Fermi surfaces in Kondo insulators

Science.gov (United States)

Liu, Hsu; Hartstein, Máté; Wallace, Gregory J.; Davies, Alexander J.; Ciomaga Hatnean, Monica; Johannes, Michelle D.; Shitsevalova, Natalya; Balakrishnan, Geetha; Sebastian, Suchitra E.

2018-04-01

We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.

Anisotropic Fermi Surface and Quantum Limit Transport in High Mobility Three-Dimensional Dirac Semimetal Cd_{3}As_{2}

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Yanfei Zhao

2015-09-01

Full Text Available Three-dimensional topological Dirac semimetals have a linear dispersion in 3D momentum space and are viewed as the 3D analogues of graphene. Here, we report angle-dependent magnetotransport on the newly revealed Cd_{3}As_{2} single crystals and clearly show how the Fermi surface evolves with crystallographic orientations. Remarkably, when the magnetic field lies in the [112] or [441[over ¯

Theoretical investigation of the Fermi surfaces of La2-xSrxCuO4 and YBa2Cu3O7

International Nuclear Information System (INIS)

Antonov, V.N.; Antonov, Vl.N.; Bar'yakhtar, V.G.; Baglyuk, A.I.; Maksimov, E.G.; Nemoshkalenko, V.V.; Perlov, A.Ya.; Savrasov, S.Yu.; Uspenskii, Yu.A.

1989-01-01

A theoretical investigation is made of the shape of the Fermi surface and of the constant-energy surfaces near the Fermi energy of the La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7 oxides by a self-consistent linear muffin-tin orbital method in the atomic sphere approximation (OMTO-ASA). It is shown that the Fermi surfaces of these compounds are strongly two-dimensional. The Fermi surface of La 2-x Sr x CuO 4 is a corrugated rounded box centered at the point Λ. The Fermi surface of YBa 2 Cu 3 O 7 consists of four sheets: an electron cushion at the point Λ and three nested hole surfaces centered at the point S. The electron cushion and one of the hole surfaces are strongly corrugated along the z direction. The theoretically calculated Fermi surfaces of La 2 CuO 4 and YBa 2 Cu 3 O 7 are compared with the experimental data on electron-positron annihilation

Two-dimensional vibrational spectroscopy of the amide I band of crystalline acetanilide: Fermi resonance, conformational substates, or vibrational self-trapping?

Science.gov (United States)

Edler, J.; Hamm, P.

2003-08-01

Two-dimensional infrared (2D-IR) spectroscopy is applied to investigate acetanilide, a molecular crystal consisting of quasi-one-dimensional hydrogen bonded peptide units. The amide-I band exhibits a double peak structure, which has been attributed to different mechanisms including vibrational self-trapping, a Fermi resonance, or the existence of two conformational substates. The 2D-IR spectrum of crystalline acetanilide is compared with that of two different molecular systems: (i) benzoylchloride, which exhibits a strong symmetric Fermi resonance and (ii) N-methylacetamide dissolved in methanol which occurs in two spectroscopically distinguishable conformations. Both 2D-IR spectra differ significantly from that of crystalline acetanilide, proving that these two alternative mechanisms cannot account for the anomalous spectroscopy of crystalline acetanilide. On the other hand, vibrational self-trapping of the amide-I band can naturally explain the 2D-IR response.

Raman scattering in a two-dimensional Fermi liquid with spin-orbit coupling

Science.gov (United States)

Maiti, Saurabh; Maslov, Dmitrii L.

2017-04-01

We present a microscopic theory of Raman scattering in a two-dimensional Fermi liquid (FL) with Rashba and Dresselhaus types of spin-orbit coupling and subject to an in-plane magnetic field (B ⃗). In the long-wavelength limit, the Raman spectrum probes the collective modes of such a FL: the chiral spin waves. The characteristic features of these modes are a linear-in-q term in the dispersion and the dependence of the mode frequency on the directions of both q ⃗ and B ⃗. All of these features have been observed in recent Raman experiments on Cd1 -xMnxTe quantum wells.

Topological states in a two-dimensional metal alloy in Si surface: BiAg/Si(111)-4 ×4 surface

Science.gov (United States)

Zhang, Xiaoming; Cui, Bin; Zhao, Mingwen; Liu, Feng

2018-02-01

A bridging topological state with a conventional semiconductor platform offers an attractive route towards future spintronics and quantum device applications. Here, based on first-principles and tight-binding calculations, we demonstrate the existence of topological states hosted by a two-dimensional (2D) metal alloy in a Si surface, the BiAg/Si(111)-4 ×4 surface, which has already been synthesized experimentally. It exhibits a topological insulating state with an energy gap of 71 meV (˜819 K ) above the Fermi level and a topological metallic state with quasiquantized conductance below the Fermi level. The underlying mechanism leading to the formation of such nontrivial states is revealed by analysis of the "charge-transfer" and "orbital-filtering" effect of the Si substrate. A minimal effective tight-binding model is employed to reveal the formation mechanism of the topological states. Our finding opens opportunities to detect topological states and measure its quantized conductance in a large family of 2D surface metal alloys, which have been or are to be grown on semiconductor substrates.

Anisotropic non-Fermi liquids

Science.gov (United States)

Sur, Shouvik; Lee, Sung-Sik

2016-11-01

We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.

Dimensional BCS-BEC crossover in ultracold Fermi gases

Energy Technology Data Exchange (ETDEWEB)

Boettcher, Igor

2014-12-10

We investigate thermodynamics and phase structure of ultracold Fermi gases, which can be realized and measured in the laboratory with modern trapping techniques. We approach the subject from a both theoretical and experimental perspective. Central to the analysis is the systematic comparison of the BCS-BEC crossover of two-component fermions in both three and two dimensions. A dimensional reduction can be achieved in experiments by means of highly anisotropic traps. The Functional Renormalization Group (FRG) allows for a description of both cases in a unified theoretical framework. In three dimensions we discuss with the FRG the influence of high momentum particles onto the density, extend previous approaches to the Unitary Fermi Gas to reach quantitative precision, and study the breakdown of superfluidity due to an asymmetry in the population of the two fermion components. In this context we also investigate the stability of the Sarma phase. For the two-dimensional system scattering theory in reduced dimension plays an important role. We present both the theoretically as well as experimentally relevant aspects thereof. After a qualitative analysis of the phase diagram and the equation of state in two dimensions with the FRG we describe the experimental determination of the phase diagram of the two-dimensional BCS-BEC crossover in collaboration with the group of S. Jochim at PI Heidelberg.

Response Functions for the Two-Dimensional Ultracold Fermi Gas: Dynamical BCS Theory and Beyond

Science.gov (United States)

Vitali, Ettore; Shi, Hao; Qin, Mingpu; Zhang, Shiwei

2017-12-01

Response functions are central objects in physics. They provide crucial information about the behavior of physical systems, and they can be directly compared with scattering experiments involving particles such as neutrons or photons. Calculations of such functions starting from the many-body Hamiltonian of a physical system are challenging and extremely valuable. In this paper, we focus on the two-dimensional (2D) ultracold Fermi atomic gas which has been realized experimentally. We present an application of the dynamical BCS theory to obtain response functions for different regimes of interaction strengths in the 2D gas with zero-range attractive interaction. We also discuss auxiliary-field quantum Monte Carlo (AFQMC) methods for the calculation of imaginary time correlations in these dilute Fermi gas systems. Illustrative results are given and comparisons are made between AFQMC and dynamical BCS theory results to assess the accuracy of the latter.

Backward scattering in the one-dimensional Fermi gas

International Nuclear Information System (INIS)

Apostol, M.

1980-05-01

The Ward identity is derived for non-relativistic fermions with two-body spin-independent interaction. Using this identity for the one-dimensional Fermi gas with backward scattering the equations of the perturbation theory are solved for the effective interaction and the collective excitations of the particle density fluctuations are obtained. (author)

Fermi surface of the one-dimensional Hubbard model. Finite-size effects

Energy Technology Data Exchange (ETDEWEB)

Bourbonnais, C.; Nelisse, H.; Reid, A.; Tremblay, A.M.S. (Dept. de Physique and Centre de Recherche en Physique du Solide (C.R.P.S.), Univ. de Sherbrooke, Quebec (Canada))

1989-12-01

The results reported here, using a standard numerical algorithm and a simple low temperature extrapolation, appear consistent with numerical results of Sorella et al. for the one-dimensional Hubbard model in the half-filled and quarter-filled band cases. However, it is argued that the discontinuity at the Fermi level found in the quarter-filled case is likely to come from the zero-temperature finite-size dependence of the quasiparticle weight Z, which is also discussed here. (orig.).

Two Dimensional Effective Electron Mass at the Fermi Level in Quantum Wells of III-V, Ternary and Quaternary Semiconductors.

Science.gov (United States)

Chakrabarti, S; Chatterjee, B; Debbarma, S; Ghatak, K P

2015-09-01

In this paper we study the influence of strong electric field on the two dimensional (2D)effective electron mass (EEM) at the Fermi level in quantum wells of III-V, ternary and quaternary semiconductors within the framework of k x p formalism by formulating a new 2D electron energy spectrum. It appears taking quantum wells of InSb, InAs, Hg(1-x)Cd(x)Te and In(1-x)Ga(x)As(1-y)P(y) lattice matched to InP as examples that the EEM increases with decreasing film thickness, increasing electric field and increases with increasing surface electron concentration exhibiting spikey oscillations because of the crossing over of the Fermi level by the quantized level in quantum wells and the quantized oscillation occurs when the Fermi energy touches the sub-band energy. The electric field makes the mass quantum number dependent and the oscillatory mass introduces quantum number dependent mass anisotropy in addition to energy. The EEM increases with decreasing alloy composition where the variations are totally band structure dependent. Under certain limiting conditions all the results for all the cases get simplified into the well-known parabolic energy bands and thus confirming the compatibility test. The content of this paper finds three applications in the fields of nano-science and technology.

Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids

International Nuclear Information System (INIS)

Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco

2014-01-01

We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler–Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the “pair amplitude” √(g(r)), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow–Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree–Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation–dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density–density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. -- Highlights: •We have studied the ground state properties of a strongly correlated two-dimensional fluid of dipolar fermions. •We have calculated the effective inter-particle interaction and the dynamical density–density response function. •We have shown that an undamped zero sound mode exists at any value of the interaction strength

Similarity of the leading contributions to the self-energy and the thermodynamics in two- and three-dimensional Fermi Liquids

International Nuclear Information System (INIS)

Coffey, D.; Bedell, K.S.

1993-01-01

We compare the self-energy and entropy of a two- and three-dimensional Fermi Liquids (FLs) using a model with a contact interaction between fermions. For a two-dimensional (2D) FL we find that there are T 2 contributions to the entropy from interactions separate from those due to the collective modes. These T 2 contributions arise from nonanalytic corrections to the real part of the self-energy and areanalogous to T 3 lnT contributions present in the entropy of a three-dimensional (3D) FL. The difference between the 2D and 3D results arises solely from the different phase space factors

Signature of Fermi surface jumps in positron spectroscopy data

International Nuclear Information System (INIS)

Adam, G.; Adam, S.

1998-12-01

A subtractionless method for solving Fermi surface sheets (FSS), from measured n-axis-projected momentum distribution histograms by two-dimensional angular correlation of the positron-electron annihilation radiation (2D-ACAR) technique, is discussed. The window least squares statistical noise smoothing filter described in Adam et al., NIM A, 337 (1993) 188, is first refined such that the window free radial parameters (WRP) are optimally adapted to the data. In an ideal single crystal, the specific jumps induced in the WRP distribution by the existing Fermi surface jumps yield straightforward information on the resolved FSS. In a real crystal, the smearing of the derived WRP optimal values, which originates from positron annihilations with electrons at crystal imperfections, is ruled out by median smoothing of the obtained distribution, over symmetry defined stars of bins. The analysis of a gigacount 2D-ACAR spectrum, measured on the archetypal high-T c compound Y Ba 2 Cu 3 O 7-δ at room temperature, illustrates the method. Both electronic FSS, the ridge along Γ Χ direction and the pillbox centered at the S point of the first Brillouin zone, are resolved. (author)

Quantum Monte Carlo calculation of the Fermi-liquid parameters in the two-dimensional electron gas

International Nuclear Information System (INIS)

Kwon, Y.; Ceperley, D.M.; Martin, R.M.

1994-01-01

Excitations of the two-dimensional electron gas, including many-body effects, are calculated with a variational Monte Carlo method. Correlated sampling is introduced to calculate small energy differences between different excitations. The usual pair-product (Slater-Jastrow) trial wave function is found to lack certain correlations entirely so that backflow correlation is crucial. From the excitation energies calculated here, we determine Fermi-liquid parameters and related physical quantities such as the effective mass and the Lande g factor of the system. Our results for the effective mass are compared with previous analytic calculations

Fermi surfaces of the pyrite-type cubic AuSb2 compared with split Fermi surfaces of the ullmannite-type cubic chiral NiSbS and PdBiSe

Science.gov (United States)

Nishimura, K.; Kakihana, M.; Nakamura, A.; Aoki, D.; Harima, H.; Hedo, M.; Nakama, T.; Ōnuki, Y.

2018-05-01

We grew high-quality single crystals of AuSb2 with the pyrite (FeS2)-type cubic structure by the Bridgman method and studied the Fermi surface properties by the de Haas-van Alphen (dHvA) experiment and the full potential LAPW band calculation. The Fermi surfaces of AuSb2 are found to be similar to those of NiSbS and PdBiSe with the ullmannite (NiSbS)-type cubic chiral structure because the crystal structures are similar each other and the number of valence electrons is the same between two different compounds. Note that each Fermi surface splits into two Fermi surfaces in NiSbS and PdBiSe, reflecting the non-centrosymmetric crystal structure.

One-dimensional versus two-dimensional electronic states in vicinal surfaces

International Nuclear Information System (INIS)

Ortega, J E; Ruiz-Oses, M; Cordon, J; Mugarza, A; Kuntze, J; Schiller, F

2005-01-01

Vicinal surfaces with periodic arrays of steps are among the simplest lateral nanostructures. In particular, noble metal surfaces vicinal to the (1 1 1) plane are excellent test systems to explore the basic electronic properties in one-dimensional superlattices by means of angular photoemission. These surfaces are characterized by strong emissions from free-electron-like surface states that scatter at step edges. Thereby, the two-dimensional surface state displays superlattice band folding and, depending on the step lattice constant d, it splits into one-dimensional quantum well levels. Here we use high-resolution, angle-resolved photoemission to analyse surface states in a variety of samples, in trying to illustrate the changes in surface state bands as a function of d

Direct Fermi-surface image of hidden nesting for NaMo6O17 and KMo6O17

International Nuclear Information System (INIS)

Gweon, G.-.; Allen, J.W.; Clack, J.A.; Zhang, Y.X.; Poirier, D.M.; Benning, P.J.; Olson, C.G.; Marcus, J.; Schlenker, C.

1997-01-01

We report direct Fermi-surface images obtained with angle-resolved photoemission spectroscopy (ARPES) for NaMo 6 O 17 and KMo 6 O 17 above the charge-density wave transition temperatures. We also report ARPES spectra of the valence band of NaMo 6 O 17 . The images imply a Fermi surface (FS) based on three underlying quasi-one-dimensional (quasi-1D) surfaces. Thus it agrees in detail with that expected in the hidden nesting picture of Whangbo et al. [Science 252, 96 (1991)], but differs greatly from a FS deduced in a previous study by Breuer et al. [Phys. Rev. Lett. 76, 3172 (1996)], which found only two underlying quasi-1D surfaces. copyright 1997 The American Physical Society

Theory of two-dimensional fermi liquids: Pt. 3

International Nuclear Information System (INIS)

Cui Shimin; Cai Jianhua

1990-01-01

The transport properties and sound propagation of 2-D Fermi liquids are discussed. Microscopic expressions for the coefficients of diffusion, viscosity and thermal conductivity are derived using Resibois method. Velocities of the zeroth and first sounds are calculated. Based on an analysis of collision integral, it is shown that a series of relaxtion time parameters is necessary to define precisely the sound propagation properties in 2-D Fermi liquids in contrast to the 3-D case

Constructive analysis of two dimensional Fermi systems at finite temperature

International Nuclear Information System (INIS)

Lu, Long

2013-01-01

We consider a dilute Fermion system in continuum two spatial dimensions with short-range interaction. We prove nonperturbatively that at low temperature the renormalized perturbation expansion has non-zero radius of convergence. The convergence radius shrinks when the energy scale goes to the infrared cutoff. The shrinking rate of the convergence radius is established to be dependent of the sign of the coupling constant g by a detailed analysis of the so-called ladder contributions. We prove further that the self-energy of the model is uniformly of C 1 , but not C 2 in the analytic domain of the theory. The proofs are based on renormalization of the Fermi surface and multiscale analysis employing mathematical renormalization group technique. Tree expansion is introduced to reorganize perturbation expansion nicely. Finally we apply these techniques to construct a half-filled Hubbard model on honeycomb bilayer lattice with local interaction.

Electronic structure, Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na3Bi from angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Liang Aiji; Chen Chaoyu; Wang Zhijun; Shi Youguo; Feng Ya; Yi Hemian; Xie Zhuojin; He Shaolong; He Junfeng; Peng Yingying; Liu Yan; Liu Defa; Hu Cheng; Zhao Lin; Liu Guodong; Dong Xiaoli; Zhang Jun; Nakatake, M; Iwasawa, H; Shimada, K

2016-01-01

The three-dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A 3 Bi ( A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission (ARPES) measurements on the two cleaved surfaces, (001) and (100), of Na 3 Bi. On the (001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k x – k y plane and by varying the photon energy to get access to different out-of-plane k z s. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the (100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the (100) plane. We directly observe two isolated 3D Dirac nodes on the (100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ∼150 meV before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na 3 Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the 3D Dirac cones, on the possible formation of surface reconstruction of the (001) surface, and on the issue of basic Brillouin zone selection for the (100) surface. (rapid communication)

Disorder effects in two-dimensional Fermi systems with conical spectrum: exact results for the density of states

International Nuclear Information System (INIS)

Nersesyan, A.A.; Tsvelik, A.M.; Wenger, F.

1995-01-01

The influence of weak non-magnetic disorder on the single-particle density of states ρ(ω) of two-dimensional electron systems with a conical spectrum is studied. We use a non-perturbative approach, based on the replica trick with subsequent mapping of the effective action onto a one-dimensional model of interacting fermions, the latter being treated by abelian and non-abelian bosonization methods. Specifically, we consider a weakly disordered p- or d-wave superconductor, in which case the problem reduces to a model of (2+1)-dimensional massless Dirac fermions coupled to random, static, generally non-abelian gauge fields. It is shown that the density of states of a two-dimensional p- or d-wave superconductor, averaged over randomness, follows a non-trivial power-law behavior near the Fermi energy: ρ(ω) similar vertical stroke ωvertical stroke α . The exponent α>0 is exactly calculated for several types of disorder. We demonstrate that the property ρ(0) = 0 is a direct consequence of a continuous symmetry of the effective fermionic model, whose breakdown is forbidden in two dimensions. As a counter example, we also discuss another model with a conical spectrum - a two-dimensional orbital antiferromagnet, where static disorder leads to a finite ρ(0) due to the breakdown of a discrete (particle-hole) symmetry. ((orig.))

Illumination-induced changes of the Fermi surface topology in three-dimensional superlattices

Czech Academy of Sciences Publication Activity Database

Goncharuk, Natalya; Smrčka, Ludvík; Svoboda, Pavel; Vašek, Petr; Kučera, Jan; Krupko, Yu.; Wegscheider, W.

2007-01-01

Roč. 75, č. 24 (2007), 245322/1-245322/7 ISSN 1098-0121 R&D Projects: GA MŠk LC510; GA AV ČR KAN400100652 Institutional research plan: CEZ:AV0Z10100521 Keywords : persistent photoconductivity * superlattice * Fermi surface Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.172, year: 2007

Hydrogenated borophene as a stable two-dimensional Dirac material with an ultrahigh Fermi velocity.

Science.gov (United States)

Xu, Li-Chun; Du, Aijun; Kou, Liangzhi

2016-10-05

The recent synthesis of monolayer borophene (triangular boron monolayer) on a substrate has opened the era of boron nanosheets (Science, 2015, 350, 1513), but the structural instability and a need to explore the novel physical properties are still open issues. Here we demonstrated that borophene can be stabilized by full surface hydrogenation (borophane), from first-principles calculations. Most interestingly, our calculations show that borophane has direction-dependent Dirac cones, which are mainly caused by the in-plane p x and p y orbitals of boron atoms. The Dirac fermions possess an ultrahigh Fermi velocity of up to 3.5 × 10 6 m s -1 under the HSE06 level, which is 4 times higher than that of graphene. The Young's moduli are calculated to be 190 and 120 GPa nm along two different directions, which are comparable to those of steel. The ultrahigh Fermi velocity and good mechanical features render borophane ideal for nanoelectronic applications.

Recent Developments in Non-Fermi Liquid Theory

Science.gov (United States)

Lee, Sung-Sik

2018-03-01

Non-Fermi liquids are unconventional metals whose physical properties deviate qualitatively from those of noninteracting fermions due to strong quantum fluctuations near Fermi surfaces. They arise when metals are subject to singular interactions mediated by soft collective modes. In the absence of well-defined quasiparticles, universal physics of non-Fermi liquids is captured by interacting field theories which replace Landau Fermi liquid theory. However, it has been difficult to understand their universal low-energy physics due to a lack of theoretical methods that take into account strong quantum fluctuations in the presence of abundant low-energy degrees of freedom. In this review, we discuss two approaches that have been recently developed for non-Fermi liquid theory with emphasis on two space dimensions. The first is a perturbative scheme based on a dimensional regularization, which achieves a controlled access to the low-energy physics by tuning the codimension of Fermi surface. The second is a nonperturbative approach which treats the interaction ahead of the kinetic term through a non-Gaussian scaling called interaction-driven scaling. Examples of strongly coupled non-Fermi liquids amenable to exact treatments through the interaction-driven scaling are discussed.

Instabilities of a Fermi gas with nested Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Schlottmann, Pedro [Department of Physics, Florida State University, Tallahassee, FL (United States)

2018-01-15

The nesting of the Fermi surfaces of an electron and a hole pocket separated by a vector Q commensurate with the lattice in conjunction with the interaction between the quasiparticles can give rise to a rich phase diagram. Of particular importance is itinerant antiferromagnetic order in the context of pnictides and heavy fermion compounds. By mismatching the nesting the order can gradually be suppressed and as the Neel temperature tends to zero a quantum critical point is obtained. A superconducting dome above the quantum critical point can be induced by the transfer of pairs of electrons between the pockets. The conditions under which such a dome arises are studied. In addition numerous other phases may arise, e.g. charge density waves, non-Fermi liquid behavior, non-s-wave superconductivity, Pomeranchuk instabilities of the Fermi surface, nematic order, and phases with persistent orbital currents. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Quantum nonlocal theory of topological Fermi arc plasmons in Weyl semimetals

Science.gov (United States)

Andolina, Gian Marcello; Pellegrino, Francesco M. D.; Koppens, Frank H. L.; Polini, Marco

2018-03-01

The surface of a Weyl semimetal (WSM) displays Fermi arcs, i.e., disjoint segments of a two-dimensional Fermi contour. We present a quantum-mechanical nonlocal theory of chiral Fermi arc plasmons in WSMs with broken time-reversal symmetry. These are collective excitations constructed from topological Fermi arc and bulk electron states and arising from electron-electron interactions, which are treated in the realm of the random phase approximation. Our theory includes quantum effects associated with the penetration of the Fermi arc surface states into the bulk and dissipation, which is intrinsically nonlocal in nature and arises from decay processes mainly involving bulk electron-hole pair excitations.

Discrete breathers in a two-dimensional hexagonal Fermi Pasta Ulam lattice

Science.gov (United States)

Butt, Imran A.; Wattis, Jonathan A. D.

2007-02-01

We consider a two-dimensional Fermi-Pasta-Ulam (FPU) lattice with hexagonal symmetry. Using asymptotic methods based on small amplitude ansatz, at third order we obtain a reduction to a cubic nonlinear Schrödinger equation (NLS) for the breather envelope. However, this does not support stable soliton solutions, so we pursue a higher order analysis yielding a generalized NLS, which includes known stabilizing terms. We present numerical results which suggest that long-lived stationary and moving breathers are supported by the lattice. We find breather solutions which move in an arbitrary direction, an ellipticity criterion for the wavenumbers of the carrier wave, asymptotic estimates for the breather energy, and a minimum threshold energy below which breathers cannot be found. This energy threshold is maximized for stationary breathers and becomes vanishingly small near the boundary of the elliptic domain where breathers attain a maximum speed. Several of the results obtained are similar to those obtained for the square FPU lattice (Butt and Wattis 2006 J. Phys. A: Math. Gen. 39 4955), though we find that the square and hexagonal lattices exhibit different properties in regard to the generation of harmonics, and the isotropy of the generalized NLS equation.

Quantum oscillations in quasi-two-dimensional conductors

CERN Document Server

Galbova, O

2002-01-01

The electronic absorption of sound waves in quasi-two-dimensional conductors in strong magnetic fields, is investigated theoretically. A longitudinal acoustic wave, propagating along the normal n-> to the layer of quasi-two-dimensional conductor (k-> = left brace 0,0,k right brace; u-> = left brace 0,0,u right brace) in magnetic field (B-> = left brace 0, 0, B right brace), is considered. The quasiclassical approach for this geometry is of no interest, due to the absence of interaction between electromagnetic and acoustic waves. The problem is of interest in strong magnetic field when quantization of the charge carriers energy levels takes place. The quantum oscillations in the sound absorption coefficient, as a function of the magnetic field, are theoretically observed. The experimental study of the quantum oscillations in quasi-two-dimensional conductors makes it possible to solve the inverse problem of determining from experimental data the extrema closed sections of the Fermi surface by a plane p sub z = ...

Bosonization of the two-dimensional t-J model in the continuum limit

International Nuclear Information System (INIS)

Schmeltzer, D.; Bishop, A.R.

1996-01-01

The t-J model in two dimensions is bosonized using a set of N, coupled two-dimensional Fermi-surface patches. Ignoring tunneling between the patches, the coherent tunneling of holes and the superfluid phase are suppressed. Within this scheme the system remains in the normal phase when temperature T→0. The main feature of this construction is the absence of screening of the dissipative transversal gauge field generated by the spinons. This dissipative gauge field is responsible for the non-Fermi-liquid behavior, which is manifested in the free energy and single-particle Green function. The deviation from Fermi-liquid behavior is due to the U(1) gauge field, and at long distances a new exponent due to the holes is identified. Experimental consequences are discussed. copyright 1996 The American Physical Society

Large optical conductivity of Dirac semimetal Fermi arc surface states

Science.gov (United States)

Shi, Li-kun; Song, Justin C. W.

2017-08-01

Fermi arc surface states, a hallmark of topological Dirac semimetals, can host carriers that exhibit unusual dynamics distinct from that of their parent bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals possess a strong and anisotropic light-matter interaction. This is characterized by a large Fermi arc optical conductivity when light is polarized transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi arc optical conductivity is significantly muted. The large surface spectral weight is locked to the wide separation between Dirac nodes and persists as a large Drude weight of Fermi arc carriers when the system is doped. As a result, large and anisotropic Fermi arc conductivity provides a novel means of optically interrogating the topological surfaces states of Dirac semimetals.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

Science.gov (United States)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-01

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

Science.gov (United States)

Misawa, Setsuo

2018-01-01

The quasiparticles in the normal state of iron-based superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of sharp Fermi surfaces, the quasiparticle energy contains, as a function of the momentum \\varvec{p}, a term of the form ( p - p_0)^3 ln {( |p-p_0|/p_0)} , where p = | \\varvec{p} | and p_0 is the Fermi momentum. The electronic specific heat coefficient, magnetic susceptibility (Knight shift), electrical resistivity, Hall coefficient and thermoelectric power divided by temperature follow, as functions of temperature T, the logarithmic formula a-b T^2 ln {(T/T^*)}, a, b and T^* being constant; these formulae have been shown to explain the observed data for all iron-based superconductors. It is shown that the concept of non-Fermi liquids or anomalous metals which appears in the literature is not needed for descriptions of the present systems. When the superconducting transition temperature TC and the b / a value for the resistivity are plotted as functions of the doping content x, there appear various characteristic diagrams in which regions of positive correlation and those of negative correlation between TC and b / a are interconnected; from these diagrams, we may make speculations about the types of superconductivity and the crossover between them.

Interacting Fermi gases in disordered one-dimensional lattices

International Nuclear Information System (INIS)

Xianlong, Gao; Polini, M.; Tosi, M. P.; Tanatar, B.

2006-01-01

Interacting two-component Fermi gases loaded in a one-dimensional (1D) lattice and subject to harmonic trapping exhibit intriguing compound phases in which fluid regions coexist with local Mott-insulator and/or band-insulator regions. Motivated by experiments on cold atoms inside disordered optical lattices, we present a theoretical study of the effects of a random potential on these ground-state phases. Within a density-functional scheme we show that disorder has two main effects: (i) it destroys the local insulating regions if it is sufficiently strong compared with the on-site atom-atom repulsion, and (ii) it induces an anomaly in the compressibility at low density from quenching of percolation

Intrinsic two-dimensional states on the pristine surface of tellurium

Science.gov (United States)

Li, Pengke; Appelbaum, Ian

2018-05-01

Atomic chains configured in a helical geometry have fascinating properties, including phases hosting localized bound states in their electronic structure. We show how the zero-dimensional state—bound to the edge of a single one-dimensional helical chain of tellurium atoms—evolves into two-dimensional bands on the c -axis surface of the three-dimensional trigonal bulk. We give an effective Hamiltonian description of its dispersion in k space by exploiting confinement to a virtual bilayer, and elaborate on the diminished role of spin-orbit coupling. These intrinsic gap-penetrating surface bands were neglected in the interpretation of seminal experiments, where two-dimensional transport was otherwise attributed to extrinsic accumulation layers.

Quasi-one-dimensional metals on semiconductor surfaces with defects

International Nuclear Information System (INIS)

Hasegawa, Shuji

2010-01-01

Several examples are known in which massive arrays of metal atomic chains are formed on semiconductor surfaces that show quasi-one-dimensional metallic electronic structures. In this review, Au chains on Si(557) and Si(553) surfaces, and In chains on Si(111) surfaces, are introduced and discussed with regard to the physical properties determined by experimental data from scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES) and electrical conductivity measurements. They show quasi-one-dimensional Fermi surfaces and parabolic band dispersion along the chains. All of them are known from STM and ARPES to exhibit metal-insulator transitions by cooling and charge-density-wave formation due to Peierls instability of the metallic chains. The electrical conductivity, however, reveals the metal-insulator transition only on the less-defective surfaces (Si(553)-Au and Si(111)-In), but not on a more-defective surface (Si(557)-Au). The latter shows an insulating character over the whole temperature range. Compared with the electronic structure (Fermi surfaces and band dispersions), the transport property is more sensitive to the defects. With an increase in defect density, the conductivity only along the metal atomic chains was significantly reduced, showing that atomic-scale point defects decisively interrupt the electrical transport along the atomic chains and hide the intrinsic property of transport in quasi-one-dimensional systems.

ROLE OF NUCLEONIC FERMI SURFACE DEPLETION IN NEUTRON STAR COOLING

Energy Technology Data Exchange (ETDEWEB)

Dong, J. M.; Zuo, W. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Lombardo, U. [Universita di Catania and Laboratori Nazionali del Sud (INFN), Catania I-95123 (Italy); Zhang, H. F. [School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000 (China)

2016-01-20

The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties that determine the neutron star (NS) thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions are calculated within the Brueckner–Hartree–Fock approach, employing the AV18 two-body force supplemented by a microscopic three-body force. Neutrino emissivity, heat capacity, and in particular neutron {sup 3}PF{sub 2} superfluidity, turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young NSs are significantly slowed.

The Fermi surface of CeSb

International Nuclear Information System (INIS)

Crabtree, G.W.; Aoki, H.; Joss, W.; Hulliger, F.

1987-01-01

This paper uses accurate Fermi surface measurements as a test of hybridization models in CeSb. Detailed measurements of the Fermi surface geometry and effective masses are presented which show a number of unusual properties associated with the magnetic structure and anisotropy. Measurements are compared with predictions of a band structure in which the f-electron is assumed to be local, interacting with the conduction electrons only through anisotropic Coulomb and exchange interactions. This model reproduces all the unusual features observed in the measurements and suggests that hybridization is not essential to describing the electronic properties of CeSb

Exotic superfluidity and pairing phenomena in atomic Fermi gases in mixed dimensions.

Science.gov (United States)

Zhang, Leifeng; Che, Yanming; Wang, Jibiao; Chen, Qijin

2017-10-11

Atomic Fermi gases have been an ideal platform for simulating conventional and engineering exotic physical systems owing to their multiple tunable control parameters. Here we investigate the effects of mixed dimensionality on the superfluid and pairing phenomena of a two-component ultracold atomic Fermi gas with a short-range pairing interaction, while one component is confined on a one-dimensional (1D) optical lattice whereas the other is in a homogeneous 3D continuum. We study the phase diagram and the pseudogap phenomena throughout the entire BCS-BEC crossover, using a pairing fluctuation theory. We find that the effective dimensionality of the non-interacting lattice component can evolve from quasi-3D to quasi-1D, leading to strong Fermi surface mismatch. Upon pairing, the system becomes effectively quasi-two dimensional in the BEC regime. The behavior of T c bears similarity to that of a regular 3D population imbalanced Fermi gas, but with a more drastic departure from the regular 3D balanced case, featuring both intermediate temperature superfluidity and possible pair density wave ground state. Unlike a simple 1D optical lattice case, T c in the mixed dimensions has a constant BEC asymptote.

Fluctuations of Imbalanced Fermionic Superfluids in Two Dimensions Induce Continuous Quantum Phase Transitions and Non-Fermi-Liquid Behavior

Directory of Open Access Journals (Sweden)

Philipp Strack

2014-04-01

Full Text Available We study the nature of superfluid pairing in imbalanced Fermi mixtures in two spatial dimensions. We present evidence that the combined effect of Fermi surface mismatch and order parameter fluctuations of the superfluid condensate can lead to continuous quantum phase transitions from a normal Fermi mixture to an intermediate Sarma-Liu-Wilczek superfluid with two gapless Fermi surfaces—even when mean-field theory (incorrectly predicts a first-order transition to a phase-separated “Bardeen-Cooper-Schrieffer plus excess fermions” ground state. We propose a mechanism for non-Fermi-liquid behavior from repeated scattering processes between the two Fermi surfaces and fluctuating Cooper pairs. Prospects for experimental observation with ultracold atoms are discussed.

Quasi-two-dimensional Fermi-liquid state in Sr2RhO4-δ

International Nuclear Information System (INIS)

Nagai, Ichiro; Shirakawa, Naoki; Umeyama, Norio; Ikeda, Shin-ichi

2010-01-01

Single crystals of layered perovskite Sr 2 RhO 4-δ (δ=0.0 and 0.1) are successfully grown by the floating-zone method. Stoichiometric single crystals (Sr 2 RhO 4.0 ) are obtained by O 2 -annealing the as-grown crystals (Sr 2 RhO 3.9 ). Sr 2 RhO 4.0 and Sr 2 RhO 3.9 show quasi-two-dimensional Fermi-liquid behavior at low temperatures, whereas there are large differences in the anisotropy of electrical resistivity ρ c (3 K)/ρ ab (3 K) and Wilson ratio R w between Sr 2 RhO 4.0 and Sr 2 RhO 3.9 : ρ c (3 K)/ρ ab (3 K)=2400 (19000) and R w =3.8 (6.4) for Sr 2 RhO 4.0 (Sr 2 RhO 3.9 ). The differences observed between the temperature dependence of the in-plane electrical resistivity (T 2 RhO 4.0 and Sr 2 RhO 3.9 are mainly derived from those between the density of states and band structure near the corresponding Fermi level. This indicates that the changes in these physical properties, which are accompanied by oxygen defects in the Sr 2 RhO 4-δ system, can be explained by the rigid band model. Moreover, these results suggest that t 2g band-filling can be controlled by adjusting the oxygen defect content δ in the Sr 2 RhO 4-δ system. Although many similarities are observed in this study between the physical properties of Sr 2 RhO 4.0 and Sr 2 RuO 4 . Sr 2 RhO 4.0 does not exhibit superconductivity down to 36 mK. (author)

Fermi surface ridge at second and third Umklapp positron annihilations in Y Ba2Cu3Oτ-γ

International Nuclear Information System (INIS)

Adam, G.; Adam, S.; Barbiellini, B.; Hoffmann, L.; Manuel, A.A.; Peter, M.

1993-06-01

Results of statistical noise smoothing of the electron momentum distribution got by two-dimensional angular correlation of the electron-positron annihilation radiation technique on untwinned Y Ba 2 Cu 3 O τ-γ single crytals are reported. Two distinct signatures of the sheet of Fermi surface related to the CuO chains (the ridge) are resolved. The first occurs at second Umklapp processes, in agreement with previous evidence. The second one, identified for the first time, occurs at third Umklapp processes. Comparison with FLAPW calculations confirms this results. (author). 13 refs, 7 figs

Probing exotic phases of interacting two-dimensional carriers using one-dimensional density modulation

Science.gov (United States)

Mueed, M. A.

In this Thesis, we present low-temperature magnetotransport studies of two-dimensional (2D) electron and hole systems confined to GaAs quantum wells and subjected to a one-dimensional, periodic density modulation. The modulation is achieved through the piezo-electric effect in GaAs as we fabricate a periodic, strain-inducing superlattice on the sample surface. Under varying perpendicular magnetic field, whenever the carriers' cyclotron orbit becomes commensurate with the modulation period, the magnetoresistance exhibits a minimum value. The resulting oscillations, known as the commensurability oscillations, directly measure the carriers' Fermi wave vector. Imposing a density modulation thus allows us to study the Fermi contour properties of 2D electrons and holes near zero field, and composite fermions (CFs) near the half filling of the lowest Landau level, i.e., filling factor nu=1/2. The application of a parallel magnetic field (B||) also features extensively in the Thesis. First, we use commensurability oscillations to capture the B||-induced deformation and the eventual splitting of the Fermi contour of 2D electrons. We also deduce the scattering time anisotropy of hole-flux CFs whose Fermi contour is rendered anisotropic by B||. Moreover, we study the anisotropic (warped) Fermi contour of 2D holes and hole-flux CFs in wide quantum well samples at B||=0. The results provide evidence that CFs inherit Fermi contour properties from their zero-field counterparts. We further investigate the fate of CFs near the bilayer quantum Hall states at nu=1 and 1/2 induced by a large B||. We observe that the commensurability features of CFs near nu=1 are consistent with half the total carrier density, implying that CFs prefer to stay in separate layers and show a two-component behavior. In contrast, close to nu=1/2, CFs appear single-layer-like (single-component) as their commensurability features correspond to the total density. This finding sheds light on the different

Fermi surface of underdoped high-Tc superconducting cuprates

International Nuclear Information System (INIS)

Dai, X.; Su, Z.; Yu, L.

1997-01-01

The coexistence of a π-flux state and a d-wave resonant-valance-bond (RVB) state is considered in this paper within the slave-boson approach. A critical value of doping concentration δ c is found, below which the coexisting π-flux and d-wave RVB state is favored in energy. The pseudo-Fermi surface of spinons and the physical electron spectral function are calculated. A clear Fermi-level crossing is found along the (0,0) to (π, π) direction, but no such crossing is detected along the (π, 0) to (π, π) direction. Also, an energy gap of d-wave symmetry appears at the Fermi level in our calculation. The above results are in agreement with the angle-resolved photoemission experiments which indicate at a d-wave pseudogap and a half-pocket-like Fermi surface in underdoped cuprates. copyright 1997 The American Physical Society

Korteweg de Vries Description of One-Dimensional Superfluid Fermi Gases

International Nuclear Information System (INIS)

Xu Yan-Xia; Duan Wen-Shan

2011-01-01

We study one-dimensional matter-wave pulses in cigar-shaped superfluid Fermi gases, including the linear and nonlinear waves of the system. A Korteweg de Vries (KdV) solitary wave is obtained for the superfluid Fermi gases in the limited case of a BEC regime, a BCS regime and unitarity. The dependences of the propagation velocity, amplitude and the width of the solitary wave on the dimensionless interaction parameter y = 1/(k F a sc ) are given for the limited cases of BEC and unitarity. (physics of gases, plasmas, and electric discharges)

Fermi-surface reconstruction and the origin of high-temperature superconductivity

International Nuclear Information System (INIS)

Norman, M.R.

2010-01-01

lattice into a d 9 configuration, with one localized hole in the 3d shell per copper site. Given the localized nature of this state, it was questioned whether a momentum-space picture was an appropriate description of the physics of the cuprates. In fact, this question relates to a long-standing debate in the physics community: Since the parent state is also an antiferromagnet, one can, in principle, map the Mott insulator to a band insulator with magnetic order. In this 'Slater' picture, Mott physics is less relevant than the magnetism itself. It is therefore unclear which of the two, magnetism or Mott physics, is more fundamentally tied to superconductivity in the cuprates. After twenty years of effort, definitive quantum oscillations that could be used to map the Fermi surface were finally observed in a high-temperature cuprate superconductor in 2007. This and subsequent studies reveal a profound rearrangement of the Fermi surface in underdoped cuprates. The cause of the reconstruction, and its implication for the origin of high-temperature superconductivity, is a subject of active debate.

Effective field theories for superconducting systems with multiple Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Braga, P.R., E-mail: pedro.rangel.braga@gmail.com [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Granado, D.R., E-mail: diegorochagrana@uerj.br [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Department of Physics and Astronomy, Ghent University, Krijgslaan 281-S9, 9000 Gent (Belgium); Guimaraes, M.S., E-mail: msguimaraes@uerj.br [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Wotzasek, C., E-mail: clovis@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, 21941-972, Rio de Janeiro (Brazil)

2016-11-15

In this work we investigate the description of superconducting systems with multiple Fermi surfaces. For the case of one Fermi surface we re-obtain the result that the superconductor is more precisely described as a topological state of matter. Studying the case of more than one Fermi surface, we obtain the effective theory describing a time reversal symmetric topological superconductor. These results are obtained by employing a general procedure to construct effective low energy actions describing states of electromagnetic systems interacting with charges and defects. The procedure consists in taking into account the proliferation or dilution of these charges and defects and its consequences for the low energy description of the electromagnetic response of the system. We find that the main ingredient entering the low energy characterization of the system with more than one Fermi surface is a non-conservation of the canonical supercurrent triggered by particular vortex configurations.

Calculated Fermi surface properties of LaSn3 and YSn3 under pressure

International Nuclear Information System (INIS)

Kanchana, V.

2012-01-01

The electronic structure, Fermi surface and elastic properties of the iso-structural and iso-electronic LaSn 3 and YSn 3 intermetallic compounds are studied under pressure within the frame work of density functional theory including spin-orbit coupling. The LaSn 3 Fermi surface consists of two sheets, of which the second is very complex. Under pressure a third sheet appears around compression V/V 0 =0.94, while a small topology changes in the second sheet is seen at compression V/V 0 =0.90. This may be in accordance with the anomalous behavior in the superconducting transition temperature observed in LaSn 3 , which has been suggested to reflect a Fermi surface topological transition, along with a non-monotonic pressure dependence of the density of states at the Fermi level. The similar behavior is not observed in YSn 3 for which the Fermi surface includes three sheets already at ambient conditions, and the topology remains unchanged under pressure. The reason for the difference in behavior between LaSn 3 and YSn 3 is the role of spin-orbit coupling and the hybridization of La-4f state with the Sn-p state in the vicinity of the Fermi level, which is well explained using the band structure calculation. The elastic constants and related mechanical properties are calculated at ambient as well as at elevated pressures. The elastic constants increase with pressure for both compounds and satisfy the conditions for mechanical stability under pressure. (author)

Fermi surface of superconducting LaFePO determined by quantum oscillations

Energy Technology Data Exchange (ETDEWEB)

Mcdonald, Ross D [Los Alamos National Laboratory; Coldea, A I [BRISTOL UNIV; Fletcher, J D [BRISTOL UNIV; Carrington, A [BRISTOL UNIV; Bangura, A F [BRISTOL UNIV; Hussey, N E [BRISTOL UNIV; Analytis, J G [STANFORD UNIV; Chu, J-h [STANFORD UNIV; Erickson, A S [STANFORD UNIV; Fisher, I R [STANFORD UNIV

2008-01-01

The recent discovery of superconductivity in ferrooxypnictides, which have a maximum transition temperature intermediate between the two other known high temperature superconductors MgB{sub 2} and the cuprate family, has generated huge interest and excitement. The most critical issue is the origin of the pairing mechanism. Whereas superconductivity in MgB{sub 2} has been shown to arise from strong electron-phonon coupling, the pairing glue in cuprate superconductors is thought by many to have a magnetic origin. The oxypnictides are highly susceptible to magnetic instabilities, prompting analogies with cuprate superconductivity. Progress on formulating the correct theory of superconductivity in these materials will be greatly aided by a detailed knowledge of the Fermi surface parameters. Here we report for the first time extensive measurements of quantum oscillations in a Fe-based superconductor, LaFePO, that provide a precise calliper of the size and shape of the Fermi surface and the effective masses of the relevant charge carriers. Our results show that the Fermi surface is composed of nearly-nested electron and hole pockets in broad agreement with the band-structure predictions but with significant enhancement of the quasiparticle masses. The correspondence in the electron and hole Fermi surface areas provides firm experimental evidence that LaFePO, whilst unreconstructed, lies extremely close to a spin-density-wave instability, thus favoring models that invoke such a magnetic origin for high-temperature superconductivity in oxypnictides.

Two-dimensional confinement of heavy fermions

International Nuclear Information System (INIS)

Shishido, Hiroaki; Shibauchi, Takasada; Matsuda, Yuji; Terashima, Takahito

2010-01-01

Metallic systems with the strongest electron correlations are realized in certain rare-earth and actinide compounds whose physics are dominated by f-electrons. These materials are known as heavy fermions, so called because the effective mass of the conduction electrons is enhanced via correlation effects up to as much as several hundreds times the free electron mass. To date the electronic structure of all heavy-fermion compounds is essentially three-dimensional. Here we report on the first realization of a two-dimensional heavy-fermion system, where the dimensionality is adjusted in a controllable fashion by fabricating heterostructures using molecular beam epitaxy. The two-dimensional heavy fermion system displays striking deviations from the standard Fermi liquid low-temperature electronic properties. (author)

A two-dimensional Fermi gas in the BEC-BCS crossover

Energy Technology Data Exchange (ETDEWEB)

Ries, Martin Gerhard

2016-01-21

This thesis reports on the preparation of a 2D Fermi gas in the BEC-BCS crossover and the observation of the BKT transition into a quasi long-range ordered superfluid phase. The pair momentum distribution of the gas is probed by means of a matter-wave focusing technique which relies on time-of-flight evolution in a weak harmonic potential. This distribution holds the coherence properties of the gas. The quasi long-range ordered phase manifests itself as a sharp low-momentum peak. The temperature where it forms is identified as the transition temperature. By tuning the temperature and the interaction strength, the phase diagram of the 2D Fermi gas in the BEC-BCS crossover is mapped out. The phase coherence is investigated in a self-interference experiment. Furthermore, algebraic decay of correlations is observed in the trap average of the first order correlation function, which is obtained from the Fourier transform of the pair momentum distribution. This is in qualitative agreement with predictions of homogeneous theory for the superfluid phase in a 2D gas. The presented results provide a foundation for future experimental and theoretical studies of strongly correlated 2D Fermi gases. They might thus help to elucidate complex systems such as the electron gas in high-T{sub c} superconductors.

Two-dimensional dynamics of a free molecular chain with a secondary structure

DEFF Research Database (Denmark)

Zolotaryuk, Alexander; Christiansen, Peter Leth; Savin, A.V.

1996-01-01

A simple two-dimensional (2D) model of an isolated (free) molecular chain with primary and secondary structures has been suggested and investigated both analytically and numerically. This model can be considered as the simplest generalization of the well-known Fermi-Pasta-Ulam model of an anharmo......A simple two-dimensional (2D) model of an isolated (free) molecular chain with primary and secondary structures has been suggested and investigated both analytically and numerically. This model can be considered as the simplest generalization of the well-known Fermi-Pasta-Ulam model...

Surface Ship Shock Modeling and Simulation: Two-Dimensional Analysis

Directory of Open Access Journals (Sweden)

Young S. Shin

1998-01-01

Full Text Available The modeling and simulation of the response of a surface ship system to underwater explosion requires an understanding of many different subject areas. These include the process of underwater explosion events, shock wave propagation, explosion gas bubble behavior and bubble-pulse loading, bulk and local cavitation, free surface effect, fluid-structure interaction, and structural dynamics. This paper investigates the effects of fluid-structure interaction and cavitation on the response of a surface ship using USA-NASTRAN-CFA code. First, the one-dimensional Bleich-Sandler model is used to validate the approach, and second, the underwater shock response of a two-dimensional mid-section model of a surface ship is predicted with a surrounding fluid model using a constitutive equation of a bilinear fluid which does not allow transmission of negative pressures.

High surface conductivity of Fermi-arc electrons in Weyl semimetals

Science.gov (United States)

Resta, Giacomo; Pi, Shu-Ting; Wan, Xiangang; Savrasov, Sergey Y.

2018-02-01

Weyl semimetals (WSMs), a new type of topological condensed matter, are currently attracting great interest due to their unusual electronic states and intriguing transport properties such as chiral anomaly induced negative magnetoresistance, a semiquantized anomalous Hall effect, and the debated chiral magnetic effect. These systems are close cousins of topological insulators (TIs) which are known for their disorder-tolerant surface states. Similarly, WSMs exhibit unique topologically protected Fermi-arc surface states. Here, we analyze electron-phonon scattering, a primary source of resistivity in metals at finite temperatures, as a function of the shape of the Fermi arc where we find that the impact on surface transport is significantly dependent on the arc curvature and disappears in the limit of a straight arc. Next, we discuss the effect of strong surface disorder on the resistivity by numerically simulating a tight-binding model with the presence of quenched surface vacancies using the coherent potential approximation and Kubo-Greenwood formalism. We find that the limit of a straight arc geometry is remarkably disorder tolerant, producing surface conductivity that is one to two orders of magnitude larger than a comparable setup with surface states of TI. This is primarily attributed to a significantly different hybridization strength of the surface states with the remaining electrons in two systems. Finally, a simulation of the effects of surface vacancies on TaAs is presented, illustrating the disorder tolerance of the topological surface states in a recently discovered WSM material.

Dark lump excitations in superfluid Fermi gases

Science.gov (United States)

Xu, Yan-Xia; Duan, Wen-Shan

2012-11-01

We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev—Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen—Cooper—Schrieffer (BCS) regime, Bose—Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.

Dark lump excitations in superfluid Fermi gases

International Nuclear Information System (INIS)

Xu Yan-Xia; Duan Wen-Shan

2012-01-01

We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev—Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen—Cooper—Schrieffer (BCS) regime, Bose—Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity

Two-dimensional thermofield bosonization

International Nuclear Information System (INIS)

Amaral, R.L.P.G.; Belvedere, L.V.; Rothe, K.D.

2005-01-01

The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized

Fermi Surface and Antiferromagnetism in Europium Metal

DEFF Research Database (Denmark)

Andersen, O. Krogh; Loucks, T. L.

1968-01-01

of the nearly cubical part of the hole surface at P, and we also discuss the effects of the electron surface at H. Since it is likely that barium and europium have similar Fermi surfaces, we have presented several extremal areas and the corresponding de Haas-van Alphen frequencies in the hope that experimental...

Prediction of Fermi-Surface Pressure Dependence in Rb and Cs

DEFF Research Database (Denmark)

Jan, J. P.; MacDonald, A. H.; Skriver, Hans Lomholt

1980-01-01

The linear muffin-tin orbitals method of band-structure calculation, combined with a Gaussian integration technique using special directions in the Brillouin zone, has been used to calculate Fermi radii and extremal cross-sectional areas of the Fermi surface in rubidium and cesium. Band shifts we......-surface pressure dependence agree with the limited experimental data available....

Comparison of two intraoral scanners based on three-dimensional surface analysis

Directory of Open Access Journals (Sweden)

Kyung-Min Lee

2018-02-01

Full Text Available Abstract Background This in vivo study evaluated the difference of two well-known intraoral scanners used in dentistry, namely iTero (Align Technology and TRIOS (3Shape. Methods Thirty-two participants underwent intraoral scans with TRIOS and iTero scanners, as well as conventional alginate impressions. The scans obtained with the two intraoral scanners were compared with each other and were also compared with the corresponding model scans by means of three-dimensional surface analysis. The average differences between the two intraoral scans on the surfaces were evaluated by color-mapping. The average differences in the three-dimensional direction between each intraoral scans and its corresponding model scan were calculated at all points on the surfaces. Results The average differences between the two intraoral scanners were 0.057 mm at the maxilla and 0.069 mm at the mandible. Color histograms showed that local deviations between the two scanners occurred in the posterior area. As for difference in the three-dimensional direction, there was no statistically significant difference between two scanners. Conclusions Although there were some deviations in visible inspection, there was no statistical significance between the two intraoral scanners.

Observation of an electron band above the Fermi level in FeTe0.55Se0.45 from in-situ surface doping

International Nuclear Information System (INIS)

Zhang, P.; Ma, J.; Qian, T.; Richard, P.; Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

2014-01-01

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe 0.55 Se 0.45 . The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe 2−x Se 2 compound.

Hydrodynamic flows of non-Fermi liquids: Magnetotransport and bilayer drag

Science.gov (United States)

Patel, Aavishkar A.; Davison, Richard A.; Levchenko, Alex

2017-11-01

We consider a hydrodynamic description of transport for generic two-dimensional electron systems that lack Galilean invariance and do not fall into the category of Fermi liquids. We study magnetoresistance and show that it is governed only by the electronic viscosity provided that the wavelength of the underlying disorder potential is large compared to the microscopic equilibration length. We also derive the Coulomb drag transresistance for double-layer non-Fermi-liquid systems in the hydrodynamic regime. As an example, we consider frictional drag between two quantum Hall states with half-filled lowest Landau levels, each described by a Fermi surface of composite fermions coupled to a U (1 ) gauge field. We contrast our results to prior calculations of drag of Chern-Simons composite particles and place our findings in the context of available experimental data.

Higher-dimensional bosonization and its application to Fermi liquids

Energy Technology Data Exchange (ETDEWEB)

Meier, Hendrik

2012-06-28

The bosonization scheme presented in this thesis allows to map models of interacting fermions onto equivalent models describing collective bosonic excitations. For simple systems that do not require plenty computational power and optimized algorithms, the positivity of the weight function in the bosonic frame has been confirmed - in particular also for those configurations in which the fermionic representation shows the minus-sign problem. The numerical tests are absolutely elementary and based on the simplest possible regularization scheme. The second part of this thesis presented an analytical study about the non-analytic corrections to thermodynamic quantities in a two-dimensional Fermi liquid. The perturbation theory developed for the exact formulation is by no means more convenient than the well-established fermionic diagram technique. The effective low-energy theory for studying the anomalous contributions to the Fermi liquid was derived focussing on the relevant soft modes of the interaction only. The final effective model took the form of a field theory for a bosonic superfield Ψ interacting in quadratic, cubic, and quartic terms in the action. This field theory turned out nontrivial and was shown to lead to logarithmic divergencies in both spin and charge channels. By means of a combined scheme of ladder diagram summations and renormalization group equations, the logarithmic terms were summed up in the first-loop order, thus yielding the renormalized effective coupling constants of the theory at low temperatures. The fully renormalized action then allowed to conveniently compute the low-temperature limit behavior of the non-analytic corrections to the Fermi-liquid thermodynamic response functions such as the low temperature non-analytic correction δc to the specific heat. The explicit formula for δc is the sum of two contributions - one due to the spin singlet and one due to the spin triplet superconducting excitations. Depending on the values of the

Surface representations of two- and three-dimensional fluid flow topology

Science.gov (United States)

Helman, James L.; Hesselink, Lambertus

1990-01-01

We discuss our work using critical point analysis to generate representations of the vector field topology of numerical flow data sets. Critical points are located and characterized in a two-dimensional domain, which may be either a two-dimensional flow field or the tangential velocity field near a three-dimensional body. Tangent curves are then integrated out along the principal directions of certain classes of critical points. The points and curves are linked to form a skeleton representing the two-dimensional vector field topology. When generated from the tangential velocity field near a body in a three-dimensional flow, the skeleton includes the critical points and curves which provide a basis for analyzing the three-dimensional structure of the flow separation. The points along the separation curves in the skeleton are used to start tangent curve integrations to generate surfaces representing the topology of the associated flow separations.

Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Paul, J.; Dey, P.; Karaiskaj, D., E-mail: karaiskaj@usf.edu [Department of Physics, University of South Florida, 4202 East Fowler Ave., Tampa, Florida 33620 (United States); Tokumoto, T.; Hilton, D. J. [Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294 (United States); Reno, J. L. [CINT, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

2014-10-07

The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of ∼4 × 10{sup 11} cm{sup −2} was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent “rephasing” (S{sub 1}) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S{sub 1} 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The “two-quantum coherence” (S{sub 3}) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations.

On the interrelation between bulk and thin-film Fermi surfaces

KAUST Repository

Schwingenschlögl, Udo

2010-12-01

A general scheme for inferring the Fermi surface of a finite slab from ab initio electronic-structure calculations for the parent bulk system is introduced. The simple cubic ReO 3 oxide is studied as an example system. We show that our scheme provides an accurate approximation of the Fermi surface even for very thin slabs. © 2010 Europhysics Letters Association.

Cross Validation Through Two-Dimensional Solution Surface for Cost-Sensitive SVM.

Science.gov (United States)

Gu, Bin; Sheng, Victor S; Tay, Keng Yeow; Romano, Walter; Li, Shuo

2017-06-01

Model selection plays an important role in cost-sensitive SVM (CS-SVM). It has been proven that the global minimum cross validation (CV) error can be efficiently computed based on the solution path for one parameter learning problems. However, it is a challenge to obtain the global minimum CV error for CS-SVM based on one-dimensional solution path and traditional grid search, because CS-SVM is with two regularization parameters. In this paper, we propose a solution and error surfaces based CV approach (CV-SES). More specifically, we first compute a two-dimensional solution surface for CS-SVM based on a bi-parameter space partition algorithm, which can fit solutions of CS-SVM for all values of both regularization parameters. Then, we compute a two-dimensional validation error surface for each CV fold, which can fit validation errors of CS-SVM for all values of both regularization parameters. Finally, we obtain the CV error surface by superposing K validation error surfaces, which can find the global minimum CV error of CS-SVM. Experiments are conducted on seven datasets for cost sensitive learning and on four datasets for imbalanced learning. Experimental results not only show that our proposed CV-SES has a better generalization ability than CS-SVM with various hybrids between grid search and solution path methods, and than recent proposed cost-sensitive hinge loss SVM with three-dimensional grid search, but also show that CV-SES uses less running time.

Theoretical reconsideration of antiferromagnetic Fermi surfaces in URu2Si2

International Nuclear Information System (INIS)

Yamagami, Hiroshi

2011-01-01

In an itinerant 5f-band model, the antiferromagnetic (AFM) Fermi surfaces of URu 2 Si 2 are reconsidered using a relativistic LAPW method within a local spin-density approximation, especially taking into account the lattice parameters dependent on pressures. The reduction of the z-coordinate of the Si sites results in the effect of flattening the Ru-Si layers of URu 2 Si 2 crystal structure, thus weakening a hybridization/mixing between the U-5f and Ru-4d states in the band structure. Consequently the 5f bands around the Fermi level are more flat in the dispersion with decreasing the z-coordinate, thus producing three closed Fermi surfaces like 'curing-stone', 'rugby-ball' and 'ball'. The origins of de Haas-van Alphen branches can be qualitatively interpreted from the obtained AFM Fermi surfaces.

Anomalous Quasiparticle Reflection from the Surface of a ^{3}He-^{4}He Dilute Solution.

Science.gov (United States)

Ikegami, Hiroki; Kim, Kitak; Sato, Daisuke; Kono, Kimitoshi; Choi, Hyoungsoon; Monarkha, Yuriy P

2017-11-10

A free surface of a dilute ^{3}He-^{4}He liquid mixture is a unique system where two Fermi liquids with distinct dimensions coexist: a three-dimensional (3D) ^{3}He Fermi liquid in the bulk and a two-dimensional (2D) ^{3}He Fermi liquid at the surface. To investigate a novel effect generated by the interaction between the two Fermi liquids, the mobility of a Wigner crystal of electrons formed on the free surface of the mixture is studied. An anomalous enhancement of the mobility, compared with the case where the 3D and 2D systems do not interact with each other, is observed. The enhancement is explained by the nontrivial reflection of 3D quasiparticles from the surface covered with the 2D ^{3}He system.

Fermi surface changes in dilute magnesium alloys: a pseudopotential band structure model

International Nuclear Information System (INIS)

Fung, W.K.

1976-01-01

The de Haas-van Alphen effect has been used to study the Fermi surface of pure magnesium and its dilute alloys containing lithium and indium. The quantum oscillations in magnetization were detected by means of a torque magnetometer in magnetic field up to 36 kilogauss and temperature range of 4.2 0 to 1.7 0 K. The results provide information on the effects of lithium and indium solutes on the Fermi surface of magnesium in changes of extremal cross sections and effective masses as well as the relaxation times associated with the orbits. The nonlocal pseudopotential model proposed by Kimball, Stark and Mueller has been fitted to the Fermi surface of magnesium and extended to include the dilute alloys, fitting all the observed de Haas-van Alphen frequencies with an accuracy of better than 1 percent. A modified rigid band interpretation including both Fermi energy and local band edge changes computed from the model, gives an overall satisfactory description of the observed frequency shifts. With the pseudo-wavefunctions provided by the nonlocal model, the relaxation times in terms of Dingle temperatures for several orbits have been predicted using Sorbello's multiple-plane-wave phase shift model. The calculation with phase shifts obtained from a model potential yields a greater anisotropy than has been observed experimentally, while a two-parameter phase shift model provides a good fit to the experimental results

Quantum critical fluctuations due to nested Fermi surface: The case of spinless fermions

International Nuclear Information System (INIS)

Schlottmann, P.

2007-01-01

A quantum critical point (QCP) can be obtained by tuning the critical temperature of a second-order phase transition to zero. A simple model of spinless fermions with nested Fermi surface leading to a charge density wave is considered. The QCP is obtained by tuning the nesting mismatch of the Fermi surface, which has the following consequences: (i) For the tuned QCP, the specific heat over T and the effective mass increase with the logarithm of the temperature as T is lowered. (ii) For the tuned QCP the linewidth of the quasi-particles is sublinear in T and ω. (iii) The specific heat and the linewidth display a crossover from non-Fermi liquid (∼T) to Fermi liquid (∼T 2 ) behavior with increasing nesting mismatch and decreasing temperature. (iv) For the tuned QCP, the dynamical charge susceptibility has a quasi-elastic peak with a linewidth proportional to T. (v) For non-critical Fermi vector mismatch the peak is inelastic. (vi) While the specific heat and the quasi-particle linewidth are only weakly dependent on the geometry of the nested Fermi surfaces, the momentum-dependent dynamical susceptibility is expected to be affected by the shape of the Fermi surface

Quasiparticles and Fermi liquid behaviour in an organic metal

Science.gov (United States)

Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

2012-01-01

Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems

Science.gov (United States)

Xiao, Cong; Li, Dingping

2016-06-01

Semiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy E F locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density n e and not inversely proportional to n e. While the magnetoresistance (MR) and Nernst coefficient vanish when E F locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when E F decreases below the BCP. Both of them are nonmonotonic functions of E F below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.

Semiclassical magnetotransport in strongly spin–orbit coupled Rashba two-dimensional electron systems

International Nuclear Information System (INIS)

Xiao, Cong; Li, Dingping

2016-01-01

Semiclassical magnetoelectric and magnetothermoelectric transport in strongly spin–orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy E F locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density n e and not inversely proportional to n e . While the magnetoresistance (MR) and Nernst coefficient vanish when E F locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when E F decreases below the BCP. Both of them are nonmonotonic functions of E F below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems. (paper)

Device for measuring the two-dimensional distribution of a radioactive substance on a surface

International Nuclear Information System (INIS)

Anon.

1986-01-01

A device is described by which, using a one-dimensional measuring proportional counter tube depending on position, one can measure the two-dimensionally distributed radioactivity of a surface and can plot this to scale two-dimensionally, after computer processing, or can show it two-dimensionally on a monitor. (orig.) [de

Unconventional superconductivity in a two-dimensional repulsive gas of fermions with spin-orbit coupling

Science.gov (United States)

Wang, Luyang; Vafek, Oskar

2014-02-01

We investigate the superconducting instability of a two-dimensional repulsive Fermi gas with Rashba spin-orbit coupling αR. Using renormalization group approach, we find the superconducting transition temperature as a function of the dimensionless ratio Θ=1}/{2}mαR2/EF where EF = 0 when the smaller Fermi surface shrinks to a (Dirac) point. The general trend is that superconductivity is enhanced as Θ increases, but in an intermediate regime Θ ∼ 0.1, a dome-like behavior appears. At a very small value of Θ, the angular momentum channel jz in which superconductivity occurs is quite high. With increasing Θ, jz decreases with a step of 2 down to jz = 6, after which we find the sequence jz = 6, 4, 6, 2, the last value of which continues to Θ → ∞. In an extended range of Θ, the superconducting gap predominantly resides on the large Fermi surface, while Josephson coupling induces a much smaller gap on the small Fermi surface. Below the superconducting transition temperature, we apply mean field theory to derive the self-consistent equations and find the condensation energies. The state with the lowest condensation energy is an unconventional superconducting state which breaks time-reversal symmetry, and in which singlet and triplet pairings are mixed. In general, these states are topologically nontrivial, and the Chern number of the state with total angular momentum jz is C = 2jz.

Interplay between magnetic quantum criticality, Fermi surface and unconventional superconductivity in UCoGe, URhGe and URu2Si2

International Nuclear Information System (INIS)

Bastien, Gael

2017-01-01

This thesis is concentrated on the ferromagnetic superconductors UCoGe and URhGe and on the hidden order state in URu 2 Si 2 . In the first part the pressure temperature phase diagram of UCoGe was studied up to 10.5 GPa. Ferromagnetism vanishes at the critical pressure pc≅1 GPa. Unconventional superconductivity and non Fermi liquid behavior can be observed in a broad pressure range around pc. The superconducting upper critical field properties were explained by the suppression of the magnetic fluctuations under field. In the second part the Fermi surfaces of UCoGe and URhGe were investigated by quantum oscillations. In UCoGe four Fermi surface pockets were observed. Under magnetic field successive Lifshitz transitions of the Fermi surface have been detected. The observed Fermi surface pockets in UCoGe evolve smoothly with pressure up to 2.5 GPa and do not show any Fermi surface reconstruction at the critical pressure pc. In URhGe, three heavy Fermi surface pockets were detected by quantum oscillations. In the last part the quantum oscillation study in the hidden order state of URu 2 Si 2 shows a strong g factor anisotropy for two Fermi surface pockets, which is compared to the macroscopic g factor anisotropy extracted from the upper critical field study. (author) [fr

Theoretical investigation of the Fermi surface of La2-xSrxCuO4 and YBa2Cu3O7

International Nuclear Information System (INIS)

Antonov, V.N.; Antonov, V.N.; Bar'yakhtar, V.G.

1989-01-01

The theoretical investigation of both the Fermi surface (FS) form and isoenergetic surfaces near the Fermi energy of La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7 is carried out by selfconsistent LMTO/method in an atomic sphere approximation. The FS of these compounds is established to have an essential two-dimensional character. The FS La 2 CuO 4 is a corrugated rounded box centered in Γ point. The FS YBa 2 Cu 3 O 7 consists of four plates: an electron ''cushion'' in Γ point and three embeded hole surfaces centered in S point. In this case the ''cushion'' and one of the hole surfaces are vigorously corrugated along the z-direction. A comparison between both the FS calculated theoretically of La 2 CuO 4 and YBa 2 Cu 3 O 7 and experimental data on electron-positron annihilation is carried out. The electron-rate maps and numerical results of various characteristics, i.e., plate areas, mean rates, mean squares of the rates, partial densities of states for each plate of the FS YBa 2 Cu 3 O 7 are given

Surface properties of semi-infinite Fermi systems

International Nuclear Information System (INIS)

Campi, X.; Stringari, S.

1979-10-01

A functional relation between the kinetic energy density and the total density is used to analyse the surface properties of semi-infinite Fermi systems. One find an explicit expression for the surface thickness in which the role of the infinite matter compressibility, binding energy and non-locality effects is clearly shown. The method, which holds both for nuclear and electronic systems (liquid metals), yields a very simple relation between the surface thickness and the surface energy

3D Quantum Hall Effect of Fermi Arc in Topological Semimetals

Science.gov (United States)

Wang, C. M.; Sun, Hai-Peng; Lu, Hai-Zhou; Xie, X. C.

2017-09-01

The quantum Hall effect is usually observed in 2D systems. We show that the Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological semimetals. Because of the topological constraint, the Fermi arc at a single surface has an open Fermi surface, which cannot host the quantum Hall effect. Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at opposite surfaces can form a complete Fermi loop and support the quantum Hall effect. The edge states of the Fermi arcs show a unique 3D distribution, giving an example of (d -2 )-dimensional boundary states. This is distinctly different from the surface-state quantum Hall effect from a single surface of topological insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall conductivity evolves from the 1 /B dependence to quantized plateaus at the Weyl nodes. This behavior can be realized by tuning gate voltages in a slab of topological semimetal, such as the TaAs family, Cd3 As2 , or Na3Bi . This work will be instructive not only for searching transport signatures of the Fermi arcs but also for exploring novel electron gases in other topological phases of matter.

Fermi surfaces of YRu2Si2 and LaRu2Si2

International Nuclear Information System (INIS)

Settai, R.; Ikezawa, H.; Toshima, H.; Takashita, M.; Ebihara, T.; Sugawara, H.; Kimura, T.; Motoki, K.; Onuki, Y.

1995-01-01

We have measured the de Haas-van Alphen effect of YRu 2 Si 2 and LaRu 2 Si 2 to clarify the Fermi surfaces and cyclotron masses. Main hole-Fermi surfaces of both compounds with a distorted ellipsoid shape are similar, occupying about half of the Brillouin zone. The small hole-Fermi surfaces with the shape of a rugby ball are three in number for LaRu 2 Si 2 , and one for YRu 2 Si 2 . An electron-Fermi surface consists of a doughnut like shape for LaRu 2 Si 2 , while a cylinder along the [001] direction and a multiply-connected shape exist for YRu 2 Si 2 . The cyclotron masses of YRu 2 Si 2 are a little larger than those of LaRu 2 Si 2 . ((orig.))

Exotic Paired States with Anisotropic Spin-Dependent Fermi Surfaces

International Nuclear Information System (INIS)

Feiguin, Adrian E.; Fisher, Matthew P. A.

2009-01-01

We propose a model for realizing exotic paired states in cold Fermi gases by using a spin-dependent optical lattice to engineer mismatched Fermi surfaces for each hyperfine species. The BCS phase diagram shows a stable paired superfluid state with coexisting pockets of momentum space with gapless unpaired carriers, similar to the Sarma state in polarized mixtures, but in our case the system is unpolarized. We propose the possible existence of an exotic 'Cooper-pair Bose-metal' phase, which has a gap for single fermion excitations but gapless and uncondensed 'Cooper-pair' excitations residing on a 'Bose surface' in momentum space.

Zero sound in a two-dimensional dipolar Fermi gas

NARCIS (Netherlands)

Lu, Z.K.; Matveenko, S.I.; Shlyapnikov, G.V.

2013-01-01

We study zero sound in a weakly interacting two-dimensional (2D) gas of single-component fermionic dipoles (polar molecules or atoms with a large magnetic moment) tilted with respect to the plane of their translational motion. It is shown that the propagation of zero sound is provided by both

On the Fermi surface of YBa2Cu3O7-δ

International Nuclear Information System (INIS)

Peter, M.; Manuel, A.A.; Hoffmann, L.; Sadowski, W.

1992-01-01

We show that the signature of a Fermi surface sheet of YBa 2 Cu 3 O 7-δ may be obtained unambiguously from twinned crystals. Comparison of electron-positron momentum density from YBa 2 Cu 3 O 7-δ measured both in insulating and (superconducting) twinned phases leads to a decisive further proof of the existence of the Fermi surface in the metallic YBa 2 Cu 3 O 7-δ . In addition, measurements on untwinned YBA 2 Cu 3 O 7-δ single crystals reveal also a ridge Fermi surface sheet attributed by band structure calculations to CuO chains. 14 refs., 3 figs

Universal behavior of strongly correlated Fermi systems

Energy Technology Data Exchange (ETDEWEB)

Shaginyan, Vasilii R [B.P. Konstantinov St. Petersburg Institute of Nuclear Physics, Russian Academy of Sciences, Gatchina, Leningrad region, Rusian Federation (Russian Federation); Amusia, M Ya [A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg (Russian Federation); Popov, Konstantin G [Komi Scientific Center, Ural Branch of the Russian Academy of Sciences, Syktyvkar (Russian Federation)

2007-06-30

This review discusses the construction of a theory and the analysis of phenomena occurring in strongly correlated Fermi systems such as high-T{sub c} superconductors, heavy-fermion metals, and quasi-two-dimensional Fermi systems. It is shown that the basic properties and the universal behavior of strongly correlated Fermi systems can be described in the framework of the Fermi-condensate quantum phase transition and the well-known Landau paradigm of quasiparticles and the order parameter. The concept of fermion condensation may be fruitful in studying neutron stars, finite Fermi systems, ultra-cold gases in traps, and quark plasma. (reviews of topical problems)

Universal behavior of strongly correlated Fermi systems

International Nuclear Information System (INIS)

Shaginyan, Vasilii R; Amusia, M Ya; Popov, Konstantin G

2007-01-01

This review discusses the construction of a theory and the analysis of phenomena occurring in strongly correlated Fermi systems such as high-T c superconductors, heavy-fermion metals, and quasi-two-dimensional Fermi systems. It is shown that the basic properties and the universal behavior of strongly correlated Fermi systems can be described in the framework of the Fermi-condensate quantum phase transition and the well-known Landau paradigm of quasiparticles and the order parameter. The concept of fermion condensation may be fruitful in studying neutron stars, finite Fermi systems, ultra-cold gases in traps, and quark plasma. (reviews of topical problems)

An interpolatory ansatz captures the physics of one-dimensional confined Fermi systems

DEFF Research Database (Denmark)

Andersen, Molte Emil Strange; Salami Dehkharghani, Amin; Volosniev, A. G.

2016-01-01

beyond the Bethe ansatz and bosonisation allow us to predict the behaviour of one-dimensional confined systems with strong short-range interactions, and new experiments with cold atomic Fermi gases have already confirmed these theories. Here we demonstrate that a simple linear combination of the strongly...

Fermi surface and quantum well states of V(110) films on W(110)

International Nuclear Information System (INIS)

Krupin, Oleg; Rotenberg, Eli; Kevan, S D

2007-01-01

Using angle-resolved photoemission spectroscopy, we have measured the Fermi surface of V(110) films epitaxially grown on a W(110) substrate. We compare our results for thicker films to existing calculations and measurements for bulk vanadium and find generally very good agreement. For thinner films, we observe and analyse a diverse array of quantum well states that split and distort the Fermi surface segments. We have searched unsuccessfully for a thickness-induced topological transition associated with contact between the zone-centre jungle gym and zone-boundary hole ellipsoid Fermi surface segments. We also find no evidence for ferromagnetic splitting of any bands on this surface

Fermi surface and quantum well states of V(110) films on W(110)

Energy Technology Data Exchange (ETDEWEB)

Krupin, Oleg [MS 6-2100, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Rotenberg, Eli [MS 6-2100, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Kevan, S D [Department of Physics, University of Oregon, Eugene, OR 97403 (United States)

2007-09-05

Using angle-resolved photoemission spectroscopy, we have measured the Fermi surface of V(110) films epitaxially grown on a W(110) substrate. We compare our results for thicker films to existing calculations and measurements for bulk vanadium and find generally very good agreement. For thinner films, we observe and analyse a diverse array of quantum well states that split and distort the Fermi surface segments. We have searched unsuccessfully for a thickness-induced topological transition associated with contact between the zone-centre jungle gym and zone-boundary hole ellipsoid Fermi surface segments. We also find no evidence for ferromagnetic splitting of any bands on this surface.

Angular studies of the magnetoresistance in the density wave state of the quasi-two-dimensional purple bronze KMo6O17

Science.gov (United States)

Guyot, H.; Dumas, J.; Kartsovnik, M. V.; Marcus, J.; Schlenker, C.; Sheikin, I.; Vignolles, D.

2007-07-01

The purple molybdenum bronze KMo6O17 is a quasi-two-dimensional compound which shows a Peierls transition towards a commensurate metallic charge density wave (CDW) state. High magnetic field measurements have revealed several transitions at low temperature and have provided an unusual phase diagram “temperature-magnetic field”. Angular studies of the interlayer magnetoresistance are now reported. The results suggest that the orbital coupling of the magnetic field to the CDW is the most likely mechanism for the field induced transitions. The angular dependence of the magnetoresistance is discussed on the basis of a warped quasi-cylindrical Fermi surface and provides information on the geometry of the Fermi surface in the low temperature density wave state.

Patterning two-dimensional free-standing surfaces with mesoporous conducting polymers

NARCIS (Netherlands)

Liu, Shaohua; Gordiichuk, Pavlo; Wu, Zhong-Shuai; Liu, Zhaoyang; Wei, Wei; Wagner, Manfred; Mohamed-Noriega, Nasser; Wu, Dongqing; Mai, Yiyong; Herrmann, Andreas; Müllen, Klaus; Feng, Xinliang

2015-01-01

The ability to pattern functional moieties with well-defined architectures is highly important in material science, nanotechnology and bioengineering. Although two-dimensional surfaces can serve as attractive platforms, direct patterning them in solution with regular arrays remains a major

Fermi surface properties of paramagnetic NpCd11 with a large unit cell

Science.gov (United States)

Homma, Yoshiya; Aoki, Dai; Haga, Yoshinori; Settai, Rikio; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Takeuchi, Tetsuya; Yamagami, Hiroshi; Ōnuki, Yoshichika

2010-03-01

We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

Two-dimensional servo control of surface motor; Surface motor no nijigen servo control

Energy Technology Data Exchange (ETDEWEB)

Ebihara, D; Takahashi, T; Watada, M [Musashi Institute of Technology, Tokyo (Japan)

1995-08-20

Two dimensional (2D) drive system is needed in many aspects of factory automation (FA) and office automation (OA) machines, such as pen drivers in X-Y plotters, X-Y stage for machining, 2D moving robots, etc. Conventional 2D drive systems are consisted from two sets of rotational motor drive and several types of rotary-to-linear transform mechanisms. Linear motors, in these days, have become to be effective as the requirement for high speed increases. We have been studying about Surface Motor which enables 2D drive on a surface by single mover, and the characteristics are measured. Main difficulty of the actuator is that it is short of thrust forces. Also the feasibility is limited because of its vocational uncertainty caused by the open loop control. Our interest is to introduce the closed loop digital control, to obtain required thrust force at any point on the stator. Since open loop control is used, that is, stability point where the thrust force is zero is moved one after another, generated thrust force within the range of synchronization is small. We have been studying about the peculiar expression of exciting currents to generate required direction at all the stator. On the basis of results, two dimensional position feedback system is assembled, which detect the two dimensional location of the mover by optical sensors and direct current instructions are generated for all the four phases of the mover. 14 refs., 11 figs., 1 tab.

Hybrid surface waves in two-dimensional Rashba-Dresselhaus materials

Science.gov (United States)

Yudin, Dmitry; Gulevich, Dmitry R.; Shelykh, Ivan A.

2017-01-01

We address the electromagnetic properties of two-dimensional electron gas confined by a dielectric environment in the presence of both Rashba and Dresselhaus spin-orbit interactions. It is demonstrated that off-diagonal components of the conductivity tensor resulting from a delicate interplay between Rashba and Dresselhaus couplings lead to the hybridization of transverse electric and transverse magnetic surface electromagnetic modes localized at the interface. We show that the characteristics of these hybrid surface waves can be controlled by additional intense external off-resonant coherent pumping.

Band Structure and Fermi Surface of Cu2Sb by the LMTO Method

DEFF Research Database (Denmark)

Jan, J. P.; Skriver, Hans Lomholt

1977-01-01

The linear muffin-tin orbital (LMTO) method of bandstructure calculation has been applied to the simple tetragonal compound Cu2Sb. The d bands of Cu lie substantially below the Fermi level, and the Fermi surface is a recognizable distortion of the free-electron model. The Fermi surface has sheets......-orbit splitting, and of another closed sheet. Earlier de Haas-van Alphen results are explained semiquantitatively by the model, which also accounts for open orbits seen in high-field magnetoresistance experiments....

Band Structure and Fermi-Surface Properties of Ordered beta-Brass

DEFF Research Database (Denmark)

Skriver, Hans Lomholt; Christensen, N. E.

1973-01-01

, but that their position relative to the Fermi level is correct. The derived Fermi-surface model allows a detailed interpretation of the de Hass-van Alphen (dHvA) data. The present model has no open orbit along for B→∥ 〈110〉. This agrees with dHvA as well as magnetoresistance measurements. Four new extremal cross sections...

Fermi surface study of organic conductors using a magneto-optical measurement under high magnetic fields

International Nuclear Information System (INIS)

Kimata, M; Ohta, H; Koyama, K; Motokawa, M; Kondo, R; Kagoshima, S; Tanaka, H; Tokumoto, M; Kobayashi, H; Kobayashi, A

2006-01-01

Magneto-optical measurements have been performed in organic conductors β''-(BEDT-TTF) 2 CsCd(SCN) 4 and λ-(BETS) 2 FeCl 4 . Although the zero magnetic field ground state of β''-(BEDT-TTF) 2 CsCd(SCN) 4 is considered as the density wave state, periodic orbit resonances (POR's) attributed to quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces (FS's) have been observed above 6 T. The existence of these FS's are predicted by the band calculation based on room temperature lattice parameters. This result may suggest the destruction of the density wave state at 6 T, and the primal metallic state revives in the high field phase above 6 T. In the case of λ-(BETS) 2 FeCl 4 , large changes of the transmission intensity of electromagnetic waves around 10 T, which correspond to the insulator-metal transition, have been observed. However, no POR-like resonance has been observed. This may be due to the restriction of the observed frequency-field region

Two dimensional electron gas confined over a spherical surface: Magnetic moment

International Nuclear Information System (INIS)

Hernando, A; Crespo, P; Garcia, M A

2011-01-01

Magnetism of capped nanoparticles, NPs, of non-magnetic substances as Au and ZnO is briefly reviewed. The source of the magnetization is discussed on the light of recent X-ray magnetic circular dichroism experiments. As magnetic dichroism analysis has pointed out impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. It is proposed that mesoscopic collective orbital magnetic moments induced at the surface states can account for the experimental magnetism characteristic of these nanoparticles. The total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10 2 or 10 3 Bohr magnetons.

Interfacial nondegenerate doping of MoS2 and other two-dimensional semiconductors.

Science.gov (United States)

Behura, Sanjay; Berry, Vikas

2015-03-24

Controlled nondegenerate doping of two-dimensional semiconductors (2DSs) with their ultraconfined carriers, high quantum capacitance, and surface-sensitive electronics can enable tuning their Fermi levels for rational device design. However, doping techniques for three-dimensional semiconductors, such as ion implantation, cannot be directly applied to 2DSs because they inflict high defect density. In this issue of ACS Nano, Park et al. demonstrate that interfacing 2DSs with substrates having dopants can controllably inject carriers to achieve nondegenerate doping, thus significantly broadening 2DSs' functionality and applications. Futuristically, this can enable complex spatial patterning/contouring of energy levels in 2DSs to form p-n junctions, integrated logic, and opto/electronic devices. The process is also extendable to biocellular-interfaced devices, band-continuum structures, and intricate 2D circuitry.

Theoretical reconsideration of antiferromagnetic Fermi surfaces in URu{sub 2}Si{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Yamagami, Hiroshi, E-mail: yamagami@cc.kyoto-su.ac.jp [Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555 (Japan)

2011-01-01

In an itinerant 5f-band model, the antiferromagnetic (AFM) Fermi surfaces of URu{sub 2}Si{sub 2} are reconsidered using a relativistic LAPW method within a local spin-density approximation, especially taking into account the lattice parameters dependent on pressures. The reduction of the z-coordinate of the Si sites results in the effect of flattening the Ru-Si layers of URu{sub 2}Si{sub 2} crystal structure, thus weakening a hybridization/mixing between the U-5f and Ru-4d states in the band structure. Consequently the 5f bands around the Fermi level are more flat in the dispersion with decreasing the z-coordinate, thus producing three closed Fermi surfaces like 'curing-stone', 'rugby-ball' and 'ball'. The origins of de Haas-van Alphen branches can be qualitatively interpreted from the obtained AFM Fermi surfaces.

Polyacene and a new class of quasi-one-dimensional conductors

International Nuclear Information System (INIS)

Kivelson, S.; Chapman, O.L.

1983-01-01

Most one-dimensional conductors are quite similar since the Fermi surface is a point and the electron energy dispersion relation near the Fermi surface is linear. It is pointed out that in polyacene the Fermi surface lies at the edge of the Brillouin zone, but that an accidental degeneracy between the valence and conduction bands makes it metallic nonetheless. The dispersion relation is therefore quadratic, and the density of states diverges at the Fermi surface. Thus, polyacene [(C 4 H 2 )/sub n/] and its possible derivatives represent a conceptually new class of quasi-one-dimensional conductors. Moreover, we find that this class of materials has the possibility of possessing interesting condensed phases including high-temperature superconductivity and ferromagnetism

Two dimensional electron gas confined over a spherical surface: Magnetic moment

Energy Technology Data Exchange (ETDEWEB)

Hernando, A; Crespo, P [Instituto de Magnetismo Aplicado, UCM-CSIC-ADIF, Las Rozas. P. O. Box 155, Madrid 28230 (Spain) and Dpto. Fisica de Materiales, Universidad Complutense (Spain); Garcia, M A, E-mail: antonio.hernando@adif.es [Instituto de Ceramica y Vidrio, CSIC c/Kelsen, 5 Madrid 28049 (Spain)

2011-04-01

Magnetism of capped nanoparticles, NPs, of non-magnetic substances as Au and ZnO is briefly reviewed. The source of the magnetization is discussed on the light of recent X-ray magnetic circular dichroism experiments. As magnetic dichroism analysis has pointed out impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. It is proposed that mesoscopic collective orbital magnetic moments induced at the surface states can account for the experimental magnetism characteristic of these nanoparticles. The total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10{sup 2} or 10{sup 3} Bohr magnetons.

Nematic order on the surface of a three-dimensional topological insulator

Science.gov (United States)

Lundgren, Rex; Yerzhakov, Hennadii; Maciejko, Joseph

2017-12-01

We study the spontaneous breaking of rotational symmetry in the helical surface state of three-dimensional topological insulators due to strong electron-electron interactions, focusing on time-reversal invariant nematic order. Owing to the strongly spin-orbit coupled nature of the surface state, the nematic order parameter is linear in the electron momentum and necessarily involves the electron spin, in contrast with spin-degenerate nematic Fermi liquids. For a chemical potential at the Dirac point (zero doping), we find a first-order phase transition at zero temperature between isotropic and nematic Dirac semimetals. This extends to a thermal phase transition that changes from first to second order at a finite-temperature tricritical point. At finite doping, we find a transition between isotropic and nematic helical Fermi liquids that is second order even at zero temperature. Focusing on finite doping, we discuss various observable consequences of nematic order, such as anisotropies in transport and the spin susceptibility, the partial breakdown of spin-momentum locking, collective modes and induced spin fluctuations, and non-Fermi-liquid behavior at the quantum critical point and in the nematic phase.

Surface-enhanced Raman scattering of dipolar molecules by the graphene Fermi surface modulation with different dipole moments

Science.gov (United States)

Zhang, Mingjia; Leng, Yandan; Huang, Jing; Yu, JiaoJiao; Lan, Zhenggang; Huang, Changshui

2017-12-01

We report the modulation of Raman scattering spectrum of chromophore/graphene hybrids by tunning the molecular polarization with different terminal groups (methyl, methoxy, nitrile, and two nitros). Based on the density functional theory, the specific dipole moment values of the chromophore molecules are calculated. An obvious surface-enhanced Raman scattering (SERS) was observed and the scattering intensity of molecule increases with enlarged dipole moment. According to the analysis of G band Raman shifts of graphene, the enhancement of the Raman signal can be attributed to strong electronic coupling between graphene and chromophore, which is closely related with the modulation of graphene Fermi surface by changing the dipole moment of the molecule. Besides, the optimization of the ground state geometry and the binding energy of the hybrids were also calculated with the Density Functional Based Tight Bonding (DFTB) method, which confirms that the enhanced Raman scattering of molecules on graphene arises from the improved energy level matching between graphene Fermi surface and molecular band, further providing a new way to design novel SERS devices.

Conductance of two-dimensional waveguide in presence of the Rashba spin-orbit interaction

Science.gov (United States)

Liu, Duan-Yang; Xia, Jian-Bai

2018-04-01

By using the transfer matrix method, we investigated spin transport in some straight structures in presence of the Rashba spin-orbit interaction. It is proved that the interference of two spin states is the same as that in one-dimensional Datta-Das spin field-effect transistor. The conductance of these structures has been calculated. Conductance quantization is common in these waveguides when we change the Fermi energy and the width of the waveguide. Using a periodic system of quadrate stubs and changing the Fermi energy, a nearly square-wave conductance can be obtained in some regions of the Fermi energy.

Quasiparticle GW calculations for solids, molecules, and two-dimensional materials

DEFF Research Database (Denmark)

Hüser, Falco; Olsen, Thomas; Thygesen, Kristian Sommer

2013-01-01

band gap is around 1eV too low. Similar relative deviations are found for the ionization potentials of a test set of 32 small molecules. The importance of substrate screening for a correct description of quasiparticle energies and Fermi velocities in supported two-dimensional (2D) materials...... of quasiparticle states....

Asymptotics for Two-dimensional Atoms

DEFF Research Database (Denmark)

Nam, Phan Thanh; Portmann, Fabian; Solovej, Jan Philip

2012-01-01

We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E^{\\TF}(\\lambd......We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E......^{\\TF}(\\lambda)$ is given by a Thomas-Fermi type variational problem and $c^{\\rm H}\\approx -2.2339$ is an explicit constant. We also show that the radius of a two-dimensional neutral atom is unbounded when $Z\\to \\infty$, which is contrary to the expected behavior of three-dimensional atoms....

The Fermi surface of a superconductor: OsB{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Hebbache, M. [Laboratoire Materiaux et Phenomenes Quantiques, Universite Paris 7 - CNRS, UMR 7162, Paris (France)

2009-07-15

Osmium diboride has been known for some time as a low compressibility material and a superhard material. It is suitable for hard coating applications. It is also a superconductor below 2.1 K. Using first-principles calculations, the author investigated the geometry of its Fermi surface (FS) and calculated the related physical quantities. The theoretical results are used to predict the frequencies of the Shubnikov-de Haas quantum oscillations. Comparison with recent measurements of the magneto-resistance oscillations in osmium diboride is made. The picture shows the FS of OsB{sub 2} consisting of three sheets: a pair of two nested ellipsoidal surfaces and a corrugated tubular surface. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

Science.gov (United States)

Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

2018-05-01

We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.

Determining the in-plane Fermi surface topology in high Tc superconductors using angle-dependent magnetic quantum oscillations

International Nuclear Information System (INIS)

Harrison, N; McDonald, R D

2009-01-01

We propose a quantum oscillation experiment by which the rotation of an underdoped YBa 2 Cu 3 O 6+x sample about two different axes with respect to the orientation of the magnetic field can be used to infer the shape of the in-plane cross-section of corrugated Fermi surface cylinder(s). Deep corrugations in the Fermi surface are expected to give rise to nodes in the quantum oscillation amplitude that depend on the magnitude and orientation of the magnetic induction B. Because the symmetries of electron and hole cylinders within the Brillouin zone are expected to be very different, the topology can provide essential clues as to the broken symmetry responsible for the observed oscillations. The criterion for the applicability of this method to the cuprate superconductors (as well as other layered metals) is that the difference in quantum oscillation frequency 2ΔF between the maximum (belly) and minimum (neck) extremal cross-sections of the corrugated Fermi surface exceeds |B|. (fast track communication)

Topological surface Fermi arcs in the magnetic Weyl semimetal Co3Sn2S2

Science.gov (United States)

Xu, Qiunan; Liu, Enke; Shi, Wujun; Muechler, Lukas; Gayles, Jacob; Felser, Claudia; Sun, Yan

2018-06-01

Very recently, the half-metallic compound Co3Sn2S2 was proposed to be a magnetic Weyl semimetal (WSM) with Weyl points only 60 meV above the Fermi level EF. Owing to the low charge carrier density and large Berry curvature induced, Co3Sn2S2 possesses both a large anomalous Hall conductivity and a large anomalous Hall angle, which provide strong evidence for the existence of Weyl points in Co3Sn2S2 . In this work, we theoretically study the surface topological feature of Co3Sn2S2 and its counterpart Co3Sn2Se2 . By cleaving the sample at the weak Sn-S/Se bonds, one can achieve two different surfaces terminated with Sn and S/Se atoms, respectively. The resulting Fermi-arc-related states can range from the energy of the Weyl points to EF-0.1 eV in the Sn-terminated surface. Therefore, it should be possible to observe the Fermi arcs in angle-resolved photoemission spectroscopy (ARPES) measurements. Furthermore, in order to simulate quasiparticle interference in scanning tunneling microscopy (STM) measurements, we also calculate the joint density of states for both terminals. This work should be helpful for a comprehensive understanding of the topological properties of these two magnetic WSMs and further ARPES and STM measurements.

Matter waves of Bose-Fermi mixtures in one-dimensional optical lattices

International Nuclear Information System (INIS)

Bludov, Yu. V.; Santhanam, J.; Kenkre, V. M.; Konotop, V. V.

2006-01-01

We describe solitary wave excitations in a Bose-Fermi mixture loaded in a one-dimensional and strongly elongated lattice. We focus on the mean-field theory under the condition that the fermion number significantly exceeds the boson number, and limit our consideration to lattice amplitudes corresponding to the order of a few recoil energies or less. In such a case, the fermionic atoms display 'metallic' behavior and are well-described by the effective mass approximation. After classifying the relevant cases, we concentrate on gap solitons and coupled gap solitons in the two limiting cases of large and small fermion density, respectively. In the former, the fermionic atoms are distributed almost homogeneously and thus can move freely along the lattice. In the latter, the fermionic density becomes negligible in the potential maxima, and this leads to negligible fermionic current in the linear regime

Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS.

Science.gov (United States)

Ali, Mazhar N; Schoop, Leslie M; Garg, Chirag; Lippmann, Judith M; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S P

2016-12-01

Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 10 5 percent at 9 T and 2 K at a 45° angle between the applied current ( I || a ) and the applied field (90° is H || c ). Approaching 90°, a "dip" is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states.

Interaction quantum quenches in the one-dimensional Fermi-Hubbard model

Science.gov (United States)

Heidrich-Meisner, Fabian; Bauer, Andreas; Dorfner, Florian; Riegger, Luis; Orso, Giuliano

2016-05-01

We discuss the nonequilibrium dynamics in two interaction quantum quenches in the one-dimensional Fermi-Hubbard model. First, we study the decay of the Néel state as a function of interaction strength. We observe a fast charge dynamics over which double occupancies are built up, while the long-time decay of the staggered moment is controlled by spin excitations, corroborated by the analysis of the entanglement dynamics. Second, we investigate the formation of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations in a spin-imbalanced system in quenches from the noninteracting case to attractive interactions. Even though the quench puts the system at a finite energy density, peaks at the characteristic FFLO quasimomenta are visible in the quasi-momentum distribution function, albeit with an exponential decay of s-wave pairing correlations. We also discuss the imprinting of FFLO correlations onto repulsively bound pairs and their rapid decay in ramps. Supported by the DFG (Deutsche Forschungsgemeinschaft) via FOR 1807.

One-dimensional Fermi accelerator model with moving wall described by a nonlinear van der Pol oscillator.

Science.gov (United States)

Botari, Tiago; Leonel, Edson D

2013-01-01

A modification of the one-dimensional Fermi accelerator model is considered in this work. The dynamics of a classical particle of mass m, confined to bounce elastically between two rigid walls where one is described by a nonlinear van der Pol type oscillator while the other one is fixed, working as a reinjection mechanism of the particle for a next collision, is carefully made by the use of a two-dimensional nonlinear mapping. Two cases are considered: (i) the situation where the particle has mass negligible as compared to the mass of the moving wall and does not affect the motion of it; and (ii) the case where collisions of the particle do affect the movement of the moving wall. For case (i) the phase space is of mixed type leading us to observe a scaling of the average velocity as a function of the parameter (χ) controlling the nonlinearity of the moving wall. For large χ, a diffusion on the velocity is observed leading to the conclusion that Fermi acceleration is taking place. On the other hand, for case (ii), the motion of the moving wall is affected by collisions with the particle. However, due to the properties of the van der Pol oscillator, the moving wall relaxes again to a limit cycle. Such kind of motion absorbs part of the energy of the particle leading to a suppression of the unlimited energy gain as observed in case (i). The phase space shows a set of attractors of different periods whose basin of attraction has a complicated organization.

Analytical and numerical studies of Bose-Fermi mixtures in a one-dimensional harmonic trap

Science.gov (United States)

Dehkharghani, A. S.; Bellotti, F. F.; Zinner, N. T.

2017-07-01

In this paper we study a mixed system of bosons and fermions with up to six particles in total. All particles are assumed to have the same mass. The two-body interactions are repulsive and are assumed to have equal strength in both the Bose-Bose and the Fermi-Boson channels. The particles are confined externally by a harmonic oscillator one-body potential. For the case of four particles, two identical fermions and two identical bosons, we focus on the strongly interacting regime and analyze the system using both an analytical approach and density matrix renormalization group calculations using a discrete version of the underlying continuum Hamiltonian. This provides us with insight into both the ground state and the manifold of excited states that are almost degenerate for large interaction strength. Our results show great variation in the density profiles for bosons and fermions in different states for strongly interacting mixtures. By moving to slightly larger systems, we find that the ground state of balanced mixtures of four to six particles tends to separate bosons and fermions for strong (repulsive) interactions. On the other hand, in imbalanced Bose-Fermi mixtures we find pronounced odd-even effects in systems of five particles. These few-body results suggest that question of phase separation in one-dimensional confined mixtures are very sensitive to system composition, both for the ground state and the excited states.

Optical conductivity of three and two dimensional topological nodal-line semimetals

Science.gov (United States)

Barati, Shahin; Abedinpour, Saeed H.

2017-10-01

The peculiar shape of the Fermi surface of topological nodal-line semimetals at low carrier concentrations results in their unusual optical and transport properties. We analytically investigate the linear optical responses of three- and two-dimensional nodal-line semimetals using the Kubo formula. The optical conductivity of a three-dimensional nodal-line semimetal is anisotropic. Along the axial direction (i.e., the direction perpendicular to the nodal-ring plane), the Drude weight has a linear dependence on the chemical potential at both low and high carrier dopings. For the radial direction (i.e., the direction parallel to the nodal-ring plane), this dependence changes from linear into quadratic in the transition from low into high carrier concentration. The interband contribution into optical conductivity is also anisotropic. In particular, at large frequencies, it saturates to a constant value for the axial direction and linearly increases with frequency along the radial direction. In two-dimensional nodal-line semimetals, no interband optical transition could be induced and the only contribution to the optical conductivity arises from the intraband excitations. The corresponding Drude weight is independent of the carrier density at low carrier concentrations and linearly increases with chemical potential at high carrier doping.

Fermi-edge singularity in one-dimensional electron systems with long-range Coulomb interactions

International Nuclear Information System (INIS)

Otani, H.; Ogawa, T.

1996-01-01

Effects of long-range Coulomb interactions on the Fermi-edge singularity in optical spectra are investigated theoretically for one-dimensional spin-1/2 fermion systems with the use of the Tomonaga-Luttinger bosonization technique. Low-energy excitation spectrum near the Fermi level shows that dispersion of the charge-density fluctuation remains gapless but is nonlinear when the electron-electron (e-e) Coulomb interaction is of the x -1 type (i.e., an infinite force range). Temporal behavior of the current-current correlation function is calculated analytically for arbitrary force ranges, λ e and λ h , of the e-e and the electron-hole (e-h) Coulomb interactions. (i) When both the e-e and the e-h interactions have large but finite force ranges (λ e h max[λ e ,λ h ]/v F . Corresponding optical spectrum near the Fermi edge (within an energy range of ℎv F /max[λ e ,λ h ]) exhibits the power-law divergence or the power-law convergence, which is an ordinary Fermi-edge singularity. (ii) When either the e-e or the e-h interaction is of the x -1 type (i.e., λ e →∞ and/or λ h →∞), an exponent of the correlation function is dependent on time to lead the faster decay than that of any power laws. Then the optical spectra show no power law dependence and always converge (become zero) at the Fermi edge, which is in striking contrast to the ordinary power-law singularity

Spin texture of the surface state of three-dimensional Dirac material Ca3PbO

Science.gov (United States)

Kariyado, Toshikaze

2015-04-01

The bulk and surface electronic structures of a candidate three-dimensional Dirac material Ca3PbO and its family are discussed especially focusing on the spin texture on the surface states. We first explain the basic features of the bulk band structure of Ca3PbO, such as emergence of Dirac fermions near the Fermi energy, and compare it with the other known three-dimensional Dirac semimetals. Then, the surface bands and spin-texture on them are investigated in detail. It is shown that the surface bands exhibit strong momentum-spin locking, which may be useful in some application for spin manipulation, induced by a combination of the inversion symmetry breaking at the surface and the strong spin-orbit coupling of Pb atoms. The surface band structure and the spin-textures are sensitive to the surface types.

Spin texture of the surface state of three-dimensional Dirac material Ca3PbO

International Nuclear Information System (INIS)

Kariyado, Toshikaze

2015-01-01

The bulk and surface electronic structures of a candidate three-dimensional Dirac material Ca 3 PbO and its family are discussed especially focusing on the spin texture on the surface states. We first explain the basic features of the bulk band structure of Ca 3 PbO, such as emergence of Dirac fermions near the Fermi energy, and compare it with the other known three-dimensional Dirac semimetals. Then, the surface bands and spin-texture on them are investigated in detail. It is shown that the surface bands exhibit strong momentum-spin locking, which may be useful in some application for spin manipulation, induced by a combination of the inversion symmetry breaking at the surface and the strong spin-orbit coupling of Pb atoms. The surface band structure and the spin-textures are sensitive to the surface types. (paper)

Chemical potential and internal energy of the noninteracting Fermi ...

Indian Academy of Sciences (India)

entropy by T, dV is the change in volume by p and µ is the chemical potential. When S .... thin films are actually not 2D objects, but fractals with Hausdorff dimensionalities between 2D ..... sharpness of the edge of the Fermi surface is lost. In the ...

Fermi surface measurements in actinide metals and compounds

International Nuclear Information System (INIS)

Arko, A.J.; Schirber, J.E.

1978-01-01

The various techniques of measuring Fermi Surface parameters are briefly discussed in terms f application to actinide systems. Particular emphasis is given the dHvA effect. Some general results found in the dHvA studies of actinide compounds are given. The dHvA effect has been measured in α-U and is presented in detail. None of the observed frequencies corresponds to closed surfaces. Results are compared to the calculations of Freeman, Koelling and Watson-Yang where qualitative agreement is observed

Itinerant Ferromagnetism in a Polarized Two-Component Fermi Gas

DEFF Research Database (Denmark)

Massignan, Pietro; Yu, Zhenhua; Bruun, Georg

2013-01-01

We analyze when a repulsively interacting two-component Fermi gas becomes thermodynamically unstable against phase separation. We focus on the strongly polarized limit, where the free energy of the homogeneous mixture can be calculated accurately in terms of well-defined quasiparticles, the repul......We analyze when a repulsively interacting two-component Fermi gas becomes thermodynamically unstable against phase separation. We focus on the strongly polarized limit, where the free energy of the homogeneous mixture can be calculated accurately in terms of well-defined quasiparticles...

Characterization of the Fermi surface of BEDT-TTF4[Hg2Cl6].PhCl by electronic band structure calculations

International Nuclear Information System (INIS)

Veiros, L.F.; Canadell, E.

1994-01-01

Tight-binding band structure calculations for the room temperature structure of BEDT-TTF 4 [Hg 2 Cl 6 ]-PhCl show the existence of closed electron and hole Fermi surfaces, in agreement with the 2D metallic conductivity of this salt. It is shown that these closed Fermi surfaces result from the hybridization of two hidden 1D Fermi surfaces. However, our study also shows that a transition associated with either a usual or a hidden nesting type mechanism is unlikely. This explains why this salt retains its metallic properties without any resistivity anomaly down to 1.3 K. Our study suggests that BEDT-TTF 4 [Hg 2 Cl 6 ]-PhCl is somewhat anisotropic 2D semimetal and should exhibit Shubnikov-de Haas oscillations corresponding to a cross-sectional area of approximately 13% of the first Brillouin zone. (orig.)

Fermi-level tuning of the Dirac surface state in (Bi1-x Sb x )2Se3 thin films

Science.gov (United States)

Satake, Yosuke; Shiogai, Junichi; Takane, Daichi; Yamada, Keiko; Fujiwara, Kohei; Souma, Seigo; Sato, Takafumi; Takahashi, Takashi; Tsukazaki, Atsushi

2018-02-01

We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi1-x Sb x )2Se3 ternary alloy thin films grown on an isostructural Bi2Se3 buffer layer on InP substrates. By angle-resolved photoemission spectroscopy, we clearly detected Dirac surface states with a large bulk band gap of 0.2-0.3 eV in the (Bi1-x Sb x )2Se3 film with x  =  0.70. In addition, we observed by Hall effect measurements that the dominant charge carrier converts from electron (n-type) to hole (p-type) at around x  =  0.7, indicating that the Fermi level can be controlled across the Dirac point. Indeed, the carrier transport was shown to be governed by Dirac surface state in 0.63  ⩽  x  ⩽  0.75. These features suggest that Fermi-level tunable (Bi1-x Sb x )2Se3-based heterostructures provide a platform for extracting exotic topological phenomena.

Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS

Science.gov (United States)

Ali, Mazhar N.; Schoop, Leslie M.; Garg, Chirag; Lippmann, Judith M.; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S. P.

2016-01-01

Magnetoresistance (MR), the change of a material’s electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual “butterfly”-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 105 percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a “dip” is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states. PMID:28028541

Fermi surface mapping: Techniques and visualization

International Nuclear Information System (INIS)

Rotenberg, E.; Denlinger, J.D.; Kevan, S.D.

1997-01-01

Angle-resolved photoemission (ARP) of valence bands is a mature technique that has achieved spectacular success in band-mapping metals, semiconductors, and insulators. The purpose of the present study was the development of experimental and analytical techniques in ARP which take advantage of third generation light sources. Here the authors studied the relatively simple Cu surface in preparation for other metals. Copper and related metals themselves are of current interest, especially due to its role as an interlayer in spin valves and other magnetic heterostructures. A major goal of this study was the development of a systematic technique to quickly (i.e. in a few hours of synchrotron beamtime) measure the FS and separate it into bulk and surface FS's. Often, one needs to avoid bulk features altogether, which one can achieve by carefully mapping their locations in k-space. The authors will also show how they systematically map Fermi surfaces throughout large volumes of k-space, and, by processing the resulting volume data sets, provide intuitive pictures of FS's, both bulk and surface

Exactly integrable two-dimensional dynamical systems related with supersymmetric algebras

International Nuclear Information System (INIS)

Leznov, A.N.

1983-01-01

A wide class of exactly integrable dynamical systems in two-dimensional space related with superalgebras, which generalize supersymmetric Liouville equation, is constructed. The equations can be interpretated as nonlinearly interacting Bose and Fermi fields belonging within classical limit to even and odd parts of the Grassman space. Explicit expressions for the solutions of the constructed systems are obtained on the basis of standard perturbation theory

On the interrelation between bulk and thin-film Fermi surfaces

KAUST Repository

Schwingenschlö gl, Udo; Fré sard, Raymond

2010-01-01

A general scheme for inferring the Fermi surface of a finite slab from ab initio electronic-structure calculations for the parent bulk system is introduced. The simple cubic ReO 3 oxide is studied as an example system. We show that our scheme

Effect of interface/surface stress on the elastic wave band structure of two-dimensional phononic crystals

International Nuclear Information System (INIS)

Liu, Wei; Chen, Jiwei; Liu, Yongquan; Su, Xianyue

2012-01-01

In the present Letter, the multiple scattering theory (MST) for calculating the elastic wave band structure of two-dimensional phononic crystals (PCs) is extended to include the interface/surface stress effect at the nanoscale. The interface/surface elasticity theory is employed to describe the nonclassical boundary conditions at the interface/surface and the elastic Mie scattering matrix embodying the interface/surface stress effect is derived. Using this extended MST, the authors investigate the interface/surface stress effect on the elastic wave band structure of two-dimensional PCs, which is demonstrated to be significant when the characteristic size reduces to nanometers. -- Highlights: ► Multiple scattering theory including the interface/surface stress effect. ► Interface/surface elasticity theory to describe the nonclassical boundary conditions. ► Elastic Mie scattering matrix embodying the interface/surface stress effect. ► Interface/surface stress effect would be significant at the nanoscale.

Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of a Weyl semimetal.

Science.gov (United States)

Inoue, Hiroyuki; Gyenis, András; Wang, Zhijun; Li, Jian; Oh, Seong Woo; Jiang, Shan; Ni, Ni; Bernevig, B Andrei; Yazdani, Ali

2016-03-11

Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials. Copyright © 2016, American Association for the Advancement of Science.

Low-energy excitations and Fermi surface topology of parent cobaltate superconductor

Energy Technology Data Exchange (ETDEWEB)

Hasan, M.Z. [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, NJ 08544 (United States)], E-mail: mzhasan@princeton.edu; Qian, D. [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, NJ 08544 (United States); Foo, M.; Cava, R.J. [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States)

2007-09-01

The essential framework for cuprate superconductivity is that of a spin-1/2 electron system in the vicinity of a half filled (Mott limit) lattice. Of all oxide superconductors, this framework is most closely matched in the sodium doped cobalt oxides except that it is realized on a triangular lattice. We employ angle-resolved photoemission spectroscopy to study the quasiparticle dynamics of the parent cobaltate superconductor. Results reveal a single hole-like Fermi surface generated by the crossing of heavy ({approx}15 m{sub e} {approx} 3m{sub LDA}) quasiparticles with a negative effective hopping (t{sub eff} < 0). The observed ground state as given by the topology of the Fermi surface is found be very close to a collective charge instability with {radical}(3)x{radical}(3) symmetry. The measured electron dynamic parameters reveal the unusual character of the parent cobaltate class likely due to small and almost isotropic Fermi velocity (v{sub F}(k{sup {yields}}){approx}v{sub F}{approx}0.4{+-}0.1 eV A) observed. ARPES data is consistent with bulk thermodynamic specific heat and quantum oscillation measurements.

Quantum oscillations and nodal pockets from Fermi surface reconstruction in the underdoped cuprates

Science.gov (United States)

Harrison, Neil

2012-02-01

Fermiology in the underdoped high Tc cuprates presents us with unique challenges, requiring experimentalists to look deeper into the data than is normally required for clues. Recent measurements of an oscillatory chemical potential affecting the oscillations at high magnetic fields provide a strong indication of a single type of carrier pocket. When considered in conjunction with photoemission and specific heat measurements, a Fermi surface comprised almost entirely of nodal pockets is suggested. The mystery of the Fermi surface is deepened, however, by a near doping-independent Fermi surface cross-sectional area and negative Hall and Seebeck coefficients. We explore ways in which these findings can be reconciled, taking an important hint from the diverging effective mass yielded by quantum oscillations at low dopings. The author wishes to thank Suchitra Sebastian, Moaz Atarawneh, Doug Bonn, Walter Hardy, Ruixing Liang, Charles Mielke and Gilbert Lonzarich who have contributed to this work. The work is supported by the NSF through the NHMFL and by the DOE project ``Science at 100 tesla.''

Two-dimensional metamaterial optics

International Nuclear Information System (INIS)

Smolyaninov, I I

2010-01-01

While three-dimensional photonic metamaterials are difficult to fabricate, many new concepts and ideas in the metamaterial optics can be realized in two spatial dimensions using planar optics of surface plasmon polaritons. In this paper we review recent progress in this direction. Two-dimensional photonic crystals, hyperbolic metamaterials, and plasmonic focusing devices are demonstrated and used in novel microscopy and waveguiding schemes

Density profiles and collective excitations of a trapped two-component Fermi vapour

International Nuclear Information System (INIS)

Amoruso, M.; Meccoli, I.; Minguzzi, A.; Tosi, M.P.

1999-08-01

We discuss the ground state and the small-amplitude excitations of a degenerate vapour of fermionic atoms placed in two hyperfine states inside a spherical harmonic trap. An equations-of-motion approach is set up to discuss the hydrodynamic dissipation processes from the interactions between the two components of the fluid beyond mean-field theory and to emphasize analogies with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The conditions for the establishment of a collisional regime via scattering against cold-atom impurities are analyzed. The equilibrium density profiles are then calculated for a two-component vapour of 40 K atoms: they are little modified by the interactions for presently relevant values of the system parameters, but spatial separation of the two components will spontaneously arise as the number of atoms in the trap is increased. The eigenmodes of collective oscillation in both the total particle number density and the concentration density are evaluated analytically in the special case of a symmetric two-component vapour in the collisional regime. The dispersion relation of the surface modes for the total particle density reduces in this case to that of a one-component Fermi vapour, whereas the frequencies of all other modes are shifted by the interactions. (author)

Trial wave functions for a composite Fermi liquid on a torus

Science.gov (United States)

Fremling, M.; Moran, N.; Slingerland, J. K.; Simon, S. H.

2018-01-01

We study the two-dimensional electron gas in a magnetic field at filling fraction ν =1/2 . At this filling the system is in a gapless state which can be interpreted as a Fermi liquid of composite fermions. We construct trial wave functions for the system on a torus, based on this idea, and numerically compare these to exact wave functions for small systems found by exact diagonalization. We find that the trial wave functions give an excellent description of the ground state of the system, as well as its charged excitations, in all momentum sectors. We analyze the dispersion of the composite fermions and the Berry phase associated with dragging a single fermion around the Fermi surface and comment on the implications of our results for the current debate on whether composite fermions are Dirac fermions.

Dimensional Crossover and Its Interplay with In-Plane Anisotropy of Upper Critical Field in β-(BDA-TTP)2SbF6

Science.gov (United States)

Yasuzuka, Syuma; Koga, Hiroaki; Yamamura, Yasuhisa; Saito, Kazuya; Uji, Shinya; Terashima, Taichi; Akutsu, Hiroki; Yamada, Jun-ichi

2017-08-01

Resistance measurements have been performed to investigate the dimensionality and the in-plane anisotropy of the upper critical field (Hc2) for β-(BDA-TTP)2SbF6 in fields H up to 15 T and at temperatures T from 1.5 to 7.5 K, where BDA-TTP stands for 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene. The upper critical fields parallel and perpendicular to the conduction layer are determined and dimensional crossover from anisotropic three-dimensional behavior to two-dimensional behavior is found at around 6 K. When the direction of H is varied within the conducting layer at 6.0 K, Hc2 shows twofold symmetry: Hc2 along the minimum Fermi wave vector (maximum Fermi velocity) is larger than that along the maximum Fermi wave vector (minimum Fermi velocity). The normal-state magnetoresistance has twofold symmetry similar to Hc2 and shows a maximum when the magnetic field is nearly parallel to the maximum Fermi wave vector. This tendency is consistent with the Fermi surface anisotropy. At 3.5 K, we found clear fourfold symmetry of Hc2 despite the fact that the normal-state magnetoresistance shows twofold symmetry arising from the Fermi surface anisotropy. The origin of the fourfold symmetry of Hc2 is discussed in terms of the superconducting gap structure in β-(BDA-TTP)2SbF6.

Dimensional crossover and its interplay with in-plane anisotropy of upper critical field in β-(BDA-TTP)_2SbF_6

International Nuclear Information System (INIS)

Yasuzuka, Syuma; Koga, Hiroaki; Yamamura, Yasuhisa; Saito, Kazuya; Uji, Shinya; Terashima, Taichi; Akutsu, Hiroki; Yamada, Jun-ichi

2017-01-01

Resistance measurements have been performed to investigate the dimensionality and the in-plane anisotropy of the upper critical field (H_c_2) for β-(BDA-TTP)_2SbF_6 in fields H up to 15 T and at temperatures T from 1.5 to 7.5 K, where BDA-TTP stands for 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene. The upper critical fields parallel and perpendicular to the conduction layer are determined and dimensional crossover from anisotropic three-dimensional behavior to two-dimensional behavior is found at around 6 K. When the direction of H is varied within the conducting layer at 6.0 K, H_c_2 shows twofold symmetry: H_c_2 along the minimum Fermi wave vector (maximum Fermi velocity) is larger than that along the maximum Fermi wave vector (minimum Fermi velocity). The normal-state magnetoresistance has twofold symmetry similar to H_c_2 and shows a maximum when the magnetic field is nearly parallel to the maximum Fermi wave vector. This tendency is consistent with the Fermi surface anisotropy. At 3.5 K, we found clear fourfold symmetry of H_c_2 despite the fact that the normal-state magnetoresistance shows twofold symmetry arising from the Fermi surface anisotropy. The origin of the fourfold symmetry of H_c_2 is discussed in terms of the superconducting gap structure in β-(BDA-TTP)_2SbF_6. (author)

Evidence for the complicated Fermi surface in 2H- and 4H-NbSe2

Indian Academy of Sciences (India)

Both single crystals show anisotropic ρ/ρ0, which are described by Kohler's rule, two-band model and magnetic breakdown model. In the present ... rule is derived only for the isotropic model of closed Fermi surface, it describes the .... [13] Witney D A, Fleming R M and Coleman R V 1976 Solid State. Commun. 18 399.

Scattering resonances in a degenerate Fermi gas

DEFF Research Database (Denmark)

Challis, Katharine; Nygaard, Nicolai; Mølmer, Klaus

2009-01-01

We consider elastic single-particle scattering from a one-dimensional trapped two-component superfluid Fermi gas when the incoming projectile particle is identical to one of the confined species. Our theoretical treatment is based on the Hartree-Fock ground state of the trapped gas...

Convective heat transfer from rough surfaces with two-dimensional ribs - transitional and laminar flow

International Nuclear Information System (INIS)

Dalle Donne, M.; Meyer, L.

1978-01-01

Measurements of friction factor and heat transfer coefficients for two rods of 18.9 mm 0.D. with two-dimensional roughness, each in two different outer smooth tubes have been performed in turbulent and laminar flow. The turbulent flow results indicate that the flow was not thermally fully established, the isothermal data however agree reasonably well with our previously obtained general correlation. Laminar flow results can be correlated best when the Reynolds and Greatz numbers are evaluated at the temperature average between the temperature of the inner rod surface and of the outer smooth surface of the annulus, the average being weighted over the two surfaces. (orig.) [de

The Fermi GBM Gamma-Ray Burst Catalog: The First Two Years

NARCIS (Netherlands)

Paciesas, W.S.; Meegan, C.A.; von Kienlin, A.; Bhat, P.N.; Bissaldi, E.; Briggs, M.S.; M. Burgess, J.; Chaplin, V.; Connaughton, V.; Diehl, R.; Fishman, G.J.; Fitzpatrick, G.; Foley, S.; H. Gibby, M.; Giles, M.; Goldstein, A.; Greiner, J.; Gruber, D.; Guiriec, S.; van der Horst, A.J.; Kippen, R.M.; Kouveliotou, C.; Lichti, G.; Lin, L.; McBreen, S.; Preece, R.D.; Rau, A.; Tierney, D.; Wilson-Hodge, C.

2012-01-01

The Fermi Gamma-ray Burst Monitor (GBM) is designed to enhance the scientific return from Fermi in studying gamma-ray bursts (GRBs). In its first two years of operation GBM triggered on 491 GRBs. We summarize the criteria used for triggering and quantify the general characteristics of the triggered

Fermi-surface reconstruction by stripe order in cuprate superconductors

Science.gov (United States)

Laliberté, Francis

2012-02-01

The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBCO, application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order [1,2,3]. In another cuprate, Eu-LSCO, the onset of stripe order - a modulation of spin and charge densities - at low temperature is well established [4]. By a comparative study of thermoelectric transport in the cuprates YBCO and Eu-LSCO, we show that the two materials exhibit a very similar process of Fermi-surface reconstruction as a function of temperature and doping [5,6]. This strongly suggests that Fermi-surface reconstruction is caused by stripe order in both cases, compelling evidence that stripe order is a generic tendency of hole-doped cuprates.[4pt] Work done in collaboration with J. Chang, N. Doiron-Leyraud, E. Hassinger, R. Daou, D. LeBoeuf, M. Rondeau, B. J. Ramshaw, R. Liang, D. A. Bonn, W. N. Hardy, S. Pyon, T. Takayama, H. Takagi, I. Sheikin, L. Malone, C. Proust, K. Behnia and L. Taillefer.[4pt] [1] N. Doiron-Leyraud et al., Nature 447, 565 (2007).[0pt] [2] D. LeBoeuf et al., Nature 450, 533 (2007).[0pt] [3] D. LeBoeuf et al., Phys. Rev. B 83, 054506 (2011).[0pt] [4] J. Fink et al., Phys. Rev. B 83, 092503 (2011).[0pt] [5] J. Chang et al., Phys. Rev. Lett. 104, 057005 (2010).[0pt] [6] F. Lalibert'e et al., Nat. Commun. 2, 432 (2011).

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas

OpenAIRE

Wang, Pei; Yi, Wei; Xianlong, Gao

2014-01-01

We study the quench dynamics of a one-dimensional ultracold Fermi gas in an optical lattice potential with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of t...

Composite Fermi surface in the half-filled Landau level with anisotropic electron mass

Science.gov (United States)

Ippoliti, Matteo; Geraedts, Scott; Bhatt, Ravindra

We study the problem of interacting electrons in the lowest Landau level at half filling in the quantum Hall regime, when the electron dispersion is given by an anisotropic mass tensor. Based on experimental observations and theoretical arguments, the ground state of the system is expected to consist of composite Fermions filling an elliptical Fermi sea, with the anisotropy of the ellipse determined by the competing effects of the isotropic Coulomb interaction and anisotropic electron mass tensor. We test this idea quantitatively by using a numerical density matrix renormalization group method for quantum Hall systems on an infinitely long cylinder. Singularities in the structure factor allow us to map the Fermi surface of the composite Fermions. We compute the composite Fermi surface anisotropy for several values of the electron mass anisotropy which allow us to deduce the functional dependence of the former on the latter. This research was supported by Department of Energy Office of Basic Energy Sciences through Grant No. DE-SC0002140.

Electron-phonon heat exchange in quasi-two-dimensional nanolayers

Science.gov (United States)

Anghel, Dragos-Victor; Cojocaru, Sergiu

2017-12-01

We study the heat power P transferred between electrons and phonons in thin metallic films deposited on free-standing dielectric membranes. The temperature range is typically below 1 K, such that the wavelengths of the excited phonon modes in the system is large enough so that the picture of a quasi-two-dimensional phonon gas is applicable. Moreover, due to the quantization of the components of the electron wavevectors perpendicular to the metal film's surface, the electrons spectrum forms also quasi two-dimensional sub-bands, as in a quantum well (QW). We describe in detail the contribution to the electron-phonon energy exchange of different electron scattering channels, as well as of different types of phonon modes. We find that heat flux oscillates strongly with thickness of the film d while having a much smoother variation with temperature (Te for the electrons temperature and Tph for the phonons temperature), so that one obtains a ridge-like landscape in the two coordinates, (d, Te) or (d, Tph), with crests and valleys aligned roughly parallel to the temperature axis. For the valley regions we find P ∝ Te3.5 - Tph3.5. From valley to crest, P increases by more than one order of magnitude and on the crests P cannot be represented by a simple power law. The strong dependence of P on d is indicative of the formation of the QW state and can be useful in controlling the heat transfer between electrons and crystal lattice in nano-electronic devices. Nevertheless, due to the small value of the Fermi wavelength in metals, the surface imperfections of the metallic films can reduce the magnitude of the oscillations of P vs. d, so this effect might be easier to observe experimentally in doped semiconductors.

Dirac and Weyl fermion dynamics on two-dimensional surface

International Nuclear Information System (INIS)

Kavalov, A.R.; Sedrakyan, A.G.; Kostov, I.K.

1986-01-01

Fermions on 2-dimensional surface, embedded into a 3-dimensional space are investigated. The determinant of induced Dirac operator for the Dirac and Weyl fermions is calculated. The reparametrization-invariant effective action is determined by conformal anomaly (giving Liouville action) and also by Lorentz anomaly leading to Wess-Zumino term, the structure of which at d=3 is determined by the Hopf topological invariant of the S 3 → S 2 map

Two dimensional layered materials: First-principle investigation

Science.gov (United States)

Tang, Youjian

Two-dimensional layered materials have emerged as a fascinating research area due to their unique physical and chemical properties, which differ from those of their bulk counterparts. Some of these unique properties are due to carriers and transport being confined to 2 dimensions, some are due to lattice symmetry, and some arise from their large surface area, gateability, stackability, high mobility, spin transport, or optical accessibility. How to modify the electronic and magnetic properties of two-dimensional layered materials for desirable long-term applications or fundamental physics is the main focus of this thesis. We explored the methods of adsorption, intercalation, and doping as ways to modify two-dimensional layered materials, using density functional theory as the main computational methodology. Chapter 1 gives a brief review of density functional theory. Due to the difficulty of solving the many-particle Schrodinger equation, density functional theory was developed to find the ground-state properties of many-electron systems through an examination of their charge density, rather than their wavefunction. This method has great application throughout the chemical and material sciences, such as modeling nano-scale systems, analyzing electronic, mechanical, thermal, optical and magnetic properties, and predicting reaction mechanisms. Graphene and transition metal dichalcogenides are arguably the two most important two-dimensional layered materials in terms of the scope and interest of their physical properties. Thus they are the main focus of this thesis. In chapter 2, the structure and electronic properties of graphene and transition metal dichalcogenides are described. Alkali adsorption onto the surface of bulk graphite and metal intecalation into transition metal dichalcogenides -- two methods of modifying properties through the introduction of metallic atoms into layered systems -- are described in chapter 2. Chapter 3 presents a new method of tuning

Entanglement rules for holographic Fermi surfaces

Directory of Open Access Journals (Sweden)

Dibakar Roychowdhury

2016-08-01

Full Text Available In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

Entanglement rules for holographic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Roychowdhury, Dibakar, E-mail: dibakarphys@gmail.com

2016-08-15

In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

Splitting Fermi Surfaces and Heavy Electronic States in Non-Centrosymmetric U3Ni3Sn4

Science.gov (United States)

Maurya, Arvind; Harima, Hisatomo; Nakamura, Ai; Shimizu, Yusei; Homma, Yoshiya; Li, DeXin; Honda, Fuminori; Sato, Yoshiki J.; Aoki, Dai

2018-04-01

We report the single-crystal growth of the non-centrosymmetric paramagnet U3Ni3Sn4 by the Bridgman method and the Fermi surface properties detected by de Haas-van Alphen (dHvA) experiments. We have also investigated single-crystal U3Ni3Sn4 by single-crystal X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. The angular dependence of the dHvA frequencies reveals many closed Fermi surfaces, which are nearly spherical in topology. The experimental results are in good agreement with local density approximation (LDA) band structure calculations based on the 5f-itinerant model. The band structure calculation predicts many Fermi surfaces, mostly with spherical shape, derived from 12 bands crossing the Fermi energy. To our knowledge, the splitting of Fermi surfaces due to the non-centrosymmetric crystal in 5f-electron systems is experimentally detected for the first time. The temperature dependence of the dHvA amplitude reveals a large cyclotron effective mass of up to 35 m0, indicating the heavy electronic state of U3Ni3Sn4 due to the proximity of the quantum critical point. From the field dependence of the dHvA amplitude, a mean free path of conduction electrons of up to 1950 Å is detected, reflecting the good quality of the grown crystal. The small splitting energy related to the antisymmetric spin-orbit interaction is most likely due to the large cyclotron effective mass.

Surface and Interface Engineering of Organometallic and Two Dimensional Semiconductor

Science.gov (United States)

Park, Jun Hong

For over half a century, inorganic Si and III-V materials have led the modern semiconductor industry, expanding to logic transistor and optoelectronic applications. However, these inorganic materials have faced two different fundamental limitations, flexibility for wearable applications and scaling limitation as logic transistors. As a result, the organic and two dimensional have been studied intentionally for various fields. In the present dissertation, three different studies will be presented with followed order; (1) the chemical response of organic semiconductor in NO2 exposure. (2) The surface and stability of WSe2 in ambient air. (3) Deposition of dielectric on two dimensional materials using organometallic seeding layer. The organic molecules rely on the van der Waals interaction during growth of thin films, contrast to covalent bond inorganic semiconductors. Therefore, the morphology and electronic property at surface of organic semiconductor in micro scale is more sensitive to change in gaseous conditions. In addition, metal phthalocyanine, which is one of organic semiconductor materials, change their electronic property as reaction with gaseous analytes, suggesting as potential chemical sensing platforms. In the present part, the growth behavior of metal phthalocyanine and surface response to gaseous condition will be elucidated using scanning tunneling microscopy (STM). In second part, the surface of layered transition metal dichalcogenides and their chemical response to exposure ambient air will be investigated, using STM. Layered transition metal dichalcogenides (TMDs) have attracted widespread attention in the scientific community for electronic device applications because improved electrostatic gate control and suppression of short channel leakage resulted from their atomic thin body. To fabricate the transistor based on TMDs, TMDs should be exposed to ambient conditions, while the effect of air exposure has not been understood fully. In this part

Exotic ferromagnetism in the two-dimensional quantum material C3N

Science.gov (United States)

Huang, Wen-Cheng; Li, Wei; Liu, Xiaosong

2018-04-01

The search for and study of exotic quantum states in novel low-dimensional quantum materials have triggered extensive research in recent years. Here, we systematically study the electronic and magnetic structures in the newly discovered two-dimensional quantum material C3N within the framework of density functional theory. The calculations demonstrate that C3N is an indirect-band semiconductor with an energy gap of 0.38 eV, which is in good agreement with experimental observations. Interestingly, we find van Hove singularities located at energies near the Fermi level, which is half that of graphene. Thus, the Fermi energy easily approaches that of the singularities, driving the system to ferromagnetism, under charge carrier injection, such as electric field gating or hydrogen doping. These findings not only demonstrate that the emergence of magnetism stems from the itinerant electron mechanism rather than the effects of local magnetic impurities, but also open a new avenue to designing field-effect transistor devices for possible realization of an insulator-ferromagnet transition by tuning an external electric field.

Two-dimensional Dirac fermions in thin films of C d3A s2

Science.gov (United States)

Galletti, Luca; Schumann, Timo; Shoron, Omor F.; Goyal, Manik; Kealhofer, David A.; Kim, Honggyu; Stemmer, Susanne

2018-03-01

Two-dimensional states in confined thin films of the three-dimensional Dirac semimetal C d3A s2 are probed by transport and capacitance measurements under applied magnetic and electric fields. The results establish the two-dimensional Dirac electronic spectrum of these states. We observe signatures of p -type conduction in the two-dimensional states as the Fermi level is tuned across their charge neutrality point and the presence of a zero-energy Landau level, all of which indicate topologically nontrivial states. The resistance at the charge neutrality point is approximately h /e2 and increases rapidly under the application of a magnetic field. The results open many possibilities for gate-tunable topological devices and for the exploration of novel physics in the zero-energy Landau level.

Orbital order and effective mass enhancement in t2 g two-dimensional electron gases

Science.gov (United States)

Tolsma, John; Principi, Alessandro; Polini, Marco; MacDonald, Allan

2015-03-01

It is now possible to prepare d-electron two-dimensional electron gas systems that are confined near oxide heterojunctions and contain t2 g electrons with a density much smaller than one electron per metal atom. I will discuss a generic model that captures all qualitative features of electron-electron interaction physics in t2 g two-dimensional electron gas systems, and the use of a GW approximation to explore t2 g quasiparticle properties in this new context. t2 g electron gases contain a high density isotropic light mass xy component and low-density xz and yz anisotropic components with light and heavy masses in orthogonal directions. The high density light mass band screens interactions within the heavy bands. As a result the wave vector dependence of the self-energy is reduced and the effective mass is increased. When the density in the heavy bands is low, the difference in anisotropy between the two heavy bands favors orbital order. When orbital order does not occur, interactions still reshape the heavy-band Fermi surfaces. I will discuss these results in the context of recently reported magnetotransport experiments.

Evidence of a 2D Fermi surface due to surface states in a p-type metallic Bi2Te3

Science.gov (United States)

Shrestha, K.; Marinova, V.; Lorenz, B.; Chu, C. W.

2018-05-01

We present a systematic quantum oscillations study on a metallic, p-type Bi2Te3 topological single crystal in magnetic fields up to B  =  7 T. The maxima/minima positions of oscillations measured at different tilt angles align to one another when plotted as a function of the normal component of magnetic field, confirming the presence of the 2D Fermi surface. Additionally, the Berry phase, β  =  0.4  ±  0.05 obtained from the Landau level fan plot, is very close to the theoretical value of 0.5 for the Dirac particles, confirming the presence of topological surface states in the Bi2Te3 single crystal. Using the Lifshitz–Kosevich analyses, the Fermi energy is estimated to be meV, which is lower than that of other bismuth-based topological systems. The detection of surface states in the Bi2Te3 crystal can be explained by our previous hypothesis of the lower position of the Fermi surface that cuts the ‘M’-shaped valence band maxima. As a result, the bulk state frequency is shifted to higher magnetic fields, which allows measurement of the surface states signal at low magnetic fields.

Fermi surface study of CeSb

International Nuclear Information System (INIS)

Aoki, H.; Crabtree, G.W.; Joss, W.; Hulliger, F.

1984-09-01

A Fermi surface study of the ferromagnetic phase of CeSb is presented. The γ frequency branches arising from the electron surfaces at the X points, three separate frequency branches from the hole surfaces at the GAMMA point and the low frequency branch α have been observed. The effective mass ratios are low and range from approx. 0.2 for the α branch to approx. 1.0 for the high frequency branch of γ. The low effective mass ratios suggest that the admixture of the conduction states with the f state is small. We have observed a drastic change in the appearance of the dHvA signal at the phase transition between the ferromagnetic and lower field antiferromagnetic phases: The low frequency α oscillation suddenly disappears as the crystal enters the antiferromagnetic phase. By utilizing the change in the signal appearance, the transition field strength has been measured as a function of the field direction. The present experimental results, particularly the origin of the α oscillation, are discussed in the light of the p-f mixing theory and recent band structure calculations based on localized f orbitals

Fermi surface study of CeSb

International Nuclear Information System (INIS)

Aoki, H.; Crabtree, G.; Joss, W.; Hulliger, F.

1985-01-01

A Fermi surface study of the ferromagnetic phase of CeSb is presented. The γ frequency branches arising from the electron surfaces at the X points, three separate frequency branches from the hole surfaces at the GAMMA point, and the low-frequency branch α have been observed. The effective mass ratios are low and range from approx.0.2 for the α branch to approx.1.0 for the high-frequency branch of γ. The low effective mass ratios suggest that the admixture of the conduction states with the f state is small. We have observed a drastic change in the appearance of the de Haas--van Alpen signal at the phase transition between the ferromagnetic and lower field antiferromagnetic phases: the low-frequency α oscillation suddenly disappears as the crystal enters the antiferromagnetic phase. By utilizing the change in the signal appearance, the transition field strength has been measured as a function of the field direction. The present experimental results particularly the origin of the α oscillation, are discussed in the light of the p-f mixing theory and recent band-structure calculations based on localized f orbitals

Fermi surface in V3Si from positron annihilation

International Nuclear Information System (INIS)

Peter, M.; Manuel, A.A.; Jarlborg, T.

1982-01-01

The recent work of the Geneva Group on the electronic structure of V 3 Si is briefly reviewed. Accurate self-consistent LMTO calculation leads to a Fermi surface and momentum distribution which is confirmed by high resolution 2-D angular correlation of positron annihilation radiation (2D-ACPAR). The bandstructure data are combined with phonon data from Junod's specific heat measurements to calculate parameters relevant to superconductivity. (orig.)

Effect of Repeated Microwave Disinfection on Surface Hardness and Dimensional Accuracy of Two Dental Stone Materials

Directory of Open Access Journals (Sweden)

Mahmood Robati Anaraki

2015-01-01

Full Text Available There is controversial evidence in relation to the effect of microwave on mechanical properties of stone casts. The present study was designed to evaluate the effect of repeated microwave disinfection on surface hardness and dimensional accuracy of dental stone. In this in vitro study, 48 cylindrical stone samples were prepared using two products of type IV stone to assess surface hardness and 48 impressions were taken from a model and poured by these stones to assess the dimensional accuracy. The evaluation of the samples was carried out consequently by a micro-hardness tester and a digital caliper after the stone samples were exposed to 7 consecutive rounds of 900 watts (W microwave irradiation for five minutes each time after cooling. Data were analyzed by t-test and ANOVA. According to the obtained results, multiple disinfections of the stone casts by microwave do not negatively affect their surface hardness and dimensional accuracy.   Key words: Dental stone; Dimensional accuracy; Hardness; Microwave

Optical microcavities based on surface modes in two-dimensional photonic crystals and silicon-on-insulator photonic crystals

DEFF Research Database (Denmark)

Xiao, Sanshui; Qiu, M.

2007-01-01

Surface-mode optical microcavities based on two-dimensional photonic crystals and silicon-on-insulator photonic crystals are studied. We demonstrate that a high-quality-factor microcavity can be easily realized in these structures. With an increasing of the cavity length, the quality factor is gr...... is gradually enhanced and the resonant frequency converges to that of the corresponding surface mode in the photonic crystals. These structures have potential applications such as sensing.......Surface-mode optical microcavities based on two-dimensional photonic crystals and silicon-on-insulator photonic crystals are studied. We demonstrate that a high-quality-factor microcavity can be easily realized in these structures. With an increasing of the cavity length, the quality factor...

Superconductivity in engineered two-dimensional electron gases

Science.gov (United States)

Chubukov, Andrey V.; Kivelson, Steven A.

2017-11-01

We consider Kohn-Luttinger mechanism for superconductivity in a two-dimensional electron gas confined to a narrow well between two grounded metallic planes with two occupied subbands with Fermi momenta kF L>kF S . On the basis of a perturbative analysis, we conclude that non-s -wave superconductivity emerges even when the bands are parabolic. We analyze the conditions that maximize Tc as a function of the distance to the metallic planes, the ratio kF L/kF S , and rs, which measures the strength of Coulomb correlations. The largest attraction is in p -wave and d -wave channels, of which p wave is typically the strongest. For rs=O (1 ) we estimate that the dimensionless coupling λ ≈10-1 , but it likely continues increasing for larger rs (where we lose theoretical control).

Manipulation of surface plasmon polariton propagation on isotropic and anisotropic two-dimensional materials coupled to boron nitride heterostructures

Energy Technology Data Exchange (ETDEWEB)

Inampudi, Sandeep; Nazari, Mina; Forouzmand, Ali; Mosallaei, Hossein, E-mail: hosseinm@coe.neu.edu [Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Ave., Boston, Massachusetts 02115 (United States)

2016-01-14

We present a comprehensive analysis of surface plasmon polariton dispersion characteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersion characteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmon polariton (SPP) dispersion characteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.

Self-energy behavior away from the Fermi surface in doped Mott insulators.

Science.gov (United States)

Merino, J; Gunnarsson, O; Kotliar, G

2016-02-03

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

De Haas-van Alphen effect of a two-dimensional ultracold atomic gas

Science.gov (United States)

Farias, B.; Furtado, C.

2016-01-01

In this paper, we show how the ultracold atom analogue of the two-dimensional de Haas-van Alphen effect in electronic condensed matter systems can be induced by optical fields in a neutral atomic system. The interaction between the suitable spatially varying laser fields and tripod-type trapped atoms generates a synthetic magnetic field which leads the particles to organize themselves in Landau levels. Initially, with the atomic gas in a regime of lowest Landau level, we display the oscillatory behaviour of the atomic energy and its derivative with respect to the effective magnetic field (B) as a function of 1/B. Furthermore, we estimate the area of the Fermi circle of the two-dimensional atomic gas.

Thermodynamics of two-parameter quantum group Bose and Fermi gases

International Nuclear Information System (INIS)

Algin, A.

2005-01-01

The high and low temperature thermodynamic properties of the two-parameter deformed quantum group Bose and Fermi gases with SU p/q (2) symmetry are studied. Starting with a SU p/q (2)-invariant bosonic as well as fermionic Hamiltonian, several thermodynamic functions of the system such as the average number of particles, internal energy and equation of state are derived. The effects of two real independent deformation parameters p and q on the properties of the systems are discussed. Particular emphasis is given to a discussion of the Bose-Einstein condensation phenomenon for the two-parameter deformed quantum group Bose gas. The results are also compared with earlier undeformed and one-parameter deformed versions of Bose and Fermi gas models. (author)

Surface effects on the propagation of sound in Fermi liquids

International Nuclear Information System (INIS)

Nagai, K.; Woelfle, P.

1981-01-01

The propagation of sound in a resonator is discussed in both the normal and superfluid Fermi liquids. A set of model hydrodynamic equations is developed for describing the transition from the hydrodynamic regime to the collisionless regime. Surface effects are incorporated by using a slip boundary condition. The resonance condition for the sound propagation in a cylindrical resonator is derived

Electromagnetic quantum waves and their effect on the low temperature magnetoacoustic response of a quasi-two-dimensional metal

International Nuclear Information System (INIS)

Zimbovskaya, Natalya A

2011-01-01

We theoretically analyze weakly attenuated electromagnetic waves in quasi-two-dimensional (Q2D) metals in high magnetic fields. Within the chosen geometry, the magnetic field is directed perpendicular to the conducting layers of a Q2D conductor. We have shown that longitudinal collective modes could propagate along the magnetic field provided that the Fermi surface is moderately corrugated. The considered wave speeds strongly depend on the magnetic field magnitude. Also, we have analyzed interactions of these quantum waves with sound waves of suitable polarization and propagation direction, and we have shown that such interaction may bring significant changes to the low temperature magnetoacoustic response of Q2D conductors.

Fermi Surface of Sr_{2}RuO_{4}: Spin-Orbit and Anisotropic Coulomb Interaction Effects.

Science.gov (United States)

Zhang, Guoren; Gorelov, Evgeny; Sarvestani, Esmaeel; Pavarini, Eva

2016-03-11

The topology of the Fermi surface of Sr_{2}RuO_{4} is well described by local-density approximation calculations with spin-orbit interaction, but the relative size of its different sheets is not. By accounting for many-body effects via dynamical mean-field theory, we show that the standard isotropic Coulomb interaction alone worsens or does not correct this discrepancy. In order to reproduce experiments, it is essential to account for the Coulomb anisotropy. The latter is small but has strong effects; it competes with the Coulomb-enhanced spin-orbit coupling and the isotropic Coulomb term in determining the Fermi surface shape. Its effects are likely sizable in other correlated multiorbital systems. In addition, we find that the low-energy self-energy matrix-responsible for the reshaping of the Fermi surface-sizably differs from the static Hartree-Fock limit. Finally, we find a strong spin-orbital entanglement; this supports the view that the conventional description of Cooper pairs via factorized spin and orbital part might not apply to Sr_{2}RuO_{4}.

Phase fluctuations in two coaxial quasi-one-dimensional superconducting cylindrical surfaces serving as a model system for superconducting nanowire bundles

Energy Technology Data Exchange (ETDEWEB)

Wong, C.H., E-mail: ch.kh.vong@urfu.ru [Institute of Physics and Technology, Ural Federal University, Clear Water Bay, Kowloon (Russian Federation); Wu, R.P.H., E-mail: pak-hong-raymond.wu@connect.polyu.hk [Department of Applied Physics, The Hong Kong Polytechnic University (Hong Kong); Lortz, R., E-mail: lortz@ust.hk [Department of Physics, Hong Kong University of Science and Technology (Hong Kong)

2017-03-15

The dimensional crossover from a 1D fluctuating state at high temperatures to a 3D phase coherent state in the low temperature regime in two coaxial weakly-coupled cylindrical surfaces formed by two-dimensional arrays of parallel nanowires is studied via an 8-state 3D-XY model. This system serves as a model for quasi-one-dimensional superconductors in the form of bundles of weakly-coupled superconducting nanowires. A periodic variation of the dimensional crossover temperature T{sub DC} is observed when the inner superconducting cylindrical surface is rotated in the angular plane. T{sub DC} reaches a maximum when the relative angle between the cylinders is 2.81°, which corresponds to the maximum separation of nanowires between the two cylindrical surfaces. We demonstrate that the relative strength of phase fluctuations in this system is controllable by the rotational angle between the two surfaces with a strong suppression of the fluctuation strength at 2.81°. The phase fluctuations are suppressed gradually upon cooling, before they abruptly vanish below T{sub DC}. Our model thus allows us to study how phase fluctuations can be suppressed in quasi-one-dimensional superconductors in order to achieve a global phase coherent state throughout the nanowire array with zero electric resistance.

Bulk Fermi surface and electronic properties of Cu0.07Bi2Se3

Science.gov (United States)

Martin, C.; Craciun, V.; Miller, K. H.; Uzakbaiuly, B.; Buvaev, S.; Berger, H.; Hebard, A. F.; Tanner, D. B.

2013-05-01

The electronic properties of Cu0.07Bi2Se3 have been investigated using Shubnikov-de Haas and optical reflectance measurements. Quantum oscillations reveal a bulk, three-dimensional Fermi surface with anisotropy kFc/kFab≈ 2 and a modest increase in free-carrier concentration and in scattering rate with respect to the undoped Bi2Se3, also confirmed by reflectivity data. The effective mass is almost identical to that of Bi2Se3. Optical conductivity reveals a strong enhancement of the bound impurity bands with Cu addition, suggesting that a significant number of Cu atoms enter the interstitial sites between Bi and Se layers or may even substitute for Bi. This conclusion is also supported by x-ray diffraction measurements, where a significant increase of microstrain was found in Cu0.07Bi2Se3, compared to Bi2Se3.

A Simple Free Surface Tracking Model for Multi-dimensional Two-Fluid Approaches

International Nuclear Information System (INIS)

Lee, Seungjun; Yoon, Han Young

2014-01-01

The development in two-phase experiments devoted to find unknown phenomenological relationships modified conventional flow pattern maps into a sophisticated one and even extended to the multi-dimensional usage. However, for a system including a large void fraction gradient, such as a pool with the free surface, the flow patterns varies spatially throughout small number of cells and sometimes results in an unstable and unrealistic prediction of flows at the large gradient void fraction cells. Then, the numerical stability problem arising from the free surface is the major interest in the analyses of a passive cooling pool convecting the decay heat naturally, which has become a design issue to increase the safety level of nuclear reactors recently. In this research, a new and simple free surface tracking method combined with a simplified topology map is presented. The method modified the interfacial drag coefficient only for the cells defined as the free surface. The performance is shown by comparing the natural convection analysis of a small scale pool with respect to single- and two-phase condition. A simple free surface tracking model with a simplified topology map is developed

Electronic structure, Fermi surface and optical properties of metallic compound Be8(B48)B2

International Nuclear Information System (INIS)

Reshak, A.H.; Azam, Sikander; Alahmed, Z.A.; Chyský, Jan

2014-01-01

The band structure, density of states, electronic charge density, Fermi surface and optical properties for B 8 (Be 48 )B 2 compound has been investigated in the support of density functional theory (DFT). The atomic positions of B 8 (Be 48 )B 2 compound were optimized by minimization of the forces acting on the atoms using the full potential linear augmented plane wave (FPLAPW) method. We have employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engal-Vosko GGA (EVGGA) to indulgence the exchange correlation potential by solving Kohn–Sham equations. The result shows that the compound is metallic with sturdy hybridization near the Fermi energy level (E F ). The density of states at Fermi energy, N(E F ), is determined by the overlaping between B-p, B-s and Be-s states. This overlaping is strong enough indicating metallic origin with different values of N(E F ). These values are 16.4, 16.27 and 14.89 states/eV, and the corresponding bare linear low-temperature electronic specific heat coefficient (γ) is found to be 2.84, 2.82 and 2.58 mJ/mol K 2 for EVGGA, GGA and LDA respectively. There exists a strong hybridization between B-s and B-p states, also between B-s and Be-p states around the Fermi level. The Fermi surface is composed of three sheets. These sheets consist of set of holes and electrons. The bonding features of the compounds are analyzed using the electronic charge density in the (101 and −101) crystallographic planes and also the analyzing of charge density shows covalent bonding between B and B. The linear optical properties are also deliberated and discussed in particulars. - Highlights: • The compound is metallic. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of three sheets. • The bonding features are analyzed using the electronic charge density

Sound waves and dynamics of superfluid Fermi gases in optical lattices

International Nuclear Information System (INIS)

Zhang Aixia; Xue Jukui

2009-01-01

The sound waves, the stability of Bloch waves, the Bloch oscillation, and the self-trapping phenomenon in interacting two-component Fermi gases throughout the BEC-BCS crossover in one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) optical lattices are discussed in detail. Within the hydrodynamical theory and by using the perturbative and tight-binding approximation, sound speed in both weak and tight 1D, 2D, 3D optical lattices, and the criteria for occurrences of instability of Bloch waves and self-trapping of Fermi gases along the whole BEC-BCS crossover in tight 1D, 2D, 3D optical lattices are obtained analytically. The results show that the sound speed, the criteria for occurrences of instability of Bloch waves and self-trapping, and the destruction of Bloch oscillation are modified dramatically by the lattice parameters (lattice dimension and lattice strength), the atom density or atom number, and the atom interaction.

Application of tomographic techniques to two-dimensional surface analysis using the Harwell nuclear microprobe

International Nuclear Information System (INIS)

Huddleston, J.; Hutchinson, I.G.; Pierce, T.B.

1983-01-01

Nuclear methods of surface analysis are discussed briefly, and the circumstances are described in which a two-dimensional analysis of the sample surface is desirable to enable the surface composition to be mapped accurately. Tomographic techniques of data manipulation are outlined. Data acquisition in the present case is performed by moving the sample in a defined sequence of positions, at each of which analytical data are gathered by the proton microprobe. The method and equipment are outlined. Data processing leading to the reconstruction of the image is summarised. (U.K.)

Strain-induced fermi contour anisotropy of GaAs 2D holes.

Science.gov (United States)

Shabani, J; Shayegan, M; Winkler, R

2008-03-07

We report measurements of magnetoresistance commensurability peaks, induced by a square array of antidots, in GaAs (311)A two-dimensional holes as a function of applied in-plane strain. The data directly probe the shapes of the Fermi contours of the two spin subbands that are split thanks to the spin-orbit interaction and strain. The experimental results are in quantitative agreement with the predictions of accurate energy band calculations, and reveal that the majority spin subband has a severely distorted Fermi contour whose anisotropy can be tuned with strain.

Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

Science.gov (United States)

Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

2016-04-01

The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

Two-dimensional topological field theories coupled to four-dimensional BF theory

International Nuclear Information System (INIS)

Montesinos, Merced; Perez, Alejandro

2008-01-01

Four-dimensional BF theory admits a natural coupling to extended sources supported on two-dimensional surfaces or string world sheets. Solutions of the theory are in one to one correspondence with solutions of Einstein equations with distributional matter (cosmic strings). We study new (topological field) theories that can be constructed by adding extra degrees of freedom to the two-dimensional world sheet. We show how two-dimensional Yang-Mills degrees of freedom can be added on the world sheet, producing in this way, an interactive (topological) theory of Yang-Mills fields with BF fields in four dimensions. We also show how a world sheet tetrad can be naturally added. As in the previous case the set of solutions of these theories are contained in the set of solutions of Einstein's equations if one allows distributional matter supported on two-dimensional surfaces. These theories are argued to be exactly quantizable. In the context of quantum gravity, one important motivation to study these models is to explore the possibility of constructing a background-independent quantum field theory where local degrees of freedom at low energies arise from global topological (world sheet) degrees of freedom at the fundamental level

Electrostatic energy and screened charge interaction near the surface of metals with different Fermi surface shape

Science.gov (United States)

Gabovich, A. M.; Il'chenko, L. G.; Pashitskii, E. A.; Romanov, Yu. A.

1980-04-01

Using the Poisson equation Green function for a self-consistent field in a spatially inhomogeneous system, expressions for the electrostatic energy and screened charge interaction near the surface of a semi-infinite metal and a thin quantizing film are derived. It is shown that the decrease law and Friedel oscillation amplitude of adsorbed atom indirect interaction are determined by the electron spectrum character and the Fermi surface shape. The results obtained enable us to explain, in particular, the submonolayer adsorbed film structure on the W and Mo surfaces.

Branch-cut singularities in thermodynamics of Fermi liquid systems.

Science.gov (United States)

Shekhter, Arkady; Finkel'stein, Alexander M

2006-10-24

The recently measured spin susceptibility of the two-dimensional electron gas exhibits a strong dependence on temperature, which is incompatible with the standard Fermi liquid phenomenology. In this article, we show that the observed temperature behavior is inherent to ballistic two-dimensional electrons. Besides the single-particle and collective excitations, the thermodynamics of Fermi liquid systems includes effects of the branch-cut singularities originating from the edges of the continuum of pairs of quasiparticles. As a result of the rescattering induced by interactions, the branch-cut singularities generate nonanalyticities in the thermodynamic potential that reveal themselves in anomalous temperature dependences. Calculation of the spin susceptibility in such a situation requires a nonperturbative treatment of the interactions. As in high-energy physics, a mixture of the collective excitations and pairs of quasiparticles can effectively be described by a pole in the complex momentum plane. This analysis provides a natural explanation for the observed temperature dependence of the spin susceptibility, both in sign and in magnitude.

Tunneling Conductance in Two-Dimensional Junctions between a Normal Metal and a Ferromagnetic Rashba Metal

Science.gov (United States)

Oshima, Daisuke; Taguchi, Katsuhisa; Tanaka, Yukio

2018-03-01

We have studied charge transport in a ferromagnetic Rashba metal (FRM), where both Rashba type spin-orbit coupling (RSOC) and exchange coupling coexist. It has nontrivial metallic states, i.e., a normal Rashba metal (NRM), anomalous Rashba metal (ARM), and Rashba ring metal (RRM), and they are manipulated by tuning the Fermi level with an applied gate voltage. We theoretically studied the tunneling conductance (G) in a normal metal/FRM junction by changing the Fermi level via an applied gate voltage (Vg) on the FRM. We found a wide variation in the Vg dependence of G, which depends on the metallic states. In an NRM, the Vg dependence of G is the same as that in a conventional two-dimensional system. However, in an ARM, the Vg dependence of G is similar to that in a conventional one- (two-)dimensional system for a large (small) RSOC. Furthermore, in an RRM, which is generated by a large RSOC, the Vg dependence of G is similar to that in the one-dimensional system. In addition, these anomalous properties stem from the density of states in the ARM and RRM caused by the large RSOC and exchange coupling rather than the spin-momentum locking of RSOC.

Bistatic scattering from a three-dimensional object above a two-dimensional randomly rough surface modeled with the parallel FDTD approach.

Science.gov (United States)

Guo, L-X; Li, J; Zeng, H

2009-11-01

We present an investigation of the electromagnetic scattering from a three-dimensional (3-D) object above a two-dimensional (2-D) randomly rough surface. A Message Passing Interface-based parallel finite-difference time-domain (FDTD) approach is used, and the uniaxial perfectly matched layer (UPML) medium is adopted for truncation of the FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. This makes the parallel FDTD algorithm easier to implement. The parallel performance with different number of processors is illustrated for one rough surface realization and shows that the computation time of our parallel FDTD algorithm is dramatically reduced relative to a single-processor implementation. Finally, the composite scattering coefficients versus scattered and azimuthal angle are presented and analyzed for different conditions, including the surface roughness, the dielectric constants, the polarization, and the size of the 3-D object.

Thomas-Fermi molecular dynamics

International Nuclear Information System (INIS)

Clerouin, J.; Pollock, E.L.; Zerah, G.

1992-01-01

A three-dimensional density-functional molecular-dynamics code is developed for the Thomas-Fermi density functional as a prototype for density functionals using only the density. Following Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)], the electronic density is treated as a dynamical variable. The electronic densities are verified against a multi-ion Thomas-Fermi algorithm due to Parker [Phys. Rev. A 38, 2205 (1988)]. As an initial application, the effect of electronic polarization in enhancing ionic diffusion in strongly coupled plasmas is demonstrated

Experimental investigation of two-dimensional critical surface structure, stimulated Raman scattering, and two-plasmon decay instability. Annual report, January 1, 1981-April 30, 1982

International Nuclear Information System (INIS)

Wong, A.Y.; Eggleston, D.L.; Tanikawa, T.; Qian, S.J.

1982-11-01

Experimental observations of the space and time evolution of resonantly enhanced electrostatic electric fields and plasma density in cylindrical geometry demonstrate the development of two-dimensional caviton structure when an initial density perturbation is imposed on the plasma in the direction perpendicular to the driver field. This two-dimensional structure is observed after the development of profile modification and grows on the ion time scale. The existence of a large azimuthal electric field component is an observational signature of two-dimensional structure. Enhanced electric field maxima are found to be azimuthally correlated with the density minima. Both the density cavities and electric field peaks exhibit increased azimuthal location with the growth of two-dimensional structure. The two-dimensional development exhibits a strong dependence on both perturbation wavenumber and driver power. The related theoretical literature is reviewed and numerical, analytical, and qualitative hybrid models for a driven, two-dimensional, inhomogeneous plasma are presented. Preliminary work is presented in the following additional areas: weak magnetic field effects on critical surface physics, optical measurements of fast electron production, two-dimensional effects in microwave-plasma interactions, Langmuir wave trapping, stimulated Raman scattering and two-plasmon decay instability

Fermi's ansatz and Bohm's quantum potential

Energy Technology Data Exchange (ETDEWEB)

Dennis, Glen, E-mail: gdennis502@gmail.com [TPRU, Birkbeck College, University of London, London, WC1E 7HX (United Kingdom); Gosson, Maurice A. de, E-mail: maurice.de.gosson@univie.ac.at [University of Vienna, Faculty of Mathematics, NuHAG, Oskar-Morgenstern-Platz 1, 1090 Vienna (Austria); Hiley, Basil J., E-mail: b.hiley@bbk.ac.uk [TPRU, Birkbeck College, University of London, London, WC1E 7HX (United Kingdom)

2014-06-27

In this paper we address the following simple question: Given a wavefunction ψ(x,t) in a one-dimensional configuration space, is it possible to give a unique two-dimensional representation ρ(x,p,t) in a position-momentum phase plane? If so, can we find the general condition that makes this possible? We will show that this is indeed possible by using an idea introduced originally by Fermi provided the boundary of the phase space area is a closed curve satisfying a certain exact quantum condition. - Highlights: • We review “Fermi's trick” which allows one to view an arbitrary wavefunction as a stationary state for some Hamiltonian operator H{sub F}. This Hamiltonian contains the quantum potential. • We study the relation between Fermi's trick and an exact quantization condition which reduces to the familiar EBK condition in the limit ħ→0. • This allows us to relate the Fermi set H{sub F}(x,p)=0 to the notion of quantum blob introduced by one of us in previous work. Quantum blobs are phase space regions corresponding to minimum uncertainty. • We discuss our results from the point of view of the quantum theory of motion.

Use of upscaled elevation and surface roughness data in two-dimensional surface water models

Science.gov (United States)

Hughes, J.D.; Decker, J.D.; Langevin, C.D.

2011-01-01

In this paper, we present an approach that uses a combination of cell-block- and cell-face-averaging of high-resolution cell elevation and roughness data to upscale hydraulic parameters and accurately simulate surface water flow in relatively low-resolution numerical models. The method developed allows channelized features that preferentially connect large-scale grid cells at cell interfaces to be represented in models where these features are significantly smaller than the selected grid size. The developed upscaling approach has been implemented in a two-dimensional finite difference model that solves a diffusive wave approximation of the depth-integrated shallow surface water equations using preconditioned Newton–Krylov methods. Computational results are presented to show the effectiveness of the mixed cell-block and cell-face averaging upscaling approach in maintaining model accuracy, reducing model run-times, and how decreased grid resolution affects errors. Application examples demonstrate that sub-grid roughness coefficient variations have a larger effect on simulated error than sub-grid elevation variations.

Modelling of Graphene Nanoribbon Fermi Energy

International Nuclear Information System (INIS)

Johari, Z.; Ahmadi, M.T.; Chek, D.C.Y.; Amin, N.A.; Ismail, R.

2010-01-01

Graphene nano ribbon (GNR) is a promising alternative to carbon nano tube (CNT) to overcome the chirality challenge as a nano scale device channel. Due to the one-dimensional behavior of plane GNR, the carrier statistic study is attractive. Research works have been done on carrier statistic study of GNR especially in the parabolic part of the band structure using Boltzmann approximation (nondegenerate regime). Based on the quantum confinement effect, we have improved the fundamental study in degenerate regime for both the parabolic and non parabolic parts of GNR band energy. Our results demonstrate that the band energy of GNR near to the minimum band energy is parabolic. In this part of the band structure, the Fermi-Dirac integrals are sufficient for the carrier concentration study. The Fermi energy showed the temperature-dependent behavior similar to any other one-dimensional device in nondegenerate regime. However in the degenerate regime, the normalized Fermi energy with respect to the band edge is a function of carrier concentration. The numerical solution of Fermi-Dirac integrals for non parabolic region, which is away from the minimum energy band structure of GNR, is also presented.

Effects of irregular two-dimensional and three-dimensional surface roughness in turbulent channel flows

International Nuclear Information System (INIS)

De Marchis, M.; Napoli, E.

2012-01-01

Highlights: ► 3D irregular rough surfaces produce higher effects than those observed over 2D. ► Effective slope is a geometrical parameter representative of the roughness effects. ► 3D rough surfaces enhance the turbulence isotropization. ► 2D and 3D irregular roughness partially support the wall similarity. ► Irregular rough surfaces shear some features with regular rough walls. - Abstract: Wall-resolved Large Eddy Simulation of fully developed turbulent channel flows over two different rough surfaces is performed to investigate on the effects of irregular 2D and 3D roughness on the turbulence. The two geometries are obtained through the superimposition of sinusoidal functions having random amplitudes and different wave lengths. In the 2D configuration the irregular shape in the longitudinal direction is replicated in the transverse one, while in the 3D case the sinusoidal functions are generated both in streamwise and spanwise directions. Both channel walls are roughened in such a way as to obtain surfaces with statistically equivalent roughness height, but different shapes. In order to compare the turbulence properties over the two rough walls and to analyse the differences with a smooth wall, the simulations are performed at the same Reynolds number Re τ = 395. The same mean roughness height h = 0.05δ (δ the half channel height) is used for the rough walls. The roughness function obtained with the 3D roughness is larger than in the 2D case, although the two walls share the same mean height. Thus, the considered irregular 3D roughness is more effective in reducing the flow velocity with respect to the 2D roughness, coherently with the literature results that identified a clear dependence of the roughness function on the effective slope (see ), higher in the generated 3D rough wall. The analysis of higher-order statistics shows that the effects of the roughness, independently on its two- or three-dimensional shape, are mainly confined in the inner

Selective growth of two-dimensional phosphorene on catalyst surface.

Science.gov (United States)

Qiu, L; Dong, J C; Ding, F

2018-02-01

Although the study of black phosphorene (BP) and its isomers has attracted enormous attention, the method of synthesizing high-quality samples in a large area is still pending. Here we explore the potential of using the chemical vapor deposition method to synthesize large-area two-dimensional (2D) phosphorene films on metal surfaces. Our ab initio calculations show that BP can be synthesized by using tin (Sn) as a catalyst, while one of its isomers, blue phosphorene (BLP), is very possible to be synthesized by using most other metals, such as Ag and Au. Besides, our study also suggests that the large binding energy between the 2D phosphorene and the active metal substrate may prohibit the exfoliation of the 2D phosphorene for real applications and, therefore, tin, silver and gold are predicted to be the most suitable catalysts for the synthesis of BP and BLP.

A Review of Surface Deformation and Strain Measurement Using Two-Dimensional Digital Image Correlation

Directory of Open Access Journals (Sweden)

Khoo Sze-Wei

2016-09-01

Full Text Available Among the full-field optical measurement methods, the Digital Image Correlation (DIC is one of the techniques which has been given particular attention. Technically, the DIC technique refers to a non-contact strain measurement method that mathematically compares the grey intensity changes of the images captured at two different states: before and after deformation. The measurement can be performed by numerically calculating the displacement of speckles which are deposited on the top of object’s surface. In this paper, the Two-Dimensional Digital Image Correlation (2D-DIC is presented and its fundamental concepts are discussed. Next, the development of the 2D-DIC algorithms in the past 33 years is reviewed systematically. The improvement of 2DDIC algorithms is presented with respect to two distinct aspects: their computation efficiency and measurement accuracy. Furthermore, analysis of the 2D-DIC accuracy is included, followed by a review of the DIC applications for two-dimensional measurements.

Zero-dimensional limit of the two-dimensional Lugiato-Lefever equation

Science.gov (United States)

Cardoso, Wesley B.; Salasnich, Luca; Malomed, Boris A.

2017-05-01

We study effects of tight harmonic-oscillator confinement on the electromagnetic field in a laser cavity by solving the two-dimensional Lugiato-Lefever (2D LL) equation, taking into account self-focusing or defocusing nonlinearity, losses, pump, and the trapping potential. Tightly confined (quasi-zero-dimensional) optical modes (pixels), produced by this model, are analyzed by means of the variational approximation, which provides a qualitative picture of the ensuing phenomena. This is followed by systematic simulations of the time-dependent 2D LL equation, which reveal the shape, stability, and dynamical behavior of the resulting localized patterns. In this way, we produce stability diagrams for the expected pixels. Then, we consider the LL model with the vortical pump, showing that it can produce stable pixels with embedded vorticity (vortex solitons) in remarkably broad stability areas. Alongside confined vortices with the simple single-ring structure, in the latter case the LL model gives rise to stable multi-ring states, with a spiral phase field. In addition to the numerical results, a qualitatively correct description of the vortex solitons is provided by the Thomas-Fermi approximation. Contribution to the Topical Issue: "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

Oscillating Casimir force between two slabs in a Fermi sea

DEFF Research Database (Denmark)

Li-Wei, Chen; Guo-Zhen, Su; Jin-Can, Chen

2012-01-01

that the Casimir force decreases monotonically with the increase of the separation L between two slabs in an electromagnetic field and a massive Bose gas, the Casimir force in a Fermi gas oscillates as a function of L. The Casimir force can be either attractive or repulsive, depending sensitively on the magnitude...... of L. In addition, it is found that the amplitude of the Casimir force in a Fermi gas decreases with the increase of the temperature, which also is contrary to the case in a Bose gas, since the bosonic Casimir force increases linearly with the increase of the temperature in the region T

Random packing of regular polygons and star polygons on a flat two-dimensional surface.

Science.gov (United States)

Cieśla, Michał; Barbasz, Jakub

2014-08-01

Random packing of unoriented regular polygons and star polygons on a two-dimensional flat continuous surface is studied numerically using random sequential adsorption algorithm. Obtained results are analyzed to determine the saturated random packing ratio as well as its density autocorrelation function. Additionally, the kinetics of packing growth and available surface function are measured. In general, stars give lower packing ratios than polygons, but when the number of vertexes is large enough, both shapes approach disks and, therefore, properties of their packing reproduce already known results for disks.

Effect of Cleaving Temperature on the Surface and Bulk Fermi Surface of Sr2RuO4 Investigated by High Resolution Angle-Resolved Photoemission

International Nuclear Information System (INIS)

Liu Shan-Yu; Zhang Wen-Tao; Weng Hong-Ming; Zhao Lin; Liu Hai-Yun; Jia Xiao-Wen; Liu Guo-Dong; Dong Xiao-Li; Zhang Jun; Dai Xi; Fang Zhong; Zhou Xing-Jiang; Mao Zhi-Qiang; Chen Chuang-Tian; Xu Zu-Yan

2012-01-01

High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr 2 RuO 4 . Unlike previous reports, which found that a high cleaving temperature can suppress the surface Fermi surface, we find that the surface Fermi surface remains obvious and strong in Sr 2 RuO 4 cleaved at high temperature, even at room temperature. This indicates that cleaving temperature is not a key effective factor in suppressing surface bands. On the other hand, the bulk bands can be enhanced in an aged surface of Sr 2 RuO 4 that has been cleaved and held for a long time. We have also carried out laser ARPES measurements on Sr 2 RuO 4 by using a vacuum ultra-violet laser (photon energy at 6.994 eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature. This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr 2 RuO 4 . In particular, the enhancement of bulk sensitivity, along with the super-high instrumental resolution of VUV laser ARPES, will be advantageous in investigating fine electronic structure and superconducting properties of Sr 2 RuO 4 in the future. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Numerical Simulations of Scattering of Light from Two-Dimensional Rough Surfaces Using the Reduced Rayleigh Equation

Directory of Open Access Journals (Sweden)

Tor eNordam

2013-09-01

Full Text Available A formalism is introduced for the non-perturbative, purely numerical, solution of the reduced Rayleigh equation for the scattering of light from two-dimensional penetrable rough surfaces. Implementation and performance issues of the method, and various consistency checks of it, are presented and discussed. The proposed method is found, within the validity of the Rayleigh hypothesis, to give reliable results. For a non-absorbing metal surface the conservation of energy was explicitly checked, and found to be satisfied to within 0.03%, or better, for the parameters assumed. This testifies to the accuracy of the approach and a satisfactory discretization. As an illustration, we calculate the full angular distribution of the mean differential reflection coefficient for the scattering of p- or s-polarized light incident on two-dimensional dielectric or metallic randomly rough surfaces defined by (isotropic or anisotropic Gaussian and cylindrical power spectra. Simulation results obtained by the proposed method agree well with experimentally measured scattering data taken from similar well-characterized, rough metal samples, or to results obtained by other numerical methods.

Absolute Negative Resistance Induced by Directional Electron-Electron Scattering in a Two-Dimensional Electron Gas

Science.gov (United States)

Kaya, Ismet I.; Eberl, Karl

2007-05-01

A three-terminal device formed by two electrostatic barriers crossing an asymmetrically patterned two-dimensional electron gas displays an unusual potential depression at the middle contact, yielding absolute negative resistance. The device displays momentum and current transfer ratios that far exceed unity. The observed reversal of the current or potential in the middle terminal can be interpreted as the analog of Bernoulli’s effect in a Fermi liquid. The results are explained by directional scattering of electrons in two dimensions.

Theory of thermionic emission from a two-dimensional conductor and its application to a graphene-semiconductor Schottky junction

Science.gov (United States)

Trushin, Maxim

2018-04-01

The standard theory of thermionic emission developed for three-dimensional semiconductors does not apply to two-dimensional materials even for making qualitative predictions because of the vanishing out-of-plane quasiparticle velocity. This study reveals the fundamental origin of the out-of-plane charge carrier motion in a two-dimensional conductor due to the finite quasiparticle lifetime and huge uncertainty of the out-of-plane momentum. The theory is applied to a Schottky junction between graphene and a bulk semiconductor to derive a thermionic constant, which, in contrast to the conventional Richardson constant, is determined by the Schottky barrier height and Fermi level in graphene.

Band structure and Fermi surface of UPd2Al3 studied by angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Fujimori, Shin-ichi; Saitoh, Yuji; Okane, Tetsuo; Yamagami, Hiroshi; Fujimori, Atsushi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

2007-01-01

We have observed the band structure and Fermi surfaces of the heavy Fermion superconductor UPd 2 Al 3 by angle-resolved photoemission experiments in the soft X-ray region. We observed renormalized quasi-particle bands in the vicinity of the Fermi level and strongly dispersive bands on the higher binding energy side. Our observation suggests that the structure previously assigned to contributions from localized states in the U 5f spectrum has strong energy dispersions

Surface acoustic waves in two dimensional phononic crystal with anisotropic inclusions

Directory of Open Access Journals (Sweden)

Ketata H.

2012-06-01

Full Text Available An analysis is given to the band structure of the two dimensional solid phononic crystal considered as a semi infinite medium. The lattice includes an array of elastic anisotropic materials with different shapes embedded in a uniform matrix. For illustration two kinds of phononic materials are assumed. A particular attention is devoted to the computational procedure which is mainly based on the plane wave expansion (PWE method. It has been adapted to Matlab environment. Numerical calculations of the dispersion curves have been achieved by introducing particular functions which transform motion equations into an Eigen value problem. Significant improvements are obtained by increasing reasonably the number of Fourier components even when a large elastic mismatch is assumed. Such approach can be generalized to different types of symmetry and permit new physical properties as piezoelectricity to be added. The actual semi infinite phononic structure with a free surface has been shown to support surface acoustic waves (SAW. The obtained dispersion curves reveal band gaps in the SAW branches. It has been found that the influence, of the filling factor and anisotropy on their band gaps, is different from that of bulk waves.

Two-dimensional transport of tokamak plasmas

International Nuclear Information System (INIS)

Hirshman, S.P.; Jardin, S.C.

1979-01-01

A reduced set of two-fluid transport equations is obtained from the conservation equations describing the time evolution of the differential particle number, entropy, and magnetic fluxes in an axisymmetric toroidal plasma with nested magnetic surfaces. Expanding in the small ratio of perpendicular to parallel mobilities and thermal conductivities yields as solubility constraints one-dimensional equations for the surface-averaged thermodynamic variables and magnetic fluxes. Since Ohm's law E +u x B =R', where R' accounts for any nonideal effects, only determines the particle flow relative to the diffusing magnetic surfaces, it is necessary to solve a single two-dimensional generalized differential equation, (partial/partialt) delpsi. (delp - J x B) =0, to find the absolute velocity of a magnetic surface enclosing a fixed toroidal flux. This equation is linear but nonstandard in that it involves flux surface averages of the unknown velocity. Specification of R' and the cross-field ion and electron heat fluxes provides a closed system of equations. A time-dependent coordinate transformation is used to describe the diffusion of plasma quantities through magnetic surfaces of changing shape

NbSe3: Fermi surface and magnetoresistance under uniaxial stress

International Nuclear Information System (INIS)

Tessema, G.X.; Gamble, B.K.; Kuh, J.; Skove, M.J.; Lacerda, A.H.; Bennett, M.

1999-01-01

The Fermi surface of NbSe 3 below the two CDW transitions is still not very clear. Large magnetoresistance and giant quantum oscillations have been seen at low temperature below the second CDW transition. The SdH oscillations are attributed to one or several small pieces of electron or hole pockets spared by the two CDW transitions at 145 and 59 K. In a previous low field study (μ 0 H<8 T) of the transverse magnetoresistance (H in the (b,c) plane) we have shown that the extremal area of one of these pockets decreases linearly with strain, ε, vanishing at ε = 2.5%. Here we extend our study into the high magnetic field regime (pulsed 60 T) and investigate the effect of uniaxial stress on the magnetoresistance (I//H). Our high field study is consistent with the fermiology study and shows that uniaxial stress leads to the obliteration of a small closed pocket. Above 1% strain the magnetoresistance is linear with H with no sign of saturation. (orig.)

Oxygen dosing the surface of SrTiO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Dudy, L.; Scheiderer, P.; Schuetz, P.; Gabel, J.; Buchwald, M.; Sing, M.; Claessen, R. [Physikalisches Institut, Universitaet Wuerzburg (Germany); Denlinger, J.D. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94270 (United States); Schlueter, C.; Lee, T.L. [Diamond Light Source Ltd., Didcot, Oxfordshire (United Kingdom)

2015-07-01

The highly mobile two-dimensional electron system (2DES) on the surface of the insulating SrTiO{sub 3}(STO) offers exciting perspectives for advanced material design. This 2DES resides in a depletion layer caused by oxygen deficiency of the surface. With photoemission spectroscopy, we monitor the appearance of quasi-particle weight (QP) at the Fermi energy and oxygen vacancy induced states in the band gap (IG). Both, QP and IG weight, increase and decrease respectively upon exposure to extreme ultraviolet (XUV) light and in-situ oxygen dosing. By a proper adjustment of oxygen dosing, any intermediate state can be stabilized providing full control over the charge carrier density. From a comparison of the charge carrier concentrations obtained from an analysis of core-level spectra and the Fermi-surface volume, we conclude on a spatially inhomogeneous surface electronic structure with at least two different phases.

Few helium atoms in quasi two-dimensional space

International Nuclear Information System (INIS)

Kilic, Srecko; Vranjes, Leandra

2003-01-01

Two, three and four 3 He and 4 He atoms in quasi two-dimensional space above graphite and cesium surfaces and in 'harmonic' potential perpendicular to the surface have been studied. Using some previously examined variational wave functions and the Diffusion Monte Carlo procedure, it has been shown that all molecules: dimers, trimers and tetramers, are bound more strongly than in pure two- and three-dimensional space. The enhancement of binding with respect to unrestricted space is more pronounced on cesium than on graphite. Furthermore, for 3 He 3 ( 3 He 4 ) on all studied surfaces, there is an indication that the configuration of a dimer and a 'free' particle (two dimers) may be equivalently established

Fermi arc mediated entropy transport in topological semimetals

Science.gov (United States)

McCormick, Timothy M.; Watzman, Sarah J.; Heremans, Joseph P.; Trivedi, Nandini

2018-05-01

The low-energy excitations of topological Weyl semimetals are composed of linearly dispersing Weyl fermions that act as monopoles of Berry curvature in the bulk momentum space. Furthermore, on the surface there exist topologically protected Fermi arcs at the projections of these Weyl points. We propose a pathway for entropy transport involving Fermi arcs on one surface connecting to Fermi arcs on the other surface via the bulk Weyl monopoles. We present results for the temperature and magnetic field dependence of the magnetothermal conductance of this conveyor belt channel. The circulating currents result in a net entropy transport without any net charge transport. We provide results for the Fermi arc mediated magnetothermal conductivity in the low-field semiclassical limit as well as in the high-field ultraquantum limit, where only chiral Landau levels are involved. Our work provides a proposed signature of Fermi arc mediated magnetothermal transport and sets the stage for utilizing and manipulating the topological Fermi arcs in thermal applications.

Faraday waves in quasi-one-dimensional superfluid Fermi-Bose mixtures

DEFF Research Database (Denmark)

Abdullaev, F. Kh.; Ögren, Magnus; Sørensen, Mads Peter

2013-01-01

The generation of Faraday waves in superfluid Fermi-Bose mixtures in elongated traps is investigated. The generation of waves is achieved by periodically changing a parameter of the system in time. Two types of modulations of parameters are considered: a variation of the fermion-boson scattering...... length and the boson-boson scattering length. We predict the properties of the generated Faraday patterns and study the parameter regions where they can be excited....

Two dimensional simulation of high power laser-surface interaction

International Nuclear Information System (INIS)

Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P.; Busch, G.E.

1998-01-01

For laser intensities in the range of 10 8 --10 9 W/cm 2 , and pulse lengths of order 10 microsec or longer, the authors have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of their treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. The authors will present an analysis of some relatively well diagnosed experiments which have been useful in developing their modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence their simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range. This work is useful in many technical areas such as materials processing

Two-dimensional potential and charge distributions of positive surface streamer

International Nuclear Information System (INIS)

Tanaka, Daiki; Matsuoka, Shigeyasu; Kumada, Akiko; Hidaka, Kunihiko

2009-01-01

Information on the potential and the field profile along a surface discharge is required for quantitatively discussing and clarifying the propagation mechanism. The sensing technique with a Pockels crystal has been developed for directly measuring the potential and electric field distribution on a dielectric material. In this paper, the Pockels sensing system consists of a pulse laser and a CCD camera for measuring the instantaneous two-dimensional potential distribution on a 25.4 mm square area with a 50 μm sampling pitch. The temporal resolution is 3.2 ns which is determined by the pulse width of the laser emission. The transient change in the potential distribution of a positive surface streamer propagating in atmospheric air is measured with this system. The electric field and the charge distributions are also calculated from the measured potential profile. The propagating direction component of the electric field near the tip of the propagating streamer reaches 3 kV mm -1 . When the streamer stops, the potential distribution along a streamer forms an almost linear profile with the distance from the electrode, and its gradient is about 0.5 kV mm -1 .

Consistent calculation of the stopping power for slow ions in two-dimensional electron gases

International Nuclear Information System (INIS)

Wang, You-Nian; Ma, Teng-Gai

1997-01-01

Within the framework of quantum scattering theory, we present a consistent calculation of the stopping power for slow protons and antiprotons moving in two-dimensional electron gases. The Friedel sum rule is used to determine the screening constant in the scattering potential. For the stopping power our results are compared with that of the random-phase approximation dielectric theory and that predicted by the linear Thomas-Fermi potential. copyright 1997 The American Physical Society

Positron study of electron momentum density and Fermi surface in titanium and zirconium

International Nuclear Information System (INIS)

Suzuki, Ryoichi; Osawa, Makoto; Tanigawa, Shoichiro; Matsumoto, Makoto; Shiotani, Nobuhiro.

1989-01-01

The three dimensional electron-positron momentum densities have been obtained on Ti and Zr from measurements of two dimensional angular correlation of positron annihilation radiation followed by an image reconstruction technique based on direct Fourier transformation. Augmented-plane wave band structure calculations have been carried out and the results are compared with the experiments. Agreement between the experiment and the theory leads to a conclusion that both Ti and Zr have electron surface sheets which are centered at H and hole surface sheets which are running along the Γ-A axis. (author)

Weyl states and Fermi arcs in parabolic bands

Science.gov (United States)

Doria, Mauro M.; Perali, Andrea

2017-07-01

Weyl fermions are shown to exist inside a parabolic band in a single electronic layer, where the kinetic energy of carriers is given by the non-relativistic Schroedinger equation. There are Fermi arcs as a direct consequence of the folding of a ring-shaped Fermi surface inside the first Brillouin zone. Our results stem from the decomposition of the kinetic energy into the sum of the square of the Weyl state, the coupling to the local magnetic field and the Rashba interaction. The Weyl fermions break the space and time reflection symmetries present in the kinetic energy, thus allowing for the onset of a weak three-dimensional magnetic field around the layer. This field brings topological stability to the current-carrying states through a Chern number. In the special limit for which the Weyl state becomes gapless, this magnetic interaction is shown to be purely attractive, thus suggesting the onset of a superconducting condensate of zero helicity states.

Wetting characteristics of 3-dimensional nanostructured fractal surfaces

Energy Technology Data Exchange (ETDEWEB)

Davis, Ethan, E-mail: ethan.davis4@huskers.unl.edu [Nano & Microsystems Research Laboratory, Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526 (United States); Liu, Ying; Jiang, Lijia; Lu, Yongfeng [Laser Assisted Nano Engineering Lab, Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, 209N Scott Engineering Center, Lincoln, NE 68588-0511 (United States); Ndao, Sidy, E-mail: sndao2@unl.edu [Nano & Microsystems Research Laboratory, Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526 (United States)

2017-01-15

Highlights: • Hierarchically structured surfaces were fabricated on the micro/nano-scale. • These structures reduced the contact angle of the inherently hydrophilic material. • Similar surfaces have applications in two-phase heat transfer and microfluidics. - Abstract: This article reports the fabrication and wetting characteristics of 3-dimensional nanostructured fractal surfaces (3DNFS). Three distinct 3DNFS surfaces, namely cubic, Romanesco broccoli, and sphereflake were fabricated using two-photon direct laser writing. Contact angle measurements were performed on the multiscale fractal surfaces to characterize their wetting properties. Average contact angles ranged from 66.8° for the smooth control surface to 0° for one of the fractal surfaces. The change in wetting behavior was attributed to modification of the interfacial surface properties due to the inclusion of 3-dimensional hierarchical fractal nanostructures. However, this behavior does not exactly obey existing surface wetting models in the literature. Potential applications for these types of surfaces in physical and biological sciences are also discussed.

Wetting characteristics of 3-dimensional nanostructured fractal surfaces

International Nuclear Information System (INIS)

Davis, Ethan; Liu, Ying; Jiang, Lijia; Lu, Yongfeng; Ndao, Sidy

2017-01-01

Highlights: • Hierarchically structured surfaces were fabricated on the micro/nano-scale. • These structures reduced the contact angle of the inherently hydrophilic material. • Similar surfaces have applications in two-phase heat transfer and microfluidics. - Abstract: This article reports the fabrication and wetting characteristics of 3-dimensional nanostructured fractal surfaces (3DNFS). Three distinct 3DNFS surfaces, namely cubic, Romanesco broccoli, and sphereflake were fabricated using two-photon direct laser writing. Contact angle measurements were performed on the multiscale fractal surfaces to characterize their wetting properties. Average contact angles ranged from 66.8° for the smooth control surface to 0° for one of the fractal surfaces. The change in wetting behavior was attributed to modification of the interfacial surface properties due to the inclusion of 3-dimensional hierarchical fractal nanostructures. However, this behavior does not exactly obey existing surface wetting models in the literature. Potential applications for these types of surfaces in physical and biological sciences are also discussed.

Engineering topological phases with a three-dimensional nodal-loop semimetal

Science.gov (United States)

Li, Linhu; Yap, Han Hoe; Araújo, Miguel A. N.; Gong, Jiangbin

2017-12-01

A three-dimensional (3D) nodal-loop semimetal phase is exploited to engineer a number of intriguing phases featuring different peculiar topological surface states. In particular, by introducing various two-dimensional gap terms to a 3D tight-binding model of a nodal-loop semimetal, we obtain a rich variety of topological phases of great interest to ongoing theoretical and experimental studies, including a chiral insulator, degenerate-surface-loop insulator, and second-order topological insulator, as well as a Weyl semimetal with tunable Fermi arc profiles. The unique concept underlying our approach is to engineer topological surface states that inherit their dispersion relations from a gap term. The results provide one rather unified principle for the creation of novel topological phases and can guide the search for new topological materials. Two-terminal transport studies are also carried out to distinguish the engineered topological phases.

Effects of stratospheric aerosol surface processes on the LLNL two-dimensional zonally averaged model

International Nuclear Information System (INIS)

Connell, P.S.; Kinnison, D.E.; Wuebbles, D.J.; Burley, J.D.; Johnston, H.S.

1992-01-01

We have investigated the effects of incorporating representations of heterogeneous chemical processes associated with stratospheric sulfuric acid aerosol into the LLNL two-dimensional, zonally averaged, model of the troposphere and stratosphere. Using distributions of aerosol surface area and volume density derived from SAGE 11 satellite observations, we were primarily interested in changes in partitioning within the Cl- and N- families in the lower stratosphere, compared to a model including only gas phase photochemical reactions

Two-color Fermi-liquid theory for transport through a multilevel Kondo impurity

Science.gov (United States)

Karki, D. B.; Mora, Christophe; von Delft, Jan; Kiselev, Mikhail N.

2018-05-01

We consider a quantum dot with K ≥2 orbital levels occupied by two electrons connected to two electric terminals. The generic model is given by a multilevel Anderson Hamiltonian. The weak-coupling theory at the particle-hole symmetric point is governed by a two-channel S =1 Kondo model characterized by intrinsic channels asymmetry. Based on a conformal field theory approach we derived an effective Hamiltonian at a strong-coupling fixed point. The Hamiltonian capturing the low-energy physics of a two-stage Kondo screening represents the quantum impurity by a two-color local Fermi liquid. Using nonequilibrium (Keldysh) perturbation theory around the strong-coupling fixed point we analyze the transport properties of the model at finite temperature, Zeeman magnetic field, and source-drain voltage applied across the quantum dot. We compute the Fermi-liquid transport constants and discuss different universality classes associated with emergent symmetries.

Two-dimensional Si nanosheets with local hexagonal structure on a MoS(2) surface.

Science.gov (United States)

Chiappe, Daniele; Scalise, Emilio; Cinquanta, Eugenio; Grazianetti, Carlo; van den Broek, Bas; Fanciulli, Marco; Houssa, Michel; Molle, Alessandro

2014-04-02

The structural and electronic properties of a Si nanosheet (NS) grown onto a MoS2 substrate by means of molecular beam epitaxy are assessed. Epitaxially grown Si is shown to adapt to the trigonal prismatic surface lattice of MoS2 by forming two-dimensional nanodomains. The Si layer structure is distinguished from the underlying MoS2 surface structure. The local electronic properties of the Si nanosheet are dictated by the atomistic arrangement of the layer and unlike the MoS2 hosting substrate they are qualified by a gap-less density of states. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-dimensional orthonormal trend surfaces for prospecting

Science.gov (United States)

Sarma, D. D.; Selvaraj, J. B.

Orthonormal polynomials have distinct advantages over conventional polynomials: the equations for evaluating trend coefficients are not ill-conditioned and the convergence power of this method is greater compared to the least-squares approximation and therefore the approach by orthonormal functions provides a powerful alternative to the least-squares method. In this paper, orthonormal polynomials in two dimensions are obtained using the Gram-Schmidt method for a polynomial series of the type: Z = 1 + x + y + x2 + xy + y2 + … + yn, where x and y are the locational coordinates and Z is the value of the variable under consideration. Trend-surface analysis, which has wide applications in prospecting, has been carried out using the orthonormal polynomial approach for two sample sets of data from India concerned with gold accumulation from the Kolar Gold Field, and gravity data. A comparison of the orthonormal polynomial trend surfaces with those obtained by the classical least-squares method has been made for the two data sets. In both the situations, the orthonormal polynomial surfaces gave an improved fit to the data. A flowchart and a FORTRAN-IV computer program for deriving orthonormal polynomials of any order and for using them to fit trend surfaces is included. The program has provision for logarithmic transformation of the Z variable. If log-transformation is performed the predicted Z values are reconverted to the original units and the trend-surface map generated for use. The illustration of gold assay data related to the Champion lode system of Kolar Gold Fields, for which a 9th-degree orthonormal trend surface was fit, could be used for further prospecting the area.

Bright solitons in Bose-Fermi mixtures

International Nuclear Information System (INIS)

Karpiuk, Tomasz; Brewczyk, Miroslaw; RzaPewski, Kazimierz

2006-01-01

We consider the formation of bright solitons in a mixture of Bose and Fermi degenerate gases confined in a three-dimensional elongated harmonic trap. The Bose and Fermi atoms are assumed to effectively attract each other whereas bosonic atoms repel each other. Strong enough attraction between bosonic and fermionic components can change the character of the interaction within the bosonic cloud from repulsive to attractive making thus possible the generation of bright solitons in the mixture. On the other hand, such structures might be in danger due to the collapse phenomenon existing in attractive gases. We show, however, that under some conditions (defined by the strength of the Bose-Fermi components attraction) the structures which neither spread nor collapse can be generated. For elongated enough traps the formation of solitons is possible even at the 'natural' value of the mutual Bose-Fermi ( 87 Rb- 40 K in our case) scattering length

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Science.gov (United States)

Terashima, Taichi; Hirose, Hishiro T.; Graf, David; Ma, Yonghui; Mu, Gang; Hu, Tao; Suzuki, Katsuhiro; Uji, Shinya; Ikeda, Hiroaki

2018-02-01

Despite the fact that 1111-type iron arsenides hold the record transition temperature of iron-based superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we comprehensively determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase π . The carrier density is of the order of 10-3 per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-B magnetoresistance and an anomalous resistivity increase above about 30 T for B ∥c , the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase (T >118 K ), which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds.

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Directory of Open Access Journals (Sweden)

Taichi Terashima

2018-02-01

Full Text Available Despite the fact that 1111-type iron arsenides hold the record transition temperature of iron-based superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we comprehensively determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase π. The carrier density is of the order of 10^{-3} per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-B magnetoresistance and an anomalous resistivity increase above about 30 T for B∥c, the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase (T>118  K, which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds.

Fermi liquids from D-branes

OpenAIRE

Moshe RozaliDepartment of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada; Darren Smyth(Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada)

2014-01-01

We discuss finite density configurations on probe D-branes, in the presence of worldvolume fermions. To this end we consider a phenomenological model whose bosonic sector is governed by the DBI action, and whose charged sector is purely fermionic. In this model, we demonstrate the existence of a compact worldvolume embedding, stabilized by a Fermi surface on the D- brane. The finite density state in the boundary QFT is a Fermi-like liquid. We comment on the possibility of realizing non-Fermi ...

Three-dimensional instability of standing waves

Science.gov (United States)

Zhu, Qiang; Liu, Yuming; Yue, Dick K. P.

2003-12-01

We investigate the three-dimensional instability of finite-amplitude standing surface waves under the influence of gravity. The analysis employs the transition matrix (TM) approach and uses a new high-order spectral element (HOSE) method for computation of the nonlinear wave dynamics. HOSE is an extension of the original high-order spectral method (HOS) wherein nonlinear wave wave and wave body interactions are retained up to high order in wave steepness. Instead of global basis functions in HOS, however, HOSE employs spectral elements to allow for complex free-surface geometries and surface-piercing bodies. Exponential convergence of HOS with respect to the total number of spectral modes (for a fixed number of elements) and interaction order is retained in HOSE. In this study, we use TM-HOSE to obtain the stability of general three-dimensional perturbations (on a two-dimensional surface) on two classes of standing waves: plane standing waves in a rectangular tank; and radial/azimuthal standing waves in a circular basin. For plane standing waves, we confirm the known result of two-dimensional side-bandlike instability. In addition, we find a novel three-dimensional instability for base flow of any amplitude. The dominant component of the unstable disturbance is an oblique (standing) wave oriented at an arbitrary angle whose frequency is close to the (nonlinear) frequency of the original standing wave. This finding is confirmed by direct long-time simulations using HOSE which show that the nonlinear evolution leads to classical Fermi Pasta Ulam recurrence. For the circular basin, we find that, beyond a threshold wave steepness, a standing wave (of nonlinear frequency Omega) is unstable to three-dimensional perturbations. The unstable perturbation contains two dominant (standing-wave) components, the sum of whose frequencies is close to 2Omega. From the cases we consider, the critical wave steepness is found to generally decrease/increase with increasing radial

Three dimensional imaging of surface geometry in SEM

International Nuclear Information System (INIS)

Slowko, W.

1997-01-01

A great advantage of scanning electron microscopy (SEM) is its ability of the surface topography in the way as a human eye is accustomed to see lights and shadows on macroobjects. However, SEM's can hardly display vertical dimensions of the structures. One of possible solutions is reconstruction of the surface profiles by directional detection of secondary electrons and proper signal processing. However, the surface profile still gives two dimensional information and the method should be extended to obtain fully three dimensional imaging. The extension consists in a simultaneous reconstruction of the surface profiles in two perpendicular directions (x and y) and their superposition. The solution proposed is based on a quadrupole detector system and a computer or analogue system for signal processing. Quantitative data of the surface topography can be displayed in many manners in the system of two or three co-ordinates with use of pseudo-colour for the altitude coding. (author)

High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

Science.gov (United States)

Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

2015-12-01

In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

A waveless two-dimensional flow in a channel against an inclined wall with surface tension effect

International Nuclear Information System (INIS)

Merzougui, Abdelkrim; Mekias, Hocine; Guechi, Fairouz

2007-01-01

Surface tension effect on a two-dimensional channel flow against an inclined wall is considered. The flow is assumed to be steady, irrotational, inviscid and incompressible. The effect of surface tension is taken into account and the effect of gravity is neglected. Numerical solutions are obtained via series truncation procedure. The problem is solved numerically for various values of the Weber number α and for various values of the inclination angle β between the horizontal bottom and the inclined wall

A waveless two-dimensional flow in a channel against an inclined wall with surface tension effect

Energy Technology Data Exchange (ETDEWEB)

Merzougui, Abdelkrim [Departement de Mathematiques, Faculte des sciences, Universite Mohamed Boudiaf, M' sila, 28000 (Algeria); Mekias, Hocine [Departement de Mathematiques, Faculte des sciences, Universite Farhat Abbas Setif 19000 (Algeria); Guechi, Fairouz [Departement de Mathematiques, Faculte des sciences, Universite Farhat Abbas Setif 19000 (Algeria)

2007-11-23

Surface tension effect on a two-dimensional channel flow against an inclined wall is considered. The flow is assumed to be steady, irrotational, inviscid and incompressible. The effect of surface tension is taken into account and the effect of gravity is neglected. Numerical solutions are obtained via series truncation procedure. The problem is solved numerically for various values of the Weber number {alpha} and for various values of the inclination angle {beta} between the horizontal bottom and the inclined wall.

Fulde-Ferrell-Like Molecular States in Spin-Orbit Coupled Ultracold Fermi Gases

Science.gov (United States)

Ye, Chong; Fu, Li-Bin

2017-08-01

We study the molecular state in three-component Fermi gases with a single impurity of 6 Li immersing in a no-interacting Fermi sea of 40 K in the presence of an equal weight combination of Rashba-type and Dresselhaus-type spin-orbit coupling. In the region where the Fermi sea has two disjointed Fermi surfaces, we find that there are two Fulde-Ferrell-like molecular states with dominating contributions from the lower helicity branch. Decreasing the scattering length or the spin-orbit coupled Fermi energy, we find the Fulde-Ferrell-like molecular state with small center-of-mass momentum is always energy favored and the other one will suddenly disappear. Supported by the National Basic Research Program of China (973 Program) under Grant Nos. 2013CBA01502, 2013CB834100, and the National Natural Science Foundation of China under Grant Nos. 11374040, 11475027, 11575027, 11274051, and 11075020

Wetting characteristics of 3-dimensional nanostructured fractal surfaces

Science.gov (United States)

Davis, Ethan; Liu, Ying; Jiang, Lijia; Lu, Yongfeng; Ndao, Sidy

2017-01-01

This article reports the fabrication and wetting characteristics of 3-dimensional nanostructured fractal surfaces (3DNFS). Three distinct 3DNFS surfaces, namely cubic, Romanesco broccoli, and sphereflake were fabricated using two-photon direct laser writing. Contact angle measurements were performed on the multiscale fractal surfaces to characterize their wetting properties. Average contact angles ranged from 66.8° for the smooth control surface to 0° for one of the fractal surfaces. The change in wetting behavior was attributed to modification of the interfacial surface properties due to the inclusion of 3-dimensional hierarchical fractal nanostructures. However, this behavior does not exactly obey existing surface wetting models in the literature. Potential applications for these types of surfaces in physical and biological sciences are also discussed.

Positron two-dimensional angular-correlation-of-annihilation-radiation study of untwinned YBa2Cu3O6.9 in the a-axis projection

International Nuclear Information System (INIS)

Smedskjaer, L.C.; Bansil, A.; Welp, U.; Fang, Y.; Bailey, K.G.

1992-01-01

We present a two-dimensional (2D)-ACAR positron annihilation study of an untwinned YBa 2 Cu 3 O 6.9 metallic sample in the a-axis projection; all existing data from untwinned samples have employed the c projection. The data show a clear presence of the Cu-O chain related ridge Fermi surface extending along the ΓZ direction and two associated umklapp images at higher momenta. These results are consistent with the previously investigated c projection of the momentum density in YBa 2 Cu 3 O 6.9 and do not appear to indicate a strong localization of these electron states along the c direction. We compare and contrast the structures in 2D-ACAR's in the a and c projections, delineating similarities and differences between the results for the two projections

One-dimensional electron liquid at a surface. Gold nanowires on Ge(001)

Energy Technology Data Exchange (ETDEWEB)

Blumenstein, Christian

2012-09-11

Self-organized nanowires at semiconductor surfaces offer the unique opportunity to study electrons in reduced dimensions. Notably the dimensionality of the system determines it's electronic properties, beyond the quasiparticle description. In the quasi-one-dimensional (1D) regime with weak lateral coupling between the chains, a Peierls instability can be realized. A nesting condition in the Fermi surface leads to a backfolding of the 1D electron band and thus to an insulating state. It is accompanied by a charge density wave (CDW) in real space that corresponds to the nesting vector. This effect has been claimed to occur in many surface-defined nanowire systems, such as the In chains on Si(111) or the Au reconstructions on the terraced Si(553) and Si(557) surfaces. Therefore a weak coupling between the nanowires in these systems has to be concluded. However theory proposes another state in the perfect 1D limit, which is completely destroyed upon slight coupling to higher dimensions. In this so-called Tomonaga-Luttinger liquid (TLL) state, the quasiparticle description of the Fermi liquid breaks down. Since the interaction between the electrons is enhanced due to the strong confinement, only collective excitations are allowed. This leads to novel effects like spin charge separation, where spin and charge degrees of freedom are decoupled and allowed to travel independently along the 1D-chain. Such rare state has not been realized at a surface until today. This thesis uses a novel approach to realize nanowires with improved confinement by studying the Au reconstructed Ge(001) surface. A new cleaning procedure using piranha solution is presented, in order to prepare a clean and long-range ordered substrate. To ensure optimal growth of the Au nanowires the phase diagram is extensively studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The structural elements of the chains are revealed and described in high detail. Remarkably

Two-dimensional linear elasticity theory of magneto-electro-elastic plates considering surface and nonlocal effects for nanoscale device applications

Science.gov (United States)

Wang, Wenjun; Li, Peng; Jin, Feng

2016-09-01

A novel two-dimensional linear elastic theory of magneto-electro-elastic (MEE) plates, considering both surface and nonlocal effects, is established for the first time based on Hamilton’s principle and the Lee plate theory. The equations derived are more general, suitable for static and dynamic analyses, and can also be reduced to the piezoelectric, piezomagnetic, and elastic cases. As a specific application example, the influences of the surface and nonlocal effects, poling directions, piezoelectric phase materials, volume fraction, damping, and applied magnetic field (i.e., constant applied magnetic field and time-harmonic applied magnetic field) on the magnetoelectric (ME) coupling effects are first investigated based on the established two-dimensional plate theory. The results show that the ME coupling coefficient has an obvious size-dependent characteristic owing to the surface effects, and the surface effects increase the ME coupling effects significantly when the plate thickness decreases to its critical thickness. Below this critical thickness, the size-dependent effect is obvious and must be considered. In addition, the output power density of a magnetic energy nanoharvester is also evaluated using the two-dimensional plate theory obtained, with the results showing that a relatively larger output power density can be achieved at the nanoscale. This study provides a mathematical tool which can be used to analyze the mechanical properties of nanostructures theoretically and numerically, as well as evaluating the size effect qualitatively and quantitatively.

Fermi surface of a disordered Cu-Al -alloy single crystal studied by high-resolution Compton scattering and electron diffraction

Science.gov (United States)

Kwiatkowska, J.; Maniawski, F.; Matsumoto, I.; Kawata, H.; Shiotani, N.; Lityńska, L.; Kaprzyk, S.; Bansil, A.

2004-08-01

We have measured high resolution Compton scattering profiles for momentum transfer along a series of 28 independent directions from Cu0.842Al0.158 disordered alloy single crystals with normals to the surfaces oriented along the [100], [110], and [111] directions. The experimental spectra are interpreted via parallel first-principles KKR-CPA (Korringa-Kohn-Rostoker coherent-potential approximation) computations of these directional profiles. The Fermi surface determined by inverting the Compton data is found to be in good agreement with the KKR-CPA predictions. An electron diffraction study of the present Cu0.842Al0.158 sample is additionally undertaken to gain insight into short-range ordering effects. The scattering pattern displays not only the familiar diffuse scattering peaks, but also shows the presence of weak streaks interconnecting the four diffuse scattering spots around the (110) reciprocal lattice points. This study provides a comprehensive picture of the evolution of the shape of the Fermi surface of Cu with the addition of Al . Our results are consistent with the notion that Fermi surface nesting is an important factor in driving short-range ordering effects in disordered alloys.

ChromAlign: A two-step algorithmic procedure for time alignment of three-dimensional LC-MS chromatographic surfaces.

Science.gov (United States)

Sadygov, Rovshan G; Maroto, Fernando Martin; Hühmer, Andreas F R

2006-12-15

We present an algorithmic approach to align three-dimensional chromatographic surfaces of LC-MS data of complex mixture samples. The approach consists of two steps. In the first step, we prealign chromatographic profiles: two-dimensional projections of chromatographic surfaces. This is accomplished by correlation analysis using fast Fourier transforms. In this step, a temporal offset that maximizes the overlap and dot product between two chromatographic profiles is determined. In the second step, the algorithm generates correlation matrix elements between full mass scans of the reference and sample chromatographic surfaces. The temporal offset from the first step indicates a range of the mass scans that are possibly correlated, then the correlation matrix is calculated only for these mass scans. The correlation matrix carries information on highly correlated scans, but it does not itself determine the scan or time alignment. Alignment is determined as a path in the correlation matrix that maximizes the sum of the correlation matrix elements. The computational complexity of the optimal path generation problem is reduced by the use of dynamic programming. The program produces time-aligned surfaces. The use of the temporal offset from the first step in the second step reduces the computation time for generating the correlation matrix and speeds up the process. The algorithm has been implemented in a program, ChromAlign, developed in C++ language for the .NET2 environment in WINDOWS XP. In this work, we demonstrate the applications of ChromAlign to alignment of LC-MS surfaces of several datasets: a mixture of known proteins, samples from digests of surface proteins of T-cells, and samples prepared from digests of cerebrospinal fluid. ChromAlign accurately aligns the LC-MS surfaces we studied. In these examples, we discuss various aspects of the alignment by ChromAlign, such as constant time axis shifts and warping of chromatographic surfaces.

Transference of Fermi Contour Anisotropy to Composite Fermions.

Science.gov (United States)

Jo, Insun; Rosales, K A Villegas; Mueed, M A; Pfeiffer, L N; West, K W; Baldwin, K W; Winkler, R; Padmanabhan, Medini; Shayegan, M

2017-07-07

There has been a surge of recent interest in the role of anisotropy in interaction-induced phenomena in two-dimensional (2D) charged carrier systems. A fundamental question is how an anisotropy in the energy-band structure of the carriers at zero magnetic field affects the properties of the interacting particles at high fields, in particular of the composite fermions (CFs) and the fractional quantum Hall states (FQHSs). We demonstrate here tunable anisotropy for holes and hole-flux CFs confined to GaAs quantum wells, via applying in situ in-plane strain and measuring their Fermi wave vector anisotropy through commensurability oscillations. For strains on the order of 10^{-4} we observe significant deformations of the shapes of the Fermi contours for both holes and CFs. The measured Fermi contour anisotropy for CFs at high magnetic field (α_{CF}) is less than the anisotropy of their low-field hole (fermion) counterparts (α_{F}), and closely follows the relation α_{CF}=sqrt[α_{F}]. The energy gap measured for the ν=2/3 FQHS, on the other hand, is nearly unaffected by the Fermi contour anisotropy up to α_{F}∼3.3, the highest anisotropy achieved in our experiments.

Fermi Surface Manipulation by External Magnetic Field Demonstrated for a Prototypical Ferromagnet

Directory of Open Access Journals (Sweden)

E. Młyńczak

2016-12-01

Full Text Available We consider the details of the near-surface electronic band structure of a prototypical ferromagnet, Fe(001. Using high-resolution angle-resolved photoemission spectroscopy, we demonstrate openings of the spin-orbit-induced electronic band gaps near the Fermi level. The band gaps, and thus the Fermi surface, can be manipulated by changing the remanent magnetization direction. The effect is of the order of ΔE=100  meV and Δk=0.1  Å^{−1}. We show that the observed dispersions are dominated by the bulk band structure. First-principles calculations and one-step photoemission calculations suggest that the effect is related to changes in the electronic ground state and not caused by the photoemission process itself. The symmetry of the effect indicates that the observed electronic bulk states are influenced by the presence of the surface, which might be understood as related to a Rashba-type effect. By pinpointing the regions in the electronic band structure where the switchable band gaps occur, we demonstrate the significance of spin-orbit interaction even for elements as light as 3d ferromagnets. These results set a new paradigm for the investigations of spin-orbit effects in the spintronic materials. The same methodology could be used in the bottom-up design of the devices based on the switching of spin-orbit gaps such as electric-field control of magnetic anisotropy or tunneling anisotropic magnetoresistance.

Two-loop anomalous dimensions for four-Fermi operators in supersymmetric theories

Directory of Open Access Journals (Sweden)

Junji Hisano

2017-09-01

Full Text Available We derive two-loop anomalous dimensions for four-Fermi operators in supersymmetric theories using the effective Kähler potential. We introduce the general forms in generic gauge theories and apply our results to the flavor-changing operators in (minimal supersymmetric standard models.

Quantum criticality of one-dimensional multicomponent Fermi gas with strongly attractive interaction

International Nuclear Information System (INIS)

He, Peng; Jiang, Yuzhu; Guan, Xiwen; He, Jinyu

2015-01-01

Quantum criticality of strongly attractive Fermi gas with SU(3) symmetry in one dimension is studied via the thermodynamic Bethe ansatz (TBA) equations. The phase transitions driven by the chemical potential μ, effective magnetic field H 1 , H 2 (chemical potential biases) are analyzed at the quantum criticality. The phase diagram and critical fields are analytically determined by the TBA equations in the zero temperature limit. High accurate equations of state, scaling functions are also obtained analytically for the strong interacting gases. The dynamic exponent z=2 and correlation length exponent ν=1/2 read off the universal scaling form. It turns out that the quantum criticality of the three-component gases involves a sudden change of density of states of one cluster state, two or three cluster states. In general, this method can be adapted to deal with the quantum criticality of multicomponent Fermi gases with SU(N) symmetry. (paper)

Fermi Surfaces in the Antiferromagnetic, Paramagnetic and Polarized Paramagnetic States of CeRh2Si2 Compared with Quantum Oscillation Experiments

Science.gov (United States)

Pourret, Alexandre; Suzuki, Michi-To; Palaccio Morales, Alexandra; Seyfarth, Gabriel; Knebel, Georg; Aoki, Dai; Flouquet, Jacques

2017-08-01

The large quantum oscillations observed in the thermoelectric power in the antiferromagnetic (AF) state of the heavy-fermion compound CeRh2Si2 disappear suddenly when entering in the polarized paramagnetic (PPM) state at Hc ˜ 26.5 T, indicating an abrupt reconstruction of the Fermi surface. The electronic band structure was calculated using [LDA+U] for the AF state taking the correct magnetic structure into account, for the PPM state, and for the paramagnetic state (PM). Different Fermi surfaces were obtained for the AF, PM, and PPM states. Due to band folding, a large number of branches was expected and observed in the AF state. The LDA+U calculation was compared with the previous LDA calculations. Furthermore, we compared both calculations with previously published de Haas-van Alphen experiments. The better agreement with the LDA approach suggests that above the critical pressure pc CeRh2Si2 enters in a mixed-valence state. In the PPM state under a high magnetic field, the 4f contribution at the Fermi level EF drops significantly compared with that in the PM state, and the 4f electrons contribute only weakly to the Fermi surface in our approach.

Thermodynamic properties of ideal Fermi gases in a harmonic potential in an n-dimensional space under the generalized uncertainty principle

Science.gov (United States)

Li, Heling; Ren, Jinxiu; Wang, Wenwei; Yang, Bin; Shen, Hongjun

2018-02-01

Using the semi-classical (Thomas-Fermi) approximation, the thermodynamic properties of ideal Fermi gases in a harmonic potential in an n-dimensional space are studied under the generalized uncertainty principle (GUP). The mean particle number, internal energy, heat capacity and other thermodynamic variables of the Fermi system are calculated analytically. Then, analytical expressions of the mean particle number, internal energy, heat capacity, chemical potential, Fermi energy, ground state energy and amendments of the GUP are obtained at low temperatures. The influence of both the GUP and the harmonic potential on the thermodynamic properties of a copper-electron gas and other systems with higher electron densities are studied numerically at low temperatures. We find: (1) When the GUP is considered, the influence of the harmonic potential is very much larger, and the amendments produced by the GUP increase by eight to nine orders of magnitude compared to when no external potential is applied to the electron gas. (2) The larger the particle density, or the smaller the particle masses, the bigger the influence of the GUP. (3) The effect of the GUP increases with the increase in the spatial dimensions. (4) The amendments of the chemical potential, Fermi energy and ground state energy increase with an increase in temperature, while the heat capacity decreases. T F0 is the Fermi temperature of the ideal Fermi system in a harmonic potential. When the temperature is lower than a certain value (0.22 times T F0 for the copper-electron gas, and this value decreases with increasing electron density), the amendment to the internal energy is positive, however, the amendment decreases with increasing temperature. When the temperature increases to the value, the amendment is zero, and when the temperature is higher than the value, the amendment to the internal energy is negative and the absolute value of the amendment increases with increasing temperature. (5) When electron

Measurement of the quantum capacitance from two-dimensional surface state of a topological insulator at room temperature

Energy Technology Data Exchange (ETDEWEB)

Choi, Hyunwoo, E-mail: chw0089@gmail.com [Department of Electrical and Computer Engineering, University of Seoul, Seoul 02504 (Korea, Republic of); Kim, Tae Geun, E-mail: tgkim1@korea.ac.kr [School of Electrical Engineering, Korea University, Seoul 02841 (Korea, Republic of); Shin, Changhwan, E-mail: cshin@uos.ac.kr [Department of Electrical and Computer Engineering, University of Seoul, Seoul 02504 (Korea, Republic of)

2017-06-15

Highlights: • The quantum capacitance in topological insulator (TI) at room temperature is directly revealed. • The physical origin of quantum capacitance, the two dimensional surface state of TI, is experimentally validated. • Theoretically calculated results of ideal quantum capacitance can well predict the experimental data. - Abstract: A topological insulator (TI) is a new kind of material that exhibits unique electronic properties owing to its topological surface state (TSS). Previous studies focused on the transport properties of the TSS, since it can be used as the active channel layer in metal-oxide-semiconductor field-effect transistors (MOSFETs). However, a TI with a negative quantum capacitance (QC) effect can be used in the gate stack of MOSFETs, thereby facilitating the creation of ultra-low power electronics. Therefore, it is important to study the physics behind the QC in TIs in the absence of any external magnetic field, at room temperature. We fabricated a simple capacitor structure using a TI (TI-capacitor: Au-TI-SiO{sub 2}-Si), which shows clear evidence of QC at room temperature. In the capacitance-voltage (C-V) measurement, the total capacitance of the TI-capacitor increases in the accumulation regime, since QC is the dominant capacitive component in the series capacitor model (i.e., C{sub T}{sup −1} = C{sub Q}{sup −1} + C{sub SiO2}{sup −1}). Based on the QC model of the two-dimensional electron systems, we quantitatively calculated the QC, and observed that the simulated C-V curve theoretically supports the conclusion that the QC of the TI-capacitor is originated from electron–electron interaction in the two-dimensional surface state of the TI.

Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.

Science.gov (United States)

Yoshimi, R; Tsukazaki, A; Kozuka, Y; Falson, J; Takahashi, K S; Checkelsky, J G; Nagaosa, N; Kawasaki, M; Tokura, Y

2015-04-14

The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi2Se3, Bi2Te3, Sb2Te3 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi1-xSbx)2Te3 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor ±1 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.

Thermoelectric transport in two-dimensional giant Rashba systems

Science.gov (United States)

Xiao, Cong; Li, Dingping; Ma, Zhongshui; Niu, Qian

Thermoelectric transport in strongly spin-orbit coupled two-dimensional Rashba systems is studied using the analytical solution of the linearized Boltzmann equation. To highlight the effects of inter-band scattering, we assume point-like potential impurities, and obtain the band-and energy-dependent transport relaxation times. Unconventional transport behaviors arise when the Fermi level lies near or below the band crossing point (BCP), such as the non-Drude electrical conducivity below the BCP, the failure of the standard Mott relation linking the Peltier coefficient to the electrical conductivity near the BCP, the enhancement of diffusion thermopower and figure of merit below the BCP, the zero-field Hall coefficient which is not inversely proportional to and not a monotonic function of the carrier density, the enhanced Nernst coefficient below the BCP, and the enhanced current-induced spin-polarization efficiency.

Optical spectroscopy and Fermi surface studies of BiTeCl and BiTeBr

Science.gov (United States)

Martin, Catalin; Suslov, A. V.; Buvaev, S.; Hebard, A. F.; Bugnon, Philippe; Berger, Helmuth; Magrez, Arnaud; Tanner, D. B.

2014-03-01

The observation of a large bulk Rashba effect in the non-centrosymmetric semiconductors BiTeX(X=Cl, Br, I) has stimulated the interest in these sys- tems, as promising candidates for studying spin related phenomena and for the realization of spin devices. Here we present a comparative study of the electronic properties of BiTeCl and BiTeBr, determined from temperature dependent infrared spectroscopy and Shubnikov-de Haas oscillations. In par- ticular, we compare the angle dependence of quantum oscillations between the two compounds and discuss possible differences between the topology of their Fermi surfaces. Supported by NSF Cooperative Agreement DMR-1157490 to the National High Magnetic Field Laboratory.

Convergent fabrication of a nanoporous two-dimensional carbon network from an aldol condensation on metal surfaces

International Nuclear Information System (INIS)

Landers, John; De Santis, Maurizio; Bendiab, Nedjma; Magaud, Laurence; Coraux, Johann; Chérioux, Frédéric; Lamare, Simon

2014-01-01

We report a convergent surface polymerization reaction scheme on Au(111), based on a triple aldol condensation, yielding a carbon-rich, covalent nanoporous two-dimensional network. The reaction is not self-poisoning and proceeds up to a full surface coverage. The deposited precursor molecules 1, 3, 5-tri(4’-acetylphenyl) first form supramolecular assemblies that are converted to the porous covalent network upon heating. The formation and structure of the network and of the intermediate steps are studied with scanning tunneling microscopy, Raman spectroscopy and density functional theory. (paper)

Quasi-two-dimensional superconductivity in wurtzite-structured InN films

International Nuclear Information System (INIS)

Ling, D.C.; Cheng, J.H.; Lo, Y.Y.; Du, C.H.; Chiu, A.P.; Chang, P.H.; Chang, C.A.

2007-01-01

C-axis oriented InN films with wurtzite structure were grown on sapphire(0001) substrate by MOCVD method. Superconductivity with transition onset temperature T c,onset around 3.5 K has been characterized by magnetotransport measurements in fields up to 9 Tesla for films with carrier concentration in the range of 1 x 10 19 cm -3 to 7 x 10 20 cm -3 . Among them, the film with a nitridation buffer layer has the highest zero-resistance temperature T c0 of 2 K. The normal-state magnetoresistance follows Kohler's rule ΔR/R∝(H/R) 2 , indicating that there is a single species of charge carrier with single scattering time at all points on the Fermi surface. The extrapolated value of zero-temperature upper critical field H c2 ab (0) and H c2 c (0) is estimated to be 5900 G and 2800 G, respectively, giving rise to the anisotropy parameter γ about 2.1. The angular dependence of the upper critical field is in good agreement with the behavior predicted by Lawrence-Doniach model in the two-dimensional (2D) limit strongly suggesting that the InN film is a quasi-2D superconductor. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Two-Dimensional Materials for Sensing: Graphene and Beyond

Directory of Open Access Journals (Sweden)

Seba Sara Varghese

2015-09-01

Full Text Available Two-dimensional materials have attracted great scientific attention due to their unusual and fascinating properties for use in electronics, spintronics, photovoltaics, medicine, composites, etc. Graphene, transition metal dichalcogenides such as MoS2, phosphorene, etc., which belong to the family of two-dimensional materials, have shown great promise for gas sensing applications due to their high surface-to-volume ratio, low noise and sensitivity of electronic properties to the changes in the surroundings. Two-dimensional nanostructured semiconducting metal oxide based gas sensors have also been recognized as successful gas detection devices. This review aims to provide the latest advancements in the field of gas sensors based on various two-dimensional materials with the main focus on sensor performance metrics such as sensitivity, specificity, detection limit, response time, and reversibility. Both experimental and theoretical studies on the gas sensing properties of graphene and other two-dimensional materials beyond graphene are also discussed. The article concludes with the current challenges and future prospects for two-dimensional materials in gas sensor applications.

Two- and three-dimensional CT analysis of ankle fractures

International Nuclear Information System (INIS)

Magid, D.; Fishman, E.K.; Ney, D.R.; Kuhlman, J.E.

1988-01-01

CT with coronal and sagittal reformatting (two-dimensional CT) and animated volumetric image rendering (three-dimensional CT) was used to assess ankle fractures. Partial volume limits transaxial CT in assessments of horizontally oriented structures. Two-dimensional CT, being orthogonal to the plafond, superior mortise, talar dome, and tibial epiphysis, often provides the most clinically useful images. Two-dimensional CT is most useful in characterizing potentially confusing fractures, such as Tillaux (anterior tubercle), triplane, osteochondral talar dome, or nondisplaced talar neck fractures, and it is the best study to confirm intraarticular fragments. Two-and three-dimensional CT best indicate the percentage of articular surface involvement and best demonstrate postoperative results or complications (hardware migration, residual step-off, delayed union, DJD, AVN, etc). Animated three-dimensional images are the preferred means of integrating the two-dimensional findings for surgical planning, as these images more closely simulate the clinical problem

Thermostatistic properties of a q-deformed ideal Fermi gas with a general energy spectrum

International Nuclear Information System (INIS)

Cai, Shukuan; Su, Guozhen; Chen, Jincan

2007-01-01

The thermostatistic problems of a q-deformed ideal Fermi gas in any dimensional space and with a general energy spectrum are studied, based on the q-deformed Fermi-Dirac distribution. The effects of the deformation parameter q on the properties of the system are revealed. It is shown that q-deformation results in some novel characteristics different from those of an ordinary system. Besides, it is found that the effects of the q-deformation on the properties of the Fermi systems are very different for different dimensional spaces and different energy spectrums

Spectral properties near the Mott transition in the two-dimensional Hubbard model

Science.gov (United States)

Kohno, Masanori

2013-03-01

Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.

Two-dimensional Yukawa interactions from nonlocal Proca quantum electrodynamics

Science.gov (United States)

Alves, Van Sérgio; Macrı, Tommaso; Magalhães, Gabriel C.; Marino, E. C.; Nascimento, Leandro O.

2018-05-01

We derive two versions of an effective model to describe dynamical effects of the Yukawa interaction among Dirac electrons in the plane. Such short-range interaction is obtained by introducing a mass term for the intermediate particle, which may be either scalar or an abelian gauge field, both of them in (3 +1 ) dimensions. Thereafter, we consider that the fermionic matter field propagates only in (2 +1 ) dimensions, whereas the bosonic field is free to propagate out of the plane. Within these assumptions, we apply a mechanism for dimensional reduction, which yields an effective model in (2 +1 ) dimensions. In particular, for the gauge-field case, we use the Stueckelberg mechanism in order to preserve gauge invariance. We refer to this version as nonlocal-Proca quantum electrodynamics (NPQED). For both scalar and gauge cases, the effective models reproduce the usual Yukawa interaction in the static limit. By means of perturbation theory at one loop, we calculate the mass renormalization of the Dirac field. Our model is a generalization of Pseudo quantum electrodynamics (PQED), which is a gauge-field model that provides a Coulomb interaction for two-dimensional electrons. Possibilities of application to Fermi-Bose mixtures in mixed dimensions, using cold atoms, are briefly discussed.

Phase diagram of strongly correlated Fermi systems

International Nuclear Information System (INIS)

Zverev, M.V.; Khodel', V.A.; Baldo, M.

2000-01-01

Phase transitions in uniform Fermi systems with repulsive forces between the particles caused by restructuring of quasiparticle filling n(p) are analyzed. It is found that in terms of variables, i.e. density ρ, nondimensional binding constant η, phase diagram of a strongly correlated Fermi system for rather a wide class of interactions reminds of a puff-pastry pie. Its upper part is filled with fermion condensate, the lower one - with normal Fermi-liquid. They are separated by a narrow interlayer - the Lifshits phase, characterized by the Fermi multibound surface [ru

Reduction of Fermi level pinning and recombination at polycrystalline CdTe surfaces by laser irradiation

Energy Technology Data Exchange (ETDEWEB)

Simonds, Brian J. [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Kheraj, Vipul [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Department of Applied Physics, S. V. National Institute of Technology, Surat 395 007 (India); Palekis, Vasilios; Ferekides, Christos [Electrical Engineering, University of South Florida, Tampa, Florida 33620 (United States); Scarpulla, Michael A., E-mail: scarpulla@eng.utah.edu [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-06-14

Laser processing of polycrystalline CdTe is a promising approach that could potentially increase module manufacturing throughput while reducing capital expenditure costs. For these benefits to be realized, the basic effects of laser irradiation on CdTe must be ascertained. In this study, we utilize surface photovoltage spectroscopy (SPS) to investigate the changes to the electronic properties of the surface of polycrystalline CdTe solar cell stacks induced by continuous-wave laser annealing. The experimental data explained within a model consisting of two space charge regions, one at the CdTe/air interface and one at the CdTe/CdS junction, are used to interpret our SPS results. The frequency dependence and phase spectra of the SPS signal are also discussed. To support the SPS findings, low-temperature spectrally-resolved photoluminescence and time-resolved photoluminescence were also measured. The data show that a modest laser treatment of 250 W/cm{sup 2} with a dwell time of 20 s is sufficient to reduce the effects of Fermi level pinning at the surface due to surface defects.

Quantum Monte Carlo simulations of the Fermi-polaron problem and bosons with Gaussian interactions

Energy Technology Data Exchange (ETDEWEB)

Kroiss, Peter Michael

2017-02-01

This thesis deals with the application of current Quantum Monte Carlo algorithms to many-body systems of fermionic and bosonic species. The first part applies the diagrammatic Monte Carlo method to the Fermi polaron problem, a system of an impurity interacting resonantly with a homogeneous Fermi bath. It is numerically shown that the three particle-hole diagrams do not contribute significantly to the final answer in a quasi-two-dimensional setup, thus demonstrating a nearly perfect destructive interference of contributions in subspaces with higher-order particle-hole lines. Consequently, for strong-enough confinement in the third direction, the transition between the polaron and the molecule ground state is found to be in good agreement with the pure two-dimensional case and agrees very well with the one found by the wave-function approach in the two-particle-hole subspace. In three-dimensional Fermi-polaron systems with mass imbalance of impurity and bath atoms, polaron energy and quasiparticle residue can be accurately determined over a broad range of impurity masses. Furthermore, the spectral function of an imbalanced polaron demonstrates the stability of the quasiparticle and also allows us to locate the repulsive polaron as an excited state. The quantitative exactness of two-particle-hole wave functions is investigated, resulting in a relative lowering of polaronic energies in the mass-imbalance phase diagram. Tan's contact coefficient for the mass-balanced polaron system is found to be in good agreement with variational methods. Mass-imbalanced systems can be studied experimentally by ultracold atom mixtures such as {sup 6}Li-{sup 40}K. In the second part of the thesis, the ground state of a two-dimensional system of Bose particles of spin zero, interacting via a repulsive Gaussian-Core potential, is investigated by means of path integral Monte Carlo simulations. The quantum phase diagram is qualitatively identical to that of two-dimensional Yukawa

Two-Dimensional Titanium Carbide (MXene) as Surface-Enhanced Raman Scattering Substrate

Energy Technology Data Exchange (ETDEWEB)

Sarycheva, Asia [Drexel Univ., Philadelphia, PA (United States); Makaryan, Taron [Drexel Univ., Philadelphia, PA (United States); Maleski, Kathleen [Drexel Univ., Philadelphia, PA (United States); Satheeshkumar, Elumalai [National Cheng Kung Univ., Tainan (Taiwan); National Institute of Technology-Trichy, Tamil Nadu (India); Melikyan, Armen [Russian-Armenian (Slavonic) State Univ., Yerevan (Armenia); Minassian, Hayk [A. Alikhanian National Science Lab., Yerevan (Armenia); Yoshimura, Masahiro [National Cheng Kung Univ., Tainan (Taiwan); Gogotsi, Yury G. [Drexel Univ., Philadelphia, PA (United States)

2017-08-22

Here, noble metal (gold or silver) nanoparticles or patterned films are typically used as substrates for surface-enhanced Raman spectroscopy (SERS). Two-dimensional (2D) carbides and nitrides (MXenes) exhibit unique electronic and optical properties, including metallic conductivity and plasmon resonance in the visible or near-infrared range, making them promising candidates for a wide variety of applications. Herein, we show that 2D titanium carbide, Ti₃C₂T_x, enhances Raman signal from organic dyes on a substrate and in solution. As a proof of concept, MXene SERS substrates were manufactured by spray-coating and used to detect several common dyes, with calculated enhancement factors reaching ~10⁶. Titanium carbide MXene demonstrates SERS effect in aqueous colloidal solutions, suggesting the potential for biomedical or environmental applications, where MXene can selectively enhance positively charged molecules.

Transport properties of diazonium functionalized graphene: chiral two-dimensional hole gases

International Nuclear Information System (INIS)

Huang Ping; Jing Long; Zhu Huarui; Gao Xueyun

2012-01-01

The electric transport properties of diazonium functionalized graphene (DFG) were investigated. The temperature dependence of the resistivity (ρ-T) and the Shubnikov-de Haas oscillation of the DFG revealed two-dimensional hole gas (2DHG) behaviors. The DFGs exhibited unusual weak localization behaviors in which both inelastic and chirality-breaking elastic scattering processes should be taken into account, meaning that graphene chirality was maintained. Because of the giant decrease in the diffusion coefficient, the scattering rates remained relatively low in the presence of suppression of the scattering lengths. The decreases of both the mean free path and the Fermi velocity were responsible for the suppression of the diffusion coefficient and hence the charge mobility. (paper)

Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors

Science.gov (United States)

Zhao, Huaisong; Gao, Deheng; Feng, Shiping

2017-03-01

One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.

Positron annihilation study on the Fermi surface of Cd-Mg alloys

International Nuclear Information System (INIS)

Koike, Shu-ichi; Hirabayashi, Makoto; Suzuki, Toshiharu; Hasegawa, Masayuki.

1979-01-01

Angular correlation measurements of annihilation photons have been made on single crystals of the Cd-Mg alloys over all compositions. It is found that the Fermi surfaces of the alloys in the Cd-rich region distort considerably from a free-electron sphere; the 3rd band ''stars'' and the 4th band horizontal ''cigars'' around the points L do not exist in Cd, and appear at 10 at % Mg accompanying an appreciable decrease of the energy gap at L. It is proposed that changes in the 4d core states cause the sudden decrease of the energy gap. (author)

Theory of heavy-fermion compounds theory of strongly correlated Fermi-systems

CERN Document Server

Amusia, Miron Ya; Shaginyan, Vasily R; Stephanovich, Vladimir A

2015-01-01

This book explains modern and interesting physics in heavy-fermion (HF) compounds to graduate students and researchers in condensed matter physics. It presents a theory of heavy-fermion (HF) compounds such as HF metals, quantum spin liquids, quasicrystals and two-dimensional Fermi systems. The basic low-temperature properties and the scaling behavior of the compounds are described within the framework of the theory of fermion condensation quantum phase transition (FCQPT). Upon reading the book, the reader finds that HF compounds with quite different microscopic nature exhibit the same non-Fermi liquid behavior, while the data collected on very different HF systems have a universal scaling behavior, and these compounds are unexpectedly uniform despite their diversity. For the reader's convenience, the analysis of compounds is carried out in the context of salient experimental results. The numerous calculations of the non-Fermi liquid behavior, thermodynamic, relaxation and transport properties, being in good...

A low Fermi scale from a simple gaugino-scalar mass relation

Energy Technology Data Exchange (ETDEWEB)

Bruemmer, F. [International School for Advanced Studies, Trieste (Italy); Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Buchmueller, W. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

2013-11-15

In supersymmetric extensions of the Standard Model, the Fermi scale of electroweak symmetry breaking is determined by the pattern of supersymmetry breaking. We present an example, motivated by a higher-dimensional GUT model, where a particular mass relation between the gauginos, third-generation squarks and Higgs fields of the MSSM leads to a Fermi scale smaller than the soft mass scale. This is in agreement with the measured Higgs boson mass. The {mu} parameter is generated independently of supersymmetry breaking, however the {mu} problem becomes less acute due to the little hierarchy between the soft mass scale and the Fermi scale as we argue. The resulting superparticle mass spectra depend on the localization of quark and lepton fields in higher dimensions. In one case, the squarks of the first two generations as well as the gauginos and higgsinos can be in the range of the LHC. Alternatively, only the higgsinos may be accessible at colliders. The lightest superparticle is the gravitino.

Low-temperature structure and Fermi surface of (La,Ce)TiGe{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Foerster, Tobias; Grasemann, Jacob; Uhlarz, Marc; Wosnitza, Jochen [Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Rosner, Helge; Stockert, Oliver [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Kittler, Wolfram; Loehneysen, Hilbert von [Karlsruhe Institute of Technology, Karlsruhe (Germany); Fritsch, Veronika [Institut fuer Physik, Universitaet Augsburg, Augsburg (Germany)

2016-07-01

CeTiGe{sub 3} presents the rare case of a ferromagnetically (T{sub C} ∼ 14 K) ordered Kondo-lattice compound and is probably the first known example of an intermetallic hexagonal perovskite of the BaNiO{sub 3} structure type. LaTiGe{sub 3} may be used as its nonmagnetic reference, since both compounds crystallize in the same crystal structure. To clarify the interplay between structural, localized, and itinerant degrees of freedom an accurate knowledge of the electronic band structure is necessary. Here, we present a detailed electronic-structure study of both compounds applying full potential density functional calculations. Since the Ge's atomic position couples strongly to the band structure at the Fermi energy, a low-temperature, high-resolution structure refinement was made. We attempt to separate the influence of different parameters on the topology of the respective Fermi surfaces and will compare our results with de Haas-van Alphen measurements.

Three-dimensional surface scanners compared with standard anthropometric measurements for head shape

NARCIS (Netherlands)

Beaumont, C.A.A. (Caroline A.A.); Knoops, P.G.M. (Paul G.M.); Borghi, A. (Alessandro); Jeelani, N.U.O. (N.U. Owase); M.J. Koudstaal (Maarten); S. Schievano (Silvia); D.J. Dunaway (David); Rodriguez-Florez, N. (Naiara)

2016-01-01

textabstractThree-dimensional (3D) surface imaging devices designed to capture and quantify craniofacial surface morphology are becoming more common in clinical environments. Such scanners overcome the limitations of two-dimensional photographs while avoiding the ionizing radiation of computed

Three-dimensional surface scanners compared with standard anthropometric measurements for head shape

NARCIS (Netherlands)

Beaumont, C.A.A. (Caroline A.A.); Knoops, P.G.M. (Paul G.M.); Borghi, A. (Alessandro); Jeelani, N.U.O. (N.U. Owase); M.J. Koudstaal (Maarten); S. Schievano (Silvia); D.J. Dunaway (David); Rodriguez-Florez, N. (Naiara)

2017-01-01

textabstractThree-dimensional (3D) surface imaging devices designed to capture and quantify craniofacial surface morphology are becoming more common in clinical environments. Such scanners overcome the limitations of two-dimensional photographs while avoiding the ionizing radiation of computed

Effect of population imbalance on the Berezinskii-Kosterlitz-Thouless phase transition in a superfluid Fermi gas

International Nuclear Information System (INIS)

Tempere, J.; Klimin, S. N.; Devreese, J. T.

2009-01-01

The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes the breakdown of superfluidity in a two-dimensional Bose gas or a two-dimensional gas of paired fermions. In the latter case, a population imbalance between the two pairing partners in the Fermi mixture is known to influence pairing characteristics. Here, we investigate the effects of imbalance on the two-dimensional BKT superfluid transition and show that superfluidity is even more sensitive to imbalance than for three-dimensional systems. Finite-temperature phase diagrams are derived using the functional integral formalism in combination with a hydrodynamic action functional for the phase fluctuations. This allows to identify a phase-separation region and tricritical points due to imbalance. In contrast to superfluidity in the three-dimensional case, the effect of imbalance is also pronounced in the strong-coupling regime.

Topological surface states scattering in antimony

KAUST Repository

Narayan, Awadhesh

2012-11-05

In this work we study the topologically protected states of the Sb(111) surface by using ab initio transport theory. In the presence of a strong surface perturbation we obtain standing-wave states resulting from the superposition of spin-polarized surface states. By Fourier analysis, we identify the underlying two dimensional scattering processes and the spin texture. We find evidence of resonant transmission across surface barriers at quantum well state energies and evaluate their lifetimes. Our results are in excellent agreement with experimental findings. We also show that despite the presence of a step edge along a different high-symmetry direction, the surface states exhibit unperturbed transmission around the Fermi energy for states with near to normal incidence. © 2012 American Physical Society.

Topological surface states scattering in antimony

KAUST Repository

Narayan, Awadhesh; Rungger, Ivan; Sanvito, Stefano

2012-01-01

In this work we study the topologically protected states of the Sb(111) surface by using ab initio transport theory. In the presence of a strong surface perturbation we obtain standing-wave states resulting from the superposition of spin-polarized surface states. By Fourier analysis, we identify the underlying two dimensional scattering processes and the spin texture. We find evidence of resonant transmission across surface barriers at quantum well state energies and evaluate their lifetimes. Our results are in excellent agreement with experimental findings. We also show that despite the presence of a step edge along a different high-symmetry direction, the surface states exhibit unperturbed transmission around the Fermi energy for states with near to normal incidence. © 2012 American Physical Society.

Two-dimensional errors

International Nuclear Information System (INIS)

Anon.

1991-01-01

This chapter addresses the extension of previous work in one-dimensional (linear) error theory to two-dimensional error analysis. The topics of the chapter include the definition of two-dimensional error, the probability ellipse, the probability circle, elliptical (circular) error evaluation, the application to position accuracy, and the use of control systems (points) in measurements

A family of crisis in a dissipative Fermi accelerator model

International Nuclear Information System (INIS)

Leonel, Edson D.; Egydio de Carvalho, R.

2007-01-01

The Fermi accelerator model is studied in the framework of inelastic collisions. The dynamics of this problem is obtained by use of a two-dimensional nonlinear area-contracting map. We consider that the collisions of the particle with both periodically time varying and fixed walls are inelastic. We have shown that the dissipation destroys the mixed phase space structure of the nondissipative case and in special, we have obtained and characterized in this problem a family of two damping coefficients for which a boundary crisis occurs

Magnetic phase transition induced by electrostatic gating in two-dimensional square metal-organic frameworks

Science.gov (United States)

Wang, Yun-Peng; Li, Xiang-Guo; Liu, Shuang-Long; Fry, James N.; Cheng, Hai-Ping

2018-03-01

We investigate theoretically magnetism and magnetic phase transitions induced by electrostatic gating of two-dimensional square metal-organic framework compounds. We find that electrostatic gating can induce phase transitions between homogeneous ferromagnetic and various spin-textured antiferromagnetic states. Electronic structure and Wannier function analysis can reveal hybridizations between transition-metal d orbitals and conjugated π orbitals in the organic framework. Mn-containing compounds exhibit a strong d -π hybridization that leads to partially occupied spin-minority bands, in contrast to compounds containing transition-metal ions other than Mn, for which electronic structure around the Fermi energy is only slightly spin split due to weak d -π hybridization and the magnetic interaction is of the Ruderman-Kittel-Kasuya-Yosida type. We use a ferromagnetic Kondo lattice model to understand the phase transition in Mn-containing compounds in terms of carrier density and illuminate the complexity and the potential to control two-dimensional magnetization.

Magnetic Weyl Semimetal in Quasi Two-dimensional Half Metallic Co$_3$Sn$_2$Se$_2$

OpenAIRE

Xu, Qiunan; Liu, Enke; Shi, Wujun; Muechler, Lukas; Felser, Claudia; Sun, Yan

2017-01-01

We have found a ferromagnetic Weyl semimetal (WSM) in half metallic Co$_3$Sn$_2$Se$_2$. The three pairs of Weyl points near Fermi level (E$_F$) are derived from nodal lines gapped by spin-orbit coupling (SOC). Though the Weyl points are 0.11 eV above the charge neutral point, Fermi arc related states in the cleaved surface can range from E$_F$ -0.15 to E$_F$ +0.11 eV in energy space, due to the surface bands dispersion. Hence, Weyl points related physics should be detected by surface measurem...

A fast Gaussian filtering algorithm for three-dimensional surface roughness measurements

International Nuclear Information System (INIS)

Yuan, Y B; Piao, W Y; Xu, J B

2007-01-01

The two-dimensional (2-D) Gaussian filter can be separated into two one-dimensional (1-D) Gaussian filters. The 1-D Gaussian filter can be implemented approximately by the cascaded Butterworth filters. The approximation accuracy will be improved with the increase of the number of the cascaded filters. A recursive algorithm for Gaussian filtering requires a relatively small number of simple mathematical operations such as addition, subtraction, multiplication, or division, so that it has considerable computational efficiency and it is very useful for three-dimensional (3-D) surface roughness measurements. The zero-phase-filtering technique is used in this algorithm, so there is no phase distortion in the Gaussian filtered mean surface. High-order approximation Gaussian filters are proposed for practical use to assure high accuracy of Gaussian filtering of 3-D surface roughness measurements

A fast Gaussian filtering algorithm for three-dimensional surface roughness measurements

Science.gov (United States)

Yuan, Y. B.; Piao, W. Y.; Xu, J. B.

2007-07-01

The two-dimensional (2-D) Gaussian filter can be separated into two one-dimensional (1-D) Gaussian filters. The 1-D Gaussian filter can be implemented approximately by the cascaded Butterworth filters. The approximation accuracy will be improved with the increase of the number of the cascaded filters. A recursive algorithm for Gaussian filtering requires a relatively small number of simple mathematical operations such as addition, subtraction, multiplication, or division, so that it has considerable computational efficiency and it is very useful for three-dimensional (3-D) surface roughness measurements. The zero-phase-filtering technique is used in this algorithm, so there is no phase distortion in the Gaussian filtered mean surface. High-order approximation Gaussian filters are proposed for practical use to assure high accuracy of Gaussian filtering of 3-D surface roughness measurements.

Two dimensional finite element thermal model of laser surface glazing for H13 tool steel

Science.gov (United States)

Kabir, I. R.; Yin, D.; Naher, S.

2016-10-01

A two dimensional (2D) transient thermal model with line-heat-source was developed by Finite Element Method (FEM) for laser surface glazing of H13 tool steel using commercial software-ANSYS 15. The geometry of the model was taken as a transverse circular cross-section of cylindrical specimen. Two different power levels (300W, 200W) were used with 0.2mm width of laser beam and 0.15ms exposure time. Temperature distribution, heating and cooling rates, and the dimensions of modified surface were analysed. The maximum temperatures achieved were 2532K (2259°C) and 1592K (1319°C) for laser power 300W and 200W respectively. The maximum cooling rates were 4.2×107 K/s for 300W and 2×107 K/s for 200W. Depths of modified zone increased with increasing laser power. From this analysis, it can be predicted that for 0.2mm beam width and 0.15ms time exposer melting temperature of H13 tool steel is achieved within 200-300W power range of laser beam in laser surface glazing.

Control of two-dimensional electronic states at anatase Ti O2(001 ) surface by K adsorption

Science.gov (United States)

Yukawa, R.; Minohara, M.; Shiga, D.; Kitamura, M.; Mitsuhashi, T.; Kobayashi, M.; Horiba, K.; Kumigashira, H.

2018-04-01

The nature of the intriguing metallic electronic structures appearing at the surface of anatase titanium dioxide (a-Ti O2 ) remains to be elucidated, mainly owing to the difficulty of controlling the depth distribution of the oxygen vacancies generated by photoirradiation. In this study, K atoms were adsorbed onto the (001) surface of a-Ti O2 to dope electrons into the a-Ti O2 and to confine the electrons in the surface region. The success of the electron doping and its controllability were confirmed by performing in situ angle-resolved photoemission spectroscopy as well as core-level measurements. Clear subband structures were observed in the surface metallic states, indicating the creation of quasi-two-dimensional electron liquid (q2DEL) states in a controllable fashion. With increasing electron doping (K adsorption), the q2DEL states exhibited crossover from polaronic liquid states with multiple phonon-loss structures originating from the long-range Fröhlich interaction to "weakly correlated metallic" states. In the q2DEL states in the weakly correlated metallic region, a kink due to short-range electron-phonon coupling was clearly observed at about 80 ±10 meV . The characteristic energy is smaller than that previously observed for the metallic states of a-Ti O2 with three-dimensional nature (˜110 meV ) . These results suggest that the dominant electron-phonon coupling is modulated by anisotropic carrier screening in the q2DEL states.

Point Measurements of Fermi Velocities by a Time-of-Flight Method

DEFF Research Database (Denmark)

Falk, David S.; Henningsen, J. O.; Skriver, Hans Lomholt

1972-01-01

The present paper describes in detail a new method of obtaining information about the Fermi velocity of electrons in metals, point by point, along certain contours on the Fermi surface. It is based on transmission of microwaves through thin metal slabs in the presence of a static magnetic field...... applied parallel to the surface. The electrons carry the signal across the slab and arrive at the second surface with a phase delay which is measured relative to a reference signal; the velocities are derived by analyzing the magnetic field dependence of the phase delay. For silver we have in this way...... obtained one component of the velocity along half the circumference of the centrally symmetric orbit for B→∥[100]. The results are in agreement with current models for the Fermi surface. For B→∥[011], the electrons involved are not moving in a symmetry plane of the Fermi surface. In such cases one cannot...

ONE-DIMENSIONAL AND TWO-DIMENSIONAL LEADERSHIP STYLES

Directory of Open Access Journals (Sweden)

Nikola Stefanović

2007-06-01

Full Text Available In order to motivate their group members to perform certain tasks, leaders use different leadership styles. These styles are based on leaders' backgrounds, knowledge, values, experiences, and expectations. The one-dimensional styles, used by many world leaders, are autocratic and democratic styles. These styles lie on the two opposite sides of the leadership spectrum. In order to precisely define the leadership styles on the spectrum between the autocratic leadership style and the democratic leadership style, leadership theory researchers use two dimensional matrices. The two-dimensional matrices define leadership styles on the basis of different parameters. By using these parameters, one can identify two-dimensional styles.

Reconstruction de la surface de Fermi dans l'etat normal d'un supraconducteur a haute Tc: Une etude du transport electrique en champ magnetique intense

Science.gov (United States)

Le Boeuf, David

Des mesures de resistance longitudinale et de resistance de Hall en champ magnetique intense transverse (perpendiculaire aux plans CuO2) ont ete effectuees au sein de monocristaux de YBa2Cu3Oy (YBCO) demacles, ordonnes et de grande purete, afin d'etudier l'etat fondamental des supraconducteurs a haute Tc dans le regime sous-dope. Cette etude a ete realisee en fonction du dopage et de l'orientation du courant d'excitation J par rapport a l'axe orthorhombique b de la structure cristalline. Les mesures en champ magnetique intense revelent par suppression de la supraconductivite des oscillations magnetiques des resistances longitudinale et de Hall dans YBa2Cu 3O6.51 et YBa2Cu4O8. La conformite du comportement de ces oscillations quantiques au formalisme de Lifshitz-Kosevich, apporte la preuve de l'existence d'une surface de Fermi fermee a caractere quasi-2D, abritant des quasiparticules coherentes respectant la statistique de Fermi-Dirac, dans la phase pseudogap d'YBCO. La faible frequence des oscillations quantiques, combinee avec l'etude de la partie monotone de la resistance de Hall en fonction de la temperature indique que la surface de Fermi d'YBCO sous-dope comprend une petite poche de Fermi occupee par des porteurs de charge negative. Cette particularite de la surface de Fermi dans le regime sous-dope incompatible avec les calculs de structure de bande est en fort contraste avec la structure electronique presente dans le regime surdope. Cette observation implique ainsi l'existence d'un point critique quantique dans le diagramme de phase d'YBCO, au voisinage duquel la surface de Fermi doit subir une reconstruction induite par l'etablissement d'une brisure de la symetrie de translation du reseau cristallin sous-jacent. Enfin, l'etude en fonction du dopage de la resistance de Hall et de la resistance longitudinale en champ magnetique intense suggere qu'un ordre du type onde de densite (DW) est responsable de la reconstruction de la surface de Fermi. L'analogie de

Small Fermi surfaces and strong correlation effects in Dirac materials with holography

Science.gov (United States)

Seo, Yunseok; Song, Geunho; Park, Chanyong; Sin, Sang-Jin

2017-10-01

Recent discovery of transport anomaly in graphene demonstrated that a system known to be weakly interacting may become strongly correlated if system parameter (s) can be tuned such that fermi surface is sufficiently small. We study the strong correlation effects in the transport coefficients of Dirac materials doped with magnetic impurity under the magnetic field using holographic method. The experimental data of magneto-conductivity are well fit by our theory, however, not much data are available for other transports of Dirac material in such regime. Therefore, our results on heat transport, thermo-electric power and Nernst coefficients are left as predictions of holographic theory for generic Dirac materials in the vicinity of charge neutral point with possible surface gap. We give detailed look over each magneto-transport observable and 3Dplots to guide future experiments.

Vortex formation in a rotating two-component Fermi gas

Energy Technology Data Exchange (ETDEWEB)

Warringa, Harmen J.; Sedrakian, Armen [Institut fuer Theoretische Physik, Goethe-Universitaet Frankfurt am Main, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany)

2011-08-15

A two-component Fermi gas with attractive s-wave interactions forms a superfluid at low temperatures. When this gas is confined in a rotating trap, fermions can unpair at the edges of the gas and vortices can arise beyond certain critical rotation frequencies. We compute these critical rotation frequencies and construct the phase diagram in the plane of scattering length and rotation frequency for different total numbers of particles. We work at zero temperature and consider a cylindrically symmetric harmonic trapping potential. The calculations are performed in the Hartree-Fock-Bogoliubov approximation which implies that our results are quantitatively reliable for weak interactions.

Instability of Fulde-Ferrell-Larkin-Ovchinnikov states in atomic Fermi gases in three and two dimensions

Science.gov (United States)

Wang, Jibiao; Che, Yanming; Zhang, Leifeng; Chen, Qijin

2018-04-01

The exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states have been actively searched for experimentally since the mean-field based FFLO theories were put forward half a century ago. Here, we investigate the stability of FFLO states in the presence of pairing fluctuations. We conclude that FFLO superfluids cannot exist in continuum in three and two dimensions, due to their intrinsic instability, associated with infinite quantum degeneracy of the pairs. These results address the absence of convincing experimental observations of FFLO phases in both condensed matter and in ultracold atomic Fermi gases with a population imbalance. We predict that the true ground state has a pair momentum distribution highly peaked on an entire constant energy surface.

Estimation of surface temperature by using inverse problem. Part 1. Steady state analyses of two-dimensional cylindrical system

International Nuclear Information System (INIS)

Takahashi, Toshio; Terada, Atsuhiko

2006-03-01

In the corrosive process environment of thermochemical hydrogen production Iodine-Sulfur process plant, there is a difficulty in the direct measurement of surface temperature of the structural materials. An inverse problem method can effectively be applied for this problem, which enables estimation of the surface temperature using the temperature data at the inside of structural materials. This paper shows analytical results of steady state temperature distributions in a two-dimensional cylindrical system cooled by impinging jet flow, and clarifies necessary order of multiple-valued function from the viewpoint of engineeringly satisfactory precision. (author)

Analytical simulation of two dimensional advection dispersion ...

African Journals Online (AJOL)

The study was designed to investigate the analytical simulation of two dimensional advection dispersion equation of contaminant transport. The steady state flow condition of the contaminant transport where inorganic contaminants in aqueous waste solutions are disposed of at the land surface where it would migrate ...

Analytical Simulation of Two Dimensional Advection Dispersion ...

African Journals Online (AJOL)

ADOWIE PERE

ABSTRACT: The study was designed to investigate the analytical simulation of two dimensional advection dispersion equation of contaminant transport. The steady state flow condition of the contaminant transport where inorganic contaminants in aqueous waste solutions are disposed of at the land surface where it would ...

Enhancement of acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities by utilizing surface acoustic waves

Energy Technology Data Exchange (ETDEWEB)

Ma, Tian-Xue [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Wang, Yue-Sheng, E-mail: yswang@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang, Chuanzeng [Department of Civil Engineering, University of Siegen, D-57068 Siegen (Germany)

2017-01-30

A phoxonic crystal is a periodically patterned material that can simultaneously localize optical and acoustic modes. The acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities is investigated numerically. The photons can be well confined in the slot owing to the large electric field discontinuity at the air/dielectric interfaces. Besides, the surface acoustic modes lead to the localization of the phonons near the air-slot. The high overlap of the photonic and phononic cavity modes near the slot results in a significant enhancement of the moving interface effect, and thus strengthens the total acousto-optical interaction. The results of two cavities with different slot widths show that the coupling strength is dependent on the slot width. It is expected to achieve a strong acousto-optical/optomechanical coupling in air-slot phoxonic crystal structures by utilizing surface acoustic modes. - Highlights: • Two-dimensional air-slot phoxonic crystal cavities which can confine simultaneously optical and acoustic waves are proposed. • The acoustic and optical waves are highly confined near/in the air-slot. • The high overlap of the photonic and phononic cavity modes significantly enhances the moving interface effect. • Different factors which affect the acousto-optical coupling are discussed.

Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy

Science.gov (United States)

Nicholson, C. W.; Berthod, C.; Puppin, M.; Berger, H.; Wolf, M.; Hoesch, M.; Monney, C.

2017-05-01

High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3 . In the low-temperature 3D regime, gaps in the electronic structure are observed due to two incommensurate CDWs, in agreement with x-ray diffraction and electronic-structure calculations. At higher temperatures we observe a spectral weight depletion that approaches the power-law behavior expected in one dimension. From the warping of the quasi-1D Fermi surface at low temperatures, we extract the energy scale of the dimensional crossover. This is corroborated by a detailed analysis of the density of states, which reveals a change in dimensional behavior dependent on binding energy. Our results offer an important insight into the dimensionality of excitations in quasi-1D materials.

Surface Reconstruction-Induced Coincidence Lattice Formation Between Two-Dimensionally Bonded Materials and a Three-Dimensionally Bonded Substrate

NARCIS (Netherlands)

Boschker, Jos E.; Momand, Jamo; Bragaglia, Valeria; Wang, Ruining; Perumal, Karthick; Giussani, Alessandro; Kooi, Bart J.; Riechert, Henning; Calarco, Raffaella

Sb2Te3 films are used for studying the epitaxial registry between two-dimensionally bonded (2D) materials and three-dimensional bonded (3D) substrates. In contrast to the growth of 3D materials, it is found that the formation of coincidence lattices between Sb2Te3 and Si(111) depends on the geometry

Direct observation of Fermi surface in YBa2Cu3O7-δ

International Nuclear Information System (INIS)

Haghighi, H.; Kaiser, J.H.; Rayner, S.; West, R.N.; Liu, J.Z.; Shelton, R.; Howell, R.H.; Solal, F.; Fluss, M.J.

1991-01-01

We have performed a high-precision measurement (5x10 8 coincidence counts) of the basal-plane electron-positron momentum density in well oxygenated, twin-free, single crystals of YBa 2 Cu 3 O 7-δ . The raw, processed, and K-space reduced spectra unambiguously show a clear image of a major Fermi surface sheet. The form and profile of that image are in substantial quantitative agreement with theoretical predictions of a Γ-X electron ridge section associated with states in the CuO chains

Laser bistatic two-dimensional scattering imaging simulation of lambert cone

Science.gov (United States)

Gong, Yanjun; Zhu, Chongyue; Wang, Mingjun; Gong, Lei

2015-11-01

This paper deals with the laser bistatic two-dimensional scattering imaging simulation of lambert cone. Two-dimensional imaging is called as planar imaging. It can reflect the shape of the target and material properties. Two-dimensional imaging has important significance for target recognition. The expression of bistatic laser scattering intensity of lambert cone is obtained based on laser radar eauqtion. The scattering intensity of a micro-element on the target could be obtained. The intensity is related to local angle of incidence, local angle of scattering and the infinitesimal area on the cone. According to the incident direction of laser, scattering direction and normal of infinitesimal area, the local incidence angle and scattering angle can be calculated. Through surface integration and the introduction of the rectangular function, we can get the intensity of imaging unit on the imaging surface, and then get Lambert cone bistatic laser two-dimensional scattering imaging simulation model. We analyze the effect of distinguishability, incident direction, observed direction and target size on the imaging. From the results, we can see that the scattering imaging simulation results of the lambert cone bistatic laser is correct.

Two-dimensional NMR spectrometry

International Nuclear Information System (INIS)

Farrar, T.C.

1987-01-01

This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t 0 ; an evolution period, t 1 ; and a detection period, t 2

Entropy excess in strongly correlated Fermi systems near a quantum critical point

Energy Technology Data Exchange (ETDEWEB)

Clark, J.W., E-mail: jwc@wuphys.wustl.edu [McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States); Zverev, M.V. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); Moscow Institute of Physics and Technology, Moscow, 123098 (Russian Federation); Khodel, V.A. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States)

2012-12-15

A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau

Seebeck effect on a weak link between Fermi and non-Fermi liquids

Science.gov (United States)

Nguyen, T. K. T.; Kiselev, M. N.

2018-02-01

We propose a model describing Seebeck effect on a weak link between two quantum systems with fine-tunable ground states of Fermi and non-Fermi liquid origin. The experimental realization of the model can be achieved by utilizing the quantum devices operating in the integer quantum Hall regime [Z. Iftikhar et al., Nature (London) 526, 233 (2015), 10.1038/nature15384] designed for detection of macroscopic quantum charged states in multichannel Kondo systems. We present a theory of thermoelectric transport through hybrid quantum devices constructed from quantum-dot-quantum-point-contact building blocks. We discuss pronounced effects in the temperature and gate voltage dependence of thermoelectric power associated with a competition between Fermi and non-Fermi liquid behaviors. High controllability of the device allows to fine tune the system to different regimes described by multichannel and multi-impurity Kondo models.

Three Dimensional Dirac Semimetals

Science.gov (United States)

Zaheer, Saad

2014-03-01

Dirac points on the Fermi surface of two dimensional graphene are responsible for its unique electronic behavior. One can ask whether any three dimensional materials support similar pseudorelativistic physics in their bulk electronic spectra. This possibility has been investigated theoretically and is now supported by two successful experimental demonstrations reported during the last year. In this talk, I will summarize the various ways in which Dirac semimetals can be realized in three dimensions with primary focus on a specific theory developed on the basis of representations of crystal spacegroups. A three dimensional Dirac (Weyl) semimetal can appear in the presence (absence) of inversion symmetry by tuning parameters to the phase boundary separating a bulk insulating and a topological insulating phase. More generally, we find that specific rules governing crystal symmetry representations of electrons with spin lead to robust Dirac points at high symmetry points in the Brillouin zone. Combining these rules with microscopic considerations identifies six candidate Dirac semimetals. Another method towards engineering Dirac semimetals involves combining crystal symmetry and band inversion. Several candidate materials have been proposed utilizing this mechanism and one of the candidates has been successfully demonstrated as a Dirac semimetal in two independent experiments. Work carried out in collaboration with: Julia A. Steinberg, Steve M. Young, J.C.Y. Teo, C.L. Kane, E.J. Mele and Andrew M. Rappe.

Correlation between phonon anomaly along [211] and the Fermi surface nesting features with associated electron-phonon interactions in Ni2FeGa: A first principles study

International Nuclear Information System (INIS)

Chabungbam, Satyananda; Sahariah, Munima B.

2015-01-01

First principles calculation reaffirms the presence of phonon anomaly along [211] direction in Ni 2 FeGa shape memory alloy supporting the experimental findings of J. Q. Li et al. Fermi surface scans have been performed in both austenite and martensite phase to see the possible Fermi nesting features in this alloy. The magnitude of observed Fermi surface nesting vectors in (211) plane exactly match the phonon anomaly wavevectors along [211] direction. Electron-phonon calculation in the austenite phase shows that there is significant electron-phonon coupling in this alloy which might arise out of the lattice coupling between lower acoustic modes and higher optical modes combined with the observed strong Fermi nesting features in the system. - Highlights: • Transverse acoustic (TA 2 ) modes show anomaly along [211] direction in Ni 2 FeGa. • The phonon anomaly wavevector has been correlated with the Fermi nesting vectors. • Electron-phonon coupling calculation shows significant coupling in this system. • Max. el-ph coupling occurs in transition frequencies from acoustic to optical modes

Laser sheet dropsizing based on two-dimensional Raman and Mie scattering.

Science.gov (United States)

Malarski, Anna; Schürer, Benedikt; Schmitz, Ingo; Zigan, Lars; Flügel, Alexandre; Leipertz, Alfred

2009-04-01

The imaging and quantification of droplet sizes in sprays is a challenging task for optical scientists and engineers. Laser sheet dropsizing (LSDS) combines the two-dimensional information of two different optical processes, one that is proportional to the droplet volume and one that depends on the droplet surface, e.g., Mie scattering. Besides Mie scattering, here we use two-dimensional Raman scattering as the volume-dependent measurement technique. Two different calibration strategies are presented and discussed. Two-dimensional droplet size distributions in a spray have been validated in comparison with the results of point-resolved phase Doppler anemometry (PDA) measurements.

Laser sheet dropsizing based on two-dimensional Raman and Mie scattering

International Nuclear Information System (INIS)

Malarski, Anna; Schuerer, Benedikt; Schmitz, Ingo; Zigan, Lars; Fluegel, Alexandre; Leipertz, Alfred

2009-01-01

The imaging and quantification of droplet sizes in sprays is a challenging task for optical scientists and engineers. Laser sheet dropsizing (LSDS) combines the two-dimensional information of two different optical processes, one that is proportional to the droplet volume and one that depends on the droplet surface, e.g., Mie scattering. Besides Mie scattering, here we use two-dimensional Raman scattering as the volume-dependent measurement technique. Two different calibration strategies are presented and discussed. Two-dimensional droplet size distributions in a spray have been validated in comparison with the results of point-resolved phase Doppler anemometry (PDA) measurements

Two dimensional generalizations of the Newcomb equation

International Nuclear Information System (INIS)

Dewar, R.L.; Pletzer, A.

1989-11-01

The Bineau reduction to scalar form of the equation governing ideal, zero frequency linearized displacements from a hydromagnetic equilibrium possessing a continuous symmetry is performed in 'universal coordinates', applicable to both the toroidal and helical cases. The resulting generalized Newcomb equation (GNE) has in general a more complicated form than the corresponding one dimensional equation obtained by Newcomb in the case of circular cylindrical symmetry, but in this cylindrical case , the equation can be transformed to that of Newcomb. In the two dimensional case there is a transformation which leaves the form of the GNE invariant and simplifies the Frobenius expansion about a rational surface, especially in the limit of zero pressure gradient. The Frobenius expansions about a mode rational surface is developed and the connection with Hamiltonian transformation theory is shown. 17 refs

Surface harmonics method for two-dimensional time-dependent neutron transport problems of square-lattice nuclear reactors

Energy Technology Data Exchange (ETDEWEB)

Boyarinov, V. F.; Kondrushin, A. E.; Fomichenko, P. A. [National Research Centre Kurchatov Institute, Kurchatov Sq. 1, Moscow (Russian Federation)

2013-07-01

Time-dependent equations of the Surface Harmonics Method (SHM) have been derived from the time-dependent neutron transport equation with explicit representation of delayed neutrons for solving the two-dimensional time-dependent problems. These equations have been realized in the SUHAM-TD code. The TWIGL benchmark problem has been used for verification of the SUHAM-TD code. The results of the study showed that computational costs required to achieve necessary accuracy of the solution can be an order of magnitude less than with the use of the conventional finite difference method (FDM). (authors)

A Study of the Surface Structure of Polymorphic Graphene and Other Two-Dimensional Materials for Use in Novel Electronics and Organic Photovoltaics

Science.gov (United States)

Grady, Maxwell

For some time there has been interest in the fundamental physical properties of low- dimensional material systems. The discovery of graphene as a stable two-dimensional form of solid carbon lead to an exponential increase in research in two-dimensional and other re- duced dimensional systems. It is now known that there is a wide range of materials which are stable in two-dimensional form. These materials span a large configuration space of struc- tural, mechanical, and electronic properties, which results in the potential to create novel electronic devices from nano-scale heterostructures with exactly tailored device properties. Understanding the material properties at the nanoscale level requires specialized tools to probe materials with atomic precision. Here I present the growth and analysis of a novel graphene-ruthenium system which exhibits unique polymorphism in its surface structure, hereby referred to as polymorphic graphene. Scanning Tunneling Microscopy (STM) investigations of the polymorphic graphene surface reveal a periodically rippled structure with a vast array of domains, each exhibiting xvia unique moire period. The majority of moire domains found in this polymorphic graphene system are previously unreported in past studies of the structure of graphene on ruthenium. To better understand many of the structural properties of this system, characterization methods beyond those available at the UNH surface science lab are employed. Further investigation using Low Energy Electron Microscopy (LEEM) has been carried out at Sandia National Laboratory's Center for Integrated Nanotechnology and the Brookhaven National Laboratory Center for Functional Nanomaterials. To aid in analysis of the LEEM data, I have developed an open source software package to automate extraction of electron reflectivity curves from real space and reciprocal space data sets. This software has been used in the study of numerous other two-dimensional materials beyond graphene. When

Anisotropy of the Seebeck Coefficient in the Cuprate Superconductor YBa_{2}Cu_{3}O_{y}: Fermi-Surface Reconstruction by Bidirectional Charge Order

Directory of Open Access Journals (Sweden)

O. Cyr-Choinière

2017-09-01

Full Text Available The Seebeck coefficient S of the cuprate YBa_{2}Cu_{3}O_{y} is measured in magnetic fields large enough to suppress superconductivity, at hole dopings p=0.11 and p=0.12, for heat currents along the a and b directions of the orthorhombic crystal structure. For both directions, S/T decreases and becomes negative at low temperature, a signature that the Fermi surface undergoes a reconstruction due to broken translational symmetry. Above a clear threshold field, a strong new feature appears in S_{b}, for conduction along the b axis only. We attribute this feature to the onset of 3D-coherent unidirectional charge-density-wave modulations seen by x-ray diffraction, also along the b axis only. Because these modulations have a sharp onset temperature well below the temperature where S/T starts to drop towards negative values, we infer that they are not the cause of Fermi-surface reconstruction. Instead, the reconstruction must be caused by the quasi-2D bidirectional modulations that develop at significantly higher temperature. The unidirectional order only confers an additional anisotropy to the already reconstructed Fermi surface, also manifest as an in-plane anisotropy of the resistivity.

Topics in Two-Dimensional Quantum Gravity and Chern-Simons Gauge Theories

Science.gov (United States)

Zemba, Guillermo Raul

A series of studies in two and three dimensional theories is presented. The two dimensional problems are considered in the framework of String Theory. The first one determines the region of integration in the space of inequivalent tori of a tadpole diagram in Closed String Field Theory, using the naive Witten three-string vertex. It is shown that every surface is counted an infinite number of times and the source of this behavior is identified. The second study analyzes the behavior of the discrete matrix model of two dimensional gravity without matter using a mathematically well-defined construction, confirming several conjectures and partial results from the literature. The studies in three dimensions are based on Chern Simons pure gauge theory. The first one deals with the projection of the theory onto a two-dimensional surface of constant time, whereas the second analyzes the large N behavior of the SU(N) theory and makes evident a duality symmetry between the only two parameters of the theory. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).

Local density of states in two-dimensional topological superconductors under a magnetic field: Signature of an exterior Majorana bound state

Science.gov (United States)

Suzuki, Shu-Ichiro; Kawaguchi, Yuki; Tanaka, Yukio

2018-04-01

We study quasiparticle states on a surface of a topological insulator (TI) with proximity-induced superconductivity under an external magnetic field. An applied magnetic field creates two Majorana bound states: a vortex Majorana state localized inside a vortex core and an exterior Majorana state localized along a circle centered at the vortex core. We calculate the spin-resolved local density of states (LDOS) and demonstrate that the shrinking of the radius of the exterior Majorana state, predicted in R. S. Akzyanov et al., Phys. Rev. B 94, 125428 (2016), 10.1103/PhysRevB.94.125428, under a strong magnetic field can be seen in LDOS without smeared out by nonzero-energy states. The spin-resolved LDOS further reveals that the spin of the exterior Majorana state is strongly spin-polarized. Accordingly, the induced odd-frequency spin-triplet pairs are found to be spin-polarized as well. In order to detect the exterior Majorana states, however, the Fermi energy should be closed to the Dirac point to avoid contributions from continuum levels. We also study a different two-dimensional topological-superconducting system where a two-dimensional electron gas with the spin-orbit coupling is sandwiched between an s -wave superconductor and a ferromagnetic insulator. We show that the radius of an exterior Majorana state can be tuned by an applied magnetic field. However, on the contrary to the results at a TI surface, neither the exterior Majorana state nor the induced odd-frequency spin-triplet pairs are spin-polarized. We conclude that the spin polarization of the Majorana state is attributed to the spin-polarized Landau level, which is characteristic for systems with the Dirac-like dispersion.

Two-dimensional heteroclinic attractor in the generalized Lotka-Volterra system

Science.gov (United States)

Afraimovich, Valentin S.; Moses, Gregory; Young, Todd

2016-05-01

We study a simple dynamical model exhibiting sequential dynamics. We show that in this model there exist sets of parameter values for which a cyclic chain of saddle equilibria, O k , k=1,\\ldots,p , have two-dimensional unstable manifolds that contain orbits connecting each O k to the next two equilibrium points O k+1 and O k+2 in the chain ({{O}p+1}={{O}1} ). We show that the union of these equilibria and their unstable manifolds form a two-dimensional surface with a boundary that is homeomorphic to a cylinder if p is even and a Möbius strip if p is odd. If, further, each equilibrium in the chain satisfies a condition called ‘dissipativity’, then this surface is asymptotically stable.

Two-dimensional manifolds with metrics of revolution

International Nuclear Information System (INIS)

Sabitov, I Kh

2000-01-01

This is a study of the topological and metric structure of two-dimensional manifolds with a metric that is locally a metric of revolution. In the case of compact manifolds this problem can be thoroughly investigated, and in particular it is explained why there are no closed analytic surfaces of revolution in R 3 other than a sphere and a torus (moreover, in the smoothness class C ∞ such surfaces, understood in a certain generalized sense, exist in any topological class)

Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

International Nuclear Information System (INIS)

Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad; Sun Yawen; Zaanen, Jan

2011-01-01

We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces. As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.

Investigations on field-effect transistors based on two-dimensional materials

Energy Technology Data Exchange (ETDEWEB)

Finge, T.; Riederer, F.; Grap, T.; Knoch, J. [Institute of Semiconductor Electronics, RWTH Aachen University (Germany); Mueller, M.R. [Institute of Semiconductor Electronics, RWTH Aachen University (Germany); Infineon Technologies, Villach (Austria); Kallis, K. [Intelligent Microsystems Chair, TU Dortmund University (Germany)

2017-11-15

In the present article, experimental and theoretical investigations regarding field-effect transistors based on two-dimensional (2D) materials are presented. First, the properties of contacts between a metal and 2D material are discussed. To this end, metal-to-graphene contacts as well to transition metal dichalcogenides (TMD) are studied. Whereas metal-graphene contacts can be tuned with an appropriate back-gate, metal-TMD contacts exhibit strong Fermi level pinning showing substantially limited maximum possible drive current. Next, tungsten diselenide (WSe{sub 2}) field-effect transistors are presented. Employing buried-triple-gate substrates allows tuning source, channel and drain by applying appropriate gate voltages so that the device can be reconfigured to work as n-type, p-type and as so-called band-to-band tunnel field-effect transistor on the same WSe{sub 2} flake. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid-base chemistry

Science.gov (United States)

Lei, Sidong; Wang, Xifan; Li, Bo; Kang, Jiahao; He, Yongmin; George, Antony; Ge, Liehui; Gong, Yongji; Dong, Pei; Jin, Zehua; Brunetto, Gustavo; Chen, Weibing; Lin, Zuan-Tao; Baines, Robert; Galvão, Douglas S.; Lou, Jun; Barrera, Enrique; Banerjee, Kaustav; Vajtai, Robert; Ajayan, Pulickel

2016-05-01

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Nanoscale measurement of Nernst effect in two-dimensional charge density wave material 1T-TaS2

Science.gov (United States)

Wu, Stephen M.; Luican-Mayer, Adina; Bhattacharya, Anand

2017-11-01

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS2 is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearly commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS2, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW → NCCDW transition.

Low-energy excitations and Fermi surface topology of parent cobaltate superconductor

International Nuclear Information System (INIS)

Hasan, M.Z.; Qian, D.; Foo, M.; Cava, R.J.

2007-01-01

The essential framework for cuprate superconductivity is that of a spin-1/2 electron system in the vicinity of a half filled (Mott limit) lattice. Of all oxide superconductors, this framework is most closely matched in the sodium doped cobalt oxides except that it is realized on a triangular lattice. We employ angle-resolved photoemission spectroscopy to study the quasiparticle dynamics of the parent cobaltate superconductor. Results reveal a single hole-like Fermi surface generated by the crossing of heavy (∼15 m e ∼ 3m LDA ) quasiparticles with a negative effective hopping (t eff F (k → )∼v F ∼0.4±0.1 eV A) observed. ARPES data is consistent with bulk thermodynamic specific heat and quantum oscillation measurements

Structure and coarsening at the surface of a dry three-dimensional aqueous foam.

Science.gov (United States)

Roth, A E; Chen, B G; Durian, D J

2013-12-01

We utilize total-internal reflection to isolate the two-dimensional surface foam formed at the planar boundary of a three-dimensional sample. The resulting images of surface Plateau borders are consistent with Plateau's laws for a truly two-dimensional foam. Samples are allowed to coarsen into a self-similar scaling state where statistical distributions appear independent of time, except for an overall scale factor. There we find that statistical measures of side number distributions, size-topology correlations, and bubble shapes are all very similar to those for two-dimensional foams. However, the size number distribution is slightly broader, and the shapes are slightly more elongated. A more obvious difference is that T2 processes now include the creation of surface bubbles, due to rearrangement in the bulk, and von Neumann's law is dramatically violated for individual bubbles. But nevertheless, our most striking finding is that von Neumann's law appears to holds on average, namely, the average rate of area change for surface bubbles appears to be proportional to the number of sides minus six, but with individual bubbles showing a wide distribution of deviations from this average behavior.

A two-dimensional finite element model of front surface current flow in cells under non-uniform, concentrated illumination

Energy Technology Data Exchange (ETDEWEB)

Mellor, A.; Domenech-Garret, J.L.; Chemisana, D.; Rosell, J.I. [Departament de Medi Ambient i C.S., University of Lleida, Av. Alcalde Rovira Roure 191, E25198 (Spain)

2009-09-15

A two-dimensional finite element model of current flow in the front surface of a PV cell is presented. In order to validate this model we perform an experimental test. Later, particular attention is paid to the effects of non-uniform illumination in the finger direction which is typical in a linear concentrator system. Fill factor, open circuit voltage and efficiency are shown to decrease with increasing degree of non-uniform illumination. It is shown that these detrimental effects can be mitigated significantly by reoptimization of the number of front surface metallization fingers to suit the degree of non-uniformity. The behavior of current flow in the front surface of a cell operating at open circuit voltage under non-uniform illumination is discussed in detail. (author)

Two dimensional infinite conformal symmetry

International Nuclear Information System (INIS)

Mohanta, N.N.; Tripathy, K.C.

1993-01-01

The invariant discontinuous (discrete) conformal transformation groups, namely the Kleinian and Fuchsian groups Gamma (with an arbitrary signature) of H (the Poincare upper half-plane l) and the unit disc Delta are explicitly constructed from the fundamental domain D. The Riemann surface with signatures of Gamma and conformally invariant automorphic forms (functions) with Peterson scalar product are discussed. The functor, where the category of complex Hilbert spaces spanned by the space of cusp forms constitutes the two dimensional conformal field theory. (Author) 7 refs

Search for Spatially Extended Fermi-LAT Sources Using Two Years of Data

Energy Technology Data Exchange (ETDEWEB)

Lande, Joshua; Ackermann, Markus; Allafort, Alice; Ballet, Jean; Bechtol, Keith; Burnett, Toby; Cohen-Tanugi, Johann; Drlica-Wagner, Alex; Funk, Stefan; Giordano, Francesco; Grondin, Marie-Helene; Kerr, Matthew; Lemoine-Goumard, Marianne

2012-07-13

Spatial extension is an important characteristic for correctly associating {gamma}-ray-emitting sources with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. We present a new method for quantifying the spatial extension of sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi). We perform a series of Monte Carlo simulations to validate this tool and calculate the LAT threshold for detecting the spatial extension of sources. We then test all sources in the second Fermi -LAT catalog (2FGL) for extension. We report the detection of seven new spatially extended sources.

Binding Direction-Based Two-Dimensional Flattened Contact Area Computing Algorithm for Protein-Protein Interactions.

Science.gov (United States)

Kang, Beom Sik; Pugalendhi, GaneshKumar; Kim, Ku-Jin

2017-10-13

Interactions between protein molecules are essential for the assembly, function, and regulation of proteins. The contact region between two protein molecules in a protein complex is usually complementary in shape for both molecules and the area of the contact region can be used to estimate the binding strength between two molecules. Although the area is a value calculated from the three-dimensional surface, it cannot represent the three-dimensional shape of the surface. Therefore, we propose an original concept of two-dimensional contact area which provides further information such as the ruggedness of the contact region. We present a novel algorithm for calculating the binding direction between two molecules in a protein complex, and then suggest a method to compute the two-dimensional flattened area of the contact region between two molecules based on the binding direction.

Binding Direction-Based Two-Dimensional Flattened Contact Area Computing Algorithm for Protein–Protein Interactions

Directory of Open Access Journals (Sweden)

Beom Sik Kang

2017-10-01

Full Text Available Interactions between protein molecules are essential for the assembly, function, and regulation of proteins. The contact region between two protein molecules in a protein complex is usually complementary in shape for both molecules and the area of the contact region can be used to estimate the binding strength between two molecules. Although the area is a value calculated from the three-dimensional surface, it cannot represent the three-dimensional shape of the surface. Therefore, we propose an original concept of two-dimensional contact area which provides further information such as the ruggedness of the contact region. We present a novel algorithm for calculating the binding direction between two molecules in a protein complex, and then suggest a method to compute the two-dimensional flattened area of the contact region between two molecules based on the binding direction.

Induced interactions in a superfluid Bose-Fermi mixture

DEFF Research Database (Denmark)

Kinnunen, Jami; Bruun, Georg

2015-01-01

We analyze a Bose-Einstein condensate (BEC) mixed with a superfluid two-component Fermi gas in the whole BCS-BEC crossover. Using a quasiparticle random-phase approximation combined with Beliaev theory to describe the Fermi superfluid and the BEC, respectively, we show that the single-particle an......We analyze a Bose-Einstein condensate (BEC) mixed with a superfluid two-component Fermi gas in the whole BCS-BEC crossover. Using a quasiparticle random-phase approximation combined with Beliaev theory to describe the Fermi superfluid and the BEC, respectively, we show that the single...... shift in the excitation spectrum of the BEC. In addition, the excitation of quasiparticles in the Fermi superfluid leads to damping of the excitations in the BEC. Besides studying induced interactions themselves, we can use these prominent effects to systematically probe the strongly interacting Fermi...

Temperature-Independent Fermi Surface in the Kondo Lattice YbRh_{2}Si_{2}

Directory of Open Access Journals (Sweden)

K. Kummer

2015-03-01

Full Text Available Strongly correlated electron systems are one of the central topics in contemporary solid-state physics. Prominent examples for such systems are Kondo lattices, i.e., intermetallic materials in which below a critical temperature, the Kondo temperature T_{K}, the magnetic moments become quenched and the effective masses of the conduction electrons approach the mass of a proton. In Ce- and Yb-based systems, this so-called heavy-fermion behavior is caused by interactions between the strongly localized 4f and itinerant electrons. A major and very controversially discussed issue in this context is how the localized electronic degree of freedom gets involved in the Fermi surface (FS upon increasing the interaction between both kinds of electrons or upon changing the temperature. In this paper, we show that the FS of a prototypic Kondo lattice, YbRh_{2}Si_{2}, does not change its size or shape in a wide temperature range extending from well below to far above the single-ion Kondo temperature T_{K}∼25  K of this system. This experimental observation, obtained by means of angle-resolved photoemission spectroscopy, is in remarkable contrast to the widely believed evolution from a large FS, including the 4f degrees of freedom, to a small FS, without the 4f’s, upon increasing temperature. Our results explicitly demonstrate a need to further advance in theoretical approaches based on the periodic Anderson model in order to elucidate the temperature dependence of Fermi surfaces in Kondo lattices.

Holographic Fermi and Non-Fermi Liquids with Transitions in Dilaton Gravity

CERN Document Server

Iizuka, Norihiro; Narayan, Prithvi; Trivedi, Sandip P

2012-01-01

We study the two-point function for fermionic operators in a class of strongly coupled systems using the gauge-gravity correspondence. The gravity description includes a gauge field and a dilaton which determines the gauge coupling and the potential energy. Extremal black brane solutions in this system typically have vanishing entropy. By analyzing a charged fermion in these extremal black brane backgrounds we calculate the two-point function of the corresponding boundary fermionic operator. We find that in some region of parameter space it is of Fermi liquid type. Outside this region no well-defined quasi-particles exist, with the excitations acquiring a non-vanishing width at zero frequency. At the transition, the two-point function can exhibit non-Fermi liquid behaviour.

Selective three-dimensional hydrophilization of microstructured polymer surfaces through confined photocatalytic oxidation

International Nuclear Information System (INIS)

Ammosova, Lena; Jiang, Yu; Suvanto, Mika; Pakkanen, Tapani A.

2015-01-01

Graphical abstract: - Highlights: • Microstructured polymer surfaces with selective 3-D anisotropy were created. • Selective UV treatment was performed to alter surface wettability. • Removable meshes resembling a photomask were applied during UV treatment. • Micropatterning by viscous polymer on solid surface was performed. - Abstract: While the conventional photomask technique gives only two-dimensional anisotropies, in this study we fabricated microstructured polymer surfaces with a selective three-dimensional anisotropy. With the applied removable mesh, we were able to confine the contacting area between the surface and photoinitiator and provide three-dimensional wettability anisotropies. Different types of meshes were used depending on the desired micropatterns shape, size and substrate material. The results revealed the three-dimensional anisotropic micropits pattern with depth profiles, which would be applicable for the confinement and patterning of cells and biomolecules. In addition, the proposed method is applicable for creating selectively activated polymer surface as a substrate for further atomic layer deposition. Moreover, we demonstrate a low cost and fast mass productive method for patterning a viscous polymer liquid in a micro-sized scale

Theory of Fermi Liquid with Flat Bands

Science.gov (United States)

Khodel, V. A.

2018-04-01

A self-consistent theory of Fermi systems hosting flat bands is developed. Compared with an original model of fermion condensation, its key point consists in proper accounting for mixing between condensate and non-condensate degrees of freedom that leads to formation of a non-BCS gap Υ (p) in the single-particle spectrum. The results obtained explain: (1) the two-gap structure of spectra of single-particle excitations of electron systems of copper oxides, revealed in ARPES studies, (2) the role of violation of the topological stability of the Landau state in the arrangement of the T-x phase diagram of this family of high-T_c superconductors, (3) the topological nature of a metal-insulator transition, discovered in homogeneous two-dimensional low-density electron liquid of MOSFETs more than 20 years ago.

Confined catalysis under two-dimensional materials

OpenAIRE

Li, Haobo; Xiao, Jianping; Fu, Qiang; Bao, Xinhe

2017-01-01

Small spaces in nanoreactors may have big implications in chemistry, because the chemical nature of molecules and reactions within the nanospaces can be changed significantly due to the nanoconfinement effect. Two-dimensional (2D) nanoreactor formed under 2D materials can provide a well-defined model system to explore the confined catalysis. We demonstrate a general tendency for weakened surface adsorption under the confinement of graphene overlayer, illustrating the feasible modulation of su...

Electronic structure, Fermi surface topology and spectroscopic optical properties of LaBaCo{sub 2}O{sub 5.5} compound

Energy Technology Data Exchange (ETDEWEB)

Reshak, A.H. [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, Pilsen 306 14 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria); Khan, Wilayat; Khan, Saleem Ayaz [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, Pilsen 306 14 (Czech Republic); Azam, Sikander, E-mail: sikander.physicst@gmail.com [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, Pilsen 306 14 (Czech Republic)

2014-08-01

We have investigated the electronic band structure, Fermi surface topology, chemical bonding and optical properties of LaBaCo{sub 2}O{sub 5.5} compound. The first-principle calculations based on density functional theory (DFT) by means of the full-potential linearized augmented plane-wave method were employed. The atomic positions of LaBaCo{sub 2}O{sub 5.5} compound were optimized by minimizing the forces acting on atoms. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. Electronic structure and bonding properties are studied throughout the calculation of densities of states, Fermi surfaces and charge densities. Furthermore, the optical properties are investigated via the calculation of the dielectric tensor component in order to characterize the linear optical properties. Optical spectra are analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of the investigated compound. - Highlights: • DFT-FPLAPW method used for calculating the properties of LaBaCo{sub 2}O{sub 5.5} compound. • This study shows that nature of the compound is metallic. • Crystallographic plane which shows covalent character of O–Co bond. • The optical properties were also calculated and analyzed. • The Fermi surface of LaBaCo{sub 2}O{sub 5.5} is composed of five bands crossing along Γ–Z direction.

Spin interaction with an ideal fermi gas

International Nuclear Information System (INIS)

Aizenstadt, V.V.; Malyshev, V.A.

1987-01-01

The authors consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice Z/sup v, v ≥ 3. They present two examples; when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interactions between them

Mode selection in two-dimensional Bragg resonators based on planar dielectric waveguides

International Nuclear Information System (INIS)

Baryshev, V R; Ginzburg, N S; Zaslavskii, V Yu; Malkin, A M; Sergeev, A S; Thumm, M

2009-01-01

Two-dimensional Bragg resonators based on planar dielectric waveguides are analysed. It is shown that the doubly periodic corrugation deposited on the dielectric surface in the form of two gratings with translational vectors directed perpendicular to each other ensures effective selection of modes along two coordinates at large Fresnel parameters. This result is obtained both by the method of coupled waves (geometrical optics approximation) and by the direct numerical simulations. Two-dimensional Bragg resonators make it possible to fabricate two-dimensional distributed feedback lasers and to provide generation of spatially coherent radiation in large-volume active media. (waveguides)

Final state effects in photoemission studies of Fermi surfaces

International Nuclear Information System (INIS)

Kurtz, Richard L; Browne, Dana A; Mankey, Gary J

2007-01-01

Photoelectron spectroscopy is one of the most important methods for extracting information about the Fermi surface (FS) of materials. An electron photoexcited from the FS is emitted from the crystal conserving the parallel momentum, k parallel , while the perpendicular momentum k perpendicular is reduced due to the surface potential barrier. A simple interpretation of the process assumes the final state is free-electron-like allowing one to 'map' the detected photoelectron back to its initial k momentum. There are multiple final state effects that can complicate the interpretation of photoelectron data and these effects are reviewed here. These can involve both energy and k broadening, which can give rise to shadow or ghost FS contours, scattering and final state diffraction effects that modify intensities, and matrix element effects which reflect the symmetries of the states involved and can be highly dependent on photon polarization. These matrix elements result in contours of photoelectron intensity that follow the dispersion in k-space of the initial state, the FS, and the final state. Locations where intensities go to zero due to matrix element and symmetry effects can result in gaps where FS contours 'disappear'. Recognition that these effects can play a significant role in determining the measured angular distributions is crucial in developing an informed model of where the FS contours actually lie in relation to measured intensity contours

Twelve inequivalent Dirac cones in two-dimensional ${\mathrm{ZrB}}_2$

Energy Technology Data Exchange (ETDEWEB)

Lopez-Bezanilla, Alejandro

2018-01-01

Theoretical evidence of the existence of 12 inequivalent Dirac cones at the vicinity of the Fermi energy in monolayered ZrB2 is presented. Two-dimensional ZrB2 is a mechanically stable d- and p-orbital compound exhibiting a unique electronic structure with two Dirac cones out of high-symmetry points in the irreducible Brillouin zone with a small electron-pocket compensation. First-principles calculations demonstrate that while one of the cones is insensitive to lattice expansion, the second cone vanishes for small perturbation of the vertical Zr position. Internal symmetry breaking with external physical stimuli, along with the relativistic effect of spin-orbit coupling, is able to remove selectively the Dirac cones. A rational explanation in terms of d- and p-orbital mixing is provided to elucidate the origin of the infrequent Dirac cones in a flat structure. The versatility of transition-metal d orbitals combined with the honeycomb lattice provided by the B atoms yields particular features in a two-dimensional material.

An Integrable Approximation for the Fermi Pasta Ulam Lattice

Science.gov (United States)

Rink, Bob

This contribution presents a review of results obtained from computations of approximate equations of motion for the Fermi-Pasta-Ulam lattice. These approximate equations are obtained as a finite-dimensional Birkhoff normal form. It turns out that in many cases, the Birkhoff normal form is suitable for application of the KAM theorem. In particular, this proves Nishida's 1971 conjecture stating that almost all low-energetic motions of the anharmonic Fermi-Pasta-Ulam lattice with fixed endpoints are quasi-periodic. The proof is based on the formal Birkhoff normal form computations of Nishida, the KAM theorem and discrete symmetry considerations.

Inhomogeneous Weyl and Dirac Semimetals: Transport in Axial Magnetic Fields and Fermi Arc Surface States from Pseudo-Landau Levels

Science.gov (United States)

Grushin, Adolfo G.; Venderbos, Jörn W. F.; Vishwanath, Ashvin; Ilan, Roni

2016-10-01

Topological Dirac and Weyl semimetals have an energy spectrum that hosts Weyl nodes appearing in pairs of opposite chirality. Topological stability is ensured when the nodes are separated in momentum space and unique spectral and transport properties follow. In this work, we study the effect of a space-dependent Weyl node separation, which we interpret as an emergent background axial-vector potential, on the electromagnetic response and the energy spectrum of Weyl and Dirac semimetals. This situation can arise in the solid state either from inhomogeneous strain or nonuniform magnetization and can also be engineered in cold atomic systems. Using a semiclassical approach, we show that the resulting axial magnetic field B5 is observable through an enhancement of the conductivity as σ ˜B52 due to an underlying chiral pseudomagnetic effect. We then use two lattice models to analyze the effect of B5 on the spectral properties of topological semimetals. We describe the emergent pseudo-Landau-level structure for different spatial profiles of B5, revealing that (i) the celebrated surface states of Weyl semimetals, the Fermi arcs, can be reinterpreted as n =0 pseudo-Landau levels resulting from a B5 confined to the surface, (ii) as a consequence of position-momentum locking, a bulk B5 creates pseudo-Landau levels interpolating in real space between Fermi arcs at opposite surfaces, and (iii) there are equilibrium bound currents proportional to B5 that average to zero over the sample, which are the analogs of bound currents in magnetic materials. We conclude by discussing how our findings can be probed experimentally.

Topological surface Fermi arcs in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$

OpenAIRE

Xu, Qiunan; Liu, Enke; Shi, Wujun; Muechler, Lukas; Felser, Claudia; Sun, Yan

2017-01-01

Very recently, the half-metallic compound Co$_3$Sn$_2$S$_2$ was predicted to be a magnetic WSM with Weyl points only 60 meV above the Fermi level ($E_F$). Owing to the low charge carrier density and large Berry curvature induced, Co$_3$Sn$_2$S$_2$ possesses both a large anomalous Hall conductivity (AHC) and a large anomalous Hall angle (AHA), which provide strong evidence for the existence of Weyl points in Co$_3$Sn$_2$S$_2$. In this work, we theoretically studied the surface topological feat...

A two-dimensional mathematical model of percutaneous drug absorption

Directory of Open Access Journals (Sweden)

Kubota K

2004-06-01

Full Text Available Abstract Background When a drug is applied on the skin surface, the concentration of the drug accumulated in the skin and the amount of the drug eliminated into the blood vessel depend on the value of a parameter, r. The values of r depend on the amount of diffusion and the normalized skin-capillary clearence. It is defined as the ratio of the steady-state drug concentration at the skin-capillary boundary to that at the skin-surface in one-dimensional models. The present paper studies the effect of the parameter values, when the region of contact of the skin with the drug, is a line segment on the skin surface. Methods Though a simple one-dimensional model is often useful to describe percutaneous drug absorption, it may be better represented by multi-dimensional models. A two-dimensional mathematical model is developed for percutaneous absorption of a drug, which may be used when the diffusion of the drug in the direction parallel to the skin surface must be examined, as well as in the direction into the skin, examined in one-dimensional models. This model consists of a linear second-order parabolic equation with appropriate initial conditions and boundary conditions. These boundary conditions are of Dirichlet type, Neumann type or Robin type. A finite-difference method which maintains second-order accuracy in space along the boundary, is developed to solve the parabolic equation. Extrapolation in time is applied to improve the accuracy in time. Solution of the parabolic equation gives the concentration of the drug in the skin at a given time. Results Simulation of the numerical methods described is carried out with various values of the parameter r. The illustrations are given in the form of figures. Conclusion Based on the values of r, conclusions are drawn about (1 the flow rate of the drug, (2 the flux and the cumulative amount of drug eliminated into the receptor cell, (3 the steady-state value of the flux, (4 the time to reach the steady

Some statistical aspects of the spinor field Fermi-Bose duality

Directory of Open Access Journals (Sweden)

V.M. Simulik

2012-12-01

Full Text Available The structure of 29-dimensional extended real Clifford-Dirac algebra, which has been introduced in our paper Phys. Lett. A, 2011, Vol. 375, 2479, is considered in brief. Using this algebra, the property of Fermi-Bose duality of the Dirac equation with nonzero mass is proved. It means that Dirac equation can describe not only the fermionic but also the bosonic states. The proof of our assertion based on the examples of bosonic symmetries, solutions and conservation laws is given. Some statistical aspects of the spinor field Fermi-Bose duality are discussed.

Analytical thermodynamics of a strongly attractive three-component Fermi gas in one dimension

International Nuclear Information System (INIS)

He Peng; Yin Xiangguo; Wang Yupeng; Guan Xiwen; Batchelor, Murray T.

2010-01-01

Ultracold three-component atomic Fermi gases in one dimension are expected to exhibit rich physics due to the presence of trions and different pairing states. Quantum phase transitions from the trion state into a paired phase and a normal Fermi liquid occur at zero temperature. We derive the analytical thermodynamics of strongly attractive three-component one-dimensional fermions with SU(3) symmetry via the thermodynamic Bethe ansatz method in unequal Zeeman splitting fields H 1 and H 2 . We find explicitly that for low temperature the system acts like either a two-component or a three-component Tomonaga-Luttinger liquid dependent on the system parameters. The phase diagrams for the chemical potential and specific heat are presented for illustrative values of the Zeeman splitting. We also demonstrate that crossover between different Tomonaga-Luttinger-liquid phases exhibit singular behavior in specific heat and entropy as the temperature tends to zero. Beyond Tomonaga-Luttinger-liquid physics, we obtain the equation of state which provides a precise description of universal thermodynamics and quantum criticality in three-component, strongly attractive Fermi gases.

Relativistic effects in the Thomas--Fermi atom

International Nuclear Information System (INIS)

Waber, J.T.; Canfield, J.M.

1975-01-01

Two methods of applying relativistic corrections to the Thomas--Fermi atom are considered, and numerical calculations are discussed. Radial charge distributions calculated from a relativistic Thomas--Fermi equation agree in gross form with those from more complicated self-consistent calculations. Energy eigenvalues for mercury, as determined from the relativistic Thomas--Fermi solution, are compared with other calculated and experimental values

Electronic structure engineering in silicene via atom substitution and a new two-dimensional Dirac structure Si3C

Science.gov (United States)

Yin, Na; Dai, Ying; Wei, Wei; Huang, Baibiao

2018-04-01

A lot of efforts have been made towards the band gap opening in two-dimensional silicene, the silicon version of graphene. In the present work, the electronic structures of single atom doped (B, N, Al and P) and codoped (B/N and Al/P) silicene monolayers are systematically examined on the base of density functional electronic calculations. Our results demonstrate that single atom doping can realize electron or hole doping in the silicene; while codoping, due to the syergistic effects, results in finite band gap in silicene at the Dirac point without significantly degrading the electronic properties. In addition, the characteristic of band gap shows dependence on the doping concentration. Importantly, we predict a new two-dimensional Dirac structure, the graphene-like Si3C, which also shows linear band dispersion relation around the Fermi level. Our results demonstrates an important perspective to engineer the electronic and optical properties of silicene.

Phase structure of strongly correlated Fermi gases

International Nuclear Information System (INIS)

Roscher, Dietrich

2015-01-01

Strongly correlated fermionic many-body systems are ubiquitous in nature. Their theoretical description poses challenging problems which are further complicated when imbalances in, e.g., the particle numbers of the involved species or their masses are introduced. In this thesis, a number of different approaches is developed and applied in order to obtain predictions for physical observables of such systems that mutually support and confirm each other. In a first step, analytically well-founded mean-field analyses are carried through. One- and three-dimensional ultracold Fermi gases with spin and mass imbalance as well as Gross-Neveu and NJL-type relativistic models at finite baryon chemical potential are investigated with respect to their analytic properties in general and the occurrence of spontaneous breaking of translational invariance in particular. Based on these studies, further methods are devised or adapted allowing for investigations also beyond the mean-field approximation. Lattice Monte Carlo simulations with imaginary imbalance parameters are employed to surmount the infamous sign problem and compute the equation of state of the respective unitary Fermi gases. Moreover, in-medium two-body analyses are used to confirm and explain the characteristics of inhomogeneously ordered phases. Finally, functional RG methods are applied to the unitary Fermi gas with spin and mass imbalance. Besides quantitatively competitive predictions for critical temperatures for the superfluid state, strong hints on the stability of inhomogeneous phases with respect to order parameter fluctuations in the regime of large mass imbalance are obtained. Combining the findings from these different theoretical studies suggests the possibility to find such phases in experiments presently in preparation.

GEPOIS: a two dimensional nonuniform mesh Poisson solver

International Nuclear Information System (INIS)

Quintenz, J.P.; Freeman, J.R.

1979-06-01

A computer code is described which solves Poisson's equation for the electric potential over a two dimensional cylindrical (r,z) nonuniform mesh which can contain internal electrodes. Poisson's equation is solved over a given region subject to a specified charge distribution with either Neumann or Dirichlet perimeter boundary conditions and with Dirichlet boundary conditions on internal surfaces. The static electric field is also computed over the region with special care given to normal electric field components at boundary surfaces

Three-body bound states of two bosonic impurities immersed in a Fermi sea in 2D

DEFF Research Database (Denmark)

Bellotti, F. F.; Frederico, T.; Yamashita, M. T.

2016-01-01

We consider two identical impurities immersed in a Fermi sea for a broad range of masses and for both interacting and non-interacting impurities. The interaction between the particles is described through attractive zero-range potentials and the problem is solved in momentum space. The two...

Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure

Science.gov (United States)

Gonnelli, R. S.; Daghero, D.; Tortello, M.; Ummarino, G. A.; Bukowski, Z.; Karpinski, J.; Reuvekamp, P. G.; Kremer, R. K.; Profeta, G.; Suzuki, K.; Kuroki, K.

2016-05-01

Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line.

Chern-Simons theory and three-dimensional surfaces

International Nuclear Information System (INIS)

Guven, Jemal

2007-01-01

There are two natural Chern-Simons theories associated with the embedding of a three-dimensional surface in Euclidean space: one is constructed using the induced metric connection and involves only the intrinsic geometry? the other is extrinsic and uses the connection associated with the gauging of normal rotations. As such, the two theories appear to describe very different aspects of the surface geometry. Remarkably, at a classical level, they are equivalent. In particular, it will be shown that their stress tensors differ only by a null contribution. Their Euler-Lagrange equations provide identical constraints on the normal curvature. A new identity for the Cotton tensor is associated with the triviality of the Chern-Simons theory for embedded hypersurfaces implied by this equivalence

Dynamical class of a two-dimensional plasmonic Dirac system.

Science.gov (United States)

Silva, Érica de Mello

2015-10-01

A current goal in plasmonic science and technology is to figure out how to manage the relaxational dynamics of surface plasmons in graphene since its damping constitutes a hinder for the realization of graphene-based plasmonic devices. In this sense we believe it might be of interest to enlarge the knowledge on the dynamical class of two-dimensional plasmonic Dirac systems. According to the recurrence relations method, different systems are said to be dynamically equivalent if they have identical relaxation functions at all times, and such commonality may lead to deep connections between seemingly unrelated physical systems. We employ the recurrence relations approach to obtain relaxation and memory functions of density fluctuations and show that a two-dimensional plasmonic Dirac system at long wavelength and zero temperature belongs to the same dynamical class of standard two-dimensional electron gas and classical harmonic oscillator chain with an impurity mass.

Micropatterning of bacteria on two-dimensional lattice protein surface observed by atomic force microscopy

International Nuclear Information System (INIS)

Oh, Y.J.; Jo, W.; Lim, J.; Park, S.; Kim, Y.S.; Kim, Y.

2008-01-01

In this study, we characterized the two-dimensional lattice of bovine serum albumin (BSA) as a chemical and physical barrier against bacterial adhesion, using fluorescence microscopy and atomic force microscopy (AFM). The lattice of BSA on glass surface was fabricated by micro-contact printing (μCP), which is a useful way to pattern a wide range of molecules into microscale features on different types of substrates. The contact-mode AFM measurements showed that the average height of the printed BSA monolayer was 5-6 nm. Escherichia coli adhered rapidly on bare glass slide, while the bacterial adhesion was minimized on the lattices in the range of 1-3 μm 2 . Especially, the bacterial adhesion was completely inhibited on a 1 μm 2 lattice. The results suggest that the anti-adhesion effects are due by the steric repulsion forces exerted by BSA

Partially gapped Fermi surface in the heavy-electron superconductor URu2Si2

International Nuclear Information System (INIS)

Maple, M.B.; Chen, J.W.; Dalichaouch, Y.; Kohara, T.; Rossel, C.; Torikachvili, M.S.; McElfresh, M.W.; Thompson, J.D.

1986-01-01

Transport, thermal, and magnetic data for the heavy electron system URu 2 Si 2 indicate that a charge- or spin-density-wave transition opens an energy gap of approx.11 meV over a portion of the Fermi surface below T 0 roughly-equal17.5 K and demonstrate that bulk superconductivity occurs below T/sub c/roughly-equal1.5 K. The pressure dependences of T 0 and T/sub c/ support this interpretation. The unusually large initial slope of the upper critical magnetic field (9.2 T/K) is consistent with the high values of the electronic-specific-heat coefficient and the electrical resistivity

Formation of halo-structures in oxygen isotopes through change of occupancy of levels near Fermi surface

International Nuclear Information System (INIS)

Bhattacharya, Rupayan

2000-01-01

Recently a new parametrisation of Skyrme interaction has been formulated in order to study the level inversions of A=9 isobars. The role of occupancy of 2s 1/2 level in determining the halo structures of O, N, C, B and Be nuclei was shown. A thorough investigation on the binding energies, rms charge, neutron and matter distribution and occupation probabilities of levels near the Fermi surface has been done in the present work

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas with spin–orbit coupling

International Nuclear Information System (INIS)

Wang, Pei; Yi, Wei; Xianlong, Gao

2015-01-01

We study the quench dynamics of a one-dimensional ultracold Fermi gas with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems. (paper)

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas with spin-orbit coupling

Science.gov (United States)

Wang, Pei; Yi, Wei; Xianlong, Gao

2015-01-01

We study the quench dynamics of a one-dimensional ultracold Fermi gas with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems.

I. A model for the magnetic equation of state of liquid 3He. II. An induced interaction model for a two-component Fermi liquid

International Nuclear Information System (INIS)

Sanchez-Castro, C.R.

1988-01-01

This dissertation is divided in six chapters. Chapter 1 is an introduction to the rest of the dissertation. In it, the author presents the different models for the magnetic equation state of liquid 3 He, a derivation of the induced interaction equations for a one component Fermi liquid, and discuss the basic hamiltonian describing the heavy fermion compounds. In Chapter 2 and Chapter 3, he presents a complete discussion of the thermodynamics and Landau theory of a spin polarized Fermi liquid. A phenomenological model is then developed to predict the polarization dependence of the longitudinal Landau parameters in liquid 3 He. This model predicts a new magnetic equation of state and the possibility of liquid 3 He being 'nearly metamagnetic' at high pressures. Chapter 4 contains a microscopic calculation of the magnetic field dependence of the Landau parameters in a strongly correlated Fermi system using the induced interaction model. The system he studied consists of a single component Fermi liquid with parabolic energy bands, and a large on-site repulsive interaction. In Chapter 5, he presents a complete discussion of the Landau theory of a two component Fermi liquid. Then, he generalizes the induced interaction equations to calculate Landau parameters and scattering amplitudes for an arbitrary, spin polarized, two component Fermi liquid. The resulting equations are used to study a model for the heavy fermion Fermi liquid state: a two band electronic system with an antiferromagnetic interaction between the two bands. Chapter 6 contains the concluding remarks of the dissertation

Resonant spin Hall effect in two dimensional electron gas

Science.gov (United States)

Shen, Shun-Qing

2005-03-01

Remarkable phenomena have been observed in 2DEG over last two decades, most notably, the discovery of integer and fractional quantum Hall effect. The study of spin transport provides a good opportunity to explore spin physics in two-dimensional electron gas (2DEG) with spin-orbit coupling and other interaction. It is already known that the spin-orbit coupling leads to a zero-field spin splitting, and competes with the Zeeman spin splitting if the system is subjected to a magnetic field perpendicular to the plane of 2DEG. The result can be detected as beating of the Shubnikov-de Haas oscillation. Very recently the speaker and his collaborators studied transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin-orbit coupling competes with the Zeeman splitting to generate additional degeneracies between different Landau levels at certain magnetic fields. It is predicted theoretically that this degeneracy, if occurring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as -lnT at low temperatures. The charge Hall conductance changes by 2e^2/h instead of e^2/h as the magnetic field changes through the resonant point. The speaker will address the resonance condition, symmetries in the spin-orbit coupling, the singularity of magnetic susceptibility, nonlinear electric field effect, the edge effect and the disorder effect due to impurities. This work was supported by the Research Grants Council of Hong Kong under Grant No.: HKU 7088/01P. *S. Q. Shen, M. Ma, X. C. Xie, and F. C. Zhang, Phys. Rev. Lett. 92, 256603 (2004) *S. Q. Shen, Y. J. Bao, M. Ma, X. C. Xie, and F. C. Zhang, cond-mat/0410169

Universal Properties of a Trapped Two-Component Fermi Gas at Unitarity

International Nuclear Information System (INIS)

Blume, D.; Stecher, J. von; Greene, Chris H.

2007-01-01

We treat the trapped two-component Fermi system, in which unlike fermions interact through a two-body short-range potential having no bound state but an infinite scattering length. By accurately solving the Schroedinger equation for up to N=6 fermions, we show that no many-body bound states exist other than those bound by the trapping potential, and we demonstrate unique universal properties of the system: Certain excitation frequencies are separated by 2(ℎ/2π)ω, the wave functions agree with analytical predictions and a virial theorem is fulfilled. Further calculations up to N=30 determine the excitation gap, an experimentally accessible universal quantity, and it agrees with recent predictions based on a density functional approach

Symmetry breaking of a Bose–Fermi mixture in a triple-well potential

International Nuclear Information System (INIS)

Yan, Pei-Gen; Wang, Yuan-Sheng; Ji, Shen-Tong; Liu, Xue-Shen

2012-01-01

We investigate the properties of a one-dimensional Bose–Fermi mixture in a triple-well potential with two equally populated spin components at zero temperature. Based on the coupled equations for a Bose–Fermi mixture, we illustrate the symmetry breaking of the Bose–Fermi mixture with different strengths of interspecies and intraspecies interactions that are induced by changing the particle numbers of bosons and fermions. The several novel density profiles of symmetric and asymmetric ground states in the phase diagram of the (N F ,N B ) plane are demonstrated. In addition, the variation of density as a function of N B at fixed N F , which clearly shows the transition among distinct types of symmetric and asymmetric ground states, is illustrated. -- Highlights: ► We demonstrate the phase diagram in (N F ,N B ) plane. ► We then illustrate distinct regions in the phase diagram of the (N F ,N B ) plane and the corresponding novel typical density profiles of ground states. ► The novel density profiles of symmetric and asymmetric ground states are demonstrated. ► We illustrate the novel phase transitions among some of these ground states.

Suppressing Fermi acceleration in two-dimensional driven billiards.

Science.gov (United States)

Leonel, Edson D; Bunimovich, Leonid A

2010-07-01

We consider a dissipative oval-like shaped billiard with a periodically moving boundary. The dissipation considered is proportional to a power of the velocity V of the particle. The three specific types of power laws used are: (i) F∝-V ; (ii) F∝-V(2) and (iii) F∝-V(δ) with 1unlimited energy gain for cases (ii) and (iii). The critical exponents obtained for the phase transition in the case (ii) are the same as those obtained for the dissipative bouncer model. Therefore near this phase transition, these two rather different models belong to the same class of universality. For all types of dissipation, the results obtained allow us to conclude that suppression of the unlimited energy growth is indeed observed.

Isotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La_{0.6}Sr_{0.4}MnO_{3}.

Science.gov (United States)

Horiba, Koji; Kitamura, Miho; Yoshimatsu, Kohei; Minohara, Makoto; Sakai, Enju; Kobayashi, Masaki; Fujimori, Atsushi; Kumigashira, Hiroshi

2016-02-19

In order to reveal the many-body interactions in three-dimensional perovskite manganites that show colossal magnetoresistance, we performed an in situ angle-resolved photoemission spectroscopy on La_{0.6}Sr_{0.4}MnO_{3} and investigated the behavior of quasiparticles. We observed quasiparticle peaks near the Fermi momentum in both the electron and the hole bands, and clear kinks throughout the entire hole Fermi surface in the band dispersion. This isotropic behavior of quasiparticles and kinks suggests that polaronic quasiparticles produced by the coupling of electrons with Jahn-Teller phonons play an important role in the colossal magnetoresistance properties of the ferromagnetic metallic phase of three-dimensional manganites.

Defects in quasi-one dimensional oxide conductors: K0.3MoO3

International Nuclear Information System (INIS)

Smith, K.E.; Breuer, K.; Goldberg, D.; Greenblatt, M.; McCarroll, W.; Hulbert, S.L.

1995-01-01

The electronic structure of the prototypical quasi-one dimensional (ID) conductor K 0.3 MoO 3 has been studied using high resolution photoemission spectroscopy. In particular, the electronic structure of defects was investigated in order to understand the mechanism for charge density wave pinning and destruction of the Peierls transition. Defects were found to radically alter the electronic structure close to the Fermi level (E F ), thus strongly modifying the structure of the Fermi surface. While a low emission intensity at E F has been interpreted as evidence for a Luttinger liquid ground state in a 1D metal, the authors show that non-stoichiometric surfaces lead to similar effects. The nature of the ground state is discussed in the context of these results

Multiple surface plasmon polaritons modes on thin silver film controlled by a two-dimensional lattice of silver nanodimers

Energy Technology Data Exchange (ETDEWEB)

Chang, Ying; Jiang, Yongyuan, E-mail: jiangyy@hit.edu.cn [Harbin Institute of Technology, Department of Physics (China)

2015-01-15

We study the optical resonant spectrum of a two-dimensional periodic array of silver nanodimers on a thin silver film using multiple scattering formalism. The excited multiple plasmonic modes on two interfaces of the silver film reveal that the dispersion relationships of surface plasmon polaritons on metallic film are modified by doubly periodic lattice due to the fact that wave vectors matching conditions are satisfied. Moreover, we demonstrate that the plasmonic modes are directly controlled by the thickness of silver film, as well as the gap between nanodimer array and silver film. These effects provide novel high-efficient and steady way for excitation in future plasmonic nanodevices.

The retrieval of two-dimensional distribution of the earth's surface aerodynamic roughness using SAR image and TM thermal infrared image

Institute of Scientific and Technical Information of China (English)

ZHANG; Renhua; WANG; Jinfeng; ZHU; Caiying; SUN; Xiaomin

2004-01-01

After having analyzed the requirement on the aerodynamic earth's surface roughness in two-dimensional distribution in the research field of interaction between land surface and atmosphere, this paper presents a new way to calculate the aerodynamic roughness using the earth's surface geometric roughness retrieved from SAR (Synthetic Aperture Radar) and TM thermal infrared image data. On the one hand, the SPM (Small Perturbation Model) was used as a theoretical SAR backscattering model to describe the relationship between the SAR backscattering coefficient and the earth's surface geometric roughness and its dielectric constant retrieved from the physical model between the soil thermal inertia and the soil surface moisture with the simultaneous TM thermal infrared image data and the ground microclimate data. On the basis of the SAR image matching with the TM image, the non-volume scattering surface geometric information was obtained from the SPM model at the TM image pixel scale, and the ground pixel surface's equivalent geometric roughness-height standard RMS (Root Mean Square) was achieved from the geometric information by the transformation of the typical topographic factors. The vegetation (wheat, tree) height retrieved from spectrum model was also transferred into its equivalent geometric roughness. A completely two-dimensional distribution map of the equivalent geometric roughness over the experimental area was produced by the data mosaic technique. On the other hand, according to the atmospheric eddy currents theory, the aerodynamic surface roughness was iterated out with the atmosphere stability correction method using the wind and the temperature profiles data measured at several typical fields such as bare soil field and vegetation field. After having analyzed the effect of surface equivalent geometric roughness together with dynamic and thermodynamic factors on the aerodynamic surface roughness within the working area, this paper first establishes a scale

Fermi Large Area Telescope

Science.gov (United States)

are available to the public, along with standard analysis software, from NASA's Fermi Science Support Center. For general questions about Fermi, Fermi science, or Fermi classroom materials, please contact Fermi has its own music: a prelude and a symphony. Gamma Ray Bursts trasformed into visual music

Stability of spinor Fermi gases in tight waveguides

International Nuclear Information System (INIS)

Campo, A. del; Muga, J. G.; Girardeau, M. D.

2007-01-01

The two- and three-body correlation functions of the ground state of an optically trapped ultracold spin-(1/2) Fermi gas (SFG) in a tight waveguide [one-dimensional (1D) regime] are calculated in the plane of even- and odd-wave coupling constants, assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave Feshbach resonance, as well as the usual repulsive zero-range even-wave interaction stemming from 3D s-wave scattering. The calculations are based on the exact mapping from the SFG to a 'Lieb-Liniger-Heisenberg' model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, and indicate that the SFG should be stable against three-body recombination in a large region of the coupling constant plane encompassing parts of both the ferromagnetic and antiferromagnetic phases. However, the limiting case of the fermionic Tonks-Girardeau gas, a spin-aligned 1D Fermi gas with infinitely attractive p-wave interactions, is unstable in this sense. Effects due to the dipolar interaction and a Zeeman term due to a resonance-generating magnetic field do not lead to shrinkage of the region of stability of the SFG

Surface conduction of topological Dirac electrons in bulk insulating Bi2Se3

Science.gov (United States)

Fuhrer, Michael

2013-03-01

The three dimensional strong topological insulator (STI) is a new phase of electronic matter which is distinct from ordinary insulators in that it supports on its surface a conducting two-dimensional surface state whose existence is guaranteed by topology. I will discuss experiments on the STI material Bi2Se3, which has a bulk bandgap of 300 meV, much greater than room temperature, and a single topological surface state with a massless Dirac dispersion. Field effect transistors consisting of thin (3-20 nm) Bi2Se3 are fabricated from mechanically exfoliated from single crystals, and electrochemical and/or chemical gating methods are used to move the Fermi energy into the bulk bandgap, revealing the ambipolar gapless nature of transport in the Bi2Se3 surface states. The minimum conductivity of the topological surface state is understood within the self-consistent theory of Dirac electrons in the presence of charged impurities. The intrinsic finite-temperature resistivity of the topological surface state due to electron-acoustic phonon scattering is measured to be ~60 times larger than that of graphene largely due to the smaller Fermi and sound velocities in Bi2Se3, which will have implications for topological electronic devices operating at room temperature. As samples are made thinner, coherent coupling of the top and bottom topological surfaces is observed through the magnitude of the weak anti-localization correction to the conductivity, and, in the thinnest Bi2Se3 samples (~ 3 nm), in thermally-activated conductivity reflecting the opening of a bandgap.

Quantum statistical entropy corresponding to cosmic horizon in five-dimensional spacetime

Institute of Scientific and Technical Information of China (English)

2008-01-01

The generalized uncertainty relation is introduced to calculate the quantum statis-tical entropy corresponding to cosmic horizon. By using the new equation of state density motivated by the generalized uncertainty relation, we discuss entropies of Bose field and Fermi field on the background of five-dimensional spacetime. In our calculation, we need not introduce cutoff. There is no divergent logarithmic term in the original brick-wall method. And it is obtained that the quantum statistical en-tropy corresponding to cosmic horizon is proportional to the area of the horizon. Further it is shown that the entropy corresponding to cosmic horizon is the entropy of quantum state on the surface of horizon. The black hole’s entropy is the intrinsic property of the black hole. The entropy is a quantum effect. In our calculation, by using the quantum statistical method, we obtain the partition function of Bose field and Fermi field on the background of five-dimensional spacetime. We provide a way to study the quantum statistical entropy corresponding to cosmic horizon in the higher-dimensional spacetime.

Drag Effect in Double-Layer Dipolar Fermi Gases

International Nuclear Information System (INIS)

Tanatar, B; Renklioglu, B; Oktel, M O

2014-01-01

We consider two parallel layers of two-dimensional spin-polarized dipolar Fermi gas without any tunneling between the layers. The effective interactions describing screening and correlation effects between the dipoles in a single layer (intra-layer) and across the layers (interlayer) are modeled within the Hubbard approximation. We calculate the rate of momentum transfer between the layers when the gas in one layer has a steady flow. The momentum transfer induces a steady flow in the second layer which is assumed initially at rest. This is the drag effect familiar from double-layer semiconductor and graphene structures. Our calculations show that the momentum relaxation time has temperature dependence similar to that in layers with charged particles which we think is related to the contributions from the collective modes of the system

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Galvis, J.A. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá (Colombia); National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States); Herrera, E.; Guillamón, I.; Vieira, S. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain); Suderow, H., E-mail: hermann.suderow@uam.es [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain)

2017-02-15

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

International Nuclear Information System (INIS)

Galvis, J.A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

2017-01-01

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Quasiparticle lifetime in a mixture of Bose and Fermi superfluids.

Science.gov (United States)

Zheng, Wei; Zhai, Hui

2014-12-31

In this Letter, we study the effect of quasiparticle interactions in a Bose-Fermi superfluid mixture. We consider the lifetime of a quasiparticle of the Bose superfluid due to its interaction with quasiparticles in the Fermi superfluid. We find that this damping rate, i.e., the inverse of the lifetime, has quite a different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant near the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because, in the BCS side, the decay process is restricted by the constraint that the fermion quasiparticle is located near the Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasiparticles of the Fermi superfluid. Our results are related to the collective mode experiment in the recently realized Bose-Fermi superfluid mixture.

Strongly interacting Fermi gases

Directory of Open Access Journals (Sweden)

Bakr W.

2013-08-01

Full Text Available Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state.

Two-dimensional condensation of physi-sorbed methane on layer-like halides

International Nuclear Information System (INIS)

Nardon, Yves

1972-01-01

Two-dimensional condensation of methane in physi-sorbed layers has been studied from sets of stepped isotherms of methane on the cleavage plane of layer-like halides (FeCl 2 , CdCl 2 , NiBr 2 , CdBr 2 , FeI 2 , CaI 2 , CaI 2 and PbI 2 ) in most cases prepared by sublimation in a rapid current of inert gas. The vertical parts of the steps of adsorption isotherms correspond to the formation of successive monomolecular layers by two-dimensional condensation. Thermodynamic analysis of experimental results, has mainly emphasized the important effect of the potential relief of adsorbent surfaces, on both the structure of the physi-sorbed layers and the two-dimensional critical temperature. From its entropy, we conclude that the first layer is a (111) plane of f.c.c.: methane which becomes more loosely packed as the dimensional compatibility of the lattices of the adsorbent and adsorbate becomes poorer. Experimental values of the two-dimensional critical temperatures in the first, second and third layers have been determined, and interpreted on the following basis. An expansion of the layer induces a lowering of the two-dimensional critical temperature by decreasing the lateral interaction energy, while a localisation of the adsorbed molecules in potential wells, when possible, induces a rise of the two-dimensional critical temperature. (author) [fr

Four-fermi anomalous dimension with adjoint fermions

CERN Document Server

Del Debbio, Luigi; Ruano, Carlos Pena

2014-01-01

The four-fermi interaction can play an important role in models of strong dynamical EW sym- metry breaking if the anomalous dimensions of the four-fermi operators become large in the IR. We discuss a number of issues that are relevant for the nonperturbative computation of the four- fermi anomalous dimensions for the SU(2) gauge theory with two flavors of Dirac fermions in the adjoint representation, using a Schrödinger functional formalism.

Globally homochiral assembly of two-dimensional molecular networks triggered by co-absorbers.

Science.gov (United States)

Chen, Ting; Yang, Wen-Hong; Wang, Dong; Wan, Li-Jun

2013-01-01

Understanding the chirality induction and amplification processes, and the construction of globally homochiral surfaces, represent essential challenges in surface chirality studies. Here we report the induction of global homochirality in two-dimensional enantiomorphous networks of achiral molecules via co-assembly with chiral co-absorbers. The scanning tunnelling microscopy investigations and molecular mechanics simulations demonstrate that the point chirality of the co-absorbers transfers to organizational chirality of the assembly units via enantioselective supramolecular interactions, and is then hierarchically amplified to the global homochirality of two-dimensional networks. The global homochirality of the network assembly shows nonlinear dependence on the enantiomeric excess of chiral co-absorber in the solution phase, demonstrating, for the first time, the validation of the 'majority rules' for the homochirality control of achiral molecules at the liquid/solid interface. Such an induction and nonlinear chirality amplification effect promises a new approach towards two-dimensional homochirality control and may reveal important insights into asymmetric heterogeneous catalysis, chiral separation and chiral crystallization.

Magneto-optical studies of low-dimensional organic conductors

Directory of Open Access Journals (Sweden)

Hitoshi Ohta, Motoi Kimata and Yugo Oshima

2009-01-01

Full Text Available Our periodic orbit resonance (POR results on quasi-two-dimensional (q2D, highly anisotropic q2D and quasi-one-dimensional (q1D organic conductors are reviewed together with our rotational cavity magneto-optical measurement system. Higher order POR up to seventh order has been observed in the q2D system (BEDT-TTF2Br(DIA, and the experimental conditions to observe POR and the cyclotron resonance (CR are discussed. Highly anisotropic q2D Fermi surface (FS in β''-(BEDT-TTF(TCNQ, which was considered to have q1D FS previously, is proposed by our POR measurements, and the possible interpretations of other experimental results of β''-(BEDT-TTF(TCNQ are discussed assuming the highly anisotropic q2D FS. Finally, detailed q1D FS of (DMET2I3, obtained from our POR results, is discussed in connection with the typical q1D system (TMTSF2ClO4.

Relativistic finite-temperature Thomas-Fermi model

Science.gov (United States)

Faussurier, Gérald

2017-11-01

We investigate the relativistic finite-temperature Thomas-Fermi model, which has been proposed recently in an astrophysical context. Assuming a constant distribution of protons inside the nucleus of finite size avoids severe divergence of the electron density with respect to a point-like nucleus. A formula for the nuclear radius is chosen to treat any element. The relativistic finite-temperature Thomas-Fermi model matches the two asymptotic regimes, i.e., the non-relativistic and the ultra-relativistic finite-temperature Thomas-Fermi models. The equation of state is considered in detail. For each version of the finite-temperature Thomas-Fermi model, the pressure, the kinetic energy, and the entropy are calculated. The internal energy and free energy are also considered. The thermodynamic consistency of the three models is considered by working from the free energy. The virial question is also studied in the three cases as well as the relationship with the density functional theory. The relativistic finite-temperature Thomas-Fermi model is far more involved than the non-relativistic and ultra-relativistic finite-temperature Thomas-Fermi models that are very close to each other from a mathematical point of view.

Tracer dispersion in two-dimensional rough fractures.

Science.gov (United States)

Drazer, G; Koplik, J

2001-05-01

Tracer diffusion and hydrodynamic dispersion in two-dimensional fractures with self-affine roughness are studied by analytic and numerical methods. Numerical simulations were performed via the lattice-Boltzmann approach, using a boundary condition for tracer particles that improves the accuracy of the method. The reduction in the diffusive transport, due to the fractal geometry of the fracture surfaces, is analyzed for different fracture apertures. In the limit of small aperture fluctuations we derive the correction to the diffusive coefficient in terms of the tortuosity, which accounts for the irregular geometry of the fractures. Dispersion is studied when the two fracture surfaces are simply displaced normally to the mean fracture plane and when there is a lateral shift as well. Numerical results are analyzed using the Lambda parameter, related to convective transport within the fracture, and simple arguments based on lubrication approximation. At very low Péclet number, in the case where fracture surfaces are laterally shifted, we show using several different methods that convective transport reduces dispersion.

The Fermiac or Fermi's Trolley

Science.gov (United States)

Coccetti, F.

2016-03-01

The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.

Two-Dimensional Free Energy Surfaces for Electron Transfer Reactions in Solution

Directory of Open Access Journals (Sweden)

Shigeo Murata

2008-01-01

Full Text Available Change in intermolecular distance between electron donor (D and acceptor (A can induce intermolecular electron transfer (ET even in nonpolar solvent, where solvent orientational polarization is absent. This was shown by making simple calculations of the energies of the initial and final states of ET. In the case of polar solvent, the free energies are functions of both D-A distance and solvent orientational polarization. On the basis of 2-dimensional free energy surfaces, the relation of Marcus ET and exciplex formation is discussed. The transient effect in fluorescence quenching was measured for several D-A pairs in a nonpolar solvent. The results were analyzed by assuming a distance dependence of the ET rate that is consistent with the above model.

Equivalence of two-dimensional gravities

International Nuclear Information System (INIS)

Mohammedi, N.

1990-01-01

The authors find the relationship between the Jackiw-Teitelboim model of two-dimensional gravity and the SL(2,R) induced gravity. These are shown to be related to a two-dimensional gauge theory obtained by dimensionally reducing the Chern-Simons action of the 2 + 1 dimensional gravity. The authors present an explicit solution to the equations of motion of the auxiliary field of the Jackiw-Teitelboim model in the light-cone gauge. A renormalization of the cosmological constant is also given

Pseudogap phenomena in ultracold atomic Fermi gases

OpenAIRE

Chen, Qijin; Wang, Jibiao

2014-01-01

The pairing and superfluid phenomena in a two-component ultracold atomic Fermi gas is an analogue of Cooper pairing and superconductivity in an electron system, in particular, the high $T_c$ superconductors. Owing to the various tunable parameters that have been made accessible experimentally in recent years, atomic Fermi gases can be explored as a prototype or quantum simulator of superconductors. It is hoped that, utilizing such an analogy, the study of atomic Fermi gases may shed light to ...

Itinerant 5f electrons and the Fermi surface properties in neptunium compounds

International Nuclear Information System (INIS)

Aoki, D.; Yamagami, H.; Homma, Y.; Sakai, H.; Ikeda, S.; Shiokawa, Y.; Yamamoto, E.; Nakamura, A.; Haga, Y.; Settai, R.; Onuki, Y.

2007-01-01

We grew high-quality single crystals of NpGe 3 , NpIn 3 , NpCoGa 5 , NpRhGa 5 and NpFe 4 P 12 by the flux method, and measured the de Haas-van Alphen (dHvA) effect, magnetic susceptibility and resistivity. The results of dHvA experiments in NpGe 3 , NpCoGa 5 and NpRhGa 5 were well explained by the energy band calculation based on the 5f-itinerant model, while the topology of Fermi surfaces in NpIn 3 is similar to those of LaIn 3 , implying the 5f-localized nature of NpIn 3 . The skutterudite compound NpFe 4 P 12 is a low carrier system with the 5f 3 configuration

Manipulation of photons at the surface of three-dimensional photonic crystals.

Science.gov (United States)

Ishizaki, Kenji; Noda, Susumu

2009-07-16

In three-dimensional (3D) photonic crystals, refractive-index variations with a periodicity comparable to the wavelength of the light passing through the crystal give rise to so-called photonic bandgaps, which are analogous to electronic bandgaps for electrons moving in the periodic electrostatic potential of a material's crystal structure. Such 3D photonic bandgap crystals are envisioned to become fundamental building blocks for the control and manipulation of photons in optical circuits. So far, such schemes have been pursued by embedding artificial defects and light emitters inside the crystals, making use of 3D bandgap directional effects. Here we show experimentally that photons can be controlled and manipulated even at the 'surface' of 3D photonic crystals, where 3D periodicity is terminated, establishing a new and versatile route for photon manipulation. By making use of an evanescent-mode coupling technique, we demonstrate that 3D photonic crystals possess two-dimensional surface states, and we map their band structure. We show that photons can be confined and propagate through these two-dimensional surface states, and we realize their localization at arbitrary surface points by designing artificial surface-defect structures through the formation of a surface-mode gap. Surprisingly, the quality factors of the surface-defect mode are the largest reported for 3D photonic crystal nanocavities (Q up to approximately 9,000). In addition to providing a new approach for photon manipulation by photonic crystals, our findings are relevant for the generation and control of plasmon-polaritons in metals and the related surface photon physics. The absorption-free nature of the 3D photonic crystal surface may enable new sensing applications and provide routes for the realization of efficient light-matter interactions.

Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices

NARCIS (Netherlands)

Walravens, Willem; De Roo, Jonathan; Drijvers, Emile; Ten Brinck, Stephanie; Solano, Eduardo; Dendooven, Jolien; Detavernier, Christophe; Infante, Ivan; Hens, Zeger

2016-01-01

Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to

Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

International Nuclear Information System (INIS)

Walukiewicz, W.

1988-02-01

The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

Science.gov (United States)

Debehets, J.; Homm, P.; Menghini, M.; Chambers, S. A.; Marchiori, C.; Heyns, M.; Locquet, J. P.; Seo, J. W.

2018-05-01

In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-level pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.

Microbunching instability in a chicane: Two-dimensional mean field treatment

Directory of Open Access Journals (Sweden)

Gabriele Bassi

2009-08-01

Full Text Available We study the microbunching instability in a bunch compressor by a parallel code with some improved numerical algorithms. The two-dimensional charge/current distribution is represented by a Fourier series, with coefficients determined through Monte Carlo sampling over an ensemble of tracked points. This gives a globally smooth distribution with low noise. The field equations are solved accurately in the lab frame using retarded potentials and a novel choice of integration variables that eliminates singularities. We apply the scheme with parameters for the first bunch compressor system of FERMI@Elettra, with emphasis on the amplification of a perturbation at a particular wavelength and the associated longitudinal bunch spectrum. Gain curves are in rough agreement with those of the linearized Vlasov system at intermediate wavelengths, but show some deviation at the smallest wavelengths treated and show the breakdown of a coasting beam assumption at long wavelengths. The linearized Vlasov system is discussed in some detail. A new 2D integral equation is derived which reduces to a well-known 1D integral equation in the coasting beam case.

Two-Dimensional Wetting Transition Modeling with the Potts Model

Science.gov (United States)

Lopes, Daisiane M.; Mombach, José C. M.

2017-12-01

A droplet of a liquid deposited on a surface structured in pillars may have two states of wetting: (1) Cassie-Baxter (CB), the liquid remains on top of the pillars, also known as heterogeneous wetting, or (2) Wenzel, the liquid fills completely the cavities of the surface, also known as homogeneous wetting. Studies show that between these two states, there is an energy barrier that, when overcome, results in the transition of states. The transition can be achieved by changes in geometry parameters of the surface, by vibrations of the surface or by evaporation of the liquid. In this paper, we present a comparison of two-dimensional simulations of the Cassie-Wenzel transition on pillar-structured surfaces using the cellular Potts model (CPM) with studies performed by Shahraz et al. In our work, we determine a transition diagram by varying the surface parameters such as the interpillar distance ( G) and the pillar height ( H). Our results were compared to those obtained by Shahraz et al. obtaining good agreement.

Solutions of the Bogoliubov–de Gennes equation with position dependent Fermi-velocity and gap profiles

Energy Technology Data Exchange (ETDEWEB)

Presilla, M. [Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli, I-06123 Perugia (Italy); Panella, O., E-mail: orlando.panella@pg.infn.it [Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, Via A. Pascoli, I-06123 Perugia (Italy); Roy, P. [Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata-700108 (India)

2017-02-19

It is shown that bound state solutions of the one dimensional Bogoliubov–de Gennes (BdG) equation may exist when the Fermi velocity becomes dependent on the space coordinate. The existence of bound states in continuum (BIC) like solutions has also been confirmed both in the normal phase as well as in the super-conducting phase. We also show that a combination of Fermi velocity and gap parameter step-like profiles provides scattering solutions with normal reflection and transmission. - Highlights: • Bound states of BdG equation via Fermi velocity modulation. • Existence of bound states in continuum in both the normal and the superconducting phase. • Scattering solutions and bound states within a combination of step-like Fermi velocity and gap profiles.

Superfluidity and BCS-BEC crossover of ultracold atomic Fermi gases in mixed dimensions

Science.gov (United States)

Zhang, Leifeng; Chen, Qijin

Atomic Fermi gases have been under active investigation in the past decade. Here we study the superfluid and pairing phenomena of a two-component ultracold atomic Fermi gas in the presence of mixed dimensionality, in which one component is confined on a 1D optical lattice whereas the other is free in the 3D continuum. We assume a short-range pairing interaction and determine the superfluid transition temperature Tc and the phase diagram for the entire BCS-BEC crossover, using a pairing fluctuation theory which includes self-consistently the contributions of finite momentum pairs. We find that, as the lattice depth increases and the lattice spacing decreases, the behavior of Tc becomes very similar to that of a population imbalance Fermi gas in a simple 3D continuum. There is no superfluidity even at T = 0 below certain threshold of pairing strength in the BCS regime. Nonmonotonic Tc behavior and intermediate temperature superfluidity emerge, and for deep enough lattice, the Tc curve will split into two parts. Implications for experiment will be discussed. References: 1. Q.J. Chen, Ioan Kosztin, B. Janko, and K. Levin, Phys. Rev. B 59, 7083 (1999). 2. Chih-Chun Chien, Qijin Chen, Yan He, and K. Levin, Phys. Rev. Lett. 97, 090402(2006). Work supported by NSF of China and the National Basic Research Program of China.

Two-dimensional condensation of pyrimidine oligonucleotides during their self-assemblies at mercury based surfaces

Energy Technology Data Exchange (ETDEWEB)

Hason, Stanislav [Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i. Kralovopolska 135, CZ-612 65 Brno (Czech Republic)], E-mail: hasons@ibp.cz; Vetterl, Vladimir [Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i. Kralovopolska 135, CZ-612 65 Brno (Czech Republic); Fojta, Miroslav [Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i. Kralovopolska 135, CZ-612 65 Brno (Czech Republic)], E-mail: fojta@ibp.cz

2008-02-15

For the first time it is shown that homopyrimidine oligodeoxynucleotides (ODNs) adsorbed at mercury or amalgam electrode surface can condensate upon applying negative potentials (around -1.35 V vs. Ag/AgCl/3M KCl). This 2D condensation resulted in formation of capacitance pits on the C-E curves resembling those observed earlier with monomeric nucleic acid bases, nucleosides and nucleotides. Differences in behavior of the condensed layers of dT{sub 30} and dC{sub 30} ODNs, reflecting different physico-chemical and electrochemical properties of thymine and cytosine, were observed. Formation of the ODN condensed film involved reorientation of the oligonucleotide molecules firmly adsorbed at the electrode and took place even in the absence of any ODN in the bulk of solution. Homopurine ODNs did not form these two-dimensional (2D) condensed monolayers under the same conditions. A preliminary thermodynamic analysis of the condensed ODN layers is presented.

Towards canonical quantum gravity for 3+1 geometries admitting maximally symmetric two-dimensional surfaces

International Nuclear Information System (INIS)

Christodoulakis, T; Doulis, G; Terzis, Petros A; Melas, E; Grammenos, Th; Papadopoulos, G O; Spanou, A

2010-01-01

The canonical decomposition of all 3+1 geometries admitting two-dimensional space-like surfaces is exhibited as a generalization of a previous work. A proposal, consisting of a specific renormalization Assumption and an accompanying Requirement, which has been put forward in the 2+1 case is now generalized to 3+1 dimensions. This enables the canonical quantization of these geometries through a generalization of Kuchar's quantization scheme in the case of infinite degrees of freedom. The resulting Wheeler-DeWitt equation is based on a renormalized manifold parameterized by three smooth scalar functionals. The entire space of solutions to this equation is analytically given, a fact that is entirely new to the present case. This is made possible through the exploitation of the residual freedom in the choice of the third functional, which is left by the imposition of the Requirement, and is proven to correspond to a general coordinate transformation in the renormalized manifold.

Measurement of the Atomic Orbital Composition of the Near-Fermi-Level Electronic States in the Lanthanum Monopnictides LaBi and LaSb

Science.gov (United States)

Nummy, Thomas; Waugh, Justin; Parham, Stephen; Li, Haoxiang; Zhou, Xiaoqing; Plumb, Nick; Tafti, Fazel; Dessau, Daniel

Angle resolved photoemission spectroscopy (ARPES) is used to measure the electronic structure of the Extreme Magnetoresistance (XMR) topological semimetal candidates LaBi and LaSb. Using a wide range of photon energies the true bulk states are cleanly disentangled from the various types of surface states, which may exist due to surface projections of bulk states as well as for topological reasons. The orbital content of the near-EF states are extracted using varying photon polarizations. The measured bulk bands are somewhat lighter and are energy shifted compared to the results of Density Functional calculations, which is a minor effect in LaBi and a more serious effect in LaSb. This bulk band structure puts LaBi in the v = 1 class of Topological Insulators (or semimetals), consistent with the measured Dirac-like surface states. LaSb on the other hand is at the verge of a topological band inversion, with a less-clear case for any distinctly topological surface states. The low-dimensional cigar-shaped bulk Fermi surfaces for both compounds are separated out by orbital content, with a crossover from pnictide d orbitals to La p orbitals around the Fermi surface, which through strong spin-orbit coupling may be relevant for the Extreme Magnetoresistance. NSF GRFP.

Emulating the 1-dimensional Fermi-Hubbard model with superconducting qubits

Energy Technology Data Exchange (ETDEWEB)

Reiner, Jan-Michael; Marthaler, Michael; Schoen, Gerd [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany)

2016-07-01

A chain of qubits with both ZZ and XX couplings is described by a Hamiltonian which coincides with the Fermi-Hubbard model in one dimension. The qubit system can thus be used to study the quantum properties of this model. We investigate the specific implementation of such an analog quantum simulator by a chain of tunable Transmon qubits, where the ZZ interaction arises due to an inductive coupling and the XX interaction due to a capacitive coupling.

Vibrational spectra and thermal rectification in three-dimensional anharmonic lattices

International Nuclear Information System (INIS)

Lan Jinghua; Li Baowen

2007-01-01

We study thermal rectification in a three-dimensional model consisting of two segments of anharmonic lattices. One segment consists of layers of harmonic oscillator arrays coupled to a substrate potential, which is a three-dimensional Frenkel-Kontorova model, and the other segment is a three-dimensional Fermi-Pasta-Ulam model. We study the vibrational bands of the two lattices analytically and numerically, and find that, by choosing the system parameters properly, the rectification can be as high as a few thousands, which is high enough to be observed in experiment. Possible experiments in nanostructures are discussed

Tuning the giant Rashba effect on a BiAg2 surface alloy: Two different approaches

International Nuclear Information System (INIS)

Frantzeskakis, E.; Crepaldi, A.; Pons, S.; Kern, K.; Grioni, M.

2010-01-01

We discuss two different approaches for tuning the giant spin-orbit splitting of a BiAg 2 surface alloy. The first approach consists of electron doping by alkaline metal deposition in order to shift the energy position of the spin-split surface states, while the second is based on the novel Si(1 1 1)-Ag-BiAg 2 trilayer system. In both cases the spin-polarized structure near the Fermi level can be controlled by an external parameter, while the second approach permits coupling the concept of giant spin-splitting with a semiconducting substrate.

Ground-state pressure of an ideal Fermi gas

International Nuclear Information System (INIS)

Delsante, A.E.; Frankel, N.E.

1979-01-01

A simple relationship between the pressure, internal energy and Fermi energy of an ideal ultra-degenerate Fermi gas is derived in two ways. The conditions for its validity and its use in simplifying calculations are discussed

The MARS15-based FermiCORD code system for calculation of the accelerator-induced residual dose

Science.gov (United States)

Grebe, A.; Leveling, A.; Lu, T.; Mokhov, N.; Pronskikh, V.

2018-01-01

The FermiCORD code system, a set of codes based on MARS15 that calculates the accelerator-induced residual doses at experimental facilities of arbitrary configurations, has been developed. FermiCORD is written in C++ as an add-on to Fortran-based MARS15. The FermiCORD algorithm consists of two stages: 1) simulation of residual doses on contact with the surfaces surrounding the studied location and of radionuclide inventories in the structures surrounding those locations using MARS15, and 2) simulation of the emission of the nuclear decay γ-quanta by the residuals in the activated structures and scoring the prompt doses of these γ-quanta at arbitrary distances from those structures. The FermiCORD code system has been benchmarked against similar algorithms based on other code systems and against experimental data from the CERF facility at CERN, and FermiCORD showed reasonable agreement with these. The code system has been applied for calculation of the residual dose of the target station for the Mu2e experiment and the results have been compared to approximate dosimetric approaches.

Discrete nature of thermodynamics in confined ideal Fermi gases

International Nuclear Information System (INIS)

Aydin, Alhun; Sisman, Altug

2014-01-01

Intrinsic discrete nature in thermodynamic properties of Fermi gases appears under strongly confined and degenerate conditions. For a rectangular confinement domain, thermodynamic properties of an ideal Fermi gas are expressed in their exact summation forms. For 1D, 2D and 3D nano domains, variations of both number of particles and internal energy per particle with chemical potential are examined. It is shown that their relation with chemical potential exhibits a discrete nature which allows them to take only some definite values. Furthermore, quasi-irregular oscillatory-like sharp peaks are observed in heat capacity. New nano devices can be developed based on these behaviors. - Highlights: • “Discrete behaviors” appear in thermodynamic properties of ideal Fermi gases at nano scale. • Variations of particle number and internal energy with chemical potential have stepwise behavior. • There are oscillations and peaks in the variation of heat capacity with domain size and particle number. • Fermi line and Fermi surface at nano scale are not continuous but “discrete”. • Heat capacity oscillations can be used for excess thermal energy storage at nano scale

Wind Tunnel Study on Flows over Various Two-dimensional Idealized Urban-liked Surfaces

Science.gov (United States)

Ho, Yat-Kiu; Liu, Chun-Ho

2013-04-01

Extensive human activities (e.g. increased traffic emissions) emit a wide range of pollutants resulting in poor urban area air quality. Unlike open, flat and homogenous rural terrain, urban surface is complicated by the presence of buildings, obstacles and narrow streets. The irregular urban surfaces thus form a random roughness that further modifies the near-surface flows and pollutant dispersion. In this study, a physical modelling approach is employed to commence a series of wind tunnel experiments to study the urban-area air pollution problems. The flow characteristics over different hypothetical urban roughness surfaces were studied in a wind tunnel in isothermal conditions. Preliminary experiments were conducted based on six types of idealized two-dimensional (2D) street canyon models with various building-height-to-street-width (aspect) ratios (ARs) 1, 1/2, 1/4, 1/8, 1/10 and 1/12. The main instrumentation is an in-house 90o X-hotwire anemometry. In each set of configuration, a sampling street canyon was selected near the end of the streamwise domain. Its roof level, i.e. the transverse between the mid points of the upstream and downstream buildings, was divided into eight segments. The measurements were then recorded on the mid-plane of the spannwise domain along the vertical profile (from building roof level to the ceiling of wind tunnel) of the eight segments. All the data acquisition processes were handled by the NI data acquisition modules, NI 9239 and CompactDAQ-9188 hardware. Velocity calculation was carried out in the post-processing stage on a digital computer. The two-component flow velocities and velocity fluctuations were calculated at each sampling points, therefore, for each model, a streamwise average of eight vertical profiles of mean velocity and velocity fluctuations was presented. A plot of air-exchange rate (ACH) against ARs was also presented in order to examine the ventilation performance of different tested models. Preliminary results

Charge transfer effects on the Fermi surface of Ba0.5K 0.5Fe2As2

KAUST Repository

Nazir, Safdar

2011-01-31

Ab-initio calculations within density functional theory are performed to obtain a more systematic understanding of the electronic structure of iron pnictides. As a prototypical compound we study Ba0.5K 0.5Fe2As2 and analyze the changes of its electronic structure when the interaction between the Fe2As 2 layers and their surrounding is modified. We find strong effects on the density of states near the Fermi energy as well as the Fermi surface. The role of the electron donor atoms in iron pnictides thus cannot be understood in a rigid band picture. Instead, the bonding within the Fe2As 2 layers reacts to a modified charge transfer from the donor atoms by adapting the intra-layer Fe-As hybridization and charge transfer in order to maintain an As3- valence state. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge transfer effects on the Fermi surface of Ba0.5K 0.5Fe2As2

KAUST Repository

Nazir, Safdar; Zhu, Zhiyong; Schwingenschlö gl, Udo

2011-01-01

Ab-initio calculations within density functional theory are performed to obtain a more systematic understanding of the electronic structure of iron pnictides. As a prototypical compound we study Ba0.5K 0.5Fe2As2 and analyze the changes of its electronic structure when the interaction between the Fe2As 2 layers and their surrounding is modified. We find strong effects on the density of states near the Fermi energy as well as the Fermi surface. The role of the electron donor atoms in iron pnictides thus cannot be understood in a rigid band picture. Instead, the bonding within the Fe2As 2 layers reacts to a modified charge transfer from the donor atoms by adapting the intra-layer Fe-As hybridization and charge transfer in order to maintain an As3- valence state. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fermi Surface Properties of Eu-Divalent and Eu-Trivalent Electronic States with the AuCu3-type Cubic Structure

International Nuclear Information System (INIS)

Nakamura, Ai; Takeuchi, Tetsuya; Tatetsu, Yasutomi; Maehira, Takahiro; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika; Harima, Hisatomo

2015-01-01

The electronic states in EuBi 3 and EuPd 3 are known to be Eu-divalent and Eu- trivalent, respectively, from the previous studies using polycrystal samples. In the present study, we succeeded in growing high-quality single crystals, and carried out the de Haas-van Alphen (dHvA) measurements and energy band calculations to clarify the Fermi surface properties

Itinerant Ferromagnetism in Ultracold Fermi Gases

DEFF Research Database (Denmark)

Heiselberg, Henning

2012-01-01

Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC. Thermodyna......Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC...

Construction of Three-Dimensional Road Surface and Application on Interaction between Vehicle and Road

Directory of Open Access Journals (Sweden)

Lu Yongjie

2018-01-01

Full Text Available The quantitative description is given to three-dimensional micro and macro self-similar characteristics of road surface from the perspective of fractal geometry using FBM stochastic midpoint displacement and diamond-square algorithm in conjunction with fractal characteristics and statistical characteristics of standard pavement determined by estimation method of box-counting dimension. The comparative analysis between reconstructed three-dimensional road surface spectrum and theoretical road surface spectrum and correlation coefficient demonstrate the high reconstruction accuracy of fractal reconstructed road spectrum. Furthermore, the bump zone is taken as an example to reconstruct a more arbitrary 3D road model through isomorphism of special road surface with stochastic road surface model. Measurement is taken to assume the tire footprint on road surface to be a rectangle, where the pressure distribution is expressed with mean stiffness, while the contact points in the contact area are replaced with a number of springs. Two-DOF vehicle is used as an example to analyze the difference between three-dimensional multipoint-and-plane contact and traditional point contact model. Three-dimensional road surface spectrum provides a more accurate description of the impact effect of tire on road surface, thereby laying a theoretical basis for studies on the dynamical process of interaction of vehicle-road surface and the road friendliness.

Borophane: Stable Two-dimensional Anisotropic Dirac Material with Ultrahigh Fermi Velocity

OpenAIRE

Xu, Lichun; Du, Aijun; Kou, Liangzhi

2016-01-01

Recent synthesis of monolayer borophene (triangle boron monolayer) on the substrate opens the era of boron nanosheet (Science, 350, 1513, $\\mathbf{2015}$), but the structural stability and novel physical properties are still open issues. Here we demonstrated borophene can be stabilized with fully surface hydrogenation, called as borophane, from first-principles calculations. Most interesting, it shows that borophane has direction-dependent Dirac cones, which are mainly contributed by in-plane...

Acousto-optical interaction of surface acoustic and optical waves in a two-dimensional phoxonic crystal hetero-structure cavity.

Science.gov (United States)

Ma, Tian-Xue; Zou, Kui; Wang, Yue-Sheng; Zhang, Chuanzeng; Su, Xiao-Xing

2014-11-17

Phoxonic crystal is a promising material for manipulating sound and light simultaneously. In this paper, we theoretically demonstrate the propagation of acoustic and optical waves along the truncated surface of a two-dimensional square-latticed phoxonic crystal. Further, a phoxonic crystal hetero-structure cavity is proposed, which can simultaneously confine surface acoustic and optical waves. The interface motion and photoelastic effects are taken into account in the acousto-optical coupling. The results show obvious shifts in eigenfrequencies of the photonic cavity modes induced by different phononic cavity modes. The symmetry of the phononic cavity modes plays a more important role in the single-phonon exchange process than in the case of the multi-phonon exchange. Under the same deformation, the frequency shift of the photonic transverse electric mode is larger than that of the transverse magnetic mode.

Nonlinear Excitations in Strongly-Coupled Fermi-Dirac Plasmas

OpenAIRE

Akbari-Moghanjoughi, M.

2012-01-01

In this paper we use the conventional quantum hydrodynamics (QHD) model in combination with the Sagdeev pseudopotential method to explore the effects of Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron exchange and ion correlation on the large-amplitude nonlinear soliton dynamics in Fermi-Dirac plasmas. It is found that in the presence of strong interactions significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in the two distinct regimes of no...

Microscopic theory of the superconducting gap in the quasi-one-dimensional organic conductor (TMTSF) 2ClO4 : Model derivation and two-particle self-consistent analysis

Science.gov (United States)

Aizawa, Hirohito; Kuroki, Kazuhiko

2018-03-01

We present a first-principles band calculation for the quasi-one-dimensional (Q1D) organic superconductor (TMTSF) 2ClO4 . An effective tight-binding model with the TMTSF molecule to be regarded as the site is derived from a calculation based on maximally localized Wannier orbitals. We apply a two-particle self-consistent (TPSC) analysis by using a four-site Hubbard model, which is composed of the tight-binding model and an onsite (intramolecular) repulsive interaction, which serves as a variable parameter. We assume that the pairing mechanism is mediated by the spin fluctuation, and the sign of the superconducting gap changes between the inner and outer Fermi surfaces, which correspond to a d -wave gap function in a simplified Q1D model. With the parameters we adopt, the critical temperature for superconductivity estimated by the TPSC approach is approximately 1 K, which is consistent with experiment.

Fermi comes to CERN

CERN Multimedia

2009-01-01

In only 10 months of scientific activity, the Fermi space observatory has already collected an unprecedented wealth of information on some of the most amazing objects in the sky. In a recent talk at CERN, Luca Latronico, a member of the Fermi collaboration, explained some of their findings and emphasized the strong links between High Energy Physics (HEP) and High Energy Astrophysics (HEA). The Fermi gamma-ray telescope was launched by NASA in June 2008. After about two months of commissioning it started sending significant data back to the Earth. Since then, it has made observations that are changing our view of the sky: from discovering a whole new set of pulsars, the greatest total energy gamma-ray burst ever, to detecting an unexplained abundance of high-energy electrons that could be a signature of dark matter, to producing a uniquely rich and high definition sky map in gamma-rays. The high performance of the instrument comes as ...

Relativistic density matrix in the diagonal momentum representation. Fermi-gas

International Nuclear Information System (INIS)

Makhlin, A.N.; Sinyukov, Yu.M.

1984-01-01

The relativistically invariant theory of ideal Fermi-gas is built in the framework of the quantum field theory. The average occupation numbers and correlation functions of statistical systems are found on the equal-time surfaces of arbitrary inertial frames. The effects of anisotropy in their behaviour are pointed out. The partition function method is developed to calculate the thermodynamic quantities of Fermi-gases moving as a whole

Low-temperature specific heat of the quasi-two-dimensional charge-density wave compound KMo6O17

Science.gov (United States)

Wang, Junfeng; Xiong, Rui; Yin, Di; Li, Changzhen; Tang, Zheng; Wang, Ququan; Shi, Jing; Wang, Yue; Wen, Haihu

2006-05-01

Low temperature specific heat (Cp) of quasi-two-dimensional charge-density wave (CDW) compound KMo6O17 has been studied by a relaxation method from 2to48K under zero and 12T magnetic fields. The results show that no specific heat anomaly is found at 16K under both zero and 12T magnetic fields, although an anomaly is clearly observed in the resistivity and magnetoresistance measurements. From the data between 2 and 4K , the density of states at Fermi level is estimated as 0.2eV-1permolecule and the Debye temperature is extracted to be 418K . A bump appearing in Cp/T3 is found between 4 and 48K centered around 12.5-15K , indicating that the phason excitations contribute to the total specific heat similarly as in quasi-one-dimensional CDW conductors. Using a modified Debye model, a pinning frequency of 0.73THz for KMo6O17 is estimated from the phason contribution.

Two-dimensional simulation of the MHD stability, (1)

International Nuclear Information System (INIS)

Kurita, Gen-ichi; Amano, Tsuneo.

1976-03-01

The two-dimensional computer code has been prepared to study MHD stability of an axisymmetric toroidal plasma with and without the surrounding vacuum region. It also includes the effect of magnetic surfaces with non-circular cross sections. The linearized equations of motion are solved as an initial value problem. The results by computer simulation are compared with those by the theory for the cylindrical plasma; they are in good agreement. (auth.)

The MARS15-based FermiCORD code system for calculation of the accelerator-induced residual dose

Energy Technology Data Exchange (ETDEWEB)

Grebe, A.; Leveling, A.; Lu, T.; Mokhov, N.; Pronskikh, V.

2018-01-01

The FermiCORD code system, a set of codes based on MARS15 that calculates the accelerator-induced residual doses at experimental facilities of arbitrary configurations, has been developed. FermiCORD is written in C++ as an add-on to Fortran-based MARS15. The FermiCORD algorithm consists of two stages: 1) simulation of residual doses on contact with the surfaces surrounding the studied location and of radionuclide inventories in the structures surrounding those locations using MARS15, and 2) simulation of the emission of the nuclear decay gamma-quanta by the residuals in the activated structures and scoring the prompt doses of these gamma-quanta at arbitrary distances from those structures. The FermiCORD code system has been benchmarked against similar algorithms based on other code systems and showed a good agreement. The code system has been applied for calculation of the residual dose of the target station for the Mu2e experiment and the results have been compared to approximate dosimetric approaches.

Dynamics of trapped two-component Fermi gas: Temperature dependence of the transition from collisionless to collisional regime

International Nuclear Information System (INIS)

Toschi, F.; Vignolo, P.; Tosi, M.P.; Succi, S.

2003-01-01

We develop a numerical method to study the dynamics of a two-component atomic Fermi gas trapped inside a harmonic potential at temperature T well below the Fermi temperature T F . We examine the transition from the collisionless to the collisional regime down to T=0.2 T F and find a good qualitative agreement with the experiments of B. DeMarco and D.S. Jin [Phys. Rev. Lett. 88, 040405 (2002)]. We demonstrate a twofold role of temperature on the collision rate and on the efficiency of collisions. In particular, we observe a hitherto unreported effect, namely, the transition to hydrodynamic behavior is shifted towards lower collision rates as temperature decreases

E Fermi

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education. E Fermi. Articles written in Resonance – Journal of Science Education. Volume 19 Issue 1 January 2014 pp 82-96 Classics. Quantization of an Ideal Monoatomic Gas · E Fermi · More Details Fulltext PDF ...

Calculation of three-dimensional fluid flow with multiple free surfaces

International Nuclear Information System (INIS)

Vander Vorst, M.J.; Chan, R.K.C.

1978-01-01

This paper presents a method for computing incompressible fluid flows with multiple free surfaces which are not restricted in their orientation. The method is presented in the context of the three-dimensional flow in a Mark I reactor pressure suppression system immediately following a postulated loss of coolant accident. The assumption of potential flow is made. The numerical method is a mixed Eulerian-Lagrangian formulation with the interior treated as Eulerian and the free surfaces as Lagrangian. The accuracy of solution hinges on the careful treatment of two important aspects. First, the Laplace equation for the potential is solved at interior points of the Eulerian finite difference mesh using a three-dimensional ''irregular star'' so that boundary conditions can be imposed at the exact position of the free surface. Second, the Lagrangian free surfaces are composed of triangular elements, upon each vertex of which is applied the fully nonlinear Bernoulli equation. One result of these calculations is the transient load on the suppression vessel during the vent clearing and bubble formation events of a loss of coolant accident

Effects of impurity and Bose-Fermi interactions on the transition temperature of a dilute dipolar Bose-Einstein condensation in trapped Bose-Fermi mixtures

Science.gov (United States)

Yavari, H.; Mokhtari, M.

2014-03-01

The effects of impurity and Bose-Fermi interactions on the transition temperature of a dipolar Bose-Einstein condensation in trapped Bose-Fermi mixture, by using the two-fluid model, are investigated. The shift of the transition temperature consists of four contributions due to contact, Bose-Fermi, dipole-dipole, and impurity interactions. We will show that in the presence of an anisotropic trap, the Bose-Fermi correction to the shift of transition temperature due to the excitation spectra of the thermal part is independent of anisotropy factor. Applying our results to trapped Bose-Fermi mixtures shows that, by knowing the impurity effect, the shift of the transition temperature due to Bose-Fermi interaction could be measured for isotropic trap (dipole-dipole contributions is zero) and Feshbach resonance technique (contact potential contribution is negligible).

Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of high temperature superconductors

Science.gov (United States)

Hu, Jiangping; Ding, Hong

2012-01-01

Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional high temperature superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials: in all high temperature superconductors, the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. We suggest that this match offers a principle guide to search for new high temperature superconductors. PMID:22536479

Quantum oscillations without a Fermi surface. The anomalous de Haas-van Alphen effect and relation to SmB{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Knolle, Johannes; Cooper, Nigel [T.C.M. Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2016-07-01

The de Haas-van Alphen effect (dHvAE), describing oscillations of the magnetization as a function of magnetic field, is commonly assumed to be a definite sign for the presence of a Fermi surface (FS). Indeed, the effect forms the basis of a well-established experimental procedure for accurately measuring FS topology and geometry of metallic systems, with parameters commonly extracted by fitting to the Lifshitz-Kosevich (LK) theory based on Fermi liquid theory. Here we show that, in contrast to this canonical situation, there can be quantum oscillations even for band insulators of certain types. We provide simple analytic formulas describing the temperature dependence of the quantum oscillations in this setting, showing strong deviations from LK theory. We draw connections to recent experiments on the tentative topological Kondo insulator SmB{sub 6}.

On the two-dimensional Saigo-Maeda fractional calculus asociated with two-dimensional Aleph TRANSFORM

Directory of Open Access Journals (Sweden)

Dinesh Kumar

2013-11-01

Full Text Available This paper deals with the study of two-dimensional Saigo-Maeda operators of Weyl type associated with Aleph function defined in this paper. Two theorems on these defined operators are established. Some interesting results associated with the H-functions and generalized Mittag-Leffler functions are deduced from the derived results. One dimensional analog of the derived results is also obtained.

NASA-VOF3D: A three-dimensional computer program for incompressible flows with free surfaces

Science.gov (United States)

Torrey, M. D.; Mjolsness, R. C.; Stein, L. R.

1987-07-01

Presented is the NASA-VOF3D three-dimensional, transient, free-surface hydrodynamics program. This three-dimensional extension of NASA-VOF2D will, in principle, permit treatment in full three-dimensional generality of the wide variety of applications that could be treated by NASA-VOF2D only within the two-dimensional idealization. In particular, it, like NASA-VOF2D, is specifically designed to calculate confined flows in a low g environment. The code is presently restricted to cylindrical geometry. The code is based on the fractional volume-of-fluid method and allows multiple free surfaces with surface tension and wall adhesion. It also has a partial cell treatment that allows curved boundaries and internal obstacles. This report provides a brief discussion of the numerical method, a code listing, and some sample problems.

Nanoscale measurement of Nernst effect in two-dimensional charge density wave material 1T-TaS₂

Energy Technology Data Exchange (ETDEWEB)

Wu, Stephen M. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627, USA; Luican-Mayer, Adina [Nanoscience and Technology Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada; Bhattacharya, Anand [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Nanoscience and Technology Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

2017-11-27

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS₂ is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearly commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS₂, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW! NCCDW transition.

The directional propagation characteristics of elastic wave in two-dimensional thin plate phononic crystals

International Nuclear Information System (INIS)

Wen Jihong; Yu, Dianlong; Wang Gang; Zhao Honggang; Liu Yaozong; Wen Xisen

2007-01-01

The directional propagation characteristics of elastic wave during pass bands in two-dimensional thin plate phononic crystals are analyzed by using the lumped-mass method to yield the phase constant surface. The directions and regions of wave propagation in phononic crystals for certain frequencies during pass bands are predicted with the iso-frequency contour lines of the phase constant surface, which are then validated with the harmonic responses of a finite two-dimensional thin plate phononic crystals with 16x16 unit cells. These results are useful for controlling the wave propagation in the pass bands of phononic crystals

A finite area scheme for shallow granular flows on three-dimensional surfaces

Science.gov (United States)

Rauter, Matthias

2017-04-01

Shallow granular flow models have become a popular tool for the estimation of natural hazards, such as landslides, debris flows and avalanches. The shallowness of the flow allows to reduce the three-dimensional governing equations to a quasi two-dimensional system. Three-dimensional flow fields are replaced by their depth-integrated two-dimensional counterparts, which yields a robust and fast method [1]. A solution for a simple shallow granular flow model, based on the so-called finite area method [3] is presented. The finite area method is an adaption of the finite volume method [4] to two-dimensional curved surfaces in three-dimensional space. This method handles the three dimensional basal topography in a simple way, making the model suitable for arbitrary (but mildly curved) topography, such as natural terrain. Furthermore, the implementation into the open source software OpenFOAM [4] is shown. OpenFOAM is a popular computational fluid dynamics application, designed so that the top-level code mimics the mathematical governing equations. This makes the code easy to read and extendable to more sophisticated models. Finally, some hints on how to get started with the code and how to extend the basic model will be given. I gratefully acknowledge the financial support by the OEAW project "beyond dense flow avalanches". Savage, S. B. & Hutter, K. 1989 The motion of a finite mass of granular material down a rough incline. Journal of Fluid Mechanics 199, 177-215. Ferziger, J. & Peric, M. 2002 Computational methods for fluid dynamics, 3rd edn. Springer. Tukovic, Z. & Jasak, H. 2012 A moving mesh finite volume interface tracking method for surface tension dominated interfacial fluid flow. Computers & fluids 55, 70-84. Weller, H. G., Tabor, G., Jasak, H. & Fureby, C. 1998 A tensorial approach to computational continuum mechanics using object-oriented techniques. Computers in physics 12(6), 620-631.

Enrico Fermi exhibition at CERN

CERN Multimedia

2002-01-01

A touring exhibition celebrating the centenary of Enrico Fermi's birth in 1901 will be on display at CERN (Main Building, Mezzanine) from 12-27 September. You are cordially invited to the opening celebration on Thursday 12 September at 16:00 (Main Building, Council Chamber), which will include speechs from: Luciano Maiani Welcome and Introduction Arnaldo Stefanini Celebrating Fermi's Centenary in Documents and Pictures Antonino Zichichi The New 'Centro Enrico Fermi' at Via Panisperna Ugo Amaldi Fermi at Via Panisperna and the birth of Nuclear Medicine Jack Steinberger Fermi in Chicago Valentin Telegdi A Close-up of Fermi and the screening of a documentary video about Fermi: Scienziati a Pisa: Enrico Fermi (Scientists at Pisa: Enrico Fermi) created by Francesco Andreotti for La Limonaia from early film, photographs and sound recordings (In Italian, with English subtitles - c. 30 mins). This will be followed by an aperitif on the Mezz...