90° unlike the result predicted by using the potential scattering theory. When the 4He+ approaches the target, virtual electron-transfer (ET) excitations between them occur. The effects of the SOC of electrons (SOEs) on the target atom in the ET intermediate state are studied within the frame of the lowest-order perturbation theory about the ET process. The ASC is caused through the combination of the quantum development of electron orbital states under the SOEs and the He nucleus motion in the intermediate state because the preferred orbital states for the ET depend on the position of the He nucleus. It is shown by a numerical calculation that the present process has the possibility of producing the ASC with a magnitude of around 0.1. In the present process, the ASC shows a θ dependence of cos θ sin θ, which changes sign at θ = 90° when the excited orbital in the ET state has the d-character like the Au and Pt cases.
Saeed, Yasir
2010-10-01
We report a first-principles study of structural, electronic and magnetic properties of crystalline alloys Zn1-xTMxS (TM = Fe, Co and Ni) at x = 0.25. Structural properties are computed from the total ground state energy convergence and it is found that the cohesive energies of Zn 1-xTMxS are greater than that of zincblende ZnS. We also study the spin-polarized electronic band structures, total and partial density of states and the effect of TM 3d states. Our results exhibit that Zn 0.75Fe0.25S, Zn0.75Co0.25S and Zn0.75Ni0.25S are half-metallic ferromagnetic with a magnetic moment of 4μB, 3μB and 2μB, respectively. Furthermore, we calculate the TM 3d spin-exchange-splitting energies Δx (d), Δx (x-d), exchange constants N0α and N0β, crystal field splitting (ΔEcrystEt2g-Eeg), and find that p-d hybridization reduces the local magnetic moment of TM from its free space charge value. Moreover, robustness of Zn1-xTMxS with respect to the variation of lattice constants is also discussed. © 2010 Elsevier B.V. All rights reserved.
Tscherbul, T V; Dalgarno, A; Zygelman, B; Pavlovic, Z; Hummon, M T; Lu, H-I; Tsikata, E; Doyle, J M
2010-01-01
We report a combined experimental and theoretical study of collision-induced dipolar relaxation in a cold spin-polarized gas of atomic nitrogen (N). We use buffer gas cooling to create trapped samples of 14N and 15N atoms with densities 5+/-2 x 10^{12} cm-3 and measure their magnetic relaxation rates at milli-Kelvin temperatures. Rigorous quantum scattering calculations based on accurate ab initio interaction potentials for the 7Sigma_u electronic state of N2 demonstrate that dipolar relaxation in N + N collisions occurs at a slow rate of ~10^{-13} cm3/s over a wide range of temperatures (1 mK to 1 K) and magnetic fields (10 mT to 2 T). The calculated dipolar relaxation rates are insensitive to small variations of the interaction potential and to the magnitude of the spin-exchange interaction, enabling the accurate calibration of the measured N atom density. We find consistency between the calculated and experimentally determined rates. Our results suggest that N atoms are promising candidates for future expe...
Dynamical fermion masses under the influence of Kaluza-Klein fermions in extra dimensions
Abe, Hiroyuki; Miguchi, Hironori; Muta, Taizo
2000-01-01
The dynamical fermion mass generation in the 4-dimensional brane is discussed in a model with 5-dimensional Kaluza-Klein fermions in interaction with 4-dimensional fermions. It is found that the dynamical fermion masses are generated beyond the critical radius of the compactified extra dimensional space and may be made small compared with masses of the Kaluza-Klein modes.
Dynamical fermion masses under the influence of Kaluza-Klein fermions in extra dimensions
Abe, H; Muta, T; Abe, Hiroyuki; Miguchi, Hironori; Muta, Taizo
2000-01-01
The dynamical fermion mass generation in the 4-dimensional brane is discussedin a model with 5-dimensional Kaluza-Klein fermions in interaction with4-dimensional fermions. It is found that the dynamical fermion masses aregenerated beyond the critical radius of the compactified extra dimensionalspace and may be made small compared with masses of the Kaluza-Klein modes.
Microscopic Conductivity of Lattice Fermions at Equilibrium. Part II: Interacting Particles
Bru, Jean-Bernard; de Siqueira Pedra, Walter
2016-01-01
We apply Lieb-Robinson bounds for multi-commutators we recently derived (Bru and de Siqueira Pedra, Lieb-Robinson bounds for multi-commutators and applications to response theory, 2015) to study the (possibly non-linear) response of interacting fermions at thermal equilibrium to perturbations of the external electromagnetic field. This analysis leads to an extension of the results for quasi-free fermions of (Bru et al. Commun Pure Appl Math 68(6):964-1013, 2015; Bru et al. J Math Phys 56:051901-1-051901-51, 2015) to fermion systems on the lattice with short-range interactions. More precisely, we investigate entropy production and charge transport properties of non-autonomous C*-dynamical systems associated with interacting lattice fermions within bounded static potentials and in presence of an electric field that is time and space dependent. We verify the 1st law of thermodynamics for the heat production of the system under consideration. In linear response theory, the latter is related with Ohm and Joule's laws. These laws are proven here to hold at the microscopic scale, uniformly with respect to the size of the (microscopic) region where the electric field is applied. An important outcome is the extension of the notion of conductivity measures to interacting fermions.
Wang, Chong; Cooper, Nigel R.; Halperin, Bertrand I.; Stern, Ady
2017-07-01
It is well known that there is a particle-hole symmetry for spin-polarized electrons with two-body interactions in a partially filled Landau level, which becomes exact in the limit where the cyclotron energy is large compared to the interaction strength; thus, one can ignore mixing between Landau levels. This symmetry is explicit in the description of a half-filled Landau level recently introduced by Son, using Dirac fermions, but it was thought to be absent in the older fermion-Chern-Simons approach, developed by Halperin, Lee, and Read (HLR) and subsequent authors. We show here, however, that when properly evaluated, the HLR theory gives results for long-wavelength low-energy physical properties—including the Hall conductance in the presence of impurities and the positions of minima in the magnetoroton spectra for fractional quantized Hall states close to half-filling—that are identical to predictions of the Dirac formulation. In fact, the HLR theory predicts an emergent particle-hole symmetry near half-filling, even when the cyclotron energy is finite.
Direct injection of spin-polarized carriers across YBa2Cu3O7-–La0.3Ca0.7MnO3 interface at 77 K
Indian Academy of Sciences (India)
K V Upadhye; K Ganesh Kumara; S C Purandare; S P Pai; R Pinto
2002-05-01
We report here injection of spin-polarized carriers from a half-metallic La0.3-Ca0.7MnO3 (LCMO) colossal magnetoresistive (CMR) thin ﬁlm into a high-temperature superconducting YBa2Cu3O7- (YBCO) thin ﬁlm studied using a micro-bridge. The LCMO and YBCO ﬁlms were grown on $\\langle 100\\rangle$ LaAlO3 (LAO) substrate sequentially using pulsed laser deposition (PLD). - measurements carried out at 77 K show that while normal critical current, $I^{n}_{c}$, of the micro-bridge is 80 mA, the critical current, $I^{p}_{c}$, through the micro-bridge when injected from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena.
Fermions as generalized Ising models
Directory of Open Access Journals (Sweden)
C. Wetterich
2017-04-01
Full Text Available We establish a general map between Grassmann functionals for fermions and probability or weight distributions for Ising spins. The equivalence between the two formulations is based on identical transfer matrices and expectation values of products of observables. The map preserves locality properties and can be realized for arbitrary dimensions. We present a simple example where a quantum field theory for free massless Dirac fermions in two-dimensional Minkowski space is represented by an asymmetric Ising model on a euclidean square lattice.
Dynamical fermions in lattice quantum chromodynamics
Energy Technology Data Exchange (ETDEWEB)
Szabo, Kalman
2007-07-01
The thesis presentS results in Quantum Chromo Dynamics (QCD) with dynamical lattice fermions. The topological susceptibilty in QCD is determined, the calculations are carried out with dynamical overlap fermions. The most important properties of the quark-gluon plasma phase of QCD are studied, for which dynamical staggered fermions are used. (orig.)
Theoretical studies of strongly correlated fermions
Energy Technology Data Exchange (ETDEWEB)
Logan, D. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Strongly correlated fermions are investigated. An understanding of strongly correlated fermions underpins a diverse range of phenomena such as metal-insulator transitions, high-temperature superconductivity, magnetic impurity problems and the properties of heavy-fermion systems, in all of which local moments play an important role. (author).
Fermion Determinant with Dynamical Chiral Symmetry Breaking
Institute of Scientific and Technical Information of China (English)
LU Qin; YANG Hua; WANG Qing
2002-01-01
One-loop fermion determinant is discussed for the case in which the dynamical chiral symmetry breakingcaused by momentum-dependent fermion self-energy ∑(p2) takes place. The obtained series generalizes the heat kernelexpansion for hard fermion mass.
Fermion Determinants: Some Recent Analytic Results
Fry, M P
2004-01-01
The use of known analytic results for the continuum fermion determinants in QCD and QED as benchmarks for zero lattice spacing extrapolations of lattice fermion determinants is proposed. Specifically, they can be used as a check on the universality hypothesis relating the continuum limits of the na\\"{\\i}ve, staggered and Wilson fermion determinants.
Anatomy of fermionic entanglement and criticality in Kitaev spin liquids
Meichanetzidis, K.; Cirio, M.; Pachos, J. K.; Lahtinen, V.
2016-09-01
We analyze in detail the effect of nontrivial band topology on the area-law behavior of the entanglement entropy in Kitaev's honeycomb model. By mapping the translationally invariant 2D spin model onto 1D fermionic subsystems, we identify those subsystems responsible for universal entanglement contributions in the gapped phases and those responsible for critical entanglement scaling in the gapless phases. For the gapped phases, we analytically show how the topological edge states contribute to the entanglement entropy and provide a universal lower bound for it. For the gapless semimetallic phases and topological phase transitions, the identification of the critical subsystems shows that they fall always into the Ising or the XY universality classes. As our study concerns the fermionic degrees of freedom in the honeycomb model, qualitatively similar results are expected to apply also to generic topological insulators and superconductors.
Electrically tunable topological superconductivity and Majorana fermions in two dimensions
Wang, Jing
2016-12-01
The external controllability of topological superconductors and Majorana fermions would be important both for fundamental and practical interests. Here we predict the electric-field control of Majorana fermions in two-dimensional topological superconductors utilizing a topological insulator thin-film proximity coupled to a conventional s -wave superconductor. With ferromagnetic ordering, the tunable structure inversion asymmetry by vertical electric field could induce topological quantum phase transition and realize a chiral topological superconductor state. A zero-energy Majorana bound state appears at the boundary of an applied electric-field spot, which can be observed by scanning tunneling microscopy. Furthermore, the structure inversion asymmetry could also enlarge the helical topological superconductor state in the phase diagram, making the realization of such an exotic state more feasible. The electrical control of topological phases could further apply to van der Waals materials such as two-dimensional transition-metal dichalcogenides.
Baryogenesis and Dark Matter with Vector-like Fermions
Fairbairn, Malcolm
2013-01-01
We show that vector-like fermions can act as the dark matter candidate in the universe whilst also playing a crucial role in electroweak baryogenesis through contributing to the barrier in the one-loop thermal scalar potential. In order for the new fermions to give rise to a strong first order phase transition, we show that one requires rather large Yukawa couplings in the new sector, which are strongly constrained by electroweak precision tests and perturbativity. Strong couplings between the dark matter candidate and the Higgs boson intuitively lead to small values of the relic density and problems with dark matter direct detection bounds. Nevertheless, when considering the most general realisation of the model, we find regions in the parameter space that respect all current constraints and may explain both mysteries simultaneously.
Gravitational contribution to fermion masses
Tiemblo, A; Tiemblo, Alfredo; Tresguerres, Romualdo
2005-01-01
In the context of a nonlinear gauge theory of the Poincar\\'e group, we show that covariant derivatives of Dirac fields include a coupling to the translational connections, manifesting itself in the matter action as a universal background mass contribution to fermions.
Constructing entanglement measures for fermions
Johansson, Markus; Raissi, Zahra
2016-10-01
In this paper we describe a method for finding polynomial invariants under stochastic local operations and classical communication (SLOCC) for a system of delocalized fermions shared between different parties, with global particle-number conservation as the only constraint. These invariants can be used to construct entanglement measures for different types of entanglement in such a system. It is shown that the invariants, and the measures constructed from them, take a nonzero value only if the state of the system allows for the observation of Bell-nonlocal correlations. Invariants of this kind are constructed for systems of two and three spin-1/2 fermions and examples of maximally entangled states are given that illustrate the different types of entanglement distinguished by the invariants. A general condition for the existence of SLOCC invariants and their associated measures is given as a relation between the number of fermions, their spin, and the number of spatial modes of the system. In addition, the effect of further constraints on the system, including the localization of a subset of the fermions, is discussed. Finally, a hybrid Ising-Hubbard Hamiltonian is constructed for which the ground state of a three-site chain exhibits a high degree of entanglement at the transition between a regime dominated by on-site interaction and a regime dominated by Ising interaction. This entanglement is well described by a measure constructed by the introduced method.