Imaging of Coulomb-Driven Quantum Hall Edge States
Lai, Keji
2011-10-01
The edges of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime are divided into alternating metallic and insulating strips, with their widths determined by the energy gaps of the QHE states and the electrostatic Coulomb interaction. Local probing of these submicrometer features, however, is challenging due to the buried 2DEG structures. Using a newly developed microwave impedance microscope, we demonstrate the real-space conductivity mapping of the edge and bulk states. The sizes, positions, and field dependence of the edge strips around the sample perimeter agree quantitatively with the self-consistent electrostatic picture. The evolution of microwave images as a function of magnetic fields provides rich microscopic information around the ν=2 QHE state. © 2011 American Physical Society.
Contacts and Edge State Equilibration in the Fractional Quantum Hall Effect
Kane, C. L.; Fisher, Matthew P. A.
1995-01-01
We develop a simple kinetic equation description of edge state dynamics in the fractional quantum Hall effect (FQHE), which allows us to examine in detail equilibration processes between multiple edge modes. As in the integer quantum Hall effect (IQHE), inter-mode equilibration is a prerequisite for quantization of the Hall conductance. Two sources for such equilibration are considered: Edge impurity scattering and equilibration by the electrical contacts. Several specific models for electric...
Edge states and integer quantum Hall effect in topological insulator thin films.
Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing
2015-08-25
The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. Here we study the Landau levels and edge states of surface Dirac fermions in topological insulators under strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect resulting from structure inversion asymmetry. The phase diagrams of the quantum Hall states are presented as functions of magnetic field, gate voltage and chemical potential. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films.
Topological edge state with zero Hall conductivity in quasi-one dimensional system
Xiao-Shan Ye
2016-09-01
Full Text Available We explore the structure of the energy spectra of quasi-one dimensional (Q1D system subjected to spin-density-wave SDW states. The structure of the energy spectra opens energy gaps with Zeeman field. Theses gaps result in plateaus for the Quantum Hall conductivity which is associated with edge states. Different from the SSH Hofstadter model, here we show that there are a doublet of edge states contribution to zero Hall conductivity. These edge states are allowed for magnetic control of spin currents. The topological effects predicted here could be tested directly in organic conductors system.
Topological edge state with zero Hall conductivity in quasi-one dimensional system
Ye, Xiao-Shan
2016-09-01
We explore the structure of the energy spectra of quasi-one dimensional (Q1D) system subjected to spin-density-wave SDW states. The structure of the energy spectra opens energy gaps with Zeeman field. Theses gaps result in plateaus for the Quantum Hall conductivity which is associated with edge states. Different from the SSH Hofstadter model, here we show that there are a doublet of edge states contribution to zero Hall conductivity. These edge states are allowed for magnetic control of spin currents. The topological effects predicted here could be tested directly in organic conductors system.
Fractional Quantum Hall Effect via Holography Chern-Simons, Edge States, and Hierarchy
Fujita, Mitsutoshi; Ryu, Shinsei; Takayanagi, Tadashi
2009-01-01
We present three holographic constructions of fractional quantum Hall effect (FQHE) via string theory. The first model studies edge states in FQHE using supersymmetric domain walls in N=6 Chern-Simons theory. We show that D4-branes wrapped on CP^1 or D8-branes wrapped on CP^3 create edge states that shift the rank or the level of the gauge group, respectively. These holographic edge states correctly reproduce the Hall conductivity. The second model presents a holographic dual to the pure U(N)_k (Yang-Mills-)Chern-Simons theory based on a D3-D7 system. Its holography is equivalent to the level-rank duality, which enables us to compute the Hall conductivity and the topological entanglement entropy. The third model introduces the first string theory embedding of hierarchical FQHEs, using IIA string on C^2/Z_n.
Hall effect, edge states, and Haldane exclusion statistics in two-dimensional space
Ye, F.; Marchetti, P. A.; Su, Z. B.; Yu, L.
2015-12-01
We clarify the relation between two kinds of statistics for particle excitations in planar systems: the braid statistics of anyons and the Haldane exclusion statistics (HES). It is shown nonperturbatively that the HES exists for incompressible anyon liquid in the presence of a Hall response. We also study the statistical properties of a specific quantum anomalous Hall model with Chern-Simons term by perturbation in both compressible and incompressible regimes, where the crucial role of edge states to the HES is shown.
Komnik, A.; Saleur, H.
2011-09-01
We verify the validity of the Cohen-Gallavotti fluctuation theorem for the strongly correlated problem of charge transfer through an impurity in a chiral Luttinger liquid, which is realizable experimentally as a quantum point contact in a fractional quantum Hall edge state device. This is accomplished via the development of an analytical method to calculate the full counting statistics of the problem in all the parameter regimes involving the temperature, the Hall voltage, and the gate voltage.
Valley-filtered edge states and quantum valley Hall effect in gated bilayer graphene.
Zhang, Xu-Long; Xu, Lei; Zhang, Jun
2017-05-10
Electron edge states in gated bilayer graphene in the quantum valley Hall (QVH) effect regime can carry both charge and valley currents. We show that an interlayer potential splits the zero-energy level and opens a bulk gap, yielding counter-propagating edge modes with different valleys. A rich variety of valley current states can be obtained by tuning the applied boundary potential and lead to the QVH effect, as well as to the unbalanced QVH effect. A method to individually manipulate the edge states by the boundary potentials is proposed.
Xu, Yong; Uddin, Salah; Wang, Jun; Wu, Jiansheng; Liu, Jun-Feng
2017-08-08
We have studied numerically the penetration depth of quantum spin hall edge states in chiral honeycomb nanoribbons based on the Green's function method. The changing of edge orientation from armchair to zigzag direction decreases the penetration depth drastically. The penetration depth is used to estimate the gap opened for the finite-size effect. Beside this, we also proposed a nonlocal transistor based on the zigzag-like chiral ribbons in which the current is carried at one edge and the manipulation is by the edge magnetization at the other edge. The difficulty that the edge magnetization is unstable in the presence of a ballistic current can be removed by this nonlocal manipulation.
Dubey, Sudipta; Deshmukh, Mandar M.
2016-07-01
We probe quantum Hall effect in a tunable 1-D lateral superlattice (SL) in graphene created using electrostatic gates. Lack of equilibration is observed along edge states formed by electrostatic gates inside the superlattice. We create strong local electric field at the interface of regions of different charge densities. Crossed electric and magnetic fields modify the wavefunction of the Landau Levels (LLs) - a phenomenon unique to graphene. In the region of copropagating electrons and holes at the interface, the electric field is high enough to modify the Landau levels resulting in increased scattering that tunes equilibration of edge states and this results in large longitudinal resistance.
Topological phase transition and quantum spin Hall edge states of antimony few layers
Kim, Sung Hwan; Jin, Kyung-Hwan; Park, Joonbum; Kim, Jun Sung; Jhi, Seung-Hoon; Yeom, Han Woong
2016-09-01
While two-dimensional (2D) topological insulators (TI’s) initiated the field of topological materials, only very few materials were discovered to date and the direct access to their quantum spin Hall edge states has been challenging due to material issues. Here, we introduce a new 2D TI material, Sb few layer films. Electronic structures of ultrathin Sb islands grown on Bi2Te2Se are investigated by scanning tunneling microscopy. The maps of local density of states clearly identify robust edge electronic states over the thickness of three bilayers in clear contrast to thinner islands. This indicates that topological edge states emerge through a 2D topological phase transition predicted between three and four bilayer films in recent theory. The non-trivial phase transition and edge states are confirmed for epitaxial films by extensive density-functional-theory calculations. This work provides an important material platform to exploit microscopic aspects of the quantum spin Hall phase and its quantum phase transition.
Netanel H. Lindner
2012-10-01
Full Text Available We study the non-Abelian statistics characterizing systems where counterpropagating gapless modes on the edges of fractional quantum Hall states are gapped by proximity coupling to superconductors and ferromagnets. The most transparent example is that of a fractional quantum spin Hall state, in which electrons of one spin direction occupy a fractional quantum Hall state of ν=1/m, while electrons of the opposite spin occupy a similar state with ν=-1/m. However, we also propose other examples of such systems, which are easier to realize experimentally. We find that each interface between a region on the edge coupled to a superconductor and a region coupled to a ferromagnet corresponds to a non-Abelian anyon of quantum dimension sqrt[2m]. We calculate the unitary transformations that are associated with the braiding of these anyons, and we show that they are able to realize a richer set of non-Abelian representations of the braid group than the set realized by non-Abelian anyons based on Majorana fermions. We carry out this calculation both explicitly and by applying general considerations. Finally, we show that topological manipulations with these anyons cannot realize universal quantum computation.
Long-distance entanglement of spin qubits via quantum Hall edge states
Yang, Guang; Hsu, Chen-Hsuan; Stano, Peter; Klinovaja, Jelena; Loss, Daniel
2016-02-01
The implementation of a functional quantum computer involves entangling and coherent manipulation of a large number of qubits. For qubits based on electron spins confined in quantum dots, which are among the most investigated solid-state qubits at present, architectural challenges are often encountered in the design of quantum circuits attempting to assemble the qubits within the very limited space available. Here, we provide a solution to such challenges based on an approach to realizing entanglement of spin qubits over long distances. We show that long-range Ruderman-Kittel-Kasuya-Yosida interaction of confined electron spins can be established by quantum Hall edge states, leading to an exchange coupling of spin qubits. The coupling is anisotropic and can be either Ising type or XY type, depending on the spin polarization of the edge state. Such a property, combined with the dependence of the electron spin susceptibility on the chirality of the edge state, can be utilized to gain valuable insights into the topological nature of various quantum Hall states.
Statistical theory of relaxation of high-energy electrons in quantum Hall edge states
Lunde, Anders Mathias; Nigg, Simon E.
2016-07-01
We investigate theoretically the energy exchange between the electrons of two copropagating, out-of-equilibrium edge states with opposite spin polarization in the integer quantum Hall regime. A quantum dot tunnel coupled to one of the edge states locally injects electrons at high energy. Thereby a narrow peak in the energy distribution is created at high energy above the Fermi level. A second downstream quantum dot performs an energy-resolved measurement of the electronic distribution function. By varying the distance between the two dots, we are able to follow every step of the energy exchange and relaxation between the edge states, even analytically under certain conditions. In the absence of translational invariance along the edge, e.g., due to the presence of disorder, energy can be exchanged by non-momentum-conserving two-particle collisions. For weakly broken translational invariance, we show that the relaxation is described by coupled Fokker-Planck equations. From these we find that relaxation of the injected electrons can be understood statistically as a generalized drift-diffusion process in energy space for which we determine the drift velocity and the dynamical diffusion parameter. Finally, we provide a physically appealing picture in terms of individual edge-state heating as a result of the relaxation of the injected electrons.
Helical edge states and fractional quantum Hall effect in a graphene electron-hole bilayer.
Sanchez-Yamagishi, Javier D; Luo, Jason Y; Young, Andrea F; Hunt, Benjamin M; Watanabe, Kenji; Taniguchi, Takashi; Ashoori, Raymond C; Jarillo-Herrero, Pablo
2017-02-01
Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.
Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state.
Young, A F; Sanchez-Yamagishi, J D; Hunt, B; Choi, S H; Watanabe, K; Taniguchi, T; Ashoori, R C; Jarillo-Herrero, P
2014-01-23
Low-dimensional electronic systems have traditionally been obtained by electrostatically confining electrons, either in heterostructures or in intrinsically nanoscale materials such as single molecules, nanowires and graphene. Recently, a new method has emerged with the recognition that symmetry-protected topological (SPT) phases, which occur in systems with an energy gap to quasiparticle excitations (such as insulators or superconductors), can host robust surface states that remain gapless as long as the relevant global symmetry remains unbroken. The nature of the charge carriers in SPT surface states is intimately tied to the symmetry of the bulk, resulting in one- and two-dimensional electronic systems with novel properties. For example, time reversal symmetry endows the massless charge carriers on the surface of a three-dimensional topological insulator with helicity, fixing the orientation of their spin relative to their momentum. Weakly breaking this symmetry generates a gap on the surface, resulting in charge carriers with finite effective mass and exotic spin textures. Analogous manipulations have yet to be demonstrated in two-dimensional topological insulators, where the primary example of a SPT phase is the quantum spin Hall state. Here we demonstrate experimentally that charge-neutral monolayer graphene has a quantum spin Hall state when it is subjected to a very large magnetic field angled with respect to the graphene plane. In contrast to time-reversal-symmetric systems, this state is protected by a symmetry of planar spin rotations that emerges as electron spins in a half-filled Landau level are polarized by the large magnetic field. The properties of the resulting helical edge states can be modulated by balancing the applied field against an intrinsic antiferromagnetic instability, which tends to spontaneously break the spin-rotation symmetry. In the resulting canted antiferromagnetic state, we observe transport signatures of gapped edge states
Yakovenko, Victor M.; Goan, Hsi-Sheng
1996-12-01
This paper reviews recent developments in the theory of the quantum Hall effect (QHE) in the magnetic-field-induced spin-density-wave (FISDW) state of the quasi-one-dimensional organic conductors (TMTSF)2X. The origin and the basic features of the FISDW are reviewed. The QHE in the pinned FISDW state is derived in several simple, transparent ways, including the edge states formulation of the problem. The temperature dependence of the Hall conductivity is found to be the same as the temperature dependence of the Fröhlich current. It is shown that, when the FISDW is free to move, it produces an additional contribution to the Hall conductivity that nullifies the total Hall effect. The paper is written on mathematically simple level, emphasizes physical meaning over sophisticated mathematical technique, and uses inductive, rather than deductive, reasoning.
Fragility of Nonlocal Edge-Mode Transport in the Quantum Spin Hall State
Mani, Arjun; Benjamin, Colin
2016-07-01
Nonlocal currents and voltages are better at withstanding the deleterious effects of dephasing than local currents and voltages in nanoscale systems. This hypothesis is known to be true in quantum Hall setups. We test this hypothesis in a four-terminal quantum spin Hall setup wherein we compare the local resistance measurement with the nonlocal one. In addition to inelastic-scattering-induced dephasing, we also test the resilience of the resistance measurements in the aforesaid setups to disorder and spin-flip scattering. We find the axiom that nonlocal resistance is less affected by the detrimental effects of disorder and dephasing to be untrue, in general, for the quantum spin Hall case. This has important consequences since it is widely communicated that nonlocal transport through edge channels in topological insulators have potential applications in low-power information processing.
Observation of chiral edge states with neutral fermions in synthetic Hall ribbons
Mancini, M; Pagano, G; Cappellini, G; Livi, L; Rider, M; Catani, J; Sias, C; Zoller, P; Inguscio, M; Dalmonte, M; Fallani, L
2015-01-01
.... By imaging individual sites along a synthetic dimension, encoded in the nuclear spin of the atoms, we detect the existence of the edge states and observe the edge-cyclotron orbits induced during quench dynamics...
Zhou, Tong; Zhang, Jiayong; Xue, Yang; Zhao, Bao; Zhang, Huisheng; Jiang, Hua; Yang, Zhongqin
2016-12-01
A novel topological insulator with tunable edge states, called a quantum spin-quantum anomalous Hall (QSQAH) insulator, is predicted in a heterostructure of a hydrogenated Sb (S b2H ) monolayer on a LaFe O3 substrate by using ab initio methods. The substrate induces a drastic staggered exchange field in the S b2H film, which plays an important role to generate the QSQAH effect. A topologically nontrivial band gap (up to 35 meV) is opened by Rashba spin-orbit coupling, which can be enlarged by strain and an electric field. To understand the underlying physical mechanism of the QSQAH effect, a tight-binding model based on px and py orbitals is constructed. With the model, the exotic behaviors of the edge states in the heterostructure are investigated. Dissipationless chiral charge edge states related to one valley are found to emerge along both sides of the sample, whereas low-dissipation spin edge states related to the other valley flow only along one side of the sample. These edge states can be tuned flexibly by polarization-sensitive photoluminescence controls and/or chemical edge modifications. Such flexible manipulations of the charge, spin, and valley degrees of freedom provide a promising route towards applications in electronics, spintronics, and valleytronics.
7/3 fractional quantum Hall effect: topology, trion excitations and edge states
Balram, Ajit C.; Wu, Ying-Hai; Sreejith, G. J.; Wójs, Arkadiusz; Jain, J. K.
2013-03-01
Exact diagonalization studies on finite systems show that the quasihole and quasiparticle excitations in the 7/3 fractional quantum Hall (FQH) state are qualitatively distinct from those of the 1/3 state, suggesting the possibility of different topological origins for the two states. We perform composite-fermion diagonalization on larger systems and also evaluate the entanglement spectrum, which shows that in spite of these strong finite size deviations, the 7/3 and 1/3 FQH states have the same topological structure in the thermodynamic limit. Nonetheless, there are substantial non-topological differences between the two, arising from the stronger residual interaction between composite fermions at 7/3. In particular, we show that the lowest energy charged excitations of the 7/3 state are complex trions of composite fermions, which have a much larger size than the charged excitations at 1/3. We discuss many observable consequences of our results.
Noise and current correlations in tunnel junctions of quantum spin Hall edge states
Dolcini, Fabrizio
2015-10-01
The edge channels of two-dimensional topological systems are protected from elastic reflection and are noiseless at low temperature. Yet, noise and cross correlations can be induced when electron waves partly transmit to the opposite edge via tunneling through a constriction. In particular, in a quantum spin Hall (QSH) system tunneling occurs via both spin-preserving (p ) and spin-flipping (f ) processes, each fulfilling time-reversal symmetry. We investigate the current correlations of a four-terminal QSH setup in the presence of a tunneling region, both at equilibrium and out of equilibrium. We find that, although p and f processes do not commute and the generic current correlation depends on both, under appropriate conditions a direct detection of two types of partition noise is possible. In particular, while the spin-preserving partitioning can be probed for any arbitrary tunnel junction with a specific configuration of terminal biases, the spin-flipping partitioning can be directly detected only under suitably designed setups and conditions. We describe two setups where these conditions can be fulfilled, and both types of partitioning can be detected and controlled.
Edge reconstructions in fractional quantum Hall systems.
Joglekar, Yogesh; Nguyen, Hoang; Murthy, Ganpathy
2003-03-01
Two dimensional electron systems exhibiting fractional quantum Hall effects are characterized by a quantized Hall conductance and a dissipationless bulk. The transport in these systems occurs only at the edges where gapless excitations are possible [1]. We present a microscopic calculation of these egde-states at filling factors ν=1/3 and ν=2/5 using the Hamiltonian theory of the fractional quantum Hall effect [2]. We find that the quantum Hall egde undergoes a reconstruction as the confining potential, produced by the background charge density, softens [3,4]. Our results have implications to the tunneling experiments into the edge of a fractional quantum Hall system [5]. 1: X. G.Wen, Phys. Rev. Lett. 64, 2206 (1990). 2: R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997). 3: C. de C. Chamon and X. G. Wen, Phys. Rev. B 49, 8227 (1994). 4: X. Wan, K. Yang, and E. H. Razayi, Phys. Rev. Lett. 88, 056802 (2002). 5: A.M.Chang et al., Phys. Rev. Lett. 86, 143 (2000).
Mani, Arjun; Benjamin, Colin
2016-04-13
On the surface of 2D topological insulators, 1D quantum spin Hall (QSH) edge modes occur with Dirac-like dispersion. Unlike quantum Hall (QH) edge modes, which occur at high magnetic fields in 2D electron gases, the occurrence of QSH edge modes is due to spin-orbit scattering in the bulk of the material. These QSH edge modes are spin-dependent, and chiral-opposite spins move in opposing directions. Electronic spin has a larger decoherence and relaxation time than charge. In view of this, it is expected that QSH edge modes will be more robust to disorder and inelastic scattering than QH edge modes, which are charge-dependent and spin-unpolarized. However, we notice no such advantage accrues in QSH edge modes when subjected to the same degree of contact disorder and/or inelastic scattering in similar setups as QH edge modes. In fact we observe that QSH edge modes are more susceptible to inelastic scattering and contact disorder than QH edge modes. Furthermore, while a single disordered contact has no effect on QH edge modes, it leads to a finite charge Hall current in the case of QSH edge modes, and thus a vanishing of the pure QSH effect. For more than a single disordered contact while QH states continue to remain immune to disorder, QSH edge modes become more susceptible--the Hall resistance for the QSH effect changes sign with increasing disorder. In the case of many disordered contacts with inelastic scattering included, while quantization of Hall edge modes holds, for QSH edge modes a finite charge Hall current still flows. For QSH edge modes in the inelastic scattering regime we distinguish between two cases: with spin-flip and without spin-flip scattering. Finally, while asymmetry in sample geometry can have a deleterious effect in the QSH case, it has no impact in the QH case.
A realistic quantum capacitance model for quantum Hall edge state based Fabry-Pérot interferometers
Kilicoglu, O.; Eksi, D.; Siddiki, A.
2017-01-01
In this work, the classical and the quantum capacitances are calculated for a Fabry-Pérot interferometer operating in the integer quantized Hall regime. We first consider a rotationally symmetric electrostatic confinement potential and obtain the widths and the spatial distribution of the insulating (incompressible) circular strips using a charge density profile stemming from self-consistent calculations. Modelling the electrical circuit of capacitors composed of metallic gates and incompressible/compressible strips, we investigate the conditions to observe Aharonov-Bohm (quantum mechanical phase dependent) and Coulomb blockade (capacitive coupling dependent) effects reflected in conductance oscillations. In a last step, we solve the Schrödinger and the Poisson equations self-consistently in a numerical manner taking into account realistic experimental geometries. We find that, describing the conductance oscillations either by Aharanov-Bohm or Coulomb blockade strongly depends on sample properties also other than size, therefore, determining the origin of these oscillations requires further experimental and theoretical investigation.
Collective edge modes in fractional quantum Hall systems
Nguyen, Hoang K.; Joglekar, Yogesh N.; Murthy, Ganpathy
2004-07-01
Over the past few years one of us (Murthy) in collaboration with Shankar has developed an extended Hamiltonian formalism capable of describing the ground-state and low-energy excitations in the fractional quantum Hall regime. The Hamiltonian, expressed in terms of composite fermion operators, incorporates all the nonperturbative features of the fractional Hall regime, so that conventional many-body approximations such as Hartree-Fock and time-dependent Hartree-Fock are applicable. We apply this formalism to develop a microscopic theory of the collective edge modes in fractional quantum Hall regime. We present the results for edge mode dispersions at principal filling factors ν=1/3 , 1/5 , and 2/5 for systems with unreconstructed edges. The primary advantage of the method is that one works in the thermodynamic limit right from the beginning, thus avoiding the finite-size effects which ultimately limit exact diagonalization studies.
Gapless modes of fractional quantum Hall edges: a Hamiltonian study
Nguyen, Hoang; Joglekar, Yogesh; Murthy, Ganpathy
2004-03-01
We study the collective modes of the fractional quantum Hall edge states using the Hamiltonian formalism [1]. In this theory, the composite fermions are fully interacting; the collective modes are obtained within a conserving approximation which respects the constraints [2]. We present the gapless edge-mode dispersions at 1/3 and 2/5 filling fractions of unreconstructed and reconstructed edges. The dispersions are found to be nonlinear due to the variation of the effective magnetic field on the composite fermions. The implications of our study to the tunneling experiments into the edge of a fractional quantum Hall system [3] are discussed*. 1. R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997). 2. G. Murthy, Phys. Rev. B 64, 195310 (2001). 3. A.M.Chang et. al., Phys. Rev. Lett. 86, 143 (2000). * Work supported by the NSF, Grant number DMR 031176.
Chen, Wei; Deng, Wei-Yin; Hou, Jing-Min; Shi, D. N.; Sheng, L.; Xing, D. Y.
2016-08-01
The quantum spin Hall insulator is characterized by helical edge states, with the spin polarization of the electron being locked to its direction of motion. Although the edge-state conduction has been observed, unambiguous evidence of the helical spin texture is still lacking. Here, we investigate the coherent edge-state transport in an interference loop pinched by two point contacts. Because of the helical character, the forward interedge scattering enforces a π spin rotation. Two successive processes can only produce a nontrivial 2 π or trivial 0 spin rotation, which can be controlled by the Rashba spin-orbit coupling. The nontrivial spin rotation results in a geometric π Berry phase, which can be detected by a π phase shift of the conductance oscillation relative to the trivial case. Our results provide smoking gun evidence for the helical spin texture of the edge states. Moreover, it also provides the opportunity to all electrically explore the trajectory-dependent spin Berry phase in condensed matter.
Induced Superconductivity in the Quantum Spin Hall Edge
Ren, Hechen; Hart, Sean; Wagner, Timo; Leubner, Philipp; Muehlbauer, Mathias; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; Yacoby, Amir
2014-03-01
Two-dimensional topological insulators have a gapped bulk and helical edge states, making it a quantum spin Hall insulator. Combining such edge states with superconductivity can be an excellent platform for observing and manipulating localized Majorana fermions. In the context of condensed matter, these are emergent electronic states that obey non-Abelian statistics and hence support fault-tolerant quantum computing. To realize such theoretical constructions, an essential step is to show these edge channels are capable of carrying coherent supercurrent. In our experiment, we fabricate Josephson junctions with HgTe/HgCdTe quantum wells, a two-dimensional material that becomes a quantum spin Hall insulator when the quantum well is thicker than 6.3 nm and the bulk density is depleted. In this regime, we observe supercurrents whose densities are confined to the edges of the junctions, with edge widths ranging from 180 nm to 408 nm. To verify the topological nature of these edges, we measure identical junctions with HgTe/HgCdTe quantum wells thinner than 6.3 nm and observe only uniform supercurrent density across the junctions. This research is supported by Microsoft Corporation Project Q, the NSF DMR-1206016, the DOE SCGF Program, the German Research Foundation, and EU ERC-AG program.
Bulk Versus Edge in the Quantum Hall Effect
Kao, Y. -C.; Lee, D.-H.
1996-01-01
The manifestation of the bulk quantum Hall effect on edge is the chiral anomaly. The chiral anomaly {\\it is} the underlying principle of the ``edge approach'' of quantum Hall effect. In that approach, $\\sxy$ should not be taken as the conductance derived from the space-local current-current correlation function of the pure one-dimensional edge problem.
Helical Aharonov-Casher edge states
Heremans, J. J.; Xu, L. L.
2010-01-01
It is shown that an Aharonov-Casher vector potential in a two-dimensional geometry can lead to helical edge states. The Aharonov-Casher vector potential is the electromagnetic dual of the magnetic vector potential, and leads to traveling states at the sample edge in analogy to the integer quantum Hall effect. The helical edge states are predicted to appear in a narrow channel geometry with parabolic or sufficiently symmetric confinement potential. The implications of the helical Aharonov-Cash...
Fractional quantum Hall edge: Effect of nonlinear dispersion and edge roton
Jolad, Shivakumar; Sen, Diptiman; Jain, Jainendra K.
2010-01-01
According to Wen's theory, a universal behavior of the fractional quantum Hall edge is expected at sufficiently low energies, where the dispersion of the elementary edge excitation is linear. A microscopic calculation shows that the actual dispersion is indeed linear at low energies, but deviates from linearity beyond certain energy, and also exhibits an "edge roton minimum." We determine the edge exponent from a microscopic approach, and find that the nonlinearity of the dispersion makes a s...
Magnetoplasmon Excitations at Graphene Vortex Hall Fluid Edge
M. Rabiu
2016-01-01
Full Text Available We investigate magnetoplasmon dynamics localized on the edges of graphene vortex Hall fluid. The vortex matter captures an anomalous term that causes vortex localization near fluid boundary and creates a double boundary layer, Δ0∝(β-1lB with β being filling factor. The term also has qualitative effect on resonant excitations of edge magnetoplasmons. We found that, for sharp edges under experimental conditions, graphene edge magnetoplasmon (EMP resonances have similar behavior as in recent experiments. Gradual distinctions arise for smooth edges in the presence of the anomalous term, where a weak EMP peak appears. The second peak becomes well noticed as the smoothness is increased. We identified the resonant mode as an Inter-EMP. It originates from the oscillations of charges in the inner boundary of the double layer. The present observation brings to light the direct cause of Inter-EMP which remained to be detected in graphene experiments.
Single-electron quantum tomography in quantum Hall edge channels
Grenier, Ch; Degiovanni, P [Universite de Lyon, Federation de Physique Andre Marie Ampere, CNRS-Laboratoire de Physique de l' Ecole Normale Superieure de Lyon, 46 Allee d' Italie, 69364 Lyon Cedex 07 (France); Herve, R; Bocquillon, E; Parmentier, F D; Placais, B; Berroir, J M; Feve, G, E-mail: Pascal.Degiovanni@ens-lyon.fr [Laboratoire Pierre Aigrain, Departement de Physique de l' Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05 (France)
2011-09-15
We propose a quantum tomography protocol to measure single-electron coherence in quantum Hall edge channels, and therefore access for the first time the wavefunction of single-electron excitations propagating in ballistic quantum conductors. Its implementation would open the way to quantitative studies of single-electron decoherence and would provide a quantitative tool for analyzing single- to few-electron sources. We show how this protocol could be implemented using ultrahigh-sensitivity noise measurement schemes.
Edge physics of the quantum spin Hall insulator from a quantum dot excited by optical absorption.
Vasseur, Romain; Moore, Joel E
2014-04-11
The gapless edge modes of the quantum spin Hall insulator form a helical liquid in which the direction of motion along the edge is determined by the spin orientation of the electrons. In order to probe the Luttinger liquid physics of these edge states and their interaction with a magnetic (Kondo) impurity, we consider a setup where the helical liquid is tunnel coupled to a semiconductor quantum dot that is excited by optical absorption, thereby inducing an effective quantum quench of the tunneling. At low energy, the absorption spectrum is dominated by a power-law singularity. The corresponding exponent is directly related to the interaction strength (Luttinger parameter) and can be computed exactly using boundary conformal field theory thanks to the unique nature of the quantum spin Hall edge.
Skyrmions and edge-spin excitations in quantum Hall droplets
Oaknin, J.H. [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, 28049, Madrid (Spain); Martin-Moreno, L. [Departamento de Fisica de la Materia Condensada, Instituto de Ciencia de Materiales de Aragon, Consejo Superior de Investigaciones Cientificas, Universidad de Zaragoza, Zaragoza 50015 (Spain); Tejedor, C. [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, 28049, Madrid (Spain)
1996-12-01
We present a microscopic analysis of spin textures in quantum Hall droplets for filling factors {nu}{approx_equal}1. We obtain analytical many-body wave functions of spin excitations which describe all of the necessary quantum numbers. An adequate linear combination of these eigenstates leads to wave functions in which the spatially dependent spinor can be factorized. This displays the topological structure of several spin textures, some of which are located at the bulk, and others at the edge. For the former, we obtain bulk charged skyrmions that can be expressed as a condensate of spin excitons interacting via a two-body repulsive interaction. The size of the skyrmion is given by the number of excitons present in the condensate. We also obtain the skyrmion energy as a function of its size for both zero and finite Zeeman energy. For the edge excitations we find that a branch of these spin textures starts with lower energy than the branch of polarized charge edge excitations. When the number of electrons is of the order of a few tenths, there are no crossings of the spin and charge branches so that edge-spin textures can be responsible for the edge reconstruction of the droplet. On the contrary, edge reconstruction is always found to be due to polarized charge excitations when the number of electrons is larger than one hundred. {copyright} {ital 1996 The American Physical Society.}
Microscopic study of the (2)/(5) fractional quantum Hall edge
Sreejith, G. J.; Jolad, Shivakumar; Sen, Diptiman; Jain, Jainendra K.
2011-12-01
This paper reports on our study of the edge of the (2)/(5) fractional quantum Hall state, which is more complicated than the edge of the (1)/(3) state because of the presence of edge sectors corresponding to different partitions of composite fermions in the lowest two Λ levels. The addition of an electron at the edge is a nonperturbative process and it is not a priori obvious in what manner the added electron distributes itself over these sectors. We show, from a microscopic calculation, that when an electron is added at the edge of the ground state in the [N1,N2] sector, where N1 and N2 are the numbers of composite fermions in the lowest two Λ levels, the resulting state lies in either [N1+1,N2] or [N1,N2+1] sectors; adding an electron at the edge is thus equivalent to adding a composite fermion at the edge. The coupling to other sectors of the form [N1+1+k,N2-k], k integer, is negligible in the asymptotically low-energy limit. This study also allows a detailed comparison with the two-boson model of the (2)/(5) edge. We compute the spectral weights and find that while the individual spectral weights are complicated and nonuniversal, their sum is consistent with an effective two-boson description of the (2)/(5) edge.
Non-abelian quantum Hall states -- exclusion statistics, K-matrices and duality
Ardonne, E.; Bouwknegt, P.; Schoutens, K.
2001-01-01
We study excitations in edge theories for non-abelian quantum Hall states, focussing on the spin polarized states proposed by Read and Rezayi and on the spin singlet states proposed by two of the authors. By studying the exclusion statistics properties of edge-electrons and edge-quasiholes, we
Reprint of : Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor
Arrachea, Liliana; von Oppen, Felix
2016-08-01
The precessing magnetization of a magnetic islands coupled to a quantum spin Hall edge pumps charge along the edge. Conversely, a bias voltage applied to the edge makes the magnetization precess. We point out that this device realizes an adiabatic quantum motor and discuss the efficiency of its operation based on a scattering matrix approach akin to Landauer-Büttiker theory. Scattering theory provides a microscopic derivation of the Landau-Lifshitz-Gilbert equation for the magnetization dynamics of the device, including spin-transfer torque, Gilbert damping, and Langevin torque. We find that the device can be viewed as a Thouless motor, attaining unit efficiency when the chemical potential of the edge states falls into the magnetization-induced gap. For more general parameters, we characterize the device by means of a figure of merit analogous to the ZT value in thermoelectrics.
Stability of edge states and edge magnetism in graphene nanoribbons
Kunstmann, Jens; Özdoğan, Cem; Quandt, Alexander; Fehske, Holger
2010-01-01
We critically discuss the stability of edge states and edge magnetism in zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge states might not exist in real systems, and show that there are at least three very natural mechanisms - edge reconstruction, edge passivation, and edge closure - which dramatically reduce the effect of edge states in ZGNRs or even totally eliminate them. Even if systems with magnetic edge states could be made, the intrinsic magnetism would not be ...
Collective modes at the fractional quantum Hall edge
Joglekar, Yogesh; Murthy, Ganpathy
2002-03-01
The fractional quantum Hall edge has been a continuing source of new ideas [1] and experimental results [2] for some time. Most theoretical approaches start with an effective bosonic theory [1] in which all fermions have been integrated out (an exception is the approach based on Chern-Simons theory [3]). Our approach is based on the lowest Landau level Hamiltonian theory of the FQHE [4]. In this theory, composite fermions are fully interacting, and We obtain the collective modes using a conserving approximation which respects the constraints. We present the edge-mode dispersions for various simple fractions. 1. X.-G.Wen, Phys. Rev. Lett. 64, 2206 (1990); A.Lopez and E.Fradkin, Phys. Rev. B 59, 15323 (1999); U. Zulicke and A.H.MacDonald, Phys. Rev. B 60, 2837 (1999); D.-H.Lee and X.-G.Wen, cond-mat/9809160. 2. A.M.Chang et al, Phys. Rev. Lett. 86, 143 (2000). 3. L.S.Levitov, A.V.Shytov, and B.I.Halperin, Phys. Rev. B 64, 075322 (2001). 4. R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997).
4pi periodic Josephson current through a Quantum Spin-Hall edge
Dahlhaus, Jan; Beenakker, Carlo; Pikulin, Dmitry; Hyart, Timo; Schomerus, Henning
2014-03-01
The helical edge state of a quantum spin-Hall insulator can carry a supercurrent in equilibrium between two superconducting electrodes (separation L, coherence length ?). We calculate the maximum (critical) current Ic that can flow without dissipation along a single edge, going beyond the short-junction restriction L?? of earlier work, and find a dependence on the fermion parity of the ground state when L becomes larger than ?. Fermion-parity conservation doubles the critical current in the low-temperature, long-junction limit, while for a short junction Ic is the same with or without parity constraints. This provides a phase-insensitive, dc signature of the 4?-periodic Josephson effect.
Topological Number of Edge States
Hashimoto, Koji
2016-01-01
We show that the edge states of the four-dimensional class A system can have topological charges, which are characterized by Abelian/non-Abelian monopoles. The edge topological charges are a new feature of relations among theories with different dimensions. From this novel viewpoint, we provide a non-Abelian analogue of the TKNN number as an edge topological charge, which is defined by an SU(2) 't Hooft-Polyakov BPS monopole through an equivalence to Nahm construction. Furthermore, putting a constant magnetic field yields an edge monopole in a non-commutative momentum space, where D-brane methods in string theory facilitate study of edge fermions.
Corner junction as a probe of helical edge states.
Hou, Chang-Yu; Kim, Eun-Ah; Chamon, Claudio
2009-02-20
We propose and analyze interedge tunneling in a quantum spin Hall corner junction as a means to probe the helical nature of the edge states. We show that electron-electron interactions in the one-dimensional helical edge states result in Luttinger parameters for spin and charge that are intertwined, and thus rather different from those for a quantum wire with spin rotation invariance. Consequently, we find that the four-terminal conductance in a corner junction has a distinctive form that could be used as evidence for the helical nature of the edge states.
Gate Bias Effects on Samples with Edge Gates in the Quantum Hall Regime
若林 淳一; 風間 重雄; 長嶋 登志夫
2001-01-01
We have fabricated GaAs/AlGaAs heterostructure Hall samples that have edge gate with several widths along both sides of the sample. The gate width dependence of an effect of the gate voltage to the Hall resistance was measured at the middle of a transition region between the adjacent quantum Hall plateaus. The results have been analyzed based on two model functions of current distribution;an exponential type and the modified Beenakker type. The results of the former have shown qualitative agr...
Parity effect of bipolar quantum Hall edge transport around graphene antidots.
Matsuo, Sadashige; Nakaharai, Shu; Komatsu, Katsuyoshi; Tsukagoshi, Kazuhito; Moriyama, Takahiro; Ono, Teruo; Kobayashi, Kensuke
2015-06-30
Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene.
Quantum Hall transport as a probe of capacitance profile at graphene edges
Vera-Marun, I. J.; Zomer, P. J.; Veligura, A.; Guimaraes, M. H. D.; Visser, L.; Tombros, N.; van Elferen, H. J.; Zeitler, U.; van Wees, B. J.
2013-01-01
The quantum Hall effect is a remarkable manifestation of quantized transport in a two-dimensional electron gas (2DEG). Given its technological relevance, it is important to understand its development in realistic nanoscale devices. In this work, we present how the appearance of different edge channe
Graphene edges; localized edge state and electron wave interference
Enoki Toshiaki
2012-03-01
Full Text Available The electronic structure of massless Dirac fermion in the graphene hexagonal bipartite is seriously modified by the presence of edges depending on the edge chirality. In the zigzag edge, strongly spin polarized nonbonding edge state is created as a consequence of broken symmetry of pseudo-spin. In the scattering at armchair edges, the K-K’ intervalley transition gives rise to electron wave interference. The presence of edge state in zigzag edges is observed in ultra-high vacuum STM/STS observations. The electron wave interference phenomenon in the armchair edge is observed in the Raman G-band and the honeycomb superlattice pattern with its fine structure in STM images.
Single-edge transport in an InAs/GaSb quantum spin Hall insulator
Couëdo, François; Irie, Hiroshi; Suzuki, Kyoichi; Onomitsu, Koji; Muraki, Koji
2016-07-01
We report transport measurements in a single edge channel of an InAs/GaSb quantum spin Hall insulator, where the conduction occurs through only one pair of counterpropagating edge modes. By using a specific sample design involving highly asymmetric current paths, we electrically isolate a single edge channel of the two-dimensional topological insulator from the other edge. This enables us to probe a single edge by multiterminal measurements. Both two-terminal and four-terminal resistances show a nearly quantized plateau around h /e2 for a 4-μ m -long edge, indicating quasiballistic transport. Our approach is advantageous in that it allows us to gain insight into a microscopic region from local measurements.
Hui, Hoi-Yin; Sau, Jay D.
2017-01-01
Time-reversal invariance places strong constraints on the properties of the quantum spin Hall edge. One such restriction is the inevitability of dissipation in a Josephson junction between two superconductors formed on such an edge without the presence of interaction. Interactions and spin-conservation breaking are key ingredients for the realization of the dissipationless ac Josephson effect on such quantum spin Hall edges. We present a simple quantum impurity model that allows us to create a dissipationless fractional Josephson effect on a quantum spin Hall edge. We then use this model to substantiate a general argument that shows that any such nondissipative Josephson effect must necessarily be 8 π periodic.
Quenching of the quantum Hall effect in graphene with scrolled edges.
Cresti, Alessandro; Fogler, Michael M; Guinea, Francisco; Castro Neto, A H; Roche, Stephan
2012-04-20
Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size.
Yue, Z.; Raikh, M. E.
2016-09-01
The Quantum anomalous Hall (QAH) effect in the films with nontrivial band structure accompanies the ferromagnetic transition in the system of magnetic dopants. Experimentally, the QAH transition manifests itself as a jump in the dependence of longitudinal resistivity on a weak external magnetic field. Microscopically, this jump originates from the emergence of a chiral edge mode on one side of the ferromagnetic transition. We study analytically the effect of an extended confinement on the structure of the edge modes. We employ the simplest model of the extended confinement in the form of a potential step next to the hard wall. It is shown that, unlike the conventional quantum Hall effect, where all edge channels are chiral, in the QAH effect, a complex structure of the boundary leads to nonchiral edge modes which are present on both sides of the ferromagnetic transition. Wave functions of nonchiral modes are different above and below the transition: on the "topological" side, where the chiral edge mode is supported, nonchiral modes are "repelled" from the boundary; i.e., they are much less localized than on the "trivial" side. Thus, the disorder-induced scattering into these modes will boost the extension of the chiral edge mode. The prime experimental manifestation of nonchiral modes is that, by contributing to longitudinal resistance, they smear the QAH transition.
Geometric Defects in Quantum Hall States
Gromov, Andrey
2016-01-01
We describe a geometric (or gravitational) analogue of the Laughlin quasiholes in the fractional quantum Hall states. Analogously to the quasiholes these defects can be constructed by an insertion of an appropriate vertex operator into the conformal block representation of a trial wavefunction, however, unlike the quasiholes these defects are extrinsic and do not correspond to true excitations of the quantum fluid. We construct a wavefunction in the presence of such defects and explain how to assign an electric charge and a spin to each defect, and calculate the adiabatic, non-abelian statistics of the defects. The defects turn out to be equivalent to the genons in that their adiabatic exchange statistics can be described in terms of representations of the mapping class group of an appropriate higher genus Riemann surface. We present a general construction that, in principle, allows to calculate the statistics of $\\mathbb Z_n$ genons for any "parent" topological phase. We illustrate the construction on the ex...
Giant edge state splitting at atomically precise graphene zigzag edges.
Wang, Shiyong; Talirz, Leopold; Pignedoli, Carlo A; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal
2016-05-16
Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron-electron interactions in these localized states.
High spatial resolution Hall sensor array for edge plasma magnetic field measurements
Liu, Yuhong; Maurer, David A.; Navratil, Gerald A.; Rivera, Nicholas
2005-09-01
A one-dimensional, high-spatial resolution, 20-element Hall sensor array has been developed to directly measure the edge plasma perpendicular magnetic field and its fluctuations as a function of radius with 4-mm resolution. The array employs new small-area, high-sensitivity indium antimonide (InSb) Hall probes in combination with a high-density seven-layer printed circuit board to provide for connections to supply Hall current, record the measured Hall voltage output signals, and mitigate inductive pickup. A combination of bench and in situ measurements is described that provides absolute calibration of the diagnostic array in the presence of a strong transverse magnetic field component that is approximately 1000 times greater than the perpendicular fluctuating field needed to be resolved by the diagnostic. The Hall probes calibrated using this method are capable of magnetic field measurements with a sensitivity of 7V/T over the frequency band from 0 to 20 kHz.
Fractional quantum Hall states of bosons on cones
Wu, Ying-Hai; Tu, Hong-Hao; Sreejith, G. J.
2017-09-01
Motivated by a recent experiment, which synthesizes Landau levels for photons on cones [Schine et al., Nature (London) 534, 671 (2016), 10.1038/nature17943], and more generally the interest in understanding gravitational responses of quantum Hall states, we study fractional quantum Hall states of bosons on cones. A variety of trial wave functions for conical systems are constructed and compared with exact diagonalization results. The tip of a cone is a localized geometrical defect with singular curvature, which can modify the density profiles of quantum Hall states. The density profiles on cones can be used to extract some universal information about quantum Hall states. The values of certain quantities are computed numerically using the density profiles of some quantum Hall states and they agree with analytical predictions.
Understanding the physics of a possible non-Abelian fractional quantum hall effect state.
Pan, Wei; Crawford, Matthew; Tallakulam, Madhu; Ross, Anthony Joseph, III
2010-10-01
We wish to present in this report experimental results from a one-year Senior Council Tier-1 LDRD project that focused on understanding the physics of a possible non-Abelian fractional quantum Hall effect state. We first give a general introduction to the quantum Hall effect, and then present the experimental results on the edge-state transport in a special fractional quantum Hall effect state at Landau level filling {nu} = 5/2 - a possible non-Abelian quantum Hall state. This state has been at the center of current basic research due to its potential applications in fault-resistant topological quantum computation. We will also describe the semiconductor 'Hall-bar' devices we used in this project. Electron physics in low dimensional systems has been one of the most exciting fields in condensed matter physics for many years. This is especially true of quantum Hall effect (QHE) physics, which has seen its intellectual wealth applied in and has influenced many seemingly unrelated fields, such as the black hole physics, where a fractional QHE-like phase has been identified. Two Nobel prizes have been awarded for discoveries of quantum Hall effects: in 1985 to von Klitzing for the discovery of integer QHE, and in 1998 to Tsui, Stormer, and Laughlin for the discovery of fractional QHE. Today, QH physics remains one of the most vibrant research fields, and many unexpected novel quantum states continue to be discovered and to surprise us, such as utilizing an exotic, non-Abelian FQHE state at {nu} = 5/2 for fault resistant topological computation. Below we give a briefly introduction of the quantum Hall physics.
Superconducting Analogue of the Parafermion Fractional Quantum Hall States
Abolhassan Vaezi
2014-07-01
Full Text Available Read-Rezayi Z_{k} parafermion wave functions describe ν=2+(k/kM+2 fractional quantum Hall (FQH states. These states support non-Abelian excitations from which protected quantum gates can be designed. However, there is no experimental evidence for these non-Abelian anyons to date. In this paper, we study the ν=2/k FQH-superconductor heterostructure and find the superconducting analogue of the Z_{k} parafermion FQH state. Our main tool is the mapping of the FQH into coupled one-dimensional chains, each with a pair of counterpropagating modes. We show that by inducing intrachain pairing and charge preserving backscattering with identical couplings, the one-dimensional chains flow into gapless Z_{k} parafermions when k<4. By studying the effect of interchain coupling, we show that every parafermion mode becomes massive except for the two outermost ones. Thus, we achieve a fractional topological superconductor whose chiral edge state is described by a Z_{k} parafermion conformal field theory. For instance, we find that a ν=2/3 FQH in proximity to a superconductor produces a Z_{3} parafermion superconducting state. This state is topologically indistinguishable from the non-Abelian part of the ν=12/5 Read-Rezayi state. Both of these systems can host Fibonacci anyons capable of performing universal quantum computation through braiding operations.
Propagating edge states in strained honeycomb lattices
Salerno, Grazia; Ozawa, Tomoki; Price, Hannah M.; Carusotto, Iacopo
2017-06-01
We investigate the helically propagating edge states associated with pseudo-Landau levels in strained honeycomb lattices. We exploit chiral symmetry to derive a general criterion for the existence of these propagating edge states in the presence of only nearest-neighbor hoppings and we verify our criterion using numerical simulations of both uniaxially and trigonally strained honeycomb lattices. We show that the propagation of the helical edge state can be controlled by engineering the shape of the edges. Sensitivity to chiral-symmetry-breaking next-nearest-neighbor hoppings is assessed. Our result opens up an avenue toward the precise control of edge modes through manipulation of the edge shape.
Color Ferromagnetism and Quantum Hall states in Quark Matter
Iwazaki, A
2003-01-01
We discuss a possibility of the presence of a stable color ferromagnetic state in SU(2) gauge theory of quark matter; a color magnetic field is spontaneously generated due tothe gluon's dynamics. The state arises between the hadronic state and the color superconducting state when the density of quarks is varied. Although the state has been known to have unstable modes, we show that unstable modes form quantum Hall states, in which the instability disappears. Namely, the quark matter possesses a stable phase with the ferromagnetic state and the quantum Hall state of gluons.
One-dimensional Topological Edge States of Bismuth Bilayers
Drozdov, Ilya; Alexandradinata, Aris; Jeon, Sangjun; Nadj-Perge, Stevan; Ji, Huiwen; Cava, Robert; Bernevig, B. Andrei; Yazdani, Ali
2014-03-01
The hallmark of a time-reversal symmetry protected topologically insulating state of matter in two-dimensions (2D) is the existence of chiral edge modes propagating along the perimeter of the sample. Bilayers of bismuth (Bi), an elemental system theoretically predicted to be a Quantum Spin Hall (QSH) insulator1, has been studied with Scanning Tunneling Microscopy (STM) and the electronic structure of its bulk and edge modes has been experimentally investigated. Spectroscopic mapping with STM reveals the presence of the state bound to the edges of the Bi-bilayer. By visualizing quantum interference of the edge state quasi-particles in confined geometries we characterize their dispersion and demonstrate that their properties are consistent with the absence of backscattering. Hybridization of the edge modes to the underlying substrate will be discussed. [1] Shuichi Murakami, Phys. Rev. Lett. 97, 236805 (2006). The work at Princeton and the Princeton Nanoscale Microscopy Laboratory was supported by ARO MURI program W911NF-12-1-0461, DARPA-SPWAR Meso program N6601-11-1-4110, NSF-DMR1104612, and NSF-MRSEC programs through the Princeton Center for Complex Materials (DMR-0819860)
Pairing in Luttinger Liquids and Quantum Hall States
Kane, Charles L.; Stern, Ady; Halperin, Bertrand I.
2017-07-01
We study spinless electrons in a single-channel quantum wire interacting through attractive interaction, and the quantum Hall states that may be constructed by an array of such wires. For a single wire, the electrons may form two phases, the Luttinger liquid and the strongly paired phase. The Luttinger liquid is gapless to one- and two-electron excitations, while the strongly paired state is gapped to the former and gapless to the latter. In contrast to the case in which the wire is proximity coupled to an external superconductor, for an isolated wire there is no separate phase of a topological, weakly paired superconductor. Rather, this phase is adiabatically connected to the Luttinger liquid phase. The properties of the one-dimensional topological superconductor emerge when the number of channels in the wire becomes large. The quantum Hall states that may be formed by an array of single-channel wires depend on the Landau-level filling factors. For odd-denominator fillings ν =1 /(2 n +1 ), wires at the Luttinger phase form Laughlin states, while wires in the strongly paired phase form a bosonic fractional quantum Hall state of strongly bound pairs at a filling of 1 /(8 n +4 ). The transition between the two is of the universality class of Ising transitions in three dimensions. For even-denominator fractions ν =1 /2 n , the two single-wire phases translate into four quantum Hall states. Two of those states are bosonic fractional quantum Hall states of weakly and strongly bound pairs of electrons. The other two are non-Abelian quantum Hall states, which originate from coupling wires close to their critical point. One of these non-Abelian states is the Moore-Read state. The transitions between all of these states are of the universality class of Majorana transitions. We point out some of the properties that characterize the different phases and the phase transitions.
Decomposition of fractional quantum Hall states: New symmetries and approximations
Thomale, R.; Estienne, B.; Regnault, N.; Bernevig, B.A.
2010-01-01
Abstract: We provide a detailed description of a new symmetry structure of the monomial (Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall states first obtained in Ref. 1, which we now extend to spin-singlet states. We show that the Haldane-Rezayi spin-singlet state can
A General Theorem Relating the Bulk Topological Number to Edge States in Two-dimensional Insulators
Qi, Xiao-Liang; /Tsinghua U., Beijing /Stanford U., Phys. Dept.; Wu, Yong-Shi; /Utah U.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept. /Tsinghua U., Beijing
2010-01-15
We prove a general theorem on the relation between the bulk topological quantum number and the edge states in two dimensional insulators. It is shown that whenever there is a topological order in bulk, characterized by a non-vanishing Chern number, even if it is defined for a non-conserved quantity such as spin in the case of the spin Hall effect, one can always infer the existence of gapless edge states under certain twisted boundary conditions that allow tunneling between edges. This relation is robust against disorder and interactions, and it provides a unified topological classification of both the quantum (charge) Hall effect and the quantum spin Hall effect. In addition, it reconciles the apparent conflict between the stability of bulk topological order and the instability of gapless edge states in systems with open boundaries (as known happening in the spin Hall case). The consequences of time reversal invariance for bulk topological order and edge state dynamics are further studied in the present framework.
Edge states of periodically kicked quantum rotors
Floß, Johannes
2015-01-01
We present a quantum localization phenomenon that exists in periodically kicked 3D rotors, but is absent in the commonly studied 2D ones: edge localization. We show that under the condition of a fractional quantum resonance there are states of the kicked rotor that are strongly localized near the edge of the angular momentum space at $J=0$. These states are analogs of surface states in crystalline solids, and they significantly affect resonant excitation of molecular rotation by laser pulse trains.
High-order multipole radiation from quantum Hall states in Dirac materials
Gullans, Michael J.; Taylor, Jacob M.; Imamoǧlu, Ataç; Ghaemi, Pouyan; Hafezi, Mohammad
2017-06-01
We investigate the optical response of strongly disordered quantum Hall states in two-dimensional Dirac materials and find qualitatively different effects in the radiation properties of the bulk versus the edge. We show that the far-field radiation from the edge is characterized by large multipole moments (>50 ) due to the efficient transfer of angular momentum from the electrons into the scattered light. The maximum multipole transition moment is a direct measure of the coherence length of the edge states. Accessing these multipole transitions would provide new tools for optical spectroscopy and control of quantum Hall edge states. On the other hand, the far-field radiation from the bulk appears as random dipole emission with spectral properties that vary with the local disorder potential. We determine the conditions under which this bulk radiation can be used to image the disorder landscape. Such optical measurements can probe submicron-length scales over large areas and provide complementary information to scanning probe techniques. Spatially resolving this bulk radiation would serve as a novel probe of the percolation transition near half filling.
Fractional quantum Hall states of bosons on cones
Wu, Ying-Hai; Sreejith, G J
2016-01-01
Motivated by a recent experiment which synthesizes Landau levels for photons on cones (Schine {\\em et al.}, arXiv: 1511.07381), and more generally the interest in understanding gravitational responses of quantum Hall systems, we study fractional quantum Hall states of bosons on cones. We construct several trial wave functions and compare them with exact diagonalization results. The tip of a cone is a localized geometrical defect with singular curvature around which excessive charges accumulate. We study the density profiles of some states on cones and show that the excessive charges agree with analytical predictions.
Moiré assisted fractional quantum Hall state spectroscopy
Wu, Fengcheng; MacDonald, A. H.
2016-12-01
Intra-Landau level excitations in the fractional quantum Hall regime are not accessible via optical absorption measurements. We point out that optical probes are enabled by the periodic potentials produced by a moiré pattern. Our observation is motivated by the recent observations of fractional quantum Hall incompressible states in moiré-patterned graphene on a hexagonal boron nitride substrate, and is theoretically based on f -sum rule considerations supplemented by a perturbative analysis of the influence of the moiré potential on many-body states.
Non-Abelian 3d Bosonization and Quantum Hall States
Radicevic, Djordje; Turner, Carl
2016-01-01
Bosonization dualities relate two different Chern-Simons-matter theories, with bosonic matter on one side replaced by fermionic matter on the other. We first describe a more general class of non-Abelian bosonization dualities. We then explore the non-relativistic physics of these theories in the quantum Hall regime. The bosonic theory lies in a condensed phase and admits vortices which are known to form a non-Abelian quantum Hall state. We ask how this same physics arises in the fermionic theory. We find that a condensed boson corresponds to a fully filled Landau level of fermions, while bosonic vortices map to fermionic holes. We confirm that the ground state of the two theories is indeed described by the same quantum Hall wavefunction.
Zimmermann, Katrin; Jordan, Anna; Gay, Frédéric; Watanabe, Kenji; Taniguchi, Takashi; Han, Zheng; Bouchiat, Vincent; Sellier, Hermann; Sacépé, Benjamin
2017-04-13
Charge carriers in the quantum Hall regime propagate via one-dimensional conducting channels that form along the edges of a two-dimensional electron gas. Controlling their transmission through a gate-tunable constriction, also called quantum point contact, is fundamental for many coherent transport experiments. However, in graphene, tailoring a constriction with electrostatic gates remains challenging due to the formation of p-n junctions below gate electrodes along which electron and hole edge channels co-propagate and mix, short circuiting the constriction. Here we show that this electron-hole mixing is drastically reduced in high-mobility graphene van der Waals heterostructures thanks to the full degeneracy lifting of the Landau levels, enabling quantum point contact operation with full channel pinch-off. We demonstrate gate-tunable selective transmission of integer and fractional quantum Hall edge channels through the quantum point contact. This gate control of edge channels opens the door to quantum Hall interferometry and electron quantum optics experiments in the integer and fractional quantum Hall regimes of graphene.
Preparation of edge states by shaking boundaries
Shi, Z.C. [Department of Physics, Fuzhou University, Fuzhou 350002 (China); Center for Quantum Sciences and School of Physics, Northeast Normal University, Changchun 130024 (China); Hou, S.C. [Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan (China); Wang, L.C. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Yi, X.X., E-mail: yixx@nenu.edu.cn [Center for Quantum Sciences and School of Physics, Northeast Normal University, Changchun 130024 (China)
2016-10-15
Preparing topological states of quantum matter, such as edge states, is one of the most important directions in condensed matter physics. In this work, we present a proposal to prepare edge states in Aubry–André–Harper (AAH) model with open boundaries, which takes advantage of Lyapunov control to design operations. We show that edge states can be obtained with almost arbitrary initial states. A numerical optimalization for the control is performed and the dependence of control process on the system size is discussed. The merit of this proposal is that the shaking exerts only on the boundaries of the model. As a by-product, a topological entangled state is achieved by elaborately designing the shaking scheme.
Preparation of edge states by shaking boundaries
Shi, Z. C.; Hou, S. C.; Wang, L. C.; Yi, X. X.
2016-10-01
Preparing topological states of quantum matter, such as edge states, is one of the most important directions in condensed matter physics. In this work, we present a proposal to prepare edge states in Aubry-André-Harper (AAH) model with open boundaries, which takes advantage of Lyapunov control to design operations. We show that edge states can be obtained with almost arbitrary initial states. A numerical optimalization for the control is performed and the dependence of control process on the system size is discussed. The merit of this proposal is that the shaking exerts only on the boundaries of the model. As a by-product, a topological entangled state is achieved by elaborately designing the shaking scheme.
Tsiper, Eugene
2006-03-01
A renormalization procedure is designed to find a subspace of high relevance in a many-body Hilbert space. Substantial reduction in the basis size can be achieved while approaching the exact diagonalization results. The idea is to search for a set of many-particle configurations that contribute the largest weight to the exact solution of the many-body Schrödinger equation, without actually computing the exact solution. We start with some suitable set of K configurations and find the ground state of the Hamiltonian in the many-body subspace that they span. We then retain K'elements with those retained. When repeated, the procedure converges after several iterations and yields some optimal set of configurations. The resulting truncation of the Hilbert space is essentially many-body, and cannot be achieved by truncating or rotating the single-particle basis. I will discuss an application of CSR to model resonant tunneling between the edges in the fractional quantum Hall regime, which has been used to experimentally observe fractional quantization of electric charge. Clusters large enough to contain two unconnected edges are modeled. The results suggest fractional quantization of the quasiparticle charge in units of e/3 and e/5 at fillings 1/3 and 2/5.
Metal-to-insulator switching in quantum anomalous Hall states
Pan, Lei; Kou, Xufeng; Wang, Jing; Fan, Yabin; Choi, Eun Sang; Shao, Qiming; Zhang, Shou Cheng; Wang, Kang Lung
Quantum anomalous Hall effect (QAHE) was recently achieved in magnetic topological insulator films as a form of dissipationless transport without external magnetic field. However, the universal phase diagram of QAHE and its relation with quantum Hall effect (QHE) remain to be investigated. Here, we report the experimental observation of the giant longitudinal resistance peak and zero Hall conductance plateau at the coercive field in the six quintuple-layer (Cr0.12Bi0.26Sb0.62)2 Te3 film, and demonstrate the metal-to-insulator switching between two opposite QAHE plateau states up to 0.3 K. The universal QAHE phase diagram is further confirmed through the angle-dependent measurements. Our results address that the quantum phase transitions in both QAHE and QHE regimes are in the same universality class, yet the microscopic details are different.
Edge States at Phase Boundaries and Their Stability
Asorey, M; Perez-Pardo, J M
2015-01-01
We analyse the effects of Robin boundary conditions on quantum field theories of spin 0, 1 and 1/2. In particular, we show that these conditions always lead to the appearance of edge states that play a significant role in quantum Hall effect and topological insulators. We prove in a rigorous way the existence of spectral lower bounds on the kinetic term of the Hamiltonian, which guarantees the stability and consistency of massive field theories when the mass is larger than the lower bound of the kinetic term. We also find an upper bound for the deepest edge state. The explicit dependence of both bounds on the boundary conditions and the size of the system is derived under very general conditions. For fermionic systems we analyse the case of Atiyah-Patodi-Singer and chiral bag boundary conditions. We point out the existence of edge states also in these cases and show that they disappear for small enough systems. Stability is granted in this case.
Diagnosing Topological Edge States via Entanglement Monogamy.
Meichanetzidis, K; Eisert, J; Cirio, M; Lahtinen, V; Pachos, J K
2016-04-01
Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this Letter, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically, and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement, we show that highly entangled states supported across a system bipartition are largely disentangled from the rest of the system, thus, usually appearing as gapless edge states. We then define an entanglement qualifier that identifies the presence of topological edge states based purely on correlations present in the ground states. We demonstrate the versatility of this qualifier by applying it to various free and interacting fermionic topological systems.
Edge states in polariton honeycomb lattices
Milićević, M.; Ozawa, T.; Andreakou, P.; Carusotto, I.; Jacqmin, T.; Galopin, E.; Lemaître, A.; Le Gratiet, L.; Sagnes, I.; Bloch, J.; Amo, A.
2015-09-01
The experimental study of edge states in atomically thin layered materials remains a challenge due to the difficult control of the geometry of the sample terminations, the stability of dangling bonds, and the need to measure local properties. In the case of graphene, localized edge modes have been predicted in zigzag and bearded edges, characterized by flat dispersions connecting the Dirac points. Polaritons in semiconductor microcavities have recently emerged as an extraordinary photonic platform to emulate 1D and 2D Hamiltonians, allowing the direct visualization of the wavefunctions in both real- and momentum-space as well as of the energy dispersion of eigenstates via photoluminescence experiments. Here we report on the observation of edge states in a honeycomb lattice of coupled micropillars. The lowest two bands of this structure arise from the coupling of the lowest energy modes of the micropillars, and emulate the π and π* bands of graphene. We show the momentum-space dispersion of the edge states associated with the zigzag and bearded edges, holding unidimensional quasi-flat bands. Additionally, we evaluate polarization effects characteristic of polaritons on the properties of these states.
Spin-orbit edge states in semiconductor two-dimensional systems
Xu, L. L.; Ren, Shaola; Heremans, J. J.; Minic, Djordje; Gaspe, C. K.; Vijeyaragunathan, S.; Mishima, T. D.; Santos, M. B.
2013-03-01
The electromagnetic duality between the Aharonov-Casher and the Aharonov-Bohm topological phases can lead to magnetoelectronic edge effects in two-dimensional systems. Based on this duality, we propose and experimentally explore a quantized Hall effect in which magnetization transport may be quantized analogously to charge transport. When the magnetic moment is fully projected, the edge effect is a magnetization dual to the integer quantum Hall effect. An analogy also exists between this dual and the bosonic quantum Hall effect currently under investigation. In experiments we search for edge states induced by the equivalent vector potential from Rashba-type spin-orbit interaction. We use mesoscopic side-gated channel structures on InGaAs/InAlAs heterostructures where backscattering between edge states can experimentally form evidence for edge states. The side-gate voltage varies the effective gauge field and resistance as function of side-gate voltage is measured across the mesoscopic structures at either low applied magnetic field or at fixed magnetic filling factors to obtain states of defined spin (DOE DE-FG02-08ER46532, NSF DMR-0520550).
Floquet edge states in germanene nanoribbons
Tahir, M.
2016-08-23
We theoretically demonstrate versatile electronic properties of germanene monolayers under circularly, linearly, and elliptically polarized light. We show for the high frequency regime that the edge states can be controlled by tuning the amplitude of the light and by applying a static electric field. For circularly polarized light the band gap in one valley is reduced and in the other enhanced, enabling single valley edge states. For linearly polarized light spin-split states are found for both valleys, being connected by time reversal symmetry. The effects of elliptically polarized light are similar to those of circularly polarized light. The transport properties of zigzag nanoribbons in the presence of disorder confirm a nontrivial nature of the edge states under circularly and elliptically polarized light.
Eilenberg, Michael
This book rests on the premises that borders such as that between Indonesia and Malaysia offer an exciting study arena that can tell us important things about how marginal citizens relate to their nation-state and in particular how alliances, with their competing and multiple loyalties, are managed...
Eilenberg, Michael
This book rests on the premises that borders such as that between Indonesia and Malaysia offer an exciting study arena that can tell us important things about how marginal citizens relate to their nation-state and in particular how alliances, with their competing and multiple loyalties, are managed...
Scaling Relations for Gaps in Fractional Quantum Hall States
Murthy, Ganpathy; Park, K.; Shankar, R.; Jain, J. K.
1998-01-01
The microscopic approach of Murthy and Shankar, which has recently been used to calculate the transport gaps of quantum Hall states with fractions p/(2ps+1), also implies scaling relations between gaps within a single sequence (fixed s) as well as between gaps of corresponding states in different sequences. This work tests these relations for a system of electrons in the lowest Landau level interacting with a model potential cutoff at high momenta due to sample thickness.
Scaling relations for gaps in fractional quantum Hall states
Murthy, Ganpathy; Park, K.; Shankar, R.; Jain, J. K.
1998-12-01
The microscopic Hamiltonian approach of Murthy and Shankar, which has recently been used to calculate the transport gaps of quantum Hall states with fractions ν=p/(2ps+1), also implies scaling relations between gaps within a single sequence (fixed s) as well as between gaps of corresponding states in different sequences. This work tests these relations for a system of electrons in the lowest Landau level interacting with a model potential cutoff at high momenta due to sample thickness.
Exploring topological edge states in photonic quasicrystals
Baboux, F; Lemaître, A; Gomez, C; Galopin, E; Gratiet, L Le; Sagnes, I; Amo, A; Bloch, J; Akkermans, E
2016-01-01
We experimentally investigate the topological properties of quasiperiodic chains using cavity polaritons confined in a potential following the Fibonacci sequence. Edge states forming in the gaps of a fractal energy spectrum are imaged both in real and momentum space. These edge states periodically traverse the gaps when varying a structural degree of freedom $\\phi$ of the Fibonacci sequence. The period and direction of the traverses are directly related to the Chern numbers assigned to each gap by the gap-labeling theorem. Additionally, we show that the Chern numbers determine the spatial symmetry properties of the edge states. These results highlight the potential of cavity polaritons to emulate nontrivial topological properties in a controlled environment.
Edge states at phase boundaries and their stability
Asorey, M.; Balachandran, A. P.; Pérez-Pardo, J. M.
2016-10-01
We analyze the effects of Robin-like boundary conditions on different quantum field theories of spin 0, 1/2 and 1 on manifolds with boundaries. In particular, we show that these conditions often lead to the appearance of edge states. These states play a significant role in physical phenomena like quantum Hall effect and topological insulators. We prove in a rigorous way the existence of spectral lower bounds on the kinetic term of different Hamiltonians, even in the case of Abelian gauge fields where it is a non-elliptic differential operator. This guarantees the stability and consistency of massive field theories with masses larger than the lower bound of the kinetic term. Moreover, we find an upper bound for the deepest edge state. In the case of Abelian gauge theories, we analyze a generalization of Robin boundary conditions. For Dirac fermions, we analyze the cases of Atiyah-Patodi-Singer and chiral bag boundary conditions. The explicit dependence of the bounds on the boundary conditions and the size of the system is derived under general assumptions.
Quantum spin Hall state in monolayer 1T'-WTe2
Tang, Shujie; Zhang, Chaofan; Wong, Dillon; Pedramrazi, Zahra; Tsai, Hsin-Zon; Jia, Chunjing; Moritz, Brian; Claassen, Martin; Ryu, Hyejin; Kahn, Salman; Jiang, Juan; Yan, Hao; Hashimoto, Makoto; Lu, Donghui; Moore, Robert G.; Hwang, Chan-Cuk; Hwang, Choongyu; Hussain, Zahid; Chen, Yulin; Ugeda, Miguel M.; Liu, Zhi; Xie, Xiaoming; Devereaux, Thomas P.; Crommie, Michael F.; Mo, Sung-Kwan; Shen, Zhi-Xun
2017-07-01
A quantum spin Hall (QSH) insulator is a novel two-dimensional quantum state of matter that features quantized Hall conductance in the absence of a magnetic field, resulting from topologically protected dissipationless edge states that bridge the energy gap opened by band inversion and strong spin-orbit coupling. By investigating the electronic structure of epitaxially grown monolayer 1T'-WTe2 using angle-resolved photoemission (ARPES) and first-principles calculations, we observe clear signatures of topological band inversion and bandgap opening, which are the hallmarks of a QSH state. Scanning tunnelling microscopy measurements further confirm the correct crystal structure and the existence of a bulk bandgap, and provide evidence for a modified electronic structure near the edge that is consistent with the expectations for a QSH insulator. Our results establish monolayer 1T'-WTe2 as a new class of QSH insulator with large bandgap in a robust two-dimensional materials family of transition metal dichalcogenides (TMDCs).
Wu, Ying-Hai; Sreejith, G. J.; Jain, Jainendra K.
2012-09-01
The edge of spin-unpolarized or spin-polarized ν=2/3 fractional quantum Hall states is predicted by the effective theory to support a backward-moving neutral mode in addition to a forward-moving charge mode. We study this issue from a microscopic perspective where these states are identified with an effective filling factor of 2 of composite fermions, but with an effective magnetic field that is antiparallel to the external field. A simple counting from the composite fermion description suggests that there might be two backward-moving edge modes, but explicit calculations show that one of these is projected out of the low-energy sector, while the remaining mode provides a good microscopic account of the actual counterpropagating edge mode. The forward-moving modes are identified as “Schur modes,” obtained by multiplying the ground-state wave function by the symmetric Schur polynomials. The edge of the 2/3 spin unpolarized state provides a particularly striking realization of “spin-charge separation” in one-dimensional Tomonaga-Luttinger liquids, with the spin and charge modes moving in opposite directions.
Refining Nodes and Edges of State Machines
Hallerstede, Stefan; Snook, Colin
2011-01-01
State machines are hierarchical automata that are widely used to structure complex behavioural specifications. We develop two notions of refinement of state machines, node refinement and edge refinement. We compare the two notions by means of examples and argue that, by adopting simple convention...... refinement theory and UML-B state machine refinement influences the style of node refinement. Hence we propose a method with direct proof of state machine refinement avoiding the detour via Event-B that is needed by UML-B....
Matthes, L.; Küfner, S.; Furthmüller, J.; Bechstedt, F.
2016-03-01
Ab initio relativistic band structure calculations are performed for the frequency-dependent spin Hall conductivity of two-dimensional atomically thin crystals and one-dimensional nanoribbons. We study the influence of topology, quantization, and topological edge states. As model systems fully halogenated germanene, GeI, and its zigzag nanoribbons are investigated. GeI represents a topological insulator (TI). For comparison, also the TI germanene and the trivial insulator hydrogenated germanene are studied. For the TIs we demonstrate the quantization of the static spin Hall conductivity. It is hardly influenced by temperature and Fermi level shift. Its frequency dependence is governed by the band-structure details. Topological edge states influence the conductivity mainly for vanishing frequencies.
Davoyan, Arthur
2013-01-01
We study propagation of transverse-magnetic (TM) electromagnetic waves in the bulk and at the surface of magnetized epsilon-near-zero (ENZ) medium in a Voigt configuration. We reveal that in a certain range of material parameters novel regimes of wave propagation emerge: we show that the transparency of the medium can be altered with the magnetization leading either to magnetically induced Hall opacity or Hall transparency of the ENZ. In our theoretical study, we demonstrate that surface waves at the interface between either a transparent or an opaque Hall medium and a homogeneous medium may, under certain conditions, be predominantly one-way. Moreover, we predict that one-way photonic surface states may exist at the interface of an opaque Hall ENZ and a regular metal, giving rise to a possibility for backscattering immune wave propagation and isolation.
Bosonization, coherent states and semiclassical quantum Hall skyrmions.
Dutta, Sreedhar B; Shankar, R
2008-07-09
We bosonize (2+1)-dimensional fermionic theory using coherent states. The gauge-invariant subspace of boson-Chern-Simons Hilbert space is mapped to fermionic Hilbert space. This subspace is then equipped with a coherent state basis. These coherent states are labelled by a dynamic spinor field. The label manifold could be assigned a physical meaning in terms of density and spin density. A path-integral representation of the evolution operator in terms of these physical variables is given. The corresponding classical theory when restricted to LLL is described by spin fluctuations alone and is found to be the NLSM with Hopf term. The formalism developed here is suitable to study quantum Hall skyrmions semiclassically and/or beyond the hydrodynamic limit. The effects of Landau level mixing or the presence of slowly varying external fields can also be easily incorporated.
Gu, Yingfei; Lee, Ching Hua; Wen, Xueda; Cho, Gil Young; Ryu, Shinsei; Qi, Xiao-Liang
2016-09-01
In this paper, we study (2 +1 ) -dimensional quantum anomalous Hall states, i.e., band insulators with quantized Hall conductance, using exact holographic mapping. Exact holographic mapping is an approach to holographic duality which maps the quantum anomalous Hall state to a different state living in (3 +1 ) -dimensional hyperbolic space. By studying topological response properties and the entanglement spectrum, we demonstrate that the holographic dual theory of a quantum anomalous Hall state is a (3 +1 ) -dimensional topological insulator. The dual description enables a characterization of topological properties of a system by the quantum entanglement between degrees of freedom at different length scales.
Fractional quantum Hall states at zero magnetic field.
Neupert, Titus; Santos, Luiz; Chamon, Claudio; Mudry, Christopher
2011-06-10
We present a simple prescription to flatten isolated Bloch bands with a nonzero Chern number. We first show that approximate flattening of bands with a nonzero Chern number is possible by tuning ratios of nearest-neighbor and next-nearest-neighbor hoppings in the Haldane model and, similarly, in the chiral-π-flux square lattice model. Then we show that perfect flattening can be attained with further range hoppings that decrease exponentially with distance. Finally, we add interactions to the model and present exact diagonalization results for a small system at 1/3 filling that support (i) the existence of a spectral gap, (ii) that the ground state is a topological state, and (iii) that the Hall conductance is quantized.
Geometry of quantum Hall states: Gravitational anomaly and transport coefficients
Can, Tankut, E-mail: tcan@scgp.stonybrook.edu [Simons Center for Geometry and Physics, Stony Brook University, Stony Brook, NY 11794 (United States); Laskin, Michael; Wiegmann, Paul B. [Department of Physics, University of Chicago, 929 57th St, Chicago, IL 60637 (United States)
2015-11-15
We show that universal transport coefficients of the fractional quantum Hall effect (FQHE) can be understood as a response to variations of spatial geometry. Some transport properties are essentially governed by the gravitational anomaly. We develop a general method to compute correlation functions of FQH states in a curved space, where local transformation properties of these states are examined through local geometric variations. We introduce the notion of a generating functional and relate it to geometric invariant functionals recently studied in geometry. We develop two complementary methods to study the geometry of the FQHE. One method is based on iterating a Ward identity, while the other is based on a field theoretical formulation of the FQHE through a path integral formalism.
Competing ν = 5/2 fractional quantum Hall states in confined geometry
Fu, Hailong; Wang, Pengjie; Shan, Pujia; Xiong, Lin; Pfeiffer, Loren N.; West, Ken; Kastner, Marc A.; Lin, Xi
2016-11-01
Some theories predict that the filling factor 5/2 fractional quantum Hall state can exhibit non-Abelian statistics, which makes it a candidate for fault-tolerant topological quantum computation. Although the non-Abelian Pfaffian state and its particle-hole conjugate, the anti-Pfaffian state, are the most plausible wave functions for the 5/2 state, there are a number of alternatives with either Abelian or non-Abelian statistics. Recent experiments suggest that the tunneling exponents are more consistent with an Abelian state rather than a non-Abelian state. Here, we present edge-current-tunneling experiments in geometrically confined quantum point contacts, which indicate that Abelian and non-Abelian states compete at filling factor 5/2. Our results are consistent with a transition from an Abelian state to a non-Abelian state in a single quantum point contact when the confinement is tuned. Our observation suggests that there is an intrinsic non-Abelian 5/2 ground state but that the appropriate confinement is necessary to maintain it. This observation is important not only for understanding the physics of the 5/2 state but also for the design of future topological quantum computation devices.
Competing ν = 5/2 fractional quantum Hall states in confined geometry.
Fu, Hailong; Wang, Pengjie; Shan, Pujia; Xiong, Lin; Pfeiffer, Loren N; West, Ken; Kastner, Marc A; Lin, Xi
2016-11-01
Some theories predict that the filling factor 5/2 fractional quantum Hall state can exhibit non-Abelian statistics, which makes it a candidate for fault-tolerant topological quantum computation. Although the non-Abelian Pfaffian state and its particle-hole conjugate, the anti-Pfaffian state, are the most plausible wave functions for the 5/2 state, there are a number of alternatives with either Abelian or non-Abelian statistics. Recent experiments suggest that the tunneling exponents are more consistent with an Abelian state rather than a non-Abelian state. Here, we present edge-current-tunneling experiments in geometrically confined quantum point contacts, which indicate that Abelian and non-Abelian states compete at filling factor 5/2. Our results are consistent with a transition from an Abelian state to a non-Abelian state in a single quantum point contact when the confinement is tuned. Our observation suggests that there is an intrinsic non-Abelian 5/2 ground state but that the appropriate confinement is necessary to maintain it. This observation is important not only for understanding the physics of the 5/2 state but also for the design of future topological quantum computation devices.
Signatures of Majorana zero-modes in nanowires, quantum spin Hall edges, and quantum dots
Mi, Shuo
2015-01-01
This thesis focuses on the investigation of Majorana zero-modes and their quantum transport properties of topological insulators and topological superconductors in several low-dimensional systems, i.e. 1D nanowire system (Chapter 2), 2D quantum spin Hall system (Chapter 3, 4) and 0D quantum dot syst
NONEQUILIBRIUM DISTRIBUTION OF EDGE AND BULK CURRENT IN A QUANTUM HALL CONDUCTOR
VANSON, PC; DEVRIES, FW; KLAPWIJK, TM
1991-01-01
A quantitative model is presented that accounts for the experimental observation that four-terminal resistances of a high-mobility quantum Hall conductor cannot be related directly to a single resistivity tensor. The key ingredient is that the highest (partly occupied) Landau level is completely dec
Absence of edge states in covalently bonded zigzag edges of graphene on Ir(111).
Li, Yan; Subramaniam, Dinesh; Atodiresei, Nicolae; Lazić, Predrag; Caciuc, Vasile; Pauly, Christian; Georgi, Alexander; Busse, Carsten; Liebmann, Marcus; Blügel, Stefan; Pratzer, Marco; Morgenstern, Markus; Mazzarello, Riccardo
2013-04-11
The zigzag edges of graphene on Ir(111) are studied by ab initio simulations and low-temperature scanning tunneling spectroscopy, providing information about their structural, electronic, and magnetic properties. No edge state is found to exist, which is explained in terms of the interplay between a strong geometrical relaxation at the edge and a hybridization of the d orbitals of Ir atoms with the graphene orbitals at the edge.
Flux and Hall states in ABJM with dynamical flavors
Bea, Yago; Lippert, Matthew; Ramallo, Alfonso V; Zoakos, Dimitrios
2014-01-01
We study the physics of probe D6-branes with quantized internal worldvolume flux in the ABJM background with unquenched massless flavors. This flux breaks parity in the (2+1)-dimensional gauge theory and allows quantum Hall states. Parity breaking is also explicitly demonstrated via the helicity dependence of the meson spectrum. We obtain general expressions for the conductivities, both in the gapped Minkowski embeddings and in the compressible black hole ones. These conductivities depend on the flux and contain a contribution from the dynamical flavors which can be regarded as an effect of intrinsic disorder due to quantum fluctuations of the fundamentals. We present an explicit, analytic family of supersymmetric solutions with nonzero charge density, electric, and magnetic fields.
Quantized Thermal Transport in the Fractional Quantum Hall Effect
Kane, C. L.; Fisher, Matthew P. A.
1996-01-01
We analyze thermal transport in the fractional quantum Hall effect (FQHE), employing a Luttinger liquid model of edge states. Impurity mediated inter-channel scattering events are incorporated in a hydrodynamic description of heat and charge transport. The thermal Hall conductance, $K_H$, is shown to provide a new and universal characterization of the FQHE state, and reveals non-trivial information about the edge structure. The Lorenz ratio between thermal and electrical Hall conductances {\\i...
Quantum Hall states stabilized in semi-magnetic bilayers of topological insulators
Yoshimi, R.; Yasuda, K.; Tsukazaki, A.; Takahashi, K. S.; Nagaosa, N.; Kawasaki, M.; Tokura, Y.
2015-01-01
By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality. PMID:26497065
Photonic simulation of topological superconductor edge state and zero-energy mode at a vortex.
Tan, Wei; Chen, Liang; Ji, Xia; Lin, Hai-Qing
2014-01-01
Photonic simulations of quantum Hall edge states and topological insulators have inspired considerable interest in recent years. Interestingly, there are theoretical predictions for another type of topological states in topological superconductors, but debates over their experimental observations still remain. Here we investigate the photonic analogue of the p(x) + ip(y) model of topological superconductor. Two essential characteristics of topological superconductor, particle-hole symmetry and p(x) + ip(y) pairing potentials, are well emulated in photonic systems. Its topological features are presented by chiral edge state and zero-energy mode at a vortex. This work may fertilize the study of photonic topological states, and open up the possibility for emulating wave behaviors in superconductors.
Fibonacci anyons from Abelian bilayer quantum Hall states.
Vaezi, Abolhassan; Barkeshli, Maissam
2014-12-05
The possibility of realizing non-Abelian statistics and utilizing it for topological quantum computation (TQC) has generated widespread interest. However, the non-Abelian statistics that can be realized in most accessible proposals is not powerful enough for universal TQC. In this Letter, we consider a simple bilayer fractional quantum Hall system with the 1/3 Laughlin state in each layer. We show that interlayer tunneling can drive a transition to an exotic non-Abelian state that contains the famous "Fibonacci" anyon, whose non-Abelian statistics is powerful enough for universal TQC. Our analysis rests on startling agreements from a variety of distinct methods, including thin torus limits, effective field theories, and coupled wire constructions. We provide evidence that the transition can be continuous, at which point the charge gap remains open while the neutral gap closes. This raises the question of whether these exotic phases may have already been realized at ν=2/3 in bilayers, as past experiments may not have definitively ruled them out.
Finite size effects on the helical edge states on the Lieb lattice
Rui, Chen; Bin, Zhou
2016-06-01
For a two-dimensional Lieb lattice, that is, a line-centered square lattice, the inclusion of the intrinsic spin-orbit (ISO) coupling opens a topologically nontrivial gap, and gives rise to the quantum spin Hall (QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap. Generally, due to the finite size effect in QSH systems, the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum. In this paper, we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions, i.e., the straight, bearded and asymmetry edges. The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice. For a strip Lieb lattice with two straight edges, the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum. Moreover, it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice, and no gap is opened in the edge band. It is concluded that the finite size effect of QSH states is absent in the case with the straight edges. However, in the other two cases with the bearded and asymmetry edges, the energy gap induced by the finite size effect is still opened with decreasing the width of the strip. It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms. Project supported by the National Natural Science Foundation of China (Grant No. 11274102), the Program for New Century Excellent Talents in University of the Ministry of Education of China (Grant No. NCET-11-0960), and the Specialized Research Fund for the Doctoral Program of the Higher Education of China (Grant No. 20134208110001).
Nonequilibrium transport through a point contact in the nu = 5/2 non-Abelian quantum Hall state.
Feiguin, Adrian; Fendley, Paul; Fisher, Matthew P A; Nayak, Chetan
2008-12-05
We analyze charge-e/4 quasiparticle tunneling between the edges of a point contact in a non-Abelian model of the nu = 5/2 quantum Hall state in the presence of a finite voltage difference using the time-dependent density-matrix renormalization group method. We confirm that, as the voltage decreases, the system is broken into two pieces. In the limits of small and large voltage, we recover the results expected from perturbation theory about the infrared and ultraviolet fixed points. We test our methods by finding the analogous nonequilibrium current through a point contact at nu = 1/3.
Analytical study of surface states caused by the edge decoration
Zhao Yuan-Yuan; Li Wei; Tao Rui-Bao
2012-01-01
Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional (1D) model and zigzag edged graphene (ZEG) are presented by means of transfer matrix method,in the frame of which the conditions for the existence of edge states are determined.For 1D model,the zero-energy surface state occurs regardless of whether the decorations exist or not,while the non-zero-energy surface states can be induced and manipulated through adjusting the edge decoration.On the other hand,the case for the semi-infinite ZEG model with nearestneighbour interaction is discussed in the analogous way.The non-zero-energy surface states can be induced by the edge decoration and moreover,the ratio between the edge hopping and the bulk hopping amplitudes should be within a certain threshold.
Orbital Edge States in a Photonic Honeycomb Lattice
Milićević, M.; Ozawa, T.; Montambaux, G.; Carusotto, I.; Galopin, E.; Lemaître, A.; Le Gratiet, L.; Sagnes, I.; Bloch, J.; Amo, A.
2017-03-01
We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of p -like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states in zigzag and armchair edges. The observations are reproduced by tight-binding and analytical calculations, which we extend to bearded edges. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent two-dimensional materials with orbital bands.
Two-dimensionally confined topological edge states in photonic crystals
Barik, Sabyasachi; Miyake, Hirokazu; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad
2016-11-01
We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
Two-Dimensionally Confined Topological Edge States in Photonic Crystals
Barik, Sabyasachi; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad
2016-01-01
We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
Topological Numbers and Edge State of Hierarchical State in Rapidly Rotating Ultracold Atoms
ZHAO Bo; CHEN Zeng-Bing
2005-01-01
The effective theory for the hierarchical fractional quantum Hall (FQH) effect is proposed. We also derive the topological numbers K matrix and t vector and the general edge excitation from the effective theory. One can find that the two issues in rapidly rotating ultracold atoms are similar to those in electron FQH liquid.
Observation of the Zero Hall Plateau in a Quantum Anomalous Hall Insulator
Feng, Yang; Feng, Xiao; Ou, Yunbo; Wang, Jing; Liu, Chang; Zhang, Liguo; Zhao, Dongyang; Jiang, Gaoyuan; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Yayu
2015-09-16
We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to a quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.
Baidya, Santu; Waghmare, Umesh V.; Paramekanti, Arun; Saha-Dasgupta, Tanusri
2016-10-01
Towards the goal of realizing topological phases in thin films of correlated oxide and heterostructures, we propose here a quantum anomalous Hall insulator (QAHI) in ultrathin films of double perovskites based on mixed 3 d -5 d or 3 d -4 d transition-metal ions, grown along the [111] direction. Considering the specific case of ultrathin Ba2FeReO6 , we present a theoretical analysis of an effective Hamiltonian derived from first principles. We establish that a strong spin-orbit coupling at the Re site, t2 g symmetry of the low-energy d bands, polarity of its [111] orientation of perovskite structure, and mixed 3 d -5 d chemistry results in room temperature magnetism with a robust QAHI state of Chern number C =1 and a large band gap. We uncover and highlight a nonrelativistic orbital Rashba-type effect in addition to the spin-orbit coupling, that governs this QAHI state. With a band gap of ˜100 meV in electronic structure and magnetic transition temperature Tc˜300 K estimated by Monte Carlo simulations, our finding of the QAHI state in ultrathin Ba2FeReO6 is expected to stimulate experimental verification along with possible practical applications of its dissipationless edge currents.
Prediction of a quantum anomalous Hall state in Co-decorated silicene
Kaloni, Thaneshwor P.
2014-01-09
Based on first-principles calculations, we demonstrate that Co-decorated silicene can host a quantum anomalous Hall state. The exchange field induced by the Co atoms combined with the strong spin-orbit coupling of the silicene opens a nontrivial band gap at the K point. As compared to other transition metals, Co-decorated silicene is unique in this respect, since usually hybridization and spin-polarization induced in the silicene suppress a quantum anomalous Hall state.
Edge states and phase diagram for graphene under polarized light
Wang, Yi-Xiang, E-mail: wangyixiang@jiangnan.edu.cn [School of Science, Jiangnan University, Wuxi 214122 (China); Li, Fuxiang [Center for Nonlinear Studies and Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2016-07-01
In this work, we investigate the topological phase transitions in graphene under the modulation of circularly polarized light, by analyzing the changes of edge states and its topological structures. A full phase diagram, with several different topological phases, is presented in the parameter space spanned by the driving frequency and light strength. We find that the high-Chern number behavior is very common in the driven system. While the one-photon resonance can create the chiral edge states in the π-gap, the two-photon resonance will induce the counter-propagating edge modes in the zero-energy gap. When the driving light strength is strong, the number and even the chirality of the edge states may change in the π-gap. The robustness of the edge states to disorder potential is also examined. We close by discussing the feasibility of experimental proposals.
Orbital edge states in a photonic honeycomb lattice
Milićević, Marijana; Montambaux, Gilles; Carusotto, Iacopo; Galopin, Elisabeth; Lemaître, Aristide; Gratiet, Luc Le; Sagnes, Isabelle; Bloch, Jacqueline; Amo, Alberto
2016-01-01
We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of $p$-like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states that emerge not only in zigzag and bearded terminations, but also in armchair edges. The observations are reproduced by tight-binding and analytical calculations. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent 2D materials with orbital bands.
One-dimensional topological edge states of bismuth bilayers
Drozdov, Ilya K.; Alexandradinata, A.; Jeon, Sangjun; Nadj-Perge, Stevan; Ji, Huiwen; Cava, R. J.; Andrei Bernevig, B.; Yazdani, Ali
2014-09-01
The hallmark of a topologically insulating state of matter in two dimensions protected by time-reversal symmetry is the existence of chiral edge modes propagating along the perimeter of the sample. Among the first systems predicted to be a two-dimensional topological insulator are bilayers of bismuth. Here we report scanning tunnelling microscopy experiments on bulk Bi crystals that show that a subset of the predicted Bi-bilayers' edge states are decoupled from the states of the substrate and provide direct spectroscopic evidence of their one-dimensional nature. Moreover, by visualizing the quantum interference of edge-mode quasi-particles in confined geometries, we demonstrate their remarkable coherent propagation along the edge with scattering properties consistent with strong suppression of backscattering as predicted for the propagating topological edge states.
Edge states and skyrmion dynamics in nanostripes of frustrated magnets
Leonov, A. O.; Mostovoy, M.
2017-01-01
Magnetic skyrmions are particle-like topological excitations recently discovered in chiral magnets. Their small size, topological protection and the ease with which they can be manipulated by electric currents generated much interest in using skyrmions for information storage and processing. Recently, it was suggested that skyrmions with additional degrees of freedom can exist in magnetically frustrated materials. Here, we show that dynamics of skyrmions and antiskyrmions in nanostripes of frustrated magnets is strongly affected by complex spin states formed at the stripe edges. These states create multiple edge channels which guide the skyrmion motion. Non-trivial topology of edge states gives rise to complex current-induced dynamics, such as emission of skyrmion–antiskyrmion pairs. The edge-state topology can be controlled with an electric current through the exchange of skyrmions and antiskyrmions between the edges of a magnetic nanostructure. PMID:28240226
Hall resistivity in the heavy Fermion normal state of ? up to 26 T
Kambe, S.; Huxley, A.; Flouquet, J.; Jansen, A. G. M.; Wyder, P.
1999-01-01
The Hall resistivity 0953-8984/11/1/018/img10 has been measured in single crystal 0953-8984/11/1/018/img11 at low temperatures (0.1-4.2 K) for magnetic field 0953-8984/11/1/018/img12-axis up to 26 T. For temperatures 0953-8984/11/1/018/img13, the Hall coefficient goes asymptotically to zero, indicating a compensated-metal ground state. Since the Hall resistivity does not show an anomaly at the metamagnetic crossover of 20 T in the Fermi-liquid state below 0.8 K, a drastic change of the Fermi surface is unlikely at the crossover. A change of the skew scattering contribution to the Hall effect has been observed around 6 and 2 K, i.e. near respectively the magnetic ordering temperature and the temperature below which the Fermi-liquid state appears.
Noiseless manipulation of helical edge state transport by a quantum magnet
Silvestrov, P. G.; Recher, P.; Brouwer, P. W.
2016-05-01
The current through a helical edge state of a quantum spin Hall insulator may be fully transmitted through a magnetically gapped region due to a combination of spin-transfer torque and spin pumping [Meng et al., Phys. Rev. B 90, 205403 (2014), 10.1103/PhysRevB.90.205403]. Using a scattering approach, we here argue that in such a system the current is effectively carried by electrons with energies below the magnet-induced gap and well below the Fermi energy. This has striking consequences, such as the absence of shot noise, an exponential suppression of thermal noise, and an obstruction of thermal transport. For two helical edges covered by the same quantum magnet, the device can act as a robust noiseless current splitter.
Edge states protected by chiral symmetry in disordered photonic graphene
Zeuner, Julia M; Nolte, Stefan; Szameit, Alexander
2013-01-01
We experimentally investigate the impact of uncorrelated composite and structural disorder in photonic graphene. We find that in case of structural disorder not only chiral symmetry, but also the vanishing of the density of states at zero energy is preserved. This is in contrast to composite disorder, where chiral symmetry as well as the vanishing of the density of states are destroyed. Our observations are experimentally proven by exciting edge states at the bearded edge in disordered photonic graphene.
Green's function approach to edge states in transition metal dichalcogenides
Farmanbar Gelepordsari, M.; Amlaki, T.; Brocks, G.
2016-01-01
The semiconducting two-dimensional transition metal dichalcogenides MX 2 show an abundance of one-dimensional metallic edges and grain boundaries. Standard techniques for calculating edge states typically model nanoribbons, and require the use of supercells. In this paper, we formulate a Green's fun
Tunneling into and between helical edge states: Fermionic approach
Aristov, D. N.; Niyazov, R. A.
2016-07-01
We study the four-terminal junction of spinless Luttinger liquid wires, which describes either a corner junction of two helical edge states of topological insulators or the tunneling from the spinful wire into the helical edge state. We use the fermionic representation and the scattering state formalism, in order to compute the renormalization group (RG) equations for the linear response conductances. We establish our approach by considering a junction between two possibly nonequivalent helical edge states and find an agreement with the earlier analysis of this situation. Tunneling from the tip of the spinful wire to the edge state is further analyzed which requires some modification of our formalism. In the latter case we demonstrate (i) the existence of both fixed lines and conventional fixed points of RG equations, and (ii) certain proportionality relations holding for conductances during renormalization. The scaling exponents and phase portraits are obtained in all cases.
Atomic level spatial variations of energy states along graphene edges.
Warner, Jamie H; Lin, Yung-Chang; He, Kuang; Koshino, Masanori; Suenaga, Kazu
2014-11-12
The local atomic bonding of carbon atoms around the edge of graphene is examined by aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). High-resolution 2D maps of the EELS combined with atomic resolution annular dark field STEM images enables correlations between the carbon K-edge EELS and the atomic structure. We show that energy states of graphene edges vary across individual atoms along the edge according to their specific C-C bonding, as well as perpendicular to the edge. Unique spectroscopic peaks from the EELS are assigned to specific C atoms, which enables unambiguous spectroscopic fingerprint identification for the atomic structure of graphene edges with unprecedented detail.
Zhu, W.; Gong, S. S.; Sheng, D. N.
2016-07-01
There has been a growing interest in realizing topologically nontrivial states of matter in band insulators, where a quantum Hall effect can appear as an intrinsic property of the band structure. While ongoing progress is under way with a number of directions, the possibility of realizing novel interaction-generated topological phases, without the requirement of a nontrivial invariant encoded in single-particle wave function or band structure, can significantly extend the class of topological materials and is thus of great importance. Here, we show an interaction-driven topological phase emerging in an extended Bose-Hubbard model on a kagome lattice, where the noninteracting band structure is topological trivial with zero Berry curvature in the Brillouin zone. By means of an unbiased state-of-the-art density-matrix renormalization group technique, we identify that the ground state in a broad parameter region is equivalent to a bosonic fractional quantum Hall Laughlin state, based on the characterization of universal properties including ground-state degeneracy, edge excitations, and anyonic quasiparticle statistics. Our work paves a way to finding an interaction-induced topological phase at the phase boundary of conventionally ordered solid phases.
Lectures on the Quantum Hall Effect
Tong, David
2016-01-01
The purpose of these lectures is to describe the basic theoretical structures underlying the rich and beautiful physics of the quantum Hall effect. The focus is on the interplay between microscopic wavefunctions, long-distance effective Chern-Simons theories, and the modes which live on the boundary. The notes are aimed at graduate students in any discipline where $\\hbar=1$. A working knowledge of quantum field theory is assumed. Contents: 1. The Basics (Landau levels and Berry phase). 2. The Integer Quantum Hall Effect. 3. The Fractional Quantum Hall Effect. 4. Non-Abelian Quantum Hall States. 5. Chern-Simons Theories. 6. Edge Modes.
Decomposition of fractional quantum Hall model states: product rule symmetries and approximations
Thomale, R.; Estienne, B.; Regnault, N.; Bernevig, B.A.
2011-01-01
We provide a detailed description of a product rule structure of the monomial (Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall (FQH) states derived recently, which we now extend to spin-singlet states. We show that the Haldane-Rezayi spin-singlet state can be obtained
Prospects of steady state magnetic diagnostic of fusion reactors based on metallic Hall sensors
Ďuran, I.; Sentkerestiová, J.; Kovařík, K.; Viererbl, L.
2012-06-01
Employment of sensors based on Hall effect (Hall sensors) is one of the candidate approaches to detection of almost steady state magnetic fields in future fusion reactors based on magnetic confinement (tokamaks, stellarators etc.), and also in possible fusion-fission hybrid systems having these fusion reactors as a neutron source and driver. This contribution reviews the initial considerations concerning application of metallic Hall sensors in fusion reactor harsh environment that include high neutron loads (>1018 cm-2) and elevated temperatures (>200°C). In particular, the candidate sensing materials, candidate technologies for sensors production, initial analysis of activation and transmutation of sensors under reactor relevant neutron loads and the tests of the the first samples of copper Hall sensors are presented.
Tunable band topology reflected by fractional quantum Hall States in two-dimensional lattices.
Wang, Dong; Liu, Zhao; Cao, Junpeng; Fan, Heng
2013-11-01
Two-dimensional lattice models subjected to an external effective magnetic field can form nontrivial band topologies characterized by nonzero integer band Chern numbers. In this Letter, we investigate such a lattice model originating from the Hofstadter model and demonstrate that the band topology transitions can be realized by simply introducing tunable longer-range hopping. The rich phase diagram of band Chern numbers is obtained for the simple rational flux density and a classification of phases is presented. In the presence of interactions, the existence of fractional quantum Hall states in both |C| = 1 and |C| > 1 bands is confirmed, which can reflect the band topologies in different phases. In contrast, when our model reduces to a one-dimensional lattice, the ground states are crucially different from fractional quantum Hall states. Our results may provide insights into the study of new fractional quantum Hall states and experimental realizations of various topological phases in optical lattices.
Gu, Yingfei; Wen, Xueda; Cho, Gil Young; Ryu, Shinsei; Qi, Xiao-Liang
2016-01-01
In this paper, we study $(2+1)$-dimensional quantum anomalous Hall states, i.e. band insulators with quantized Hall conductance, using the exact holographic mapping. The exact holographic mapping is an approach to holographic duality which maps the quantum anomalous Hall state to a different state living in $(3+1)$-dimensional hyperbolic space. By studying topological response properties and the entanglement spectrum, we demonstrate that the holographic dual theory of a quantum anomalous Hall state is a $(3+1)$-dimensional topological insulator. The dual description enables a new characterization of topological properties of a system by the quantum entanglement between degrees of freedom at different length scales.
Edge states and quantum phase transition in graphene under in-plane effective exchange fields
Liu, Zheng-Fang; Wu, Qing-Ping; Chen, Ai-Xi; Xiao, Xian-Bo; Liu, Nian-Hua; Miao, Guo-Xing
2017-02-01
We investigated the edge states and quantum phase transition in graphene under an in-plane effective exchange field. The result shows that the combined effects of the in-plane effective exchange field and a staggered sublattice potential can induce zero-energy flat bands of edge states. Such flat-band edge states can evolve into helical-like ones in the presence of intrinsic spin-orbit coupling, with a unique spin texture. We also find that the bulk energy gap induced by the spin-orbit coupling and staggered sublattice potential can be closed and reopened with the in-plane effective exchange field, and the reopened bulk gap can be even larger than that induced by only the spin-orbit coupling and staggered sublattice potential, which is different from the case of an out-of-plane effective exchange field. The calculated spin-dependent Chern numbers suggest that the bulk gap closing and reopening is accompanied by a quantum phase transition from a trivial insulator phase across a metal phase into a spin-dependent quantum Hall phase.
Coupling and manipulation of edge states in multilayer phosphorene nanoribbons
Lv, Z. T.; Gao, J. H.; Zhang, X. D.; Jiang, Z. T.
2017-10-01
We investigate the couplings among the edge states of the normal zigzag and skewed armchair multilayer phosphorene nanoribbons, as well as the effect of the electric field on the corresponding energy levels, by using the tight-binding Hamiltonian approach. It is found that there appear different transitions from the coupled to uncoupled edge states in the normal zigzag and skewed armchair nanoribbons with the increasing of the nanoribbon width, which is fundamentally attributed to the edge asymmetry of the multilayer phosphorene nanoribbons. Moreover, the energy bands of the multilayer phosphorene nanoribbons can be effectively adjusted by applying the perpendicular electric field. Therefore, this research should be thought of as a useful reference for determining the width, the edge types, and the layer numbers of the nanoribbons in manipulating the properties of the multilayer phosphorene nanoribbons.
Magnetic edge states and magnetotransport in graphene antidot barriers
Thomsen, M. R.; Power, S. R.; Jauho, A.-P.; Pedersen, T. G.
2016-07-01
Magnetic fields are often used for characterizing transport in nanoscale materials. Recent magnetotransport experiments have demonstrated that ballistic transport is possible in graphene antidot lattices (GALs). These experiments have inspired the present theoretical study of GALs in a perpendicular magnetic field. We calculate magnetotransport through graphene antidot barriers (GABs), which are finite rows of antidots arranged periodically in a pristine graphene sheet, using a tight-binding model and the Landauer-Büttiker formula. We show that GABs behave as ideal Dirac mass barriers for antidots smaller than the magnetic length and demonstrate the presence of magnetic edge states, which are localized states on the periphery of the antidots due to successive reflections on the antidot edge in the presence of a magnetic field. We show that these states are robust against variations in lattice configuration and antidot edge chirality. Moreover, we calculate the transmittance of disordered GABs and find that magnetic edge states survive a moderate degree of disorder. Due to the long phase-coherence length in graphene and the robustness of these states, we expect magnetic edge states to be observable in experiments as well.
Non-Hermitian approach of edge states and quantum transport in a magnetic field
Ostahie, B.; NiÅ£a, M.; Aldea, A.
2016-11-01
We develop a manifest non-Hermitian approach of spectral and transport properties of two-dimensional mesoscopic systems in a strong magnetic field. The finite system to which several terminals are attached constitutes an open system that can be described by an effective Hamiltonian. The lifetime of the quantum states expressed by the energy imaginary part depends specifically on the lead-system coupling and makes the difference among three regimes: resonant, integer quantum Hall effect, and superradiant. The discussion is carried on in terms of edge state lifetime in different gaps, channel formation, role of hybridization, and transmission coefficients quantization. A toy model helps in understanding non-Hermitian aspects in open systems.
Matthias, Ruth
This program was devised in an attempt to train more effective resident advisors for the 1972-73 school year at a dormitory at California State University. The special characteristics of the dormitory--racially mixed and discordant--seemed to indicate a need for a special kind of resident advisor training program, one that attempted to better…
Toru Tomimatsu
2015-08-01
Full Text Available Electric-field-induced nuclear resonance (NER: nuclear electric resonance involving quantum Hall states (QHSs was studied at various filling factors by exploiting changes in nuclear spins polarized at quantum Hall breakdown. Distinct from the magnetic dipole interaction in nuclear magnetic resonance, the interaction of the electric-field gradient with the electric quadrupole moment plays the dominant role in the NER mechanism. The magnitude of the NER signal strongly depends on whether electronic states are localized or extended. This indicates that NER is sensitive to the screening capability of the electric field associated with QHSs.
Dirac and Majorana edge states in graphene and topological superconductors
Akhmerov, Anton Roustiamovich
2011-01-01
This dissertation is about transport and electronic properties of two types of electronic states occuring at the edges, which are protected by symmetry between positive and negative energies. One type of these states is shown to occur universally in graphene. It is also described how another type of
Rudner, Mark Spencer; Lindner, Netanel; Berg, Erez;
2013-01-01
the crucial distinctions between static and driven 2D systems, and construct a new topological invariant that yields the correct edge-state structure in the driven case. We provide formulations in both the time and frequency domains, which afford additional insight into the origins of the “anomalous” spectra...... that arise in driven systems. Possibilities for realizing these phenomena in solid-state and cold-atomic systems are discussed....
Quantum anomalous Hall effect and tunable topological states in 3d transition metals doped silicene.
Zhang, Xiao-Long; Liu, Lan-Feng; Liu, Wu-Ming
2013-10-09
Silicene is an intriguing 2D topological material which is closely analogous to graphene but with stronger spin orbit coupling effect and natural compatibility with current silicon-based electronics industry. Here we demonstrate that silicene decorated with certain 3d transition metals (Vanadium) can sustain a stable quantum anomalous Hall effect using both analytical model and first-principles Wannier interpolation. We also predict the quantum valley Hall effect and electrically tunable topological states could be realized in certain transition metal doped silicene where the energy band inversion occurs. Our findings provide new scheme for the realization of quantum anomalous Hall effect and platform for electrically controllable topological states which are highly desirable for future nanoelectronics and spintronics application.
The Existence of Topological Edge States in Honeycomb Plasmonic Lattices
Wang, Li; Xiao, Meng; Han, Dezhuan; Chan, C T; Wen, Weijia
2016-01-01
In this paper, we investigate the band properties of 2D honeycomb plasmonic lattices consisting of metallic nanoparticles. By means of the coupled dipole method and quasi-static approximation, we theoretically analyze the band structures stemming from near-field interaction of localized surface plasmon polaritons for both the infinite lattice and ribbons. Naturally, the interaction of point dipoles decouples into independent out-of-plane and in-plane polarizations. For the out-of-plane modes, both the bulk spectrum and the range of the momentum $k_{\\parallel}$ where edge states exist in ribbons are similar to the electronic bands in graphene. Nevertheless, the in-plane polarized modes show significant differences, which do not only possess additional non-flat edge states in ribbons, but also have different distributions of the flat edge states in reciprocal space. For in-plane polarized modes, we derived the bulk-edge correspondence, namely, the relation between the number of flat edge states at a fixed $k_\\p...
Zhang, Junyi; Beugnon, Jérôme; Nascimbene, Sylvain
2016-10-01
We describe a protocol to prepare clusters of ultracold bosonic atoms in strongly interacting states reminiscent of fractional quantum Hall states. Our scheme consists in injecting a controlled amount of angular momentum to an atomic gas using Raman transitions carrying orbital angular momentum. By injecting one unit of angular momentum per atom, one realizes a single-vortex state, which is well described by mean-field theory for large enough particle numbers. We also present schemes to realize fractional quantum Hall states, namely, the bosonic Laughlin and Moore-Read states. We investigate the requirements for adiabatic nucleation of such topological states, in particular comparing linear Landau-Zener ramps and arbitrary ramps obtained from optimized control methods. We also show that this protocol requires excellent control over the isotropic character of the trapping potential.
High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic
Duran, I.; Entler, S.; Kohout, M.; Kočan, M.; Vayakis, G.
2016-11-01
Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."
THE SIGN REVERSAL AND SCALING RELATIONS OF HALL ANOMALY IN THE MIXED STATE TYPE-II SUPERCONDUCTORS
WEI YEU CHEN; MING JU CHOU; HUANG ZHONG BING
2000-01-01
We present a new model for the anomalous Hall effect in the mixed state of type-II superconductors. In this model we consider the thermally activated motion of the many body correlating vortex lattice system. The sign change of the Hall resistivity is the result of the competition between the motion of effective antivortices and the motion of the pinned vortex lattice together with the interstitial vortices. Within this model many essential experimental results for the complicated Hall effect can be explained.
Scattering-Free Optical Edge States between Heterogeneous Photonic Topological Insulators
Ma, Tzuhsuan
2015-01-01
We propose a set of three simple photonic platforms capable of emulating quantum topologically insulating phases corresponding to Hall, spin-Hall, and valley-Hall effects. It is shown that an interface between any two of these heterogeneous photonic topological insulators supports scattering-free surface states. Spin and valley degrees of freedom characterizing such topologically protected surface waves determine their unique pathways through complex photonic circuits comprised of multiple heterogeneous interfaces.
Bosonic analogs of the fractional quantum Hall state in the vicinity of Mott states
Kuno, Yoshihito; Shimizu, Keita; Ichinose, Ikuo
2017-01-01
In this paper, the Bose-Hubbard model (BHM) with the nearest-neighbor (NN) repulsions is studied from the viewpoint of possible bosonic analogs of the fractional quantum Hall (FQH) state in the vicinity of the Mott insulator (MI). First, by means of the Gutzwiller approximation, we obtain the phase diagram of the BHM in a magnetic field. Then, we introduce an effective Hamiltonian describing excess particles on a MI and calculate the vortex density, momentum distribution, and the energy gap. These calculations indicate that the vortex solid forms for small NN repulsions, but a homogeneous featureless "Bose metal" takes the place of it as the NN repulsion increases. We consider particular filling factors at which the bosonic FQH state is expected to form. Chern-Simons (CS) gauge theory to the excess particle is introduced, and a modified Gutzwiller wave function, which describes bosons with attached flux quanta, is introduced. The energy of the excess particles in the bosonic FQH state is calculated using that wave function, and it is compared with the energy of the vortex solid and Bose metal. We found that the energy of the bosonic FQH state is lower than that of the Bose metal and comparable with the vortex solid. Finally, we clarify the condition that the composite fermion appears by using CS theory on the lattice that we previously proposed for studying the electron FQH effect.
Realizing Tao-Thouless-like state in fractional quantum spin Hall effect
Liu, Chen-Rong; Guo, Yao-Wu; Li, Zhuo-Jun; Li, Wei; Chen, Yan
2016-09-01
The quest for exotic quantum states of matter has become one of the most challenging tasks in modern condensed matter communications. Interplay between topology and strong electron-electron interactions leads to lots of fascinating effects since the discovery of the fractional quantum Hall effect. Here, we theoretically study the Rashba-type spin-orbit coupling effect on a fractional quantum spin Hall system by means of finite size exact diagonalization. Numerical evidences from the ground degeneracies, states evolutions, entanglement spectra, and static structure factor calculations demonstrate that non-trivial fractional topological Tao-Thouless-like quantum state can be realized in the fractional quantum spin Hall effect in a thin torus geometric structure by tuning the strength of spin-orbit coupling. Furthermore, the experimental realization of the Tao-Thouless-like state as well as its evolution in optical lattices are also proposed. The importance of this prediction provides significant insight into the realization of exotic topological quantum states in optical lattice, and also opens a route for exploring the exotic quantum states in condensed matters in future.
Realizing Tao-Thouless-like state in fractional quantum spin Hall effect.
Liu, Chen-Rong; Guo, Yao-Wu; Li, Zhuo-Jun; Li, Wei; Chen, Yan
2016-09-21
The quest for exotic quantum states of matter has become one of the most challenging tasks in modern condensed matter communications. Interplay between topology and strong electron-electron interactions leads to lots of fascinating effects since the discovery of the fractional quantum Hall effect. Here, we theoretically study the Rashba-type spin-orbit coupling effect on a fractional quantum spin Hall system by means of finite size exact diagonalization. Numerical evidences from the ground degeneracies, states evolutions, entanglement spectra, and static structure factor calculations demonstrate that non-trivial fractional topological Tao-Thouless-like quantum state can be realized in the fractional quantum spin Hall effect in a thin torus geometric structure by tuning the strength of spin-orbit coupling. Furthermore, the experimental realization of the Tao-Thouless-like state as well as its evolution in optical lattices are also proposed. The importance of this prediction provides significant insight into the realization of exotic topological quantum states in optical lattice, and also opens a route for exploring the exotic quantum states in condensed matters in future.
Periodically bursting edge states in plane Poiseuille flow
Zammert, Stefan
2013-01-01
We investigate the laminar-turbulent boundary in plane Poiseuille flow by the method of edge tracking. In short and narrow computational domains we find for a wide range in Reynolds number that all states in the boundary converge to a period orbit with a period of the order of $10^{3}$ time units. The attracting states in these small domains are periodically extended in the spanwise and streamwise direction, but always localized to one side of the channel in the normal direction. In short and wide domains the edge states are localized in the spanwise direction. The periodic motion found in the small domains then induces a large variety of dynamical activity. The findings are very similar to the ones in the asymptotic suction boundary layer.
Gilgour, Joseph G.
2012-01-01
Community colleges in the United States have long been known as institutions of equal opportunity and affordable education. One facet of student life appearing at more and more community colleges is the addition of residence halls. Still, the number of community colleges with on-campus living is relatively small, and for the campuses with…
Linear scaling calculation of band edge states and doped semiconductors.
Xiang, H J; Yang, Jinlong; Hou, J G; Zhu, Qingshi
2007-06-28
Linear scaling methods provide total energy, but no energy levels and canonical wave functions. From the density matrix computed through the density matrix purification methods, we propose an order-N [O(N)] method for calculating both the energies and wave functions of band edge states, which are important for optical properties and chemical reactions. In addition, we also develop an O(N) algorithm to deal with doped semiconductors based on the O(N) method for band edge states calculation. We illustrate the O(N) behavior of the new method by applying it to boron nitride (BN) nanotubes and BN nanotubes with an adsorbed hydrogen atom. The band gap of various BN nanotubes are investigated systematically and the acceptor levels of BN nanotubes with an isolated adsorbed H atom are computed. Our methods are simple, robust, and especially suited for the application in self-consistent field electronic structure theory.
Edge-state blockade of transport in quantum dot arrays
Benito, Mónica; Niklas, Michael; Platero, Gloria; Kohler, Sigmund
2016-03-01
We propose a transport blockade mechanism in quantum dot arrays and conducting molecules based on an interplay of Coulomb repulsion and the formation of edge states. As a model we employ a dimer chain that exhibits a topological phase transition. The connection to a strongly biased electron source and drain enables transport. We show that the related emergence of edge states is manifest in the shot noise properties as it is accompanied by a crossover from bunched electron transport to a Poissonian process. For both regions we develop a scenario that can be captured by a rate equation. The resulting analytical expressions for the Fano factor agree well with the numerical solution of a full quantum master equation.
Anomalous edge state in a non-Hermitian lattice
Lee, Tony E
2016-01-01
We show that the bulk-boundary correspondence for topological insulators can be modified in the presence of non-Hermiticity. We consider a one-dimensional tight-binding model with gain and loss as well as long-range hopping. The system is described by a non-Hermitian Hamiltonian that encircles an exceptional point in momentum space. The winding number has a fractional value of 1/2. There is only one dynamically stable zero-energy edge state due to the defectiveness of the Hamiltonian. This edge state is robust to disorder due to protection by a chiral symmetry. We also discuss experimental realization with arrays of coupled resonator optical waveguides.
Fate of extended states and origin of localized states in quantum Hall regime
Ana Luiza Cardoso Pereira
2005-01-01
Resumo: Esse trabalho é dedicado ao estudo de dois problemas de interesse atual em sistemas quânticos de baixa dimensionalidade. Ambos são relacionados ao processo de localização eletrônica no regime Hall quântico. O primeiro problema diz respeito ao destino dos estados estendidos no limite de baixos campos magnéticos ou forte desordem, onde ocorre a transição de líquido de Hall para o isolante de Hall. O problema é abordado através de simulações numéricas, com um modelo de rede bidimensional...
Parameswaran, S A; Kivelson, S A; Shankar, R; Sondhi, S L; Spivak, B Z
2012-12-07
We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.
Sixteen-state magnetic memory based on the extraordinary Hall effect
Segal, A.; Karpovski, M. [Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Tel Aviv (Israel); Gerber, A., E-mail: gerber@post.tau.ac.il [Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Tel Aviv (Israel)
2012-04-15
We report on a proof-of-concept study of split-cell magnetic storage in which multi-bit magnetic memory cells are composed of several multilevel ferromagnetic dots with perpendicular magnetic anisotropy. Extraordinary Hall effect is used for reading the data. Feasibility of the approach is supported by realization of four-, eight- and sixteen- state cells. - Highlights: Black-Right-Pointing-Pointer We propose a novel structure of multi-bit magnetic random access memory. Black-Right-Pointing-Pointer Each cell contains several interconnected storage dots. Black-Right-Pointing-Pointer Extraordinary Hall effect is used for reading the data. Black-Right-Pointing-Pointer Four-, eight- and sixteen-state cells have been realized.
Can, T.; Chiu, Y. H.; Laskin, M.; Wiegmann, P.
2016-12-01
We study quantum Hall states on surfaces with conical singularities. We show that the electronic fluid at the cone tip possesses an intrinsic angular momentum, which is due solely to the gravitational anomaly. We also show that quantum Hall states behave as conformal primaries near singular points, with a conformal dimension equal to the angular momentum. Finally, we argue that the gravitational anomaly and conformal dimension determine the fine structure of the electronic density at the conical point. The singularities emerge as quasiparticles with spin and exchange statistics arising from adiabatically braiding conical singularities. Thus, the gravitational anomaly, which appears as a finite size correction on smooth surfaces, dominates geometric transport on singular surfaces.
Jain states in a matrix theory of the quantum Hall effect
Cappelli, Andrea [I.N.F.N. and Dipartimento di Fisica, Via G. Sansone 1, 50019 Sesto Fiorentino, Florence (Italy); Rodriguez, Ivan D. [I.N.F.N. and Dipartimento di Fisica, Via G. Sansone 1, 50019 Sesto Fiorentino, Florence (Italy)
2006-12-15
The U(N) Maxwell-Chern-Simons matrix gauge theory is proposed as an extension of Susskind's noncommutative approach. The theory describes D0-branes, nonrelativistic particles with matrix coordinates and gauge symmetry, that realize a matrix generalization of the quantum Hall effect. Matrix ground states obtained by suitable projections of higher Landau levels are found to be in one-to-one correspondence with the expected Laughlin and Jain hierarchical states. The Jain composite-fermion construction follows by gauge invariance via the Gauss law constraint. In the limit of commuting, 'normal' matrices the theory reduces to eigenvalue coordinates that describe realistic electrons with Calogero interaction. The Maxwell-Chern-Simons matrix theory improves earlier noncommutative approaches and could provide another effective theory of the fractional Hall effect.
Majorana edge states in superconductor-noncollinear magnet interfaces
Chen, Wei; Schnyder, Andreas P.
2015-12-01
Through s -d coupling, a superconducting thin film interfaced to a noncollinear magnetic insulator inherits its magnetic order, which may induce unconventional superconductivity that hosts Majorana edge states. We present a unified formalism that covers the cycloidal, helical, and tilted conical order discovered in multiferroics, as well as Bloch and Neel domain walls of ferromagnetic insulators, and show that they induce (px+py )-wave pairing that supports Majorana edge modes. The advantages over one-dimensional proposals are that the Majorana states can exist without fine tuning of the chemical potential, can be stabilized in a much larger parameter space, and can be separated over the distance of long-range noncollinear order that is known to reach a macroscopic scale. A skyrmion spin texture, on the other hand, induces a nonuniform (pr+i pφ )-wave-like pairing under the influence of an emergent electromagnetic field, yielding a vortex state that displays both a bulk persistent current and a topological edge current.
Quantum spin Hall states in graphene interacting with WS2 or WSe2
Kaloni, T. P.
2014-12-08
In the framework of first-principles calculations, we investigate the structural and electronic properties of graphene in contact with as well as sandwiched between WS2 and WSe2 monolayers. We report the modification of the band characteristics due to the interaction at the interface and demonstrate that the presence of the dichalcogenide results in quantum spin Hall states in the absence of a magnetic field.
Helical bound states in the continuum of the edge states in two dimensional topological insulators
Sablikov, Vladimir A., E-mail: sablikov@gmail.com; Sukhanov, Aleksei A.
2015-09-04
We study bound states embedded into the continuum of edge states in two-dimensional topological insulators. These states emerge in the presence of a short-range potential of a structural defect coupled to the boundary. In this case the edge states flow around the defect and have two resonances in the local density of states. The bound state in continuum (BIC) arises due to an interference of the resonances when they are close to the degeneracy. We find the condition under which the BIC appears, study the spacial distribution of the electron density, and show that the BIC has a helical structure with an electron current circulating around the defect. - Highlights: • We find bound states in the continuum of edge states in 2D topological insulators. • The bound states are induced by an impurity potential and topological order. • The bound state in the continuum has a helical structure of spin and current density.
AHMED, Maher
2011-01-01
In this work, the tridiagonal method is used to distinguish between edges modes and area modes to study the edge sites properties effect on edge localized states of semi-infinite zigzag 2D honeycomb graphene sheet. The results show a realistic behavior for the dependance of edge localized states of zigzag graphene on the edge sites properties which explaining the experimental results of measured local density of states at the edge of graphene, while at the same time removing the inconsistence...
Łepkowski, S P; Bardyszewski, W
2017-02-08
Combining the k · p method with the third-order elasticity theory, we perform a theoretical study of the pressure-induced topological phase transition and the pressure evolution of topologically protected edge states in InN/GaN and In-rich InGaN/GaN quantum wells. We show that for a certain range of the quantum well parameters, thanks to a negative band gap pressure coefficient, it is possible to continuously drive the system from the normal insulator state through the topological insulator into the semimetal phase. The critical pressure for the topological phase transition depends not only on the quantum well thickness but also on the width of the Hall bar, which determines the coupling between the edge states localized at the opposite edges. We also find that in narrow Hall bar structures, near the topological phase transition, a significant Rashba-type spin splitting of the lower and upper branches of the edge state dispersion curve appears. This effect originates from the lack of the mirror symmetry of the quantum well potential caused by the built-in electric field, and can be suppressed by increasing the Hall bar width. When the pressure increases, the energy dispersion of the edge states becomes more parabolic-like and the spin splitting decreases. A further increase of pressure leads to the transition to a semimetal phase, which occurs due to the closure of the indirect 2D bulk band gap. The difference between the critical pressure at which the system becomes semimetallic, and the pressure for the topological phase transition, correlates with the variation of the pressure coefficient of the band gap in the normal insulator state.
Łepkowski, S. P.; Bardyszewski, W.
2017-02-01
Combining the k · p method with the third-order elasticity theory, we perform a theoretical study of the pressure-induced topological phase transition and the pressure evolution of topologically protected edge states in InN/GaN and In-rich InGaN/GaN quantum wells. We show that for a certain range of the quantum well parameters, thanks to a negative band gap pressure coefficient, it is possible to continuously drive the system from the normal insulator state through the topological insulator into the semimetal phase. The critical pressure for the topological phase transition depends not only on the quantum well thickness but also on the width of the Hall bar, which determines the coupling between the edge states localized at the opposite edges. We also find that in narrow Hall bar structures, near the topological phase transition, a significant Rashba-type spin splitting of the lower and upper branches of the edge state dispersion curve appears. This effect originates from the lack of the mirror symmetry of the quantum well potential caused by the built-in electric field, and can be suppressed by increasing the Hall bar width. When the pressure increases, the energy dispersion of the edge states becomes more parabolic-like and the spin splitting decreases. A further increase of pressure leads to the transition to a semimetal phase, which occurs due to the closure of the indirect 2D bulk band gap. The difference between the critical pressure at which the system becomes semimetallic, and the pressure for the topological phase transition, correlates with the variation of the pressure coefficient of the band gap in the normal insulator state.
Direct imaging of topological edge states in cold-atom systems.
Goldman, Nathan; Dalibard, Jean; Dauphin, Alexandre; Gerbier, Fabrice; Lewenstein, Maciej; Zoller, Peter; Spielman, Ian B
2013-04-23
Detecting topological order in cold-atom experiments is an ongoing challenge, the resolution of which offers novel perspectives on topological matter. In material systems, unambiguous signatures of topological order exist for topological insulators and quantum Hall devices. In quantum Hall systems, the quantized conductivity and the associated robust propagating edge modes--guaranteed by the existence of nontrivial topological invariants--have been observed through transport and spectroscopy measurements. Here, we show that optical-lattice-based experiments can be tailored to directly visualize the propagation of topological edge modes. Our method is rooted in the unique capability for initially shaping the atomic gas and imaging its time evolution after suddenly removing the shaping potentials. Our scheme, applicable to an assortment of atomic topological phases, provides a method for imaging the dynamics of topological edge modes, directly revealing their angular velocity and spin structure.
Robust edge states in amorphous gyromagnetic photonic lattices
Mansha, Shampy; Chong, Y. D.
2017-09-01
We numerically study amorphous analogs of a two-dimensional photonic Chern insulator. The amorphous lattices consist of gyromagnetic rods that break time-reversal symmetry, with the lattice sites generated by a close-packing algorithm. The level of short-range order is adjustable, and there is no long-range order. The topologically nontrivial gaps of the photonic Chern insulator are found to persist into the amorphous regime, so long as there is sufficient short-range order. Strongly nonreciprocal robust transmission occurs via edge states, which are shown to propagate ballistically despite the absence of long-range order, and to be exponentially localized along the lattice edge. Interestingly, there is an enhancement of nonreciprocal transmission even at very low levels of short-range order, where there are no discernible spectral gaps.
Description of plasma focus current sheath as the Turner relaxed state of a Hall magnetofluid
Auluck, S. K. H.
2009-12-01
The central mystery of plasma focus research is the two orders-of-magnitude-higher-than-thermal fusion reaction rate and the fact that both the space-resolved neutron spectra and space-resolved reaction proton spectra show features which can be ascribed only to a rotational motion of the center-of-mass of the reacting deuteron population. It has been suggested earlier [S. K. H. Auluck, IEEE Trans. Plasma Sci. 25, 37 (1997)] that this and other experimental observations can be consistently explained in terms of a hypothesis involving rotation of the current carrying plasma annulus behind the imploding gas-dynamic shock. Such rotation (more generally, mass flow) is an in-built feature of relaxed state of a two-fluid plasma [R. N. Sudan, Phys. Rev. Lett. 42, 1277 (1979)]. Relaxation in the "Hall magnetofluid" approximation, in which the generalized Ohm's law includes the Hall effect term and the magnetic convection term but omits the contributions to the electric field from resistive dissipation, electron pressure gradient, thermoelectric effect, electron inertia, etc., has been extensively studied by many authors. In the present paper, Turner's [IEEE Trans. Plasma Sci. PS-14, 849 (1986)] degenerate solution for the relaxed state of the Hall magnetohydrodynamic plasma has been adapted to the case of an infinitely long annular current carrying plasma, a tractable idealization of the current sheath of a plasma focus. The resulting model is consistent with experimental values of ion kinetic energy and observation of predominantly radially directed neutron emission in good shots.
Hall resistivity in the heavy Fermion normal state of UPt{sub 3} up to 26 T
Kambe, S. [Grenoble High Magnetic Field Laboratory, Max-Planck-Institut fuer Festkoerperforschung and Centre National de la Recherche Scientifique, BP 166, 38042 Grenoble Cedex 9 (France); CEA/DSM - Departement de Recherche Fondamentale sur la Matiere Condensee SPSMS, CEA-CENG, 38054 Grenoble Cedex 9 (France); Huxley, A.; Flouquet, J. [CEA/DSM - Departement de Recherche Fondamentale sur la Matiere Condensee SPSMS, CEA-CENG, 38054 Grenoble Cedex 9 (France); Jansen, A.G.M.; Wyder, P. [Grenoble High Magnetic Field Laboratory, Max-Planck-Institut fuer Festkoerperforschung and Centre National de la Recherche Scientifique, BP 166, 38042 Grenoble Cedex 9 (France)
1999-01-11
The Hall resistivity {rho}xy has been measured in single crystal UPt{sub 3} at low temperatures (0.1-4.2 K) for magnetic field H parallel a-axis up to 26 T. For temperatures T {yields} 0 K, the Hall coefficient goes asymptotically to zero, indicating a compensated-metal ground state. Since the Hall resistivity does not show an anomaly at the metamagnetic crossover of 20 T in the Fermi-liquid state below 0.8 K, a drastic change of the Fermi surface is unlikely at the crossover. A change of the skew scattering contribution to the Hall effect has been observed around 6 and 2 K, i.e. near respectively the magnetic ordering temperature and the temperature below which the Fermi-liquid state appears. (author)
Supersymmetry in the Fractional Quantum Hall Regime
Sagi, Eran
2016-01-01
Supersymmetry (SUSY) is a symmetry transforming bosons to fermions and vice versa. Indications of its existence have been extensively sought after in high-energy experiments. However, signatures of SUSY have yet to be detected. In this manuscript we propose a condensed matter realization of SUSY on the edge of a Read-Rezayi quantum Hall state, given by filling factors of the form $\
Hyperspherical Slater determinant approach to few-body fractional quantum Hall states
Yan, Bin, E-mail: yanbin@purdue.edu; Wooten, Rachel E.; Daily, Kevin M.; Greene, Chris H.
2017-05-15
In a recent study (Daily et al., 2015), a hyperspherical approach has been developed to study few-body fractional quantum Hall states. This method has been successfully applied to the exploration of few boson and fermion problems in the quantum Hall region, as well as the study of inter-Landau level collective excitations (Rittenhouse et al., 2016; Wooten et al., 2016). However, the hyperspherical method as it is normally implemented requires a subsidiary (anti-)symmetrization process, which limits its computational effectiveness. The present work overcomes these difficulties and extends the power of this method by implementing a representation of the hyperspherical many-body basis space in terms of Slater determinants of single particle eigenfunctions. A clear connection between the hyperspherical representation and the conventional single particle picture is presented, along with a compact operator representation of the theoretical framework. - Highlights: • A hyperspherical method has been implemented to study the quantum Hall effect. • The hyperspherical many-body basis space is represented with Slater determinants. • Example numerical studies of the 4- and 8-electron systems are presented.
Observation of fractional Bloch band quantum Hall states in graphene/h-BN superlattices
Wang, Lei; Gao, Yuanda; Wen, Bo; Hone, James; Dean, Cory
The Hofstadter energy spectrum provides a uniquely tunable system to study emergent topological order in the regime of strong interactions. Previous experiments, however, have been limited to low Bloch band fillings where only the Landau level index plays a role. Here we report measurements of high mobility graphene superlattices where the complete unit cell of the Hofstadter spectrum is accessible. We observe coexistence of conventional fractional quantum Hall effect (QHE) states together with the integer QHE states associated with the fractal Hofstadter spectrum. At large magnetic field, we observe signatures of another series of states, which appears at fractional Bloch filling index. These fractional Bloch band QHE states are not anticipated by existing theoretical pictures and point towards a distinct type of many-body state.
Entanglement and Majorana edge states in the Kitaev model
Mandal, Saptarshi; Maiti, Moitri; Varma, Vipin Kerala
2016-07-01
We investigate the von Neumann entanglement entropy and Schmidt gap in the vortex-free ground state of the Kitaev model on the honeycomb lattice for square/rectangular and cylindrical subsystems. We find that, for both the subsystems, the free-fermionic contribution to the entanglement entropy SE exhibits signatures of the phase transitions between the gapless and gapped phases. However, within the gapless phase, we find that SE does not show an expected monotonic behavior as a function of the coupling Jz between the suitably defined one-dimensional chains for either geometry; moreover, the system generically reaches a point of minimum entanglement within the gapless phase before the entanglement saturates or increases again until the gapped phase is reached. This may be attributed to the onset of gapless modes in the bulk spectrum and the competition between the correlation functions along various bonds. In the gapped phase, on the other hand, SE always monotonically varies with Jz independent of the subregion size or shape. Finally, further confirming the Li-Haldane conjecture, we find that the Schmidt gap Δ defined from the entanglement spectrum also signals the topological transitions but only if there are corresponding zero-energy Majorana edge states that simultaneously appear or disappear across the transitions. We analytically corroborate some of our results on entanglement entropy, the Schmidt gap, and the bulk-edge correspondence using perturbation theory.
Exotic Non-Abelian Topological Defects in Lattice Fractional Quantum Hall States
Liu, Zhao; Möller, Gunnar; Bergholtz, Emil J.
2017-09-01
We investigate extrinsic wormholelike twist defects that effectively increase the genus of space in lattice versions of multicomponent fractional quantum Hall systems. Although the original band structure is distorted by these defects, leading to localized midgap states, we find that a new lowest flat band representing a higher genus system can be engineered by tuning local single-particle potentials. Remarkably, once local many-body interactions in this new band are switched on, we identify various Abelian and non-Abelian fractional quantum Hall states, whose ground-state degeneracy increases with the number of defects, i.e, with the genus of space. This sensitivity of topological degeneracy to defects provides a "proof of concept" demonstration that genons, predicted by topological field theory as exotic non-Abelian defects tied to a varying topology of space, do exist in realistic microscopic models. Specifically, our results indicate that genons could be created in the laboratory by combining the physics of artificial gauge fields in cold atom systems with already existing holographic beam shaping methods for creating twist defects.
Magnetic edge states in MoS2 characterized using density-functional theory
Vojvodic, Aleksandra; Hinnemann, B.; Nørskov, Jens Kehlet
2009-01-01
It is known that the edges of a two-dimensional slab of insulating MoS2 exhibit one-dimensional metallic edge states, the so-called "brim states." Here, we find from density-functional theory calculations that several edge structures, which are relevant for the hydrodesulfurization process, are m...
Edge and line oriented contour detection : State of the art
Papari, Giuseppe; Petkov, Nicolai
We present an overview of various edge and line oriented approaches to contour detection that have been proposed in the last two decades. By edge and line oriented we mean methods that do not rely on segmentation. Distinction is made between edges and contours. Contour detectors are divided in local
Edge and line oriented contour detection : State of the art
Papari, Giuseppe; Petkov, Nicolai
2011-01-01
We present an overview of various edge and line oriented approaches to contour detection that have been proposed in the last two decades. By edge and line oriented we mean methods that do not rely on segmentation. Distinction is made between edges and contours. Contour detectors are divided in local
Robustness of edge states in topological quantum dots against global electric field
Qu, Jin-Xian; Zhang, Shu-Hui; Liu, Ding-Yang; Wang, Ping; Yang, Wen
2017-07-01
The topological insulator has attracted increasing attention as a new state of quantum matter featured by the symmetry-protected edge states. Although the qualitative robustness of the edge states against local perturbations has been well established, it is not clear how these topological edge states respond quantitatively to a global perturbation. Here, we study the response of topological edge states in a HgTe quantum dot to an external in-plane electric field—a paradigmatic global perturbation in solid-state environments. We find that the stability of the topological edge state could be larger than that of the ground bulk state by several orders of magnitudes. This robustness may be verified by standard transport measurements in the Coulomb blockage regime. Our work may pave the way towards utilizing these topological edge states as stable memory devices for charge and/or spin information and stable emitter of single terahertz photons or entangled terahertz photon pairs for quantum communication.
Braiding and Berry's phases in non-Abelian quantum hall states
Zikos, Georgios
If one could be built, a quantum computer would be capable of storing and manipulating quantum states with sufficient accuracy to carry out computations that no classical computer can do (most notably factoring integers in polynomial time). The greatest obstacle to building such a device is the problem of error and decoherence. Classical computers can exploit the physical robustness of ordered states to protect classical information (as in, for example, the magnetically ordered state of a hard drive). Remarkably, a type of quantum order known as topological order can, in principle, play the same role for quantum information. The best studied topologically ordered states are quantum Hall states. These states arise when a two-dimensional electron gas is placed in a strong magnetic field and cooled to low temperatures. Under the right conditions, the electrons condense into an incompressible quantum liquid whose excitations are particle-like objects with fractional charge (quasiparticles). Certain quantum Hall states are thought to be non Abelian. This means that when a finite number of quasiparticles are present and fixed in space there is a low energy Hilbert space with finite dimension, rather than a unique state. Unitary operations can then be carried out on this Hilbert space by adiabatically dragging quasiparticles around one another so that their world-lines sweep out braids in 2+1 dimensional space time. A quantum computer which stores quantum information in this Hilbert space and computes by braiding is known as a topological quantum computer. In this thesis I review our work on determining precisely how one would carry out a computation on a topological quantum computer. I focus on the so-called Fibonacci anyons---quasiparticles which may exist in the experimentally observed quantum Hall state at Landau level filling fraction nu = 12/5. I give explicit prescriptions for encoding qubits (quantum bits) using Fibonacci anyons, and show how one would carry out a
Edge states for the Dirac operator on manifolds with boundary
Govindarajan, T R
2015-01-01
We investigate the properties of the Dirac operator on manifolds with boundaries in presence of the Atiyah-Patodi-Singer boundary condition. An exact counting of the number of edge states for boundaries with isometry of a sphere is given. We show that the problem with the above boundary condition can be mapped to one where the manifold is extended beyond the boundary and the boundary condition is replaced by a delta function potential of suitable strength. We also briefly highlight how the problem of the self-adjointness of the operators in the presence of moving boundaries can be simplified by suitable transformations which render the boundary fixed and modify the Hamiltonian and the boundary condition to reflect the effect of moving boundary.
Quantum Anomalous Hall State in Ferromagnetic SrRuO3 (111) Bilayers
Si, Liang; Janson, Oleg; Li, Gang; Zhong, Zhicheng; Liao, Zhaoliang; Koster, Gertjan; Held, Karsten
2017-07-01
SrRuO 3 heterostructures grown in the (111) direction are a rare example of thin film ferromagnets. By means of density functional theory plus dynamical mean field theory we show that the half-metallic ferromagnetic state with an ordered magnetic moment of 2 μB /Ru survives the ultimate dimensional confinement down to a bilayer, even at elevated temperatures of 500 K. In the minority channel, the spin-orbit coupling opens a gap at the linear band crossing corresponding to 3/4 filling of the t2 g shell. We predict that the emergent phase is Haldane's quantum anomalous Hall state with Chern number C =1 , without an external magnetic field or magnetic impurities.
Non-destructive analytical methods to study the conservation state of Apadana Hall of Persepolis.
Gallello, Gianni; Ghorbani, Shervin; Ghorbani, Sharona; Pastor, Agustin; de la Guardia, Miguel
2016-02-15
Atmospheric and biological agents are the main enemies of the building material conservation. In this work an innovative methodological approach, based on Near Infrared Spectroscopy (NIR) and X-Ray Fluorescence Spectroscopy (XRF), has been employed to evaluate the conservation state of Persepolis limestone samples collected both, under a protective shelter and outside the shelter, at Apadana Audience Hall area in Persepolis. The use of NIR spectra permitted to discriminate, by using Principal Component Analysis (PCA), the differences between samples collected inside and outside the protective shelter and we have been able to identify a major degradation state of the out shelter stone samples due to a major presence of organic compounds. Copyright © 2015 Elsevier B.V. All rights reserved.
Quantum spin Hall and Z2 metallic states in an organic material
Zhao, Bao; Zhang, Jiayong; Feng, Wanxiang; Yao, Yugui; Yang, Zhongqin
2014-11-01
Motivated by recently searching for topological states in organic materials as well as successful experimental synthesis of a graphitelike metal-organic framework Ni3(C18H12N6 )2 [Sheberla et al., J. Am. Chem. Soc. 136, 8859 (2014), 10.1021/ja502765n], we systematically investigated the electronic and topological properties of the Ni3(C18H12N6 )2 monolayer using an ab initio method combined with a tight-binding model. Our calculations demonstrate that the material can be in a quantum spin Hall or Z2 metallic state in different electron-doped concentrations, which are experimentally accessible with currently electrostatic gating technologies. The tight-binding model also shows that the real next-nearest-neighbor interaction is essential to drive the Z2 metallic phase in Ni3(C18H12N6 )2-type lattices.
Current correlations in quantum spin Hall insulators.
Schmidt, Thomas L
2011-08-26
We consider a four-terminal setup of a two-dimensional topological insulator (quantum spin Hall insulator) with local tunneling between the upper and lower edges. The edge modes are modeled as helical Luttinger liquids and the electron-electron interactions are taken into account exactly. Using perturbation theory in the tunneling, we derive the cumulant generating function for the interedge current. We show that different possible transport channels give rise to different signatures in the current noise and current cross correlations, which could be exploited in experiments to elucidate the interplay between electron-electron interactions and the helical nature of the edge states.
Mukherjee, Sutirtha; Mandal, Sudhansu
The internal structure and topology of the ground states for fractional quantum Hall effect (FQHE) are determined by the relative angular momenta between all the possible pairs of electrons. Laughlin wave function is the only known microscopic wave function for which these relative angular momenta are homogeneous (same) for any pair of electrons and depend solely on the filling factor. Without invoking any microscopic theory, considering only the relationship between number of flux quanta and particles in spherical geometry, and allowing the possibility of inhomogeneous (different) relative angular momenta between any two electrons, we develop a general method for determining a closed-form ground state wave function for any incompressible FQHE state. Our procedure provides variationally obtained very accurate wave functions, yet having simpler structure compared to any other known complex microscopic wave functions for the FQHE states. This method, thus, has potential in predicting a very accurate ground state wave function for the puzzling states such as the state at filling fraction 5/2. We acknowledge support from Department of Science and Technology, India.
Metcalf, Mekena; Lai, Chen-Yen; Wright, Kevin; Chien, Chih-Chun
2017-06-01
Topological behavior has been observed in quantum systems including ultracold atoms. However, background harmonic traps for cold atoms hinder the direct detection of topological edge states arising at the boundary because the distortion fuses the edge states into the bulk. We propose experimentally feasible protocols to probe localized edge states and dimerization of ultracold fermions. By confining cold atoms in a ring lattice and changing the boundary condition from periodic to open using an off-resonant laser sheet to cut open the ring, topological edge states can be generated. A lattice in a topological configuration can trap a single particle released at the edge as the system evolves in time. Alternatively, depleting an initially filled lattice away from the boundary reveals the occupied edge states. Signatures of dimerization in the presence of contact interactions can be found in selected correlations as the system boundary suddenly changes from periodic to open and exhibit memory effects of the initial state distinguishing different configurations.
Anisotropic Quantum Hall Liquid States with No Translational Invariance in the Lowest Landau Level
Ciftja, Orion
2016-05-01
Strongly correlated two-dimensional electron systems in a high perpendicular magnetic field have displayed remarkable new physics leading to the discovery of phenomena such as the integer and the fractional quantum Hall effect, to mention a few. Laughlin's theoretical model and the composite fermion's (CFs) approach provide a good description of the liquid electronic phases in the lowest Landau level (LLL) at relatively large filling factors. Other electronic phases at smaller filling factors of the LLL likely represent electronic Wigner solid states. It is believed that no other phases with intermediate order stabilize at the liquid-solid transition region. The current study deals with filling factor 1/6 in the LLL, a state which is very close to the critical filling factor where the liquid-solid transition takes place. With the assumption that the underlying signs of crystalline order are starting to appear at this transitional regime, we focus our attention and study the properties of a hybrid electronic phase that lacks translational invariance. To describe such a state, we consider a wave function that lies entirely in the LLL but, unlike a typical quantum Hall liquid phase, does not possess translational invariance. Although inspired by Laughlin's approach, the wave function we introduce differs from Laughlin's or CFs wave functions that describe translationally invariant uniform electronic phases. We perform quantum Monte Carlo simulations in a standard disk geometry to gain a better understanding of the properties of this wave function that may be considered as a precursor to the more conventional Wigner crystal phase.
Observation of a fractional quantum Hall state at v=1/4 in a wide GaAs quantum well.
Pan, Wei; Tsui, Daniel Chee (Princeton University, Princeton, NJ); Baldwin, K. W. (Bell Labs, Lucent Technologies, Murray Hill, NJ); West, Ken W. (Bell Labs, Lucent Technologies, Murray Hill, NJ); Pfeiffer, Loren N.; Luhman, D. R. (Princeton University, Princeton, NJ)
2008-10-01
We report the observation of an even-denominator fractional quantum Hall state at {nu}=1/4 in a high quality, wide GaAs quantum well. The sample has a quantum well width of 50 nm and an electron density of n{sub e}=2.55 x 10{sup 11} cm{sup -2}. We have performed transport measurements at T{approx}35 mK in magnetic fields up to 45 T. When the sample is perpendicular to the applied magnetic field, the diagonal resistance displays a kink at {nu}=1/4. Upon tilting the sample to an angle of {theta}=20.3{sup o} a clear fractional quantum Hall state emerges at {nu}=1/4 with a plateau in the Hall resistance and a strong minimum in the diagonal resistance.
Composite Fermion Theory for the Fractional Quantum Hall Wigner Crystal State
Narevich, Romanas; Murthy, Ganpathy; Fertig, Herbert
2000-03-01
The low filling fraction Quantum Hall Effect is reexamined using the recent hamiltonian composite fermion theory developed by Shankar and Murthy [SM] (R. Shankar and G. Murthy, Phys. Rev. Lett. 79), 4437, (1997); G. Murthy and R. Shankar, Chapter 4 of "Composite Fermions", O. Heinonen, Ed. (World Scientific, Teaneck, NJ, 1998).. Previous studies have either concentrated on Wigner crystal states of electrons in the Hartree-Fock approximation (D. Yoshioka and H. Fukuyama, J. Phys. Soc. Japan 47), 394 (1979); D. Yoshioka and P. A. Lee, Phys. Rev. B 27, 4986 (1983); A. H. MacDonald, Phys. Rev. B 30, 4392 (1984); R. Cote and A. H. MacDonald, Phys. Rev. B 44, 8759 (1991). or studied correlated crystal states numerically (P. K. Lam and S. M. Girvin, Phys. Rev. B 30), 473 (1984); H. Yi and H. A. Fertig, Phys. Rev. B, 58, 4019 (1998).. Using the new SM approach we study the correlated states as Hartree-Fock states of composite fermions, which is known to work reasonably well for translationally invariant composite fermion states. We present the calculation of the gaps for the stable states that we found as well as the dispersion relations of the collective modes.
Classification of bi-qutrit PPT entangled edge states by their ranks
Kte, Seung-Hyeok
2012-01-01
We construct $3\\otimes 3$ PPT entangled edge states with maximal ranks, to complete the classification of $3\\otimes 3$ PPT entangled edge states by their types. The ranks of the states and their partial transposes are 8 and 6, respectively. These examples also disprove claims in the literature.
Terahertz spectroscopy on Faraday and Kerr rotations in a quantum anomalous Hall state.
Okada, Ken N; Takahashi, Youtarou; Mogi, Masataka; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S; Ogawa, Naoki; Kawasaki, Masashi; Tokura, Yoshinori
2016-07-20
Electrodynamic responses from three-dimensional topological insulators are characterized by the universal magnetoelectric term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental indication of the topological magnetoelectric effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall states of magnetic topological insulator surfaces by terahertz magneto-optics. The universal relation composed of the observed Faraday and Kerr rotation angles but not of any material parameters (for example, dielectric constant and magnetic susceptibility) well exhibits the trajectory towards the fine structure constant in the quantized limit.
Exogenous antioxidants—Double-edged swords in cellular redox state
Bohn, Torsten
2010-01-01
The balance between oxidation and antioxidation is believed to be critical in maintaining healthy biological systems. Under physiological conditions, the human antioxidative defense system including e.g., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH) and others, allows the elimination of excess reactive oxygen species (ROS) including, among others superoxide anions (O2.-), hydroxyl radicals (OH.), alkoxyl radicals (RO.) and peroxyradicals (ROO.). However, our endogenous antioxidant defense systems are incomplete without exogenous originating reducing compounds such as vitamin C, vitamin E, carotenoids and polyphenols, playing an essential role in many antioxidant mechanisms in living organisms. Therefore, there is continuous demand for exogenous antioxidants in order to prevent oxidative stress, representing a disequilibrium redox state in favor of oxidation. However, high doses of isolated compounds may be toxic, owing to prooxidative effects at high concentrations or their potential to react with beneficial concentrations of ROS normally present at physiological conditions that are required for optimal cellular functioning. This review aims to examine the double-edged effects of dietary originating antioxidants with a focus on the most abundant compounds, especially polyphenols, vitamin C, vitamin E and carotenoids. Different approaches to enrich our body with exogenous antioxidants such as via synthetic antioxidants, diets rich in fruits and vegetables and taking supplements will be reviewed and experimental and epidemiological evidences discussed, highlighting that antioxidants at physiological doses are generally safe, exhibiting interesting health beneficial effects. PMID:20972369
Wurstbauer, U.; Levy, A. L.; Pinczuk, A.; West, K. W.; Pfeiffer, L. N.; Manfra, M. J.; Gardner, G. C.; Watson, J. D.
2015-12-01
We report the observation of low-lying collective charge and spin excitations in the second Landau level at ν =2 +1 /3 and also for the very fragile states at ν =2 +2 /5 and 2 +3 /8 in inelastic light scattering experiments. These modes exhibit a clear dependence on filling factor and temperature substantiating the unique access to the characteristic neutral excitation spectra of the incompressible fractional quantum Hall effect (FQHE) states. A detailed mode analysis reveals low-energy modes at around 70 μ eV and a sharp mode slightly below the Zeeman energy interpreted as gap and spin-wave excitation, respectively. The lowest-energy collective charge excitation spectrum at ν =2 +1 /3 exhibits significant qualitative similarities with its cousin state in the lowest Landau level at ν =1 /3 suggesting similar magnetoroton minima in the neutral excitations. The mode energies differ by a scaling of 0.15 indicating different interaction physics in the N =0 and N =1 Landau levels. The striking polarization dependence in elastic and inelastic light scattering is discussed in the framework of anisotropic electron phases that allow for the stabilization of nematic FQHE states. The observed excitation spectra provide new insights by accessing quantum phases in the bulk of electron systems and facilitate comparison with different theoretical descriptions of those enigmatic FQHE states.
Edge state and crisis in the Pierce diode
Munoz, Pablo R.; Rempel, Erico L. [Institute of Aeronautical Technology (ITA) and World Institute for Space Environment Research (WISER), CTA/ITA/IEFM, Sao Jose dos Campos-SP 12228-900 (Brazil); Barroso, Joaquim J. [National Institute for Space Research (INPE) and World Institute for Space Environment Research (WISER), P. O. Box 515, Sao Jose dos Campos-SP 12227-010 (Brazil); Chian, Abraham C.-L. [National Institute for Space Research (INPE) and World Institute for Space Environment Research (WISER), P. O. Box 515, Sao Jose dos Campos-SP 12227-010 (Brazil); Observatoire de Paris, LESIA, CNRS, 92195 Meudon (France)
2012-09-15
We study the chaotic dynamics of the Pierce diode, a simple spatially extended system for collisionless bounded plasmas, focusing on the concept of edge of chaos, the boundary that separates transient from asymptotic dynamics. We fully characterize an interior crisis at the end of a periodic window, thereby showing direct evidence of the collision between a chaotic attractor, a chaotic saddle, and the edge of chaos, formed by a period-3 unstable periodic orbit and its stable manifold. The edge of chaos persists after the interior crisis, when the global attractor of the system increases its size in the phase space.
Edge states of graphene wrinkles in single-layer graphene grown on Ni(111)
Liu, Liwei; Xiao, Wende; Wang, Dongfei; Yang, Kai; Tao, Lei; Gao, Hong-Jun
2016-10-01
As quasi-one-dimensional (1D) structures with characteristic widths of nanometer scale, graphene wrinkles (GWs) have been widely observed in graphene grown by chemical vapor deposition. Similar to conventional 1D graphene-based nanostructures, e.g., carbon nanotubes and graphene nanoribbons, 1D electron confinement has been observed in the GWs. However, it remains an open question whether the GWs have effective edges and exhibit corresponding edge states. Here, we report on the edge states of the GWs in single-layer graphene grown on Ni(111) by means of low temperature scanning tunneling microscopy and spectroscopy. We show that the GWs are decoupled from the substrate, while the surrounding planar graphene are strongly coupled with the substrate. The different graphene-substrate coupling leads to effective edges and 1D character of the GWs. The chiral edges of the GWs give rise to pronounced edge states around the Fermi level in the density of states.
The Band-Edge Behavior of the Density of Surfacic States
Kirsch, Werner [Ruhr Universitaet Bochum, Fakultaet fuer Mathematik and SFB-TR 12 (Germany)], E-mail: werner.kirsch@rub.de; Klopp, Frederic [Universite de Paris-Nord, LAGA, UMR 7539 CNRS, Institut Galilee (France)], E-mail: klopp@math.univ-paris13.fr
2006-05-15
This paper is devoted to the asymptotics of the density of surfacic states near the spectral edges for a discrete surfacic Anderson model. Two types of spectral edges have to be considered: fluctuating edges and stable edges. Each type has its own type of asymptotics. In the case of fluctuating edges, one obtains Lifshitz tails the parameters of which are given by the initial operator suitably 'reduced' to the surface. For stable edges, the surface density of states behaves like the surface density of states of a constant (equal to the expectation of the random potential) surface potential. Among the tools used to establish this are the asymptotics of the surface density of states for constant surface potentials.
Topological Invariants of Edge States for Periodic Two-Dimensional Models
Avila, Julio Cesar; Schulz-Baldes, Hermann, E-mail: schuba@mi.uni-erlangen.de; Villegas-Blas, Carlos [Instituto de Matematicas, UNAM (Mexico)
2013-06-15
Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z{sub 2} -invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.
Effect of edge vacancies on localized states in semi-infinite zigzag graphene sheet
Glebov, A. A.; Katkov, V. L.; Osipov, V. A.
2016-12-01
The effect of vacancies on the robustness of zero-energy edge electronic states in zigzag-type graphene layer is studied at different concentrations and distributions of defects. All calculations are performed by using the Green's function method and the tight-binding approximation. It is found that the arrangement of defects plays a crucial role in the destruction of the edge states. We have specified a critical distance between edge vacancies when their mutual influence becomes significant and affects markedly the density of electronic states at graphene edge.
Topological invariants of edge states for periodic two-dimensional models
Avila, Julio Cesar; Villegas-Blas, Carlos
2012-01-01
Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z_2-invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.
Zhang, Xue-Feng; Eggert, Sebastian
2013-10-01
We consider the extended hard-core Bose-Hubbard model on a kagome lattice with boundary conditions on two edges. We find that the sharp edges lift the degeneracy and freeze the system into a striped order at 1/3 and 2/3 filling for zero hopping. At small hopping strengths, holes spontaneously appear and separate into fractional charges which move to the edges of the system. This leads to a novel edge liquid phase, which is characterized by fractional charges near the edges and a finite edge compressibility but no superfluid density. The compressibility is due to excitations on the edge which display a chiral symmetry breaking that is reminiscent of the quantum Hall effect and topological insulators. Large scale Monte Carlo simulations confirm the analytical considerations.
Topological fate of edge states of single Bi bilayer on Bi(111)
Yeom, Han Woong; Jin, Kyung-Hwan; Jhi, Seung-Hoon
2016-02-01
We address the topological nature of electronic states of step edges of Bi(111) films by first-principles band structure calculations. We confirm that the dispersion of step-edge states reflects the topological nature of underlying films, which become topologically trivial at a thickness larger than eight bilayers. This result clearly conflicts with recent claims that the step-edge state at the surface of a bulk Bi(111) crystal or a sufficiently thick Bi(111) film represents nontrivial edge states of the two-dimensional topological insulator phase expected for a very thin Bi(111) film. The trivial step-edge states have a gigantic spin splitting of one-dimensional Rashba bands and substantial intermixing with electronic states of the bulk, which might be exploited further.
Beggi, Andrea; Bordone, Paolo; Buscemi, Fabrizio; Bertoni, Andrea
2015-12-01
We compute the exact single-particle time-resolved dynamics of electronic Mach-Zehnder interferometers based on Landau edge-states transport, and assess the effect of the spatial localization of carriers on the interference pattern. The exact carrier dynamics is obtained by solving numerically the time-dependent Schrödinger equation with a suitable 2D potential profile reproducing the interferometer design. An external magnetic field, driving the system to the quantum Hall regime with filling factor one, is included. The injected carriers are represented by a superposition of edge states, and their interference pattern—controlled via magnetic field and/or area variation—reproduces the one of (Ji et al 2003 Nature 422 415). By tuning the system towards different regimes, we find two additional features in the transmission spectra, both related to carrier localization, namely a damping of the Aharonov-Bohm oscillations with increasing difference in the arms length, and an increased mean transmission that we trace to the energy-dependent transmittance of quantum point contacts. Finally, we present an analytical model, also accounting for the finite spatial dispersion of the carriers, able to reproduce the above effects.
Novel optical probe for quantum Hall system
Biswajit Karmakar; Brij Mohan Arora
2006-07-01
Surface photovoltage (SPV) spectroscopy has been used for the first time to explore Landau levels of a two-dimensional electron gas (2DEG) in modulation doped InP/InGaAs/InP QW in the quantum Hall regime. The technique gives spectroscopically distinct signals from the bulk Landau levels and the edge states. Evolution of the bulk Landau levels and the edge electronic states is investigated at 2.0 K for magnetic field up to 8 T using SPV spectroscopy.
Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-01-15
The quantum Hall liquid is a novel state of matter with profound emergent properties such as fractional charge and statistics. Existence of the quantum Hall effect requires breaking of the time reversal symmetry caused by an external magnetic field. In this work, we predict a quantized spin Hall effect in the absence of any magnetic field, where the intrinsic spin Hall conductance is quantized in units of 2 e/4{pi}. The degenerate quantum Landau levels are created by the spin-orbit coupling in conventional semiconductors in the presence of a strain gradient. This new state of matter has many profound correlated properties described by a topological field theory.
Mixed-State Hall Effect in Chemically-Substituted YBa_2Cu_3O_7-δ Single Crystals
Han, S. H.; Herrmann, J.; Gajewski, D. A.; Paulius, L. M.; Almasan, C. C.; Maple, M. B.
1996-03-01
Longitudinal resistivity and Hall effect measurements on single crystals of Y_1-xPr_xBa_2Cu_3O_7-δ, YBa_2Cu_3O_7-y, and YBa_2Cu_3-zZn_zO_7-δ in the mixed-state reveal a ``negative Hall anomaly'' below T_c. The negative Hall signal decreases with decreasing CuO2 plane hole concentration and increasing disorder. The Hall conductivity has been analyzed using the expression σ_xy = C_1/B + C_2B + C_3, where C_1/B and C_2B are associated with the motion of the magnetic vortices and of the quasiparticles in the vortex cores, respectively. We extracted the scaling behavior of the parameters C1 and C2 with temperature in the form of A(1-T/T_c)^α and B_1(T_c/T)^β + B_2, respectively. We discovered a delayed onset of a finite transverse resistance with increasing applied magnetic fields, as compared to the longitudinal resistance. The results will be discussed in terms of a model involving quasiparticle density fluctuations in the vortex cores. This work was supported by the U. S. Department of Energy DE-FG03-86ER-45230. Financial support from LANL/INCOR (UC-91-6-A-110) (SHH) and DAAD (JH) is acknowledged. *Present Address: Department of Physics, Western Michigan University **Present Address: Department of Physics, Kent State University
"Hall viscosity" and intrinsic metric of incompressible fractional Hall fluids
Haldane, F. D. M.
2009-01-01
The (guiding-center) "Hall viscosity" is a fundamental tensor property of incompressible ``Hall fluids'' exhibiting the fractional quantum Hall effect; it determines the stress induced by a non-uniform electric field, and the intrinsic dipole moment on (unreconstructed) edges. It is characterized by a rational number and an intrinsic metric tensor that defines distances on an ``incompressibility lengthscale''. These properties do not require rotational invariance in the 2D plane. The sign of ...
Kleinbaum, Ethan; Deng, Nianpei; Gardner, Geoffrey; Manfra, Michael; Csathy, Gabor
2015-03-01
The unique character and potential application of the even denominator v =5/2 fractional quantum hall state has elicited significant interest. Yet, the most basic properties of this ground state remain unexplained. One poorly understood effect is that of the various types of disorder. We report energy gaps at the filling factor v =7/2 in a series of samples into which we intentionally added aluminum impurities during the MBE growth. These data, together with the availability of energy gaps at v =5/2 in the same samples, allows us to quantify the disorder broadening and the intrinsic gap of the even denominator fractional quantum Hall states. This work was supported by DOE DE-SC000671.
Sublattice Localized Electronic States in Atomically Resolved Graphene-Pt(111) Edge-Boundaries
Merino-Mateo, Pablo; Pinardi, Anna Lisa; Méndez, Javier; López, María Francisca; Pérez, Rubén; Martín-Gago, José A.
2014-01-01
Understanding the connection of graphene with metal surfaces is a necessary step for developing atomically precise graphene-based technology. Combining high-resolution STM experiments and DFT calculations, we have unambiguously unveiled the atomic structure of the boundary between a graphene zigzag edge and a Pt(111) step. The graphene edges minimize their strain by inducing a 3-fold edge-reconstruction on the metal side. We show the existence of an unoccupied electronic state that is mostly ...
Effet Hall quantique, liquides de Luttinger et charges fractionnaires
Roche, Patrice; Rodriguez, V.; Glattli, D. Christian
We review some basic properties of the Fractional Quantum Hall Effect and particularly address the physics of the edge states. The chiral Luttinger liquid properties of the edges are discussed and probed experimentally using transport measurements. Shot noise measurements, which allow determination of the quasiparticle charge are also discussed. To cite this article: P. Roche et al., C. R. Physique 3 (2002) 717-732.
Spin states of zigzag-edged Mobius graphene nanoribbons from first principles
Jiang, De-en
2007-01-01
Mobius graphene nanoribbons have only one edge topologically. How the magnetic structures, previously associated with the two edges of zigzag-edged flat nanoribbons or cyclic nanorings, would change for their Mobius counterparts is an intriguing question. Using spin-polarized density functional theory, we shed light on this question. We examine spin states of zigzag-edged Mobius graphene nanoribbons (ZMGNRs) with different widths and lengths. We find a triplet ground state for a Mobius cyclacene, while the corresponding two-edged cyclacene has an open-shell singlet ground state. For wider ZMGNRs, the total magnetization of the ground state is found to increase with the ribbon length. For example, a quintet ground state is found for a ZMGNR. Local magnetic moments on the edge carbon atoms form domains of majority and minor spins along the edge. Spins at the domain boundaries are found to be frustrated. Our findings show that the Mobius topology (i.e., only one edge) causes ZMGNRs to favor one spin over the oth...
Darko Butina
2004-12-01
Full Text Available Performance of the E-state descriptors was tested against simple counts of the 35 atom types that the Kier-Hall E-states are based upon, by building PLS models for clogP, aqueous solubility, human intestinal absorption (HIA and blood brain barrier (BBB. The results indicate that the simple counts work at least as well as E-state descriptors in building models for solubility and BBB, while surprisingly, simple counts have outperformed E-states by 18% and 30%, respectively, when building the models for HIA and clogP.
Direct imaging of topological edge states at a bilayer graphene domain wall
Yin, Long-Jing; Jiang, Hua; Qiao, Jia-Bin; He, Lin
2016-06-01
The AB-BA domain wall in gapped graphene bilayers is a rare naked structure hosting topological electronic states. Although it has been extensively studied in theory, a direct imaging of its topological edge states is still missing. Here we image the topological edge states at the graphene bilayer domain wall by using scanning tunnelling microscope. The simultaneously obtained atomic-resolution images of the domain wall provide us unprecedented opportunities to measure the spatially varying edge states within it. The one-dimensional conducting channels are observed to be mainly located around the two edges of the domain wall, which is reproduced quite well by our theoretical calculations. Our experiment further demonstrates that the one-dimensional topological states are quite robust even in the presence of high magnetic fields. The result reported here may raise hopes of graphene-based electronics with ultra-low dissipation.
Electronic states of zigzag graphene nanoribbons with edges reconstructed with topological defects
Pincak, R., E-mail: pincak@saske.sk [Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Kosice (Slovakia); Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region (Russian Federation); Smotlacha, J., E-mail: smota@centrum.cz [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region (Russian Federation); Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 110 00 Prague (Czech Republic); Osipov, V.A., E-mail: osipov@theor.jinr.ru [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region (Russian Federation)
2015-10-15
The energy spectrum and electronic density of states (DOS) of zigzag graphene nanoribbons with edges reconstructed with topological defects are investigated within the tight-binding method. In case of the Stone–Wales zz(57) edge the low-energy spectrum is markedly changed in comparison to the pristine zz edge. We found that the electronic DOS at the Fermi level is different from zero at any width of graphene nanoribbons. In contrast, for ribbons with heptagons only at one side and pentagons at another one the energy gap at the Fermi level is open and the DOS is equal to zero. The reason is the influence of uncompensated topological charges on the localized edge states, which are topological in nature. This behavior is similar to that found for the structured external electric potentials along the edges.
Edge states as mediators of bypass transition in boundary-layer flows
Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Eckhardt, Bruno; Henningson, Dan S
2016-01-01
The concept of edge state is investigated in the asymptotic suction boundary layer in relation with the receptivity process to noisy perturbations and the nucleation of turbulent spots. Edge tracking is first performed numerically, without imposing any discrete symmetry, in a large computational domain allowing for full spatial localisation of the perturbation velocity. The edge state is a three-dimensional localised structure recurrently characterised by a single low-speed streak that experiences erratic bursts and planar shifts. This recurrent streaky structure is then compared with predecessors of individual spot nucleation events, triggered by non-localised initial noise. The present results suggest a nonlinear picture, rooted in dynamical systems theory, of the nucleation process of turbulent spots in boundary-layer flows, in which the localised edge state play the role of state-space mediator.
Edge states as mediators of bypass transition in boundary-layer flows
Khapko, T.; Kreilos, T.; Schlatter, P.; Duguet, Y.; Eckhardt, B.; Henningson, D. S.
2016-08-01
The concept of edge state is investigated in the asymptotic suction boundary layer in relation with the receptivity process to noisy perturbations and the nucleation of turbulent spots. Edge tracking is first performed numerically, without imposing any discrete symmetry, in a large computational domain allowing for full spatial localisation of the perturbation velocity. The edge state is a three-dimensional localised structure recurrently characterised by a single low-speed streak that experiences erratic bursts and planar shifts. This recurrent streaky structure is then compared with predecessors of individual spot nucleation events, triggered by non-localised initial noise. The present results suggest a nonlinear picture, rooted in dynamical systems theory, of the nucleation process of turbulent spots in boundary-layer flows, in which the localised edge state play the role of state-space mediator.
Bounds on probability of state transfer with respect to readout time and edge weight
Gordon, Whitney; Kirkland, Steve; Li, Chi-Kwong; Plosker, Sarah; Zhang, Xiaohong
2016-02-01
We analyze the sensitivity of a spin chain modeled by an undirected weighted connected graph exhibiting perfect state transfer to small perturbations in readout time and edge weight in order to obtain physically relevant bounds on the probability of state transfer. At the heart of our analysis is the concept of the numerical range of a matrix; our analysis of edge weight errors additionally makes use of the spectral and Frobenius norms.
One-dimensional metallic edge states in MoS2
Bollinger, Mikkel; Lauritsen, J.V.; Jacobsen, Karsten Wedel;
2001-01-01
By the use of density functional calculations it is shown that the edges of a two-dimensional slab of insulating MoS2 exhibit several metallic states. These edge states can be viewed as one-dimensional conducting wires, and we show that they can be observed directly using scanning tunneling...... microscopy for single-layer MoS2 nanoparticles grown on a support....
Emergence of Dirac and quantum spin Hall states in fluorinated monolayer As and AsSb
Zhang, Qingyun
2016-01-21
Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer As and AsSb. While the pristine monolayers are semiconductors (direct band gap at the Γ point), fluorination results in Dirac cones at the K points. Fluorinated monolayer As shows a band gap of 0.16 eV due to spin-orbit coupling, and fluorinated monolayer AsSb a larger band gap of 0.37 eV due to inversion symmetry breaking. Spin-orbit coupling induces spin splitting similar to monolayer MoS2. Phonon calculations confirm that both materials are dynamically stable. Calculations of the edge states of nanoribbons by the tight-binding method demonstrate that fluorinated monolayer As is topologically nontrivial in contrast to fluorinated monolayer AsSb.
Local probe of fractional edge states of S=1 Heisenberg spin chains.
Delgado, F; Batista, C D; Fernández-Rossier, J
2013-10-18
Spin chains are among the simplest physical systems in which electron-electron interactions induce novel states of matter. Here we propose to combine atomic scale engineering and spectroscopic capabilities of state of the art scanning tunnel microscopy to probe the fractionalized edge states of individual atomic scale S=1 spin chains. These edge states arise from the topological order of the ground state in the Haldane phase. We also show that the Haldane gap and the spin-spin correlation length can be measured with the same technique.
Spin-orbit or Aharonov-Casher edge states in semiconductor two-dimensional systems
Xu, L. L.; Heremans, J. J.; Gaspe, C. K.; Vijeyaragunathan, S.; Mishima, T. D.; Santos, M. B.
2012-02-01
In semiconductors with spin-orbit interaction we experimentally search for edge states induced by the Aharonov-Casher vector potential or Rashba-type spin-orbit interaction. The Aharonov-Casher effect is electromagnetically dual to the Aharonov-Bohm effect and is predicted to lead to a possibly helical edge state structure at two-dimensional sample edges. We use InGaAs/InAlAs heterostructures patterned into mesoscopic side-gated channel structures, where the edge states can be induced, and where backscattering between edge states can be experimentally measured in the resistance. Sweeping side-gate voltage, low temperature resistances are measured across such mesoscopic closed-path structures at either low applied magnetic field, in-plane or normal to the plane, or at fixed magnetic filling factors of 5, 6, 7, and 8 to obtain states of defined spin. Resistance oscillations are observed at low magnetic fields and around filling factor 6 as function of side-gate voltage, and we analyze the oscillations in the light of the search for the edge states (DOE DE-FG02-08ER46532, NSF DMR-0520550).
Device-width dependence of plateau width in quantum Hall states
Kawaji, S.; Hirakawa, K.; Nagata, M.
1993-02-01
Hall bar type devices having a total length of 2900 μm, a source and drain electrode width of 400 μm and different widths w ranging from 10 to 120 μm in its central 600 μm long part are fabricated from a GaAs/AlGaAs wafer with electron mobility of 21 m 2V -1s -1. The current at which the quantum Hall plateau for i=2 at B=9.7T at T=1.2K disappears is proportional to w. The average critical current density is Jcr=(1.6±0.2) A m -1
Bending strain engineering in quantum spin hall system for controlling spin currents
Huang, Bing; Jin, Kyung-Hwan; Cui, Bin; Zhai, Feng; Mei, Jiawei; Liu, Feng
2017-06-01
Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. Here the concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. We show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Furthermore, the curved quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.
Yu, H. L.; Jiang, C.; Zhai, Z. Y.
2017-01-01
We investigate numerically the integer quantum Hall effect in a three-band triangular-lattice model. The three bands own the Chern number C=2,-1,-1, respectively. The lowest topological flat band carrying Chern number C=2, which leads to the Hall plateau σH = 2 (e2 / h) . This Hall plateau is sensitive to the disorder scattering and is rapidly destroyed by the weak disorder. Further increasing the strength of disorder, the gap of density of states always disappears before the vanishing of the corresponding Hall plateau. The scaling behavior of quantum phase transition between an insulator and a quantum Hall plateau is studied. We find that the insulator-plateau transition becomes sharper with increasing the size of system. Due to the different of edge states, the critical energy Ec1 gradually shifts to the center of Hall plateau while Ec2 is unaffected with increasing the disorder strength.
Observation of conducting edge states in graphene at zero magnetic field
Allen, Monica; Fulga, Ion; Shtanko, Oles; Watanabi, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo; Akhmerov, Anton; Levitov, Leonid; Yacoby, Amir
2015-03-01
The electronic nature of edge states confined to the boundaries of a graphene crystal remains an outstanding question. Proposals range from Anderson localization to chiral zero-energy edge modes, but a full microscopic picture of edge transport remains elusive. We directly image current transmission in real space by coupling superconducting electrodes to a graphene crystal and measuring quantum interference as a function of applied magnetic flux. To obtain a more quantitative picture, we employ Fourier techniques to extract the real space current distribution with nanoscale precision. We observe robust confinement of current to the edges of the crystal approaching the Dirac point and show that relative edge and bulk contributions are tunable via electrostatic gating. A strong candidate consistent with our data is the proposal of chiral edge modes that arise from sublattice symmetry breaking at the edge, sustained in all crystallographic edge orientations except atomically perfect armchair. Our techniques also open the door to fast spatial imaging of current distributions along more complicated networks of domains in larger crystals.
Murthy, Ganpathy
2000-01-01
It is well known that the ν = 2/5 state is unpolarized at zero Zeeman energy, while it is fully polarized at large Zeeman energies. A novel state with a charge/spin density wave order for composite fermions is proposed to exist at intermediate values of the Zeeman coupling for ν = 2/5. This state has half the maximum possible polarization, and can be extended to other incompressible fractions. A Hartree-Fock calculation based on the new approach for all fractional quantum Hall states developed by R. Shankar and the author is used to demonstrate the stability of this state to single-particle excitations and to compute gaps. A very recent experiment shows direct evidence for this state.
Murthy
2000-01-10
It is well known that the nu = 2/5 state is unpolarized at zero Zeeman energy, while it is fully polarized at large Zeeman energies. A novel state with a charge/spin density wave order for composite fermions is proposed to exist at intermediate values of the Zeeman coupling for nu = 2/5. This state has half the maximum possible polarization, and can be extended to other incompressible fractions. A Hartree-Fock calculation based on the new approach for all fractional quantum Hall states developed by R. Shankar and the author is used to demonstrate the stability of this state to single-particle excitations and to compute gaps. A very recent experiment shows direct evidence for this state.
Robust quantum state transfer via topologically protected edge channels in dipolar arrays
Dlaska, C.; Vermersch, B.; Zoller, P.
2017-03-01
We show how to realise quantum state transfer between distant qubits using the chiral edge states of a two-dimensional topological spin system. Our implementation based on Rydberg atoms allows to realise the quantum state transfer protocol in state-of-the-art experimental setups. In particular, we show how to adapt the standard state transfer protocol to make it robust against dispersive and disorder effects.
Claiming Authority at the Edges of the State
Eilenberg, Michael
This paper examines state-local relations in the border region of West Kalimantan since decentralisation, with a focus on five ethnic Iban dominated subdistricts within the remote district of Kapuas Hulu, on the border of the Malaysian state of Sarawak. It tracks the fate of a political movement ...... for a new district in this resource-rich region, arguing that the borderlands can be seen as a critical site for exemplifying the changing dynamics of state-local interactions that Indonesia is experiencing in the wake of decentralisation....
Nuclear-spin-induced localization of edge states in two-dimensional topological insulators
Hsu, Chen-Hsuan; Stano, Peter; Klinovaja, Jelena; Loss, Daniel
2017-08-01
We investigate the influence of nuclear spins on the resistance of helical edge states of two-dimensional topological insulators (2DTIs). Via the hyperfine interaction, nuclear spins allow electron backscattering, otherwise forbidden by time-reversal symmetry. We identify two backscattering mechanisms, depending on whether the nuclear spins are ordered or not. Their temperature dependence is distinct but both give resistance, which increases with the edge length, decreasing temperature, and increasing strength of the electron-electron interaction. Overall, we find that the nuclear spins will typically shut down the conductance of the 2DTI edges at zero temperature.
Topological Edge States at a Tilt Boundary in Gated Multilayer Graphene
Abolhassan Vaezi
2013-06-01
Full Text Available Despite much interest in engineering new topological surface (edge states using structural defects, such topological surface states have not been observed yet. We show that recently imaged tilt boundaries in gated multilayer graphene should support topologically protected gapless edge states. We approach the problem from two perspectives: the microscopic perspective of a tight-binding model and an ab initio calculation on a bilayer, and the symmetry-protected topological (SPT state perspective for a general multilayer. Hence, we establish the tilt-boundary edge states as the first concrete example of the edge states of symmetry-protected Z-type SPT, protected by no-valley mixing, electron-number conservation, and time-reversal T symmetries. Further, we discuss possible phase transitions between distinct SPTs upon symmetry changes. Combined with a recently imaged tilt-boundary network, our findings may explain the long-standing puzzle of subgap conductance in gated bilayer graphene. This proposal can be tested through future transport experiments on tilt boundaries. In particular, the tilt boundaries offer an opportunity for the in situ imaging of topological edge transport.
Electronic States of LaCoO3: Co K-edge and La L-edge X-ray Absorption Studies
Pandey,S.; Kumar, A.; Khalid, S.; Pimpale, A.
2006-01-01
Room-temperature Co K-edge and La L-edge x-ray absorption studies have been carried out on LaCoO{sub 3}. Experimental near-edge structures have been analyzed by theoretical LDA+U density of states (DOS) and multiple scattering (MS) calculations. Use of both MS and DOS calculations yields additional information about hybridization of the states of the central atom with neighboring atoms responsible for producing the near-edge structures. Absorption processes at the Co K-edge, and the La L1-, L2-, and L3-edges have been attributed to electronic transitions from Co1s {yields} Co4p, La2s {yields} La6p, La 2{sub 1/2}{yields} La 5d, and La 2p{sub 3/2} {yields} La5d, respectively. All the pre-edge and post-edge features including the shape of the main absorption edge have been generated by taking the convolution of the calculated DOS, indicating that single particle approximation is sufficient to express all experimentally observed major structures. Two pre-edge structures observed in the Co K-edge spectrum are attributed to Co1s {yields} e{sub g}{sup {up_arrow}} and e{sub g}{sup {down_arrow}} quadrupole transitions in contrast to earlier identification of the same to Co1s {yields} t{sub 2g} and e{sub g} transitions. The influence of La 6p states on the Co 4p states is such that the inclusion of La atoms in the MS calculations is necessary to generate post-edge structures in the Co K-edge spectrum. The importance of the hybridization of the O 2p state with La 6p and 5d in the L-edge absorption processes is also discussed. A 10% contribution of the quadrupole channel has been estimated in the La L-edges.
Liu, Zhao; Vaezi, Abolhassan; Lee, Kyungmin; Kim, Eun-Ah
2015-08-01
Recent theoretical insights into the possibility of non-Abelian phases in ν =2 /3 fractional quantum Hall states revived the interest in the numerical phase diagram of the problem. We investigate the effect of various kinds of two-body interlayer couplings on the (330) bilayer state and exactly solve the Hamiltonian for up to 14 electrons on sphere and torus geometries. We consider interlayer tunneling, short-ranged repulsive/attractive pseudopotential interactions, and Coulomb repulsion. We find a 6-fold ground-state degeneracy on the torus when the interlayer hollow-core interaction is dominant. To identify the topological nature of this phase we measure the orbital-cut entanglement spectrum, quasihole counting, topological entanglement entropy, and wave-function overlap. Comparing the numerical results to the theoretical predictions, we interpret this 6-fold ground-state degeneracy phase to be the non-Abelian bilayer Fibonacci state.
Repellin, Cécile; Neupert, Titus; Bernevig, B. Andrei; Regnault, Nicolas
2015-09-01
Multilayer fractional quantum Hall wave functions can be used to construct the non-Abelian states of the Zk Read-Rezayi series upon symmetrization over the layer index. Unfortunately, this construction does not yield the complete set of Zk ground states on the torus. We develop an alternative projective construction of Zk Read-Rezayi states that complements the existing one. On the multilayer torus geometry, our construction consists of introducing twisted boundary conditions connecting the layers before performing the symmetrization. We give a comprehensive account of this construction for bosonic states, and numerically show that the full ground state and quasihole manifolds are recovered for all computationally accessible system sizes. Furthermore, we analyze the neutral excitation modes above the Moore-Read on the torus through an extensive exact diagonalization study. We show numerically that our construction can be used to obtain excellent approximations to these modes. Finally, we extend our symmetrization scheme to the plane and sphere geometries.
Properties of Edge States at the Graphene P-N Junction Interface
Le, Son; Klimov, Nikolai; Newell, David; Yan, Jun; Lee, Ji Ung; Richter, Curt
The Landau level edge states from the p- and the n-section of a graphene P/N junction (pnJ) interact with each other differently across the junction depending upon the properties of the junction and the graphene. Full equilibration was reported for a two terminal graphene pnJ device in Williams et al.. In our four-terminal device, however, only the lowest Landau level edge state is equilibrated across the pnJ. When the two devices are compared, the LL energy spacings, the length of the edge states along the pnJ interface, and the carrier mobility are similar. Electrostatic simulations for our device geometry and that of contrast the rate of change of the electrostatic potential across the pnJs. Edge states at an electrostatically smooth junction are spatially further apart than those at a relatively abrupt junction, which decreases the probability of edge states mixing. Thus, we attribute the difference in equilibration in our device and that of to the dramatic difference in the shape of the electrostatic junction.
The Two-Dimensional MnO2/Graphene Interface: Half-metallicity and Quantum Anomalous Hall State
Gan, Liyong
2015-10-07
We explore the electronic properties of the MnO2/graphene interface by first-principles calculations, showing that MnO2 becomes half-metallic. MnO2 in the MnO2/graphene/MnO2 system provides time-reversal and inversion symmetry breaking. Spin splitting by proximity occurs at the Dirac points and a topologically nontrivial band gap is opened, enabling a quantum anomalous Hall state. The half-metallicity, spin splitting, and size of the band gap depend on the interfacial interaction, which can be tuned by strain engineering.
Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.
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.
A (5,5) and (6,6) PPT edge state
Clarisse, L
2006-01-01
Entangled states with a positive partial transpose (PPTES) have interest both in quantum information and in the theory of positive maps. In $3\\otimes 3$ there is a conjecture by Sanpera, Bru{\\ss} and Lewenstein [PRA, 63, 050301] that all PPTES have Schmidt number two (or equivalently that every 2-positive map between $3\\times 3$ matrices is decomposable). In order to prove or disprove the conjecture it is sufficient to look at edge PPTES. Here the rank m of the PPTES and the rank n of its partial transpose seem to play an important role. Until recently all known examples of edge PPTES had ranks (4,4) or (6,7). In a recent paper Ha and Kye [quant-ph/0509079] managed to find edge PPTES for all ranks except (5,5) and (6,6). Here we complement their work and present edge PPTES with those ranks.
Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure.
Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A; Kuk, Young
2016-08-09
Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.
Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure
Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young
2016-08-01
Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.
Spatially Resolving Spin-split Edge States of Chiral Graphene Nanoribbons
Crommie, M. F.
2011-03-01
A central question in the field of graphene-related research is how graphene behaves when it is patterned at the nanometer scale with different edge geometries. The most fundamental shape in this regard is the graphene nanoribbon (GNR), a narrow strip of graphene that is characterized by its width and chirality. GNRs have been predicted to exhibit a wide range of behavior that includes tunable energy gaps and unique 1D edge states with unusual magnetic structure. I will discuss a scanning tunneling microscopy and spectroscopy (STS) study of GNRs that allows us to examine how GNR electronic structure depends on the chirality of atomically well-defined GNR edges. Our STS measurements reveal the presence of 1D GNR edge states that closely match theoretical expectations for GNRs of similar width and chirality. We additionally observe width-dependent energy splitting in GNR edge states, providing compelling evidence of their magnetic nature. This work performed in collaboration with Chenggang Tao, Liying Jiao, Oleg V. Yazyev, Yen-Chia Chen, Juanjuan Feng, Xiaowei Zhang, Rodrigo B. Capaz, James M. Tour, Alex Zettl, Steven G. Louie, and Hongjie Dai.
A comparative study on the edge states in phosphorene quantum dots and rings
Jiang, Z.T., E-mail: jiangzhaotan@bit.edu.cn; Liang, F.X.; Zhang, X.D.
2017-01-30
Using the tight-binding Hamiltonian approach, we comparatively investigate the energy spectrums of triangular zigzag phosphorene quantum dots (PQDs) and rings (PQRs), as well as their potential applications. In comparison with the outer edge states in the PQD, new extra inner edge states can be produced in the PQR by its internal hole. A transition from the uncoupled to coupled edge states can be induced by decreasing the width between the outer and inner edges of the PQR. Also, the edge states in PQD/PQR are all anisotropically localized in one side, rather than three sides as in triangular graphene quantum dots (QDs) and rings (QRs). Furthermore, the PQD/PQR energy levels can be anisotropically manipulated by the external electric fields and strains, clearly demonstrating their potential applications in field effect transistors or electromechanical devices. In the meanwhile, we also consider the electron probability distributions corresponding to the different energy levels, clearly exposing the characteristics of the PQD/PQR energy levels. The comparison between the asymmetrical triangular PQDs/PQRs and the symmetrical triangular QDs/QRs in graphene should be instructive for understanding the similar triangular QDs/QRs in other two-dimensional layered materials, as well as other types of QDs/QRs of different shapes. - Highlights: • We make a comparative study on the energy levels of the phosphorene quantum dots and rings. • The energy levels can be anisotropically controlled by the electric field and the strains, different from those in graphene counterparts. • The edge states in phosphorene triangular quantum dot and rings are anisotropic. • A helpful reference for understanding phosphorene nanostructures of other shapes and designing devices.
Quantum anomalous Hall effect in real materials
Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Yang, Zhongqin
2016-11-01
Under a strong magnetic field, the quantum Hall (QH) effect can be observed in two-dimensional electronic gas systems. If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field, then it will give rise to a new quantum state, the quantum anomalous Hall (QAH) state. The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics. The realization of the QAH effect in real materials is of great significance. In this paper, we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures, including magnetically doped topological insulators, graphene-based systems, silicene-based systems, two-dimensional organometallic frameworks, quantum wells, and functionalized Sb(111) monolayers, etc. Our paper can help our readers to quickly grasp the recent developments in this field. Project supported by the National Basic Research Program of China (Grant No. 2011CB921803), the National Natural Science Foundation of China (Grant No. 11574051), the Natural Science Foundation of Shanghai, China (Grant No. 14ZR1403400), and Fudan High-end Computing Center, China.
Gate-defined graphene quantum point contact in the quantum Hall regime.
Nakaharai, S; Williams, J R; Marcus, C M
2011-07-15
We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5h/e2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.
Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals
Mei, Jun
2016-09-02
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the Î
Influence of the Geometry of Beveled Edges on the Stress-Strain State of Hydraulic Cylinders
Buyalich, G. B.; Anuchin, A. V.; Serikov, K. P.
2016-04-01
The studies were carried out to determine the influence of forms obtained when preparing edges for welding a cylinder for hydraulic legs; the maximum stresses were defined at the location of weld roots, depending on variable parameters. The stress-strain states were calculated using finite element method.
Edge state preparation in a one-dimensional lattice by quantum Lyapunov control
Zhao, X. L.; Shi, Z. C.; Qin, M.; Yi, X. X.
2017-01-01
Quantum Lyapunov control uses a feedback control methodology to determine control fields applied to control quantum systems in an open-loop way. In this work, we employ two Lyapunov control schemes to prepare an edge state for a fermionic chain consisting of cold atoms loaded in an optical lattice. Such a chain can be described by the Harper model. Corresponding to the two schemes, two types of quantum Lyapunov functions are considered. The results show that both the schemes are effective at preparing the edge state within a wide range of parameters. We found that the edge state can be prepared with high fidelity even if there are moderate fluctuations of on-site or hopping potentials. Both control schemes can be extended to similar chains (3m + d, d = 2) of different lengths. Since a regular amplitude control field is easier to apply in practice, an amplitude-modulated control field is used to replace the unmodulated one. Such control approaches provide tools to explore the edge states of one-dimensional topological materials.
Odd-Integer Quantum Hall States and Giant Spin Susceptibility in p -Type Few-Layer WSe2
Xu, Shuigang; Shen, Junying; Long, Gen; Wu, Zefei; Bao, Zhi-qiang; Liu, Cheng-Cheng; Xiao, Xiao; Han, Tianyi; Lin, Jiangxiazi; Wu, Yingying; Lu, Huanhuan; Hou, Jianqiang; An, Liheng; Wang, Yuanwei; Cai, Yuan; Ho, K. M.; He, Yuheng; Lortz, Rolf; Zhang, Fan; Wang, Ning
2017-02-01
We fabricate high-mobility p -type few-layer WSe2 field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p -type few-layer WSe2 , in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe2 offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.
Local Convertibility and the Quantum Simulation of Edge States in Many-Body Systems
Fabio Franchini
2014-11-01
Full Text Available In some many-body systems, certain ground-state entanglement (Rényi entropies increase even as the correlation length decreases. This entanglement nonmonotonicity is a potential indicator of nonclassicality. In this work, we demonstrate that such a phenomenon, known as lack of local convertibility, is due to the edge-state (deconstruction occurring in the system. To this end, we employ the example of the Ising chain, displaying an order-disorder quantum phase transition. Employing both analytical and numerical methods, we compute entanglement entropies for various system bipartitions (A|B and consider ground states with and without Majorana edge states. We find that the thermal ground states, enjoying the Hamiltonian symmetries, show lack of local convertibility if either A or B is smaller than, or of the order of, the correlation length. In contrast, the ordered (symmetry-breaking ground state is always locally convertible. The edge-state behavior explains all these results and could disclose a paradigm to understand local convertibility in other quantum phases of matter. The connection we establish between convertibility and nonlocal, quantum correlations provides a clear criterion of which features a universal quantum simulator should possess to outperform a classical machine.
Lee, Kayoung; Kim, Seyoung; Fallahazad, Babak; Tutuc, Emanuel
2011-03-01
Graphene bilayers in Bernal stacking exhibit a transverse electric field dependent energy gap, thanks to the on-site electron energy asymmetry between the two layers. In a perpendicular magnetic field, the applied transverse electric field (E) will induce a quantum Hall state (QHS) at the charge neutrality point (filling factor ν = 0) marked by a insulating behavior of the longitudinal resistance (ρxx) , and a plateau in the Hall conductivity. Using dual-gated graphene bilayers, we investigate here the E -field dependence of the ν = 0 QHS in high perpendicular magnetic fields (B) , up to 30T. The temperature dependence of ρxx measured at ν = 0 shows an insulating behavior, which is strongest in the vicinity of E = 0 as well as at large E -fields. At a fixed B -field, as a function of the applied E -field the ν = 0 QHS undergoes a transition, marked by a ρxx minimum, as well as a temperature independent ρxx at a finite E -field value. This observation can be explained by a transition from a spin polarized ν = 0 QHS at small E -fields, to a valley (layer) polarized ν = 0 QHS at large E -fields. The E -field value at which the transition occurs follows a linear dependence on the applied perpendicular magnetic field, with a slope of ~ 18 mV/ nm . T. We thank NRI and NSF for support.
Dynamics of skyrmions and edge states in the resistive regime of mesoscopic p-wave superconductors
Fernández Becerra, V.; Milošević, M. V.
2017-02-01
In a mesoscopic sample of a chiral p-wave superconductor, novel states comprising skyrmions and edge states have been stabilized in out-of-plane applied magnetic field. Using the time-dependent Ginzburg-Landau equations we shed light on the dynamic response of such states to an external applied current. Three different regimes are obtained, namely, the superconducting (stationary), resistive (non-stationary) and normal regime, similarly to conventional s-wave superconductors. However, in the resistive regime and depending on the external current, we found that moving skyrmions and the edge state behave distinctly different from the conventional kinematic vortex, thereby providing new fingerprints for identification of p-wave superconductivity.
Spin-Filter Effect Induced by Magnetic Edge States of Zigzag Carbon Nanotube
JIANG Zhan-Feng; LI Jian; SHEN Shun-Qing; LIU Wu-Ming
2008-01-01
@@ Spin-filter effect is predicted in a weak coupled junction composed of a nonmagnetic metal electrode and a zigzag carbon nanotube. This effect is induced by the magnetic edge states of the nanotube, and can produce spinpolarized current in the absence of an external magnetic field. We find that the spin polarization of the current changes its sign at the half-filling point of the nanotube, thus electric field control of spin transport can be realized. Furthermore, we find the coupling strength of the junction may cause a magnetic transition on the edge of the nanotube.
Tsuda, Shibun; Nguyen, Minh-Hai; Terasawa, Daiju; Fukuda, Akira; Sawada, Anju
2016-03-01
We investigate the huge longitudinal resistance (HLR) at which the magnetoresistance of the ν =2/3 fractional quantum Hall state (QHS) is increased with dynamic nuclear spin polarization. We measure the magnetoresistance temperature dependence in the resistively saturated HLR by increasing the temperature of the sample rapidly in order to prevent relaxation of the nuclear spin polarization. The obtained results indicate that the magnetoresistance decreases as the temperature increases. The Hall resistance in the HLR is also measured and found to exhibit a plateau close to a quantized value. We discuss the negative magnetoresistance temperature dependence with a stripe-shaped domain state deformed by the nuclear spin polarization.
Livi, Lorenzo; Alippi, Cesare
2016-01-01
It is a widely accepted fact that the computational capability of recurrent neural networks is maximized on the so-called "edge of criticality". Once in this configuration, the network performs efficiently on a specific application both in terms of (i) low prediction error and (ii) high short-term memory capacity. Since the behavior of recurrent networks is strongly influenced by the particular input signal driving the dynamics, a universal, application-independent method for determining the edge of criticality is still missing. In this paper, we propose a theoretically motivated method based on Fisher information for determining the edge of criticality in recurrent neural networks. It is proven that Fisher information is maximized for (finite-size) systems operating in such critical regions. However, Fisher information is notoriously difficult to compute and either requires the probability density function or the conditional dependence of the system states with respect to the model parameters. The paper expl...
Edge States of a Periodic Chain with Four-Band Energy Spectrum
Eliashvili, Merab; Kereselidze, Davit; Tsitsishvili, George; Tsitsishvili, Mikheil
2017-07-01
Tight-binding model on a finite chain is studied with four-fold alternated hopping parameters t1,2,3,4. Imposing the open boundary conditions, the corresponding recursion is solved analytically with special attention paid to the occurrence of edge states. Corresponding results are strongly corroborated by numeric calculations. It is shown that in the system there exist four different edge phases if the number of sites is odd, and eight edges phases if the chain comprises even number of sites. Phases are labelled by σ1 ≡ sgn(t1t3 - t2t4), σ2 ≡ sgn(t1t4 - t2t3), and σ3 ≡ sgn(t1t2 - t3t4). It is shown that σ1,2,3 represent gauge invariant topological indices emerging in the corresponding infinite chains.
Photonic analogue of quantum spin Hall effect
He, Cheng; Liu, Xiao-ping; Lu, Ming-Hui; Chen, Yulin; Feng, Liang; Chen, Yan-Feng
2014-01-01
Symmetry-protected photonic topological insulator exhibiting robust pseudo-spin-dependent transportation, analogous to quantum spin Hall (QSH) phases and topological insulators, are of great importance in fundamental physics. Such transportation robustness is protected by time-reversal symmetry. Since electrons (fermion) and photons (boson) obey different statistics rules and associate with different time-reversal operators (i.e., Tf and Tb, respectively), whether photonic counterpart of Kramers degeneracy is topologically protected by bosonic Tb remains unidentified. Here, we construct the degenerate gapless edge states of two photonic pseudo-spins (left/right circular polarizations) in the band gap of a two-dimensional photonic crystal with strong magneto-electric coupling. We further demonstrated that the topological edge states are in fact protected by Tf rather than commonly believed Tb and their pseudo-spin dependent transportation is robust against Tf invariant impurities, discovering for the first tim...
Topological origin of edge states in two-dimensional inversion-symmetric insulators and semimetals
van Miert, Guido; Ortix, Carmine; Morais Smith, Cristiane
2017-03-01
Symmetries play an essential role in identifying and characterizing topological states of matter. Here, we classify topologically two-dimensional (2D) insulators and semimetals with vanishing spin-orbit coupling using time-reversal ({ T }) and inversion ({ I }) symmetry. This allows us to link the presence of edge states in { I } and { T } symmetric 2D insulators, which are topologically trivial according to the Altland-Zirnbauer table, to a {{{Z}}}2 topological invariant. This invariant is directly related to the quantization of the Zak phase. It also predicts the generic presence of edge states in Dirac semimetals, in the absence of chiral symmetry. We then apply our findings to bilayer black phosphorus and show the occurrence of a gate-induced topological phase transition, where the {{{Z}}}2 invariant changes.
Liu, Fei; Wang, Jian; Guo, Hong
2016-10-27
Black phosphorus (BP) tunneling field effect transistors (TFETs) using heterojunctions (Hes) are investigated by atomistic quantum transport simulations. It is observed that edge states have a great impact on the transport characteristics of BP He-TFETs, which results in the potential pinning effect and deterioration of gate control. However, the on-state current can be effectively enhanced by using hydrogen to saturate the edge dangling bonds in BP He-TFETs, by which means edge states are quenched. By extending layered BP with a smaller band gap to the channel region and modulating the BP thickness, the device performance of BP He-TFETs can be further optimized and can fulfil the requirements of the international technology road-map for semiconductors (ITRS) 2013 for low power applications. In 15 nm 3L-1L and 4L-1L BP He-TFETs along the armchair direction the on-state currents are over two times larger than the current required by ITRS 2013 and can reach above 10(3) μA μm(-1) with the fixed off-state current of 10 pA μm(-1). It is also found that the ambipolar effect can be effectively suppressed in BP He-TFETs.
Precise quantization of anomalous Hall effect near zero magnetic field
Bestwick, Andrew; Fox, Eli; Kou, Xufeng; Pan, Lei; Wang, Kang; Goldhaber-Gordon, David
2015-03-01
The quantum anomalous Hall effect (QAHE) has recently been of great interest due to its recent experimental realization in thin films of Cr-doped (Bi, Sb)2Te3, a ferromagnetic 3D topological insulator. The presence of ferromagnetic exchange breaks time-reversal symmetry, opening a gap in the surface states, but gives rise to dissipationless chiral conduction at the edge of a magnetized film. Ideally, this leads to vanishing longitudinal resistance and Hall resistance quantized to h /e2 , where h is Planck's constant and e is the electron charge, but perfect quantization has so far proved elusive. Here, we study the QAHE in the limit of zero applied magnetic field, and measure Hall resistance quantized to within one part per 10,000. Deviation from quantization is due primarily to thermally activated carriers, which can be nearly eliminated through adiabatic demagnetization cooling. This result demonstrates an important step toward dissipationless electron transport in technologically relevant conditions.
Seismic refraction study of the continental edge off the eastern united states
Sheridan, R.E.; Grow, J.A.; Behrendt, John C.; Bayer, K.C.
1979-01-01
Three long, strike-parallel, seismic-refraction profiles were made on the continental shelf edge, slope and upper rise off New Jersey during 1975. The shelf edge line lies along the axis of the East Coast Magnetic Anomaly (ECMA), while the continental rise line lies 80 km seaward of the shelf edge. Below the unconsolidated sediments (1.7-3.6 km/sec), high-velocity sedimentary rocks (4.2-6.2 km/sec) were found at depths of 2.6-8.2 km and are inferred to be cemented carbonates. Although multichannel seismic-reflection profiles and magnetic depth-to-source data predicted the top of oceanic basement at 6-8 km beneath the shelf edge and 10-11 km beneath the rise, no refracted events occurred as first arrivals from either oceanic basement (layer 2, approximately 5.5 km/ sec) or the upper oceanic crust (layer 3A, approximately 6.8 km/sec). Second arrivals from 10.5 km depth beneath the shelf edge are interpreted as events from a 5.9 km/sec refractor within igneous basement. Other refracted events from either layers 2 or 3A could not be resolved within the complex second arrivals. A well-defined crustal layer with a compressional velocity of 7.1-7.2 km/sec, which can be interpreted as oceanic layer 3B, occurred at 15.8 km depth beneath the shelf and 12.9 km beneath the upper rise. A well-reversed mantle velocity of 8.3 km/sec was measured at 18-22 km depth beneath the upper continental rise. Comparison with other deep-crustal profiles along the continental edge of the Atlantic margin off the United States, specifically in the inner magnetically quiet zone, indicates that the compressional wave velocities and layer depths determined on the U.S.G.S. profiles are very similar to those of nearby profiles. This suggests that the layers are continuous and that the interpretation of the oceanic layer 3B under the shelf edge east of New Jersey implies progradation of the shelf outward over the oceanic crust in that area. This agrees with magnetic anomaly evidence which shows the
Federal Laboratory Consortium — Hall C's initial complement of equipment (shown in the figure), includes two general-purpose magnetic spectrometers. The High Momentum Spectrometer (HMS) has a large...
Federal Laboratory Consortium — The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electroand photo-induced reactions at very high luminosity...
Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals.
Mei, Jun; Chen, Zeguo; Wu, Ying
2016-09-02
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the Γ point, we can construct pseudo-time-reversal symmetry as well as pseudo-spin states in this classical system. We develop an effective Hamiltonian for the associated dispersion bands around the Brillouin zone center, and find the inherent link between the band inversion and the topological phase transition. With numerical simulations, we unambiguously demonstrate the unidirectional propagation of acoustic edge states along the interface between a topologically nontrivial acoustic crystal and a trivial one, and the robustness of the edge states against defects with sharp bends. Our work provides a new design paradigm for manipulating and transporting acoustic waves in a topologically protected manner. Technological applications and devices based on our design are expected in various frequency ranges of interest, spanning from infrasound to ultrasound.
Observation of Quantum Spin Hall States in InAs/GaSb Bilayers under Broken Time-Reversal Symmetry
Du, Lingjie; Knez, Ivan; Sullivan, Gerard; Du, Rui-Rui
2014-03-01
Topological insulators (TIs) are a novel class of materials with nontrivial surface or edge states. Time-reversal symmetry (TRS) protected TIs are characterized by the Z2 topological invariant. The fate of the Z2 TIs under broken TRS is a fundamental question in understanding the physics of topological matter but remains largely unanswered. Here we show, a two-dimensional TI is realized in an inverted electron-hole bilayer engineered from InAs/GaSb semiconductors which retains robust helical liquid (HL) edge states under a strong magnetic field. Wide conductance plateaus of 2e2/h value are observed; they persist to 10T applied in-plane field before transitioning to a trivial semimetal. In a perpendicular field up to 35T, broken TRS leads to a spatial separation of the movers in Kramers pair and consequently the intra-pair backscattering phase space vanishes, i.e., the conductance increases from 2e2/h in strong fields manifesting chiral edge transport. We propose a phenomenological phases diagram, where inside the topological gap the HL transfers into a ``canned helical state'' driven by perpendicular fields. Our findings suggest that once established, the HL is remarkably resilient and only undergoes adiabatic deformation under TRS breaking. The work at Rice was supported by DOE, NSF, and Welch Foundation.
Berry curvature and various thermal Hall effects
Zhang, Lifa
2016-10-01
Applying the approach of semiclassical wave packet dynamics, we study various thermal Hall effects where carriers can be electron, phonon, magnon, etc. A general formula of thermal Hall conductivity is obtained to provide an essential physics for various thermal Hall effects, where the Berry phase effect manifests naturally. All the formulas of electron thermal Hall effect, phonon Hall effect, and magnon Hall effect can be directly reproduced from the general formula. It is also found that the Strěda formula can not be directly applied to the thermal Hall effects, where only the edge magnetization contributes to the Hall effects. Furthermore, we obtain a combined formula for anomalous Hall conductivity, thermal Hall electronic conductivity and thermal Hall conductivity for electron systems, where the Berry curvature is weighted by a different function. Finally, we discuss particle magnetization and its relation to angular momentum of the carrier, change of which could induce a mechanical rotation; and possible experiments for thermal Hall effect associated with a mechanical rotation are also proposed.
Time-reversal-breaking induced quantum spin Hall effect
Luo, Wei; Shao, D. X.; Deng, Ming-Xun; Deng, W. Y.; Sheng, L.
2017-01-01
We show that quantum spin Hall (QSH) effect does not occur in a square lattice model due to cancellation of the intrinsic spin-orbit coupling coming from different hopping paths. However, we show that QSH effect can be induced by the presence of staggered magnetic fluxes alternating directions square by square. When the resulting Peierls phase takes a special value , the system has a composite symmetry ΘΡ− with Θ the time-reversal operator and Ρ− transforming the Peierls phase from γ to γ − , which protects the gapless edge states. Once the phase deviates from , the edge states open a gap, as the composite symmetry is broken. We further investigate the effect of a Zeeman field on the QSH state, and find that the edge states remain gapless for . This indicates that the QSH effect is immune to the magnetic perturbation. PMID:28220858
Floquet topological phase transitions and chiral edge states in a kagome lattice
He, Chaocheng; Zhang, Zhiyong, E-mail: zyzhang@nju.edu.cn
2014-09-05
The Floquet topological phases and chiral edge states in a kagome lattice under a circularly-polarized driving field are studied. In the off-resonant case, the system exhibits the similar character as the kagome lattice model with staggered magnetic fluxes, but the total band width is damped in oscillation. In the on-resonant case, the degeneracy splitting at the Γ point does not always result in a gap. The positions of the other two gaps are influenced by the flat band. With the field intensity increased, these two gaps undergo closing-then-reopening processes, accompanied with the changing of the winding numbers. - Highlights: • A kagome lattice under a circularly-polarized driving field is studied. • The band structures and chiral edge states are studied via exact Floquet method. • Various modifications of the Floquet band structure are found. • Floquet topological phase transitions appear in both off- and on-resonant cases.
Theory of edge-state optical absorption in two-dimensional transition metal dichalcogenide flakes
Trushin, Maxim; Kelleher, Edmund J. R.; Hasan, Tawfique
2016-10-01
We develop an analytical model to describe sub-band-gap optical absorption in two-dimensional semiconducting transition metal dichalcogenide (s-TMD) nanoflakes. The material system represents an array of few-layer molybdenum disulfide crystals, randomly orientated in a polymer matrix. We propose that optical absorption involves direct transitions between electronic edge states and bulk bands, depends strongly on the carrier population, and is saturable with sufficient fluence. For excitation energies above half the band gap, the excess energy is absorbed by the edge-state electrons, elevating their effective temperature. Our analytical expressions for the linear and nonlinear absorption could prove useful tools in the design of practical photonic devices based on s-TMDs.
All-Si Valley-Hall Photonic Topological Insulator
Ma, Tzuhsuan
2016-01-01
An all-Si photonic structure emulating the quantum-valley-Hall effect is proposed. We show that it acts as a photonic topological insulator (PTI), and that an interface between two such PTIs can support edge states that are free from scattering. The conservation of the valley degree of freedom enables efficient in- and out-coupling of light between the free space and the photonic structure. The topological protection of the edge waves can be utilized for designing arrays of resonant time- delay photonic cavities that do not suffer from reflections and cross-talk.
Effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons
Ma, R.; Geng, H.; Deng, W. Y.; Chen, M. N.; Sheng, L.; Xing, D. Y.
2016-09-01
We study numerically the effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons (ZPNRs) based on the tight-binding model and the scattering-matrix method. It is interesting to find that the band dispersion, conductance, and thermopower can be modulated by applying a bias voltage and boundary potentials to the two layers of the ZPNRs. Under a certain bias voltage, the twofold-degenerate quasi-flat-edge bands split perfectly. The conductance can be switched off, and the thermopower around zero energy increases. In addition, when only the boundary potential of the top layer or bottom layer is adjusted, only one edge band bends and merges into the bulk band. The first conductance plateau is strongly decreased to e2/h around zero energy. In particular, when the two boundary potentials are adjusted, all the edge bands bend and fully merge into the bulk band, and the bulk energy gap is maximized. More interestingly, a pronounced conductance plateau with G =0 is found around zero energy, which is attributable to the opening of the bulk energy gap between the valence and conduction bands. Meanwhile, the thermopower can be enhanced more than twice compared to that of the perfect ZPNRs. The large magnitude of thermopower is ascribed to the appearance of the bulk energy gap around zero energy. Our results show that the modulated ZPNRs are more reliable in a thermoelectric application.
Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons
Wang, Tzu-Cheng; Hsu, Chia-Hsiu; Huang, Zhi-Quan; Chuang, Feng-Chuan; Su, Wan-Sheng; Guo, Guang-Yu
2016-12-01
The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.7 eV. The last controllability would allow us to develop magnetic on-off nano-switches. Furthermore, ZNRs such as SiI, Ge, GeI and SnH, have fully spin-polarized metallic edge states and thus are promising materials for spintronics. The calculated magnetocrystalline anisotropy energy can be as large as ~9 meV/edge-site, being 2×103 time greater than that of bulk Ni and Fe (~5 μeV/atom), and thus has great potential for high density magneto-electric data-storage devices. Finally, the calculated exchange coupling strength and thus magnetic transition temperature increases as the applied strain goes from ‑5% to 5%. Our findings thus show that these ZNRs would have exciting applications in next-generation electronic and spintronic nano-devices.
Alegria-Barrero, Eduardo; Chan, Pak Hei; Paulo, Manuel;
2012-01-01
MitraClip® therapy is a percutaneous edge-to-edge plication of the mitral leaflets, mimicking the Alfieri surgical technique. MitraClip® implantation is a safe procedure, and survival outcomes in high-surgical-risk patients are superior to historical controls. Despite these results, questions...... remain concerning long-term efficacy and durability. The MitraClip® device has been studied in a safety and feasibility trial in the USA, a randomized pivotal trial against surgical mitral valve repair. Moreover, MitraClip® now has over 2 years of CE-mark approval and a rapidly expanding clinical...... available clinical data and procedural steps are herein reviewed. Because the MitraClip® procedure is still relatively new, continued investigation is required to further better define the patient populations that will benefit most....
MacWilliams, Bryon
2009-01-01
In this article, the author describes Reading Hall No. 1 of the Russian State Library. He was placed in the first reading hall in the mid-1990s, when the Russian government still honored Soviet traditions of granting certain privileges to certain foreigners. In the first hall, the rules are different. He can request as many books as he wants. He…
A topological Dirac insulator in a quantum spin Hall phase
Hsieh, David; Qian, Dong; Wray, Lewis; Xia, Yuqi; San Hor, Yew; Cava, Robert; Hasan, Zahid
2009-03-01
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi1-xSbx single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy, we report the direct observation of massive Dirac particles in the bulk of Bi0.9Sb0.1 and provide a comprehensive mapping of the Dirac insulators gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the topological metal.
Edge excitations in fractional Chern insulators
Luo, Wei-Wei; Chen, Wen-Chao; Wang, Yi-Fei; Gong, Chang-De
2013-10-01
Recent theoretical papers have demonstrated the realization of fractional quantum anomalous Hall states (also called fractional Chern insulators) in topological flat band lattice models without an external magnetic field. Such newly proposed lattice systems play a vital role in obtaining a large class of fractional topological phases. Here we report the exact numerical studies of edge excitations for such systems in a disk geometry loaded with hard-core bosons, which will serve as a more viable experimental probe for such topologically ordered states. We find convincing numerical evidence of a series of edge excitations characterized by the chiral Luttinger liquid theory for the bosonic fractional Chern insulators in both the honeycomb disk Haldane model and the kagome-lattice disk model. We further verify these current-carrying chiral edge states by inserting a central flux to test their compressibility.
Topological phase and edge states dependence of the RKKY interaction in zigzag silicene nanoribbon
Zare, Moslem; Parhizgar, Fariborz; Asgari, Reza
2016-07-01
We propose versatile materials based on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in a zigzag silicene nanoribbon (ZSNR) on half filling in the presence of an out-of-plane electric field. We show that the topological phase transition in the band dispersion of ZSNR can be probed by using the RKKY interaction. We find that, due to the zero-energy edge states of the ZSNR, the exchange coupling is significantly enhanced when the impurities are located on the zigzag edges, and also explore that the strength of the interaction in the topological insulator phase is much greater than that when the system is in the band insulator region. We present a model to investigate the phase of a system of two magnetic impurities located on the edge of the ZSNR and find that three different magnetic phases, spiral, ferromagnetic, and antiferromagnetic, are possible for different values of the electric field. This electrical tunability of the magnetic phases in silicene can be explored by using current experimental techniques and can be of interest in the field of spintronics.
Uncovering edge states and electrical inhomogeneity in MoS2 field-effect transistors.
Wu, Di; Li, Xiao; Luan, Lan; Wu, Xiaoyu; Li, Wei; Yogeesh, Maruthi N; Ghosh, Rudresh; Chu, Zhaodong; Akinwande, Deji; Niu, Qian; Lai, Keji
2016-08-02
The understanding of various types of disorders in atomically thin transition metal dichalcogenides (TMDs), including dangling bonds at the edges, chalcogen deficiencies in the bulk, and charges in the substrate, is of fundamental importance for TMD applications in electronics and photonics. Because of the imperfections, electrons moving on these 2D crystals experience a spatially nonuniform Coulomb environment, whose effect on the charge transport has not been microscopically studied. Here, we report the mesoscopic conductance mapping in monolayer and few-layer MoS2 field-effect transistors by microwave impedance microscopy (MIM). The spatial evolution of the insulator-to-metal transition is clearly resolved. Interestingly, as the transistors are gradually turned on, electrical conduction emerges initially at the edges before appearing in the bulk of MoS2 flakes, which can be explained by our first-principles calculations. The results unambiguously confirm that the contribution of edge states to the channel conductance is significant under the threshold voltage but negligible once the bulk of the TMD device becomes conductive. Strong conductance inhomogeneity, which is associated with the fluctuations of disorder potential in the 2D sheets, is also observed in the MIM images, providing a guideline for future improvement of the device performance.
City and Town Halls; townHalls13
University of Rhode Island Geospatial Extension Program — Locations of city and town halls in Rhode Island. Derived using information originally compiled by the State of Rhode Island (http://www.ri.gov), and built upon...
Evolution of Edge States and Critical Phenomena in the Rashba Superconductor with Magnetization
Yamakage, Ai; Tanaka, Yukio; Nagaosa, Naoto
2012-02-01
We study Andreev bound states (ABS) and the resulting charge transport of a Rashba superconductor (RSC) where two-dimensional semiconductor (2DSM) heterostructures are sandwiched by spin-singlet s-wave superconductor and ferromagnet insulator. ABS becomes a chiral Majorana edge mode in the topological phase (TP). We clarify two types of quantum criticality about the topological change of ABS near a quantum critical point (QCP), whether or not ABS exists at QCP. In the former type, ABS has an energy gap and does not cross at zero energy in the nontopological phase. These complex properties can be detected by tunneling conductance between normal metal-RSC junctions.
Oscillating edge states in one-dimensional MoS2 nanowires
Xu, Hai; Liu, Shuanglong; Ding, Zijing; Tan, Sherman J. R.; Yam, Kah Meng; Bao, Yang; Nai, Chang Tai; Ng, Man-Fai; Lu, Jiong; Zhang, Chun; Loh, Kian Ping
2016-10-01
Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge density wave and quantum correlation effects arising from edge states. The greater flexibility of a molecular scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topology. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact atomic force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topographical modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.
Robust spin-polarized midgap states at step edges of topological crystalline insulators
Sessi, Paolo; Di Sante, Domenico; Szczerbakow, Andrzej; Glott, Florian; Wilfert, Stefan; Schmidt, Henrik; Bathon, Thomas; Dziawa, Piotr; Greiter, Martin; Neupert, Titus; Sangiovanni, Giorgio; Story, Tomasz; Thomale, Ronny; Bode, Matthias
2016-12-01
Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three-dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight-binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This nontrivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature.
Light-induced electron localization in a quantum Hall system
Arikawa, T.; Hyodo, K.; Kadoya, Y.; Tanaka, K.
2017-07-01
An insulating bulk state is a prerequisite for the protection of topological edge states. In quantum Hall systems, the thermal excitation of delocalized electrons is the main route to breaking bulk insulation. In equilibrium, the only way to achieve a clear bulk gap is to use a high-quality crystal under high magnetic field at low temperature. However, bulk conduction could also be suppressed in a system driven out of equilibrium such that localized states in the Landau levels are selectively occupied. Here we report a transient suppression of bulk conduction induced by terahertz wave excitation between the Landau levels in a GaAs quantum Hall system. Strikingly, the Hall resistivity almost reaches the quantized value at a temperature where the exact quantization is normally disrupted by thermal fluctuations. The electron localization is realized by the long-range potential fluctuations, which are a unique and inherent feature of quantum Hall systems. Our results demonstrate a new means of effecting dynamical control of topology by manipulating bulk conduction using light.
Dorothea Sommer
2010-02-01
Full Text Available This paper describes a project carried out by the German National Library, the University and State Library Sachsen-Anhalt in Halle and Semantics GmbH Aachen to establish routines of persistent identification for individual pages of web publications in order to enable and facilitate reliable and long-term valid citation practices for the academic community. The project originated in a pilot project to digitise approximately 10,000 German imprints from the seventeenth century comprising altogether about 600,000 pages, which had to be completed within two years. The material of the ‘Ponickau Collection’ had been catalogued in the German national bibliography of seventeenth-century imprints (VD 17, which was enriched and turned into a virtual library by adding the digitised texts. This article investigates the means of presentation and indexing of digitised imprints in order to ensure their usability. It also sketches the workflow among the various partners involved in the process. The article highlights the application of Visual Library, which contains various tools for automated creation of metadata, the implementation of persistent identifiers (URN and the automated enrichment of catalogue entries by the regional cataloguing cooperative Gemeinsamer Bibliotheksverbund (GBV. Special emphasis is given to questions of quality management; the quality is guaranteed by a combination of automated tools and intellectual control at various stages of the digitisation process.
Edge states in the climate system: exploring global instabilities and critical transitions
Lucarini, Valerio; Bódai, Tamás
2017-07-01
Multistability is a ubiquitous feature in systems of geophysical relevance and provides key challenges for our ability to predict a system’s response to perturbations. Near critical transitions small causes can lead to large effects and—for all practical purposes—irreversible changes in the properties of the system. As is well known, the Earth climate is multistable: present astronomical and astrophysical conditions support two stable regimes, the warm climate we live in, and a snowball climate characterized by global glaciation. We first provide an overview of methods and ideas relevant for studying the climate response to forcings and focus on the properties of critical transitions in the context of both stochastic and deterministic dynamics, and assess strengths and weaknesses of simplified approaches to the problem. Following an idea developed by Eckhardt and collaborators for the investigation of multistable turbulent fluid dynamical systems, we study the global instability giving rise to the snowball/warm multistability in the climate system by identifying the climatic edge state, a saddle embedded in the boundary between the two basins of attraction of the stable climates. The edge state attracts initial conditions belonging to such a boundary and, while being defined by the deterministic dynamics, is the gate facilitating noise-induced transitions between competing attractors. We use a simplified yet Earth-like intermediate complexity climate model constructed by coupling a primitive equations model of the atmosphere with a simple diffusive ocean. We refer to the climatic edge states as Melancholia states and provide an extensive analysis of their features. We study their dynamics, their symmetry properties, and we follow a complex set of bifurcations. We find situations where the Melancholia state has chaotic dynamics. In these cases, we have that the basin boundary between the two basins of attraction is a strange geometric set with a nearly zero
Giant anisotropic magnetoresistance in a quantum anomalous Hall insulator
Kandala, Abhinav; Richardella, Anthony; Kempinger, Susan; Liu, Chao-Xing; Samarth, Nitin
2015-07-01
When a three-dimensional ferromagnetic topological insulator thin film is magnetized out-of-plane, conduction ideally occurs through dissipationless, one-dimensional (1D) chiral states that are characterized by a quantized, zero-field Hall conductance. The recent realization of this phenomenon, the quantum anomalous Hall effect, provides a conceptually new platform for studies of 1D transport, distinct from the traditionally studied quantum Hall effects that arise from Landau level formation. An important question arises in this context: how do these 1D edge states evolve as the magnetization is changed from out-of-plane to in-plane? We examine this question by studying the field-tilt-driven crossover from predominantly edge-state transport to diffusive transport in Crx(Bi,Sb)2-xTe3 thin films. This crossover manifests itself in a giant, electrically tunable anisotropic magnetoresistance that we explain by employing a Landauer-Büttiker formalism. Our methodology provides a powerful means of quantifying dissipative effects in temperature and chemical potential regimes far from perfect quantization.
Prati, Enrico
2015-07-01
Long living coherent quantum states have been observed in biological systems up to room temperature. Light harvesting in chromophoresis realized by excitonic systems living at the edge of quantum chaos, where energy level distribution becomes semi-Poissonian. On the other hand, artificial materials suffer the loss of coherence of quantum states in quantum information processing, but semiconductor materials are known to exhibit quantum chaotic conditions, so the exploitation of similar conditions are to be considered. The advancements of nanofabrication, together with the control of implantation of individual atoms at nanometric precision, may open the experimental study of such special regime at the edge of the phase transitions for the electronic systems obtained by implanting impurity atoms in a silicon transistor. Here I review the recent advancements made in the field of theoretical description of the light harvesting in biological system in its connection with phase transitions at the few atoms scale and how it would be possible to achieve transition point to quantum chaotic regime. Such mechanism may thus preserve quantum coherent states at room temperature in solid state devices, to be exploited for quantum information processing as well as dissipation-free quantum electronics.
United State Collaboration working in the Atlas hall experiment (B180).
Maximilien Brice
2006-01-01
It's a small world; at least you might think so after a visit to Building 180. Inside, about 30 engineers and physicists weld, measure and hammer away. They hail from Pakistan, Israel, Japan, China, Russia and the United States and they work toward one common goal: the completion of the ATLAS muon chamber endcaps
Tunable spin-orbit coupling and symmetry-protected edge states in graphene/WS2
Yang, Bowen; Tu, Min-Feng; Kim, Jeongwoo; Wu, Yong; Wang, Hui; Alicea, Jason; Wu, Ruqian; Bockrath, Marc; Shi, Jing
2016-09-01
We demonstrate clear weak anti-localization (WAL) effect arising from induced Rashba spin-orbit coupling (SOC) in WS2-covered single-layer and bilayer graphene devices. Contrary to the uncovered region of a shared single-layer graphene flake, WAL in WS2-covered graphene occurs over a wide range of carrier densities on both electron and hole sides. At high carrier densities, we estimate the Rashba SOC relaxation rate to be ˜ 0.2 {{ps}}-1 and show that it can be tuned by transverse electric fields. In addition to the Rashba SOC, we also predict the existence of a‘valley-Zeeman’ SOC from first-principles calculations. The interplay between these two SOC’s can open a non-topological but interesting gap in graphene; in particular, zigzag boundaries host four sub-gap edge states protected by time-reversal and crystalline symmetries. The graphene/WS2 system provides a possible platform for these novel edge states.
Jug, Giancarlo; Ziegler, Klaus
1997-10-01
We present a calculation for the second moment of the local density of states in a model of a two-dimensional quantum dot array near the quantum Hall transition. The quantum dot array model is a realistic adaptation of the lattice model for the quantum Hall transition in the two-dimensional electron gas in an external magnetic field proposed by Ludwig, Fisher, Shankar, and Grinstein. We make use of a Dirac fermion representation for the Green's functions in the presence of fluctuations for the quantum dot energy levels. A saddle-point approximation yields nonperturbative results for the first and second moments of the local density of states, showing interesting fluctuation behavior near the quantum Hall transition. To our knowledge we discuss here one of the first analytic characterizations of chaotic behavior for a two-dimensional mesoscopic structure. The connection with possible experimental investigations of the local density of states in the quantum dot array structures (by means of NMR Knight-shift or single-electron-tunneling techniques) and our work is also established.
Engineering a Robust Quantum Spin Hall State in Graphene via Adatom Deposition
Conan Weeks
2011-10-01
Full Text Available The 2007 discovery of quantized conductance in HgTe quantum wells delivered the field of topological insulators (TIs its first experimental confirmation. While many three-dimensional TIs have since been identified, HgTe remains the only known two-dimensional system in this class. Difficulty fabricating HgTe quantum wells has, moreover, hampered their widespread use. With the goal of breaking this logjam, we provide a blueprint for stabilizing a robust TI state in a more readily available two-dimensional material—graphene. Using symmetry arguments, density functional theory, and tight-binding simulations, we predict that graphene endowed with certain heavy adatoms realizes a TI with substantial band gap. For indium and thallium, our most promising adatom candidates, a modest 6% coverage produces an estimated gap near 80 K and 240 K, respectively, which should be detectable in transport or spectroscopic measurements. Engineering such a robust topological phase in graphene could pave the way for a new generation of devices for spintronics, ultra-low-dissipation electronics, and quantum information processing.
Kim, Gye Hyun; Thompson, Carl V., E-mail: cthomp@mit.edu [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239 (United States); Ma, Wen [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239 (United States); Yildiz, Bilge [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239 (United States); Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239 (United States)
2016-08-21
During solid-state dewetting of thin single crystal films, film edges retract at a rate that is strongly dependent on their crystallographic orientations. Edges with kinetically stable in-plane orientations remain straight as they retract, while those with other in-plane orientations develop in-plane facets as they retract. Kinetically stable edges have retraction rates that are lower than edges with other orientations and thus determine the shape of the natural holes that form during solid-state dewetting. In this paper, measurements of the retraction rates of kinetically stable edges for single crystal (110) and (100) Ni films on MgO are presented. Relative retraction rates of kinetically stable edges with different crystallographic orientations are observed to change under different annealing conditions, and this accordingly changes the initial shapes of growing holes. The surfaces of (110) and (100) films were also characterized using low energy electron diffraction, and different surface reconstructions were observed under different ambient conditions. The observed surface structures were found to correlate with the observed changes in the relative retraction rates of the kinetically stable edges.
The effect of Ni and Fe doping on Hall anomaly in vortex state of doped YBCO samples
M Nazarzadeh
2010-09-01
Full Text Available We have investigated hall effect on YBa2Cu3-xMxO7-δ (M=Ni, Fe bulk samples, with dopant amount 0 ≤ x ≤ 0.045 for Ni and 0 ≤ x ≤ 0.03 for Fe, with magnetic field (H=2.52, 4.61, 6.27 kOe perpendicular to sample’s surface with constant current 100 mA. Our study shows that as both dopants increases, TC decreases and it decreases faster by Ni . In these ranges of dopant and magnetic field the Hall sign reversal has been observed in all samples once and also ∆max has occurred in lower temperatures, its magnitude increases by Ni, and in Fe doped samples except in sample with dopant amount x=0.03, which almost decreases, that it can show effect of magnetic doping on hall effect.
Mehraeen, Shafigh
2013-05-01
We compare the merits of a hopping model and a mobility edge model in the description of the effect of charge-carrier concentration on the electrical conductivity, carrier mobility, and Fermi energy of organic semiconductors. We consider the case of a composite electronic density of states (DOS) that consists of a superposition of a Gaussian DOS and an exponential DOS. Using kinetic Monte Carlo simulations, we apply the two models in order to interpret the recent experimental data reported for n-doped C60 films. While both models are capable of reproducing the experimental data very well and yield qualitatively similar characteristic parameters for the density of states, some discrepancies are found at the quantitative level. © 2013 American Physical Society.
Lin, S.; Zhang, G.; Li, C.; Song, Z.
2016-08-01
We study the tight-binding model for a graphene tube with perimeter N threaded by a magnetic field. We show exactly that this model has different nontrivial topological phases as the flux changes. The winding number, as an indicator of topological quantum phase transition (QPT) fixes at N/3 if N/3 equals to its integer part [N/3], otherwise it jumps between [N/3] and [N/3] + 1 periodically as the flux varies a flux quantum. For an open tube with zigzag boundary condition, exact edge states are obtained. There exist two perfect midgap edge states, in which the particle is completely located at the boundary, even for a tube with finite length. The threading flux can be employed to control the quantum states: transferring the perfect edge state from one end to the other, or generating maximal entanglement between them.
Fukuyama, H. [Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)
2006-07-03
Interband effects of magnetic field on orbital susceptibility and Hall conductivity have been theoretically studied with special reference to single crystal bismuth (Bi), whose energy bands near the band-edges are similar to those of Dirac electrons. It has long been known that orbital susceptibilty in Bi has a maximum when the Fermi energy is located in the band-gap and then the density of states at the Fermi energy is vanishing. This implies that the magnetic field induces persistent current even in the insulating state. On the other hand, weak-field Hall conductivity, which reflects transport current, has turned out to be vanishing if the Fermi energy is in the band-gap. Interesting possibility has been pointed out of the inter-band contributions to the Hall conductivity once the Fermi energy lies slightly in the energy band. (Abstract Copyright [2006], Wiley Periodicals, Inc.)
Universal transport signatures of topological superconductivity in quantum spin Hall architectures
Lee, Shu-Ping; Aasen, David; Karzig, Torsten; Alicea, Jason
2015-03-01
Interfacing s-wave superconductors with quantum spin Hall systems provides a promising route to ``engineered'' topological superconductivity. Given exciting recent progress on the fabrication side, identifying experiments that definitively expose the topological superconducting phase (and clearly distinguish it from a trivial state) raises an increasingly important problem. With this goal in mind we use renormalization group methods to extract universal transport characteristics of superconductor/quantum spin Hall heterostructures where the native edge states serve as a lead. Interestingly, arbitrarily weak interactions induce qualitative changes in the behavior relative to the free-fermion limit, leading to a sharp dichotomy in conductance for the trivial (narrow superconductor) and topological (wide superconductor) cases. Furthermore, we find that strong interactions can in principle induce power-law-localized ``parafermion'' excitations at a superconductor/quantum spin Hall junction. NSF Grant DMR-1341822. (2) Institute for Quantum Information and Matter, an NSF physics frontier center with support from the Moore Foundation.
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Emergent particle-hole symmetry in spinful bosonic quantum Hall systems
Geraedts, S. D.; Repellin, C.; Wang, Chong; Mong, Roger S. K.; Senthil, T.; Regnault, N.
2017-08-01
When a fermionic quantum Hall system is projected into the lowest Landau level, there is an exact particle-hole symmetry between filling fractions ν and 1 -ν . We investigate whether a similar symmetry can emerge in bosonic quantum Hall states, where it would connect states at filling fractions ν and 2 -ν . We begin by showing that the particle-hole conjugate to a composite fermion "Jain state" is another Jain state, obtained by reverse flux attachment. We show how information such as the shift and the edge theory can be obtained for states which are particle-hole conjugates. Using the techniques of exact diagonalization and infinite density matrix renormalization group, we study a system of two-component (i.e., spinful) bosons, interacting via a δ -function potential. We first obtain real-space entanglement spectra for the bosonic integer quantum Hall effect at ν =2 , which plays the role of a filled Landau level for the bosonic system. We then show that at ν =4 /3 the system is described by a Jain state which is the particle-hole conjugate of the Halperin (221) state at ν =2 /3 . We show a similar relationship between nonsinglet states at ν =1 /2 and 3 /2 . We also study the case of ν =1 , providing unambiguous evidence that the ground state is a composite Fermi liquid. Taken together our results demonstrate that there is indeed an emergent particle-hole symmetry in bosonic quantum Hall systems.
Spin Hall effect induced spin transfer through an insulator
Chen, Wei; Sigrist, Manfred; Manske, Dirk
2016-09-01
When charge current passes through a normal metal that exhibits the spin Hall effect, spin accumulates at the edge of the sample in the transverse direction. We predict that this spin accumulation, or spin voltage, enables quantum tunneling of spin through an insulator or vacuum to reach a ferromagnet without transferring charge. In a normal metal/insulator/ferromagnetic insulator trilayer (such as Pt/oxide/YIG), the quantum tunneling explains the spin-transfer torque and spin pumping that exponentially decay with the thickness of the insulator. In a normal metal/insulator/ferromagnetic metal trilayer (such as Pt/oxide/Co), the spin transfer in general does not decay monotonically with the thickness of the insulator. Combining with the spin Hall magnetoresistance, this tunneling mechanism points to the possibility of a tunneling spectroscopy that can probe the magnon density of states of a ferromagnetic insulator in an all-electrical and noninvasive manner.
Quantum Hall effect in epitaxial graphene with permanent magnets
Parmentier, F. D.; Cazimajou, T.; Sekine, Y.; Hibino, H.; Irie, H.; Glattli, D. C.; Kumada, N.; Roulleau, P.
2016-12-01
We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.
Peterson, Michael
2009-03-01
The fractional quantum Hall effect (FQHE) in the second orbital Landau level at even-denominator filling factor 5/2 remains mysterious and is currently motivating many scientists not only because of its connection to a possible implementation of a fault tolerant topological quantum computer (Das Sarma et al., PRL 94, 166802(2005)). In this work, we theoretically consider the effect of the quasi-two-dimensional nature of the experimental fractional quantum Hall systems on a number of FQHE states in the lowest three orbital Landau levels. Our primary result is that the finite width of the quasi-two-dimensional systems produce a physical environment sufficient to stabilize the Moore-Read Pfaffian state thought to describe the FQHE at filling factor 5/2. This conclusion is based on exact calculations performed in the spherical and torus geometries, studying wave function overlap and ground state degeneracy. Furthermore, our results open the possibility of creating optimal experimental systems where the 5/2 FQHE state would more likely be described by the Moore-Read Pfaffian. We also discuss the role of the three-body interaction Hamiltonian that produces the Moore-Read Pfaffian as an exact ground state and particle-hole symmetry in the FQHE at 5/2. We acknowledge support from Microsoft Project Q. Work done in collaboration with Sankar Das Sarma, Thierry Jolicoeur, and Kwon Park.
A short course on topological insulators band structure and edge states in one and two dimensions
Asbóth, János K; Pályi, András
2016-01-01
This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dimensional case (the Su-Schrieffer-Heeger model for polyacetylene) to two-dimensional time-reversal invariant topological insulators (the Bernevig-Hughes-Zhang model for HgTe). In each case the discussion of simple toy models is followed by the formulation of the general arguments regarding topological insulators. The only prerequisite for the reader is a working knowledge in quantum mechanics, the relevant solid state physics background is provided as part of this self-contained text, which is complemented by end-of-chapter problems.
Ting, Xie [College of Mathematics and Statistics, Chongqing University, Chongqing 401331 (China); School of Mathematics and Statistic, Chongqing University of Technology, Chongqing 400054 (China); Rui, Wang, E-mail: rcwang@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100190 (China); Shaofeng, Wang [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); Xiaozhi, Wu, E-mail: xiaozhiwu@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China)
2016-10-15
Highlights: • The properties of SW defects in silicene and ZSNRs are obtained. • The SW defects at the edge of ZSNRs induce a sizable gap. • The charge transfer of edge states is resulted from SW defects in ZSNRS. - Abstract: Stone–Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.
Accretion through the inner edges of protoplanetary disks by a giant solid state pump
Kelling, Thorben
2013-01-01
At the inner edge of a protoplanetary disk solids are illuminated by stellar light. This illumination heats the solids and creates temperature gradients along their surfaces. Interactions with ambient gas molecules lead to a radial net gas flow. Every illuminated solid particle within the edge is an individual small gas pump transporting gas inward. In total the inner edge can provide local mass flow rates as high as $\\dot{M} = 10^{-5} M_{\\odot}$ yr$^{-1}$.
$W_{\\infty}$ algebra in the integer quantum Hall effects
Azuma, Hiroo
1994-01-01
We investigate the $W_{\\infty}$ algebra in the integer quantum Hall effects. Defining the simplest vacuum, the Dirac sea, we evaluate the central extension for this algebra. A new algebra which contains the central extension is called the $W_{1+\\infty}$ algebra. We show that this $W_{1+\\infty}$ algebra is an origin of the Kac-Moody algebra which determines the behavior of edge states of the system. We discuss the relation between the $W_{1+\\infty}$ algebra and the incompressibility of the int...
Unconventional spin texture in a noncentrosymmetric quantum spin Hall insulator
Mera Acosta, C.; Babilonia, O.; Abdalla, L.; Fazzio, A.
2016-07-01
We propose that the simultaneous presence of both Rashba and band inversion can lead to a Rashba-like spin splitting formed by two bands with the same in-plane helical spin texture. Because of this unconventional spin texture, the backscattering is forbidden in edge and bulk conductivity channels. We propose a noncentrosymmetric honeycomb-lattice quantum spin Hall (QSH) insulator family formed by the IV, V, and VII elements with this property. The system formed by Bi, Pb, and I atoms is mechanically stable and has both a large Rashba spin splitting of 60 meV and a large nontrivial band gap of 0.14 eV. Since the edge and the bulk states are protected by the time-reversal (TR) symmetry, contrary to what happens in most doped QSH insulators, the bulk states do not contribute to the backscattering in the electronic transport, allowing the construction of a spintronic device with less energy loss.
Experiments on Quantum Hall Topological Phases in Ultra Low Temperatures
Du, Rui-Rui [Rice Univ., Houston, TX (United States). Dept. of Physics and Astronomy
2015-02-14
This project is to cool electrons in semiconductors to extremely low temperatures and to study new states of matter formed by low-dimensional electrons (or holes). At such low temperatures (and with an intense magnetic field), electronic behavior differs completely from ordinary ones observed at room temperatures or regular low temperature. Studies of electrons at such low temperatures would open the door for fundamental discoveries in condensed matter physics. Present studies have been focus on topological phases in the fractional quantum Hall effect in GaAs/AlGaAs semiconductor heterostructures, and the newly discovered (by this group) quantum spin Hall effect in InAs/GaSb materials. This project consists of the following components: 1) Development of efficient sample cooling techniques and electron thermometry: Our goal is to reach 1 mK electron temperature and reasonable determination of electron temperature; 2) Experiments at ultra-low temperatures: Our goal is to understand the energy scale of competing quantum phases, by measuring the temperature-dependence of transport features. Focus will be placed on such issues as the energy gap of the 5/2 state, and those of 12/5 (and possible 13/5); resistive signature of instability near 1/2 at ultra-low temperatures; 3) Measurement of the 5/2 gaps in the limit of small or large Zeeman energies: Our goal is to gain physics insight of 5/2 state at limiting experimental parameters, especially those properties concerning the spin polarization; 4) Experiments on tuning the electron-electron interaction in a screened quantum Hall system: Our goal is to gain understanding of the formation of paired fractional quantum Hall state as the interaction pseudo-potential is being modified by a nearby screening electron layer; 5) Experiments on the quantized helical edge states under a strong magnetic field and ultralow temperatures: our goal is to investigate both the bulk and edge states in a quantum spin Hall insulator under time
Ting, Xie; Rui, Wang; Shaofeng, Wang; Xiaozhi, Wu
2016-10-01
Stone-Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.
Quantum spin Hall effect in twisted bilayer graphene
Finocchiaro, F.; Guinea, F.; San-Jose, P.
2017-06-01
Motivated by a recent experiment (Sanchez-Yamagishi et al 2016 Nat. Nanotechnol. 214) reporting evidence of helical spin-polarized edge states in layer-biased twisted bilayer graphene under a magnetic flux, we study the possibility of stabilising a quantum spin Hall (QSH) phase in such a system, without Zeeman or spin-orbit couplings, and with a QSH gap induced instead by electronic interactions. We analyse how magnetic flux, electric field, interlayer rotation angle, and interactions (treated at a mean field level) combine to produce a pseudo-QSH with broken time-reversal symmetry, and spin-polarized helical edge states. The effect is a consequence of a robust interaction-induced ferrimagnetic ordering of the quantum Hall ground state under an interlayer bias, provided the two rotated layers are effectively decoupled at low energies. We discuss in detail the electronic structure and the constraints on system parameters, such as the angle, interactions and magnetic flux, required to reach the pseudo-QSH phase. We find, in particular, that purely local electronic interactions are not sufficient to account for the experimental observations, which demand at least nearest-neighbour interactions to be included.
Cutting edge technology to enhance nursing classroom instruction at Coppin State University.
Black, Crystal Day; Watties-Daniels, A Denyce
2006-01-01
Educational technologies have changed the paradigm of the teacher-student relationship in nursing education. Nursing students expect to use and to learn from cutting edge technology during their academic careers. Varied technology, from specified software programs (Tegrity and Blackboard) to the use of the Internet as a research medium, can enhance student learning. The authors provide an overview of current cutting edge technologies in nursing classroom instruction and its impact on future nursing practice.
Nonlocal Polarization Feedback in a Fractional Quantum Hall Ferromagnet.
Hennel, Szymon; Braem, Beat A; Baer, Stephan; Tiemann, Lars; Sohi, Pirouz; Wehrli, Dominik; Hofmann, Andrea; Reichl, Christian; Wegscheider, Werner; Rössler, Clemens; Ihn, Thomas; Ensslin, Klaus; Rudner, Mark S; Rosenow, Bernd
2016-04-01
In a quantum Hall ferromagnet, the spin polarization of the two-dimensional electron system can be dynamically transferred to nuclear spins in its vicinity through the hyperfine interaction. The resulting nuclear field typically acts back locally, modifying the local electronic Zeeman energy. Here we report a nonlocal effect arising from the interplay between nuclear polarization and the spatial structure of electronic domains in a ν=2/3 fractional quantum Hall state. In our experiments, we use a quantum point contact to locally control and probe the domain structure of different spin configurations emerging at the spin phase transition. Feedback between nuclear and electronic degrees of freedom gives rise to memristive behavior, where electronic transport through the quantum point contact depends on the history of current flow. We propose a model for this effect which suggests a novel route to studying edge states in fractional quantum Hall systems and may account for so-far unexplained oscillatory electronic-transport features observed in previous studies.
The quantum anomalous Hall effect in kagomé lattices.
Zhang, Zhi-Yong
2011-09-14
The quantum anomalous Hall (QAH) effect in kagomé lattices is investigated in the presence of both Rashba spin-orbit coupling and an exchange field. In addition to the gap at the Dirac points as found in graphene, a new topological energy gap is opened at the Γ point. With the Fermi energy lying in the first gap, the Chern number = 2 as in graphene, whereas with it lying in the second one, = 1. The distribution of Berry curvature is obtained to reveal the nontrivial topological properties in momentum space. For stripes with 'armchair' and 'zigzag' edges, the topological characteristics of gapless edge states on the genus g = 2 Riemann surface are studied. The obtained nonzero winding numbers also demonstrate the QAH effe
The quantum anomalous Hall effect in kagome lattices
Zhang Zhiyong, E-mail: zyzhang@nju.edu.cn [Department of Physics, Nanjing University, Nanjing 210093 (China)
2011-09-14
The quantum anomalous Hall (QAH) effect in kagome lattices is investigated in the presence of both Rashba spin-orbit coupling and an exchange field. In addition to the gap at the Dirac points as found in graphene, a new topological energy gap is opened at the {Gamma} point. With the Fermi energy lying in the first gap, the Chern number c = 2 as in graphene, whereas with it lying in the second one, c = 1. The distribution of Berry curvature is obtained to reveal the nontrivial topological properties in momentum space. For stripes with 'armchair' and 'zigzag' edges, the topological characteristics of gapless edge states on the genus g = 2 Riemann surface are studied. The obtained nonzero winding numbers also demonstrate the QAH effect. (paper)
Munoz, M.; Vidal, O.; Marcaillou, C.; Pascarelli, S.; Mathon, O.; Farges, F.
2012-04-01
Iron oxidation state in minerals is often a crucial indicator for the understanding of mineralogical reactions related to hydrothermalism, or various natural processes. We investigated here the influence of the linear polarization of the synchrotron X-ray beam on the determination of the iron oxidation state in phyllosilicates. Fe K-edge XANES spectra and pre-peaks of biotite (Bt), chlorite (Chl), talc (Tlc) and antigorite (Atg) crystals have been recorded at different crystal orientations. As a function of the crystal orientation, the experimental results show, 1) important changes both for XANES and pre-peaks, 2) typical changes of spectral signatures for all mineral species, 3) uncorrelated changes between XANES and pre-peaks, 4) important changes of the pre-peak energies, but no significant change of the integrated areas. Ab initio XANES calculations, performed for 6 orientations of the Bt structure are consistent with the experimental measurements. The energy position of the pre-peak centroids changes with crystal orientation by 0.4 eV for Bt and Tlc crystals, and by 0.2 eV for Chl and Atg, which correspond to XFe(apparent)3+ variations (2δ) of 0.22 and 0.15, respectively. Measurements on powdered crystals show that - (2/3)2δ
Frame and edge seal technology: A state of the art survey
Thyholt, Marit; Andresen, Inger; Hugdal, Berit; Aschehoug, Oeyvind
1994-04-01
In windows, the glazing is traditionally mounted in an operable or fixed frame, made of wood, metal (steel or aluminum), or PVC. The glazing component in solar collectors and solar walls is also typically mounted in a frame. The purpose of the frame is to protect the vulnerable edge of the glazing and give structural stability, which is especially important in operable windows. Sealed multipane glazings are almost exclusively fabricated with a metal (aluminum or galvanized steel) spacer bar along the edges. New advanced glazings will require new types of frame and edge seal products. As the insulation properties of the glazing itself reach a performance close to that of well-insulated opaque walls, the thermal bridging caused by the spacer bars and the frames will be unacceptable, even for wooden windows. The new glazings will also integrate other functions, which again will influence the design of the frames. There are already quite a few new technological developments in this field. New materials and products for the edge seal and the frame are being developed, and computer calculations gradually take over the manual analysis and laboratory testing of new products. The objective of this IEA Task 18 Case Study is to investigate the influence of the frame and glazing edge seal on the total U-value of a glazing system, to develop improved test and calculation methods, and to design, construct, and test low thermal loss frames for use in advanced glazing applications.
Laughlin's argument for the quantized thermal Hall effect
Nakai, Ryota; Nomura, Kentaro
2016-01-01
We extend Laughlin's magnetic-flux-threading argument to the quantized thermal Hall effect. A proper analogue of Laughlin's adiabatic magnetic-flux threading process for the case of the thermal Hall effect is given in terms of an external gravitational field. From the perspective of the edge theories of quantum Hall systems, the quantized thermal Hall effect is closely tied to the breakdown of large diffeomorphism invariance, that is, a global gravitational anomaly. In addition, we also give an argument from the bulk perspective in which a free energy, decomposed into its Fourier modes, is adiabatically transferred under an adiabatic process involving external gravitational perturbations.
Electronic transport in two-dimensional systems in the quantum hall regime
Tarquini, Vinicio
The integer and the fractional quantum Hall effects are essential to the exploration of quantum matters characterized by topological phases. A quantum Hall system hosts one-dimensional (1D) chiral edge channels that manifest zero magnetoresistance, dissipationless due to the broken time reversal symmetry, and quantized Hall resistance vhe2 with v being the topological invariant (or Chern number). The 1-1 correspondence between the conducting gapless edge channels to the gapped incompressible bulk states is a defining character of a topological insulator (TI). Understanding this correspondence in real systems, especially the origin of its robustness (in terms of the limit of breakdown), is important both fundamentally and practically (i.e. in relation to spintronics). However, the breakdown mechanism, especially in light of the edge-bulk correlation, is still an open question. We adopt GaAs two-dimensional (2D) high-mobility hole systems confined in a 20 nm wide (100)-GaAs quantum wells and have perform transport measurement for a range of charge densities between 4 and 5 x 1010 cm -2 with a carrier mobility of 2 - 4 x 106 cm 2/V·s down to millikelvin temperatures. Systematic characterization of the 2D systems through Shubnikov-de Haas (SdH) oscillations yields an effective mass between 0.30 and 0.50me, in good agreement with the cyclotron resonance results. We then modify a regular Hall bar system into a unique anti-Hall bar geometry that provides an extra set of independent chiral edge channels without altering the topological invariant. We perform systematic measurement of quantum oscillations via chiral edges while simultaneously probing the bulk dynamics, through measuring across independent edges, in respond to the edge excitations. The edge-bulk correspondence reveals a non-equilibrium dynamical development of the incompressible bulk states that leads to a novel asymmetrical 1-0 Hall potential distribution. Moreover, probing the breakdown via inner and outer
Destruction of the Fractional Quantum Hall Effect by Disorder
Laughlin, R. B.
1985-07-01
It is suggested that Hall steps in the fractional quantum Hall effect are physically similar to those in the ordinary quantum Hall effect. This proposition leads to a simple scaling diagram containing a new type of fixed point, which is identified with the destruction of the fractional states by disorder. 15 refs., 3 figs.
Quantum Hall Effect in Higher Dimensions
Karabali, Dimitra; Karabali, Dimitra
2002-01-01
Following recent work on the quantum Hall effect on $S^4$, we solve the Landau problem on the complex projective spaces ${\\bf C}P^k$ and discuss quantum Hall states for such spaces. Unlike the case of $S^4$, a finite spatial density can be obtained with a finite number of internal states for each particle. We treat the case of ${\\bf C}P^2$ in some detail considering both Abelian and nonabelian background fields. The wavefunctions are obtained and incompressibility of the Hall states is shown. The case of ${\\bf C}P^3$ is related to the case of $S^4$.
Golnak, Ronny; Xiao, Jie; Atak, Kaan; Stevens, Joanna S; Gainar, Adrian; Schroeder, Sven L M; Aziz, Emad F
2015-11-21
X-ray absorption/emission spectroscopy (XAS/XES) at the N K-edge of iron protoporphyrin IX chloride (FePPIX-Cl, or hemin) has been carried out for dissolved monomers in DMSO, dimers in water and for the solid state. This sequence of samples permits identification of characteristic spectral features associated with the hemin intermolecular bonding. These characteristic features are further analyzed and understood at the molecular orbital (MO) level based on the DFT calculations.
Gerhardts, Rolf R.
2017-01-01
Recent low-temperature scanning-force-microscopy experiments on narrow Hall bars, under the conditions of the integer quantum Hall effect (IQHE) and its breakdown, have revealed an interesting position dependence of the Hall potential, which changes drastically with the applied magnetic field and the strength of the imposed current through the sample. The present paper shows, that inclusion of Joule heating into an existing self-consistent theory of screening and magneto-transport, which assumes translation invariant Hall bars with a homogeneous background charge due to doping, can explain the experimental results on the breakdown of the IQHE in the so called edge-dominated regime.
Topological edge states in a high-temperature superconductor FeSe/SrTiO3(001) film
Wang, Z. F.; Zhang, Huimin; Liu, Defa; Liu, Chong; Tang, Chenjia; Song, Canli; Zhong, Yong; Peng, Junping; Li, Fangsen; Nie, Caina; Wang, Lili; Zhou, X. J.; Ma, Xucun; Xue, Q. K.; Liu, Feng
2016-09-01
Superconducting and topological states are two most intriguing quantum phenomena in solid materials. The entanglement of these two states, the topological superconducting state, will give rise to even more exotic quantum phenomena. While many materials are found to be either a superconductor or a topological insulator, it is very rare that both states exist in one material. Here, we demonstrate by first-principles theory as well as scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy experiments that the recently discovered `two-dimensional (2D) superconductor' of single-layer FeSe also exhibits 1D topological edge states within an energy gap of ~40 meV at the M point below the Fermi level. It is the first 2D material that supports both superconducting and topological states, offering an exciting opportunity to study 2D topological superconductors through the proximity effect.
Topological edge states in a high-temperature superconductor FeSe/SrTiO3(001) film.
Wang, Z F; Zhang, Huimin; Liu, Defa; Liu, Chong; Tang, Chenjia; Song, Canli; Zhong, Yong; Peng, Junping; Li, Fangsen; Nie, Caina; Wang, Lili; Zhou, X J; Ma, Xucun; Xue, Q K; Liu, Feng
2016-09-01
Superconducting and topological states are two most intriguing quantum phenomena in solid materials. The entanglement of these two states, the topological superconducting state, will give rise to even more exotic quantum phenomena. While many materials are found to be either a superconductor or a topological insulator, it is very rare that both states exist in one material. Here, we demonstrate by first-principles theory as well as scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy experiments that the recently discovered 'two-dimensional (2D) superconductor' of single-layer FeSe also exhibits 1D topological edge states within an energy gap of ∼40 meV at the M point below the Fermi level. It is the first 2D material that supports both superconducting and topological states, offering an exciting opportunity to study 2D topological superconductors through the proximity effect.
The enigma of the ν =2 +3 /8 fractional quantum Hall effect
Hutasoit, Jimmy A.; Balram, Ajit C.; Mukherjee, Sutirtha; Wu, Ying-Hai; Mandal, Sudhansu S.; Wójs, A.; Cheianov, Vadim; Jain, J. K.
2017-03-01
The fractional quantum Hall effect at ν =2 +3 /8 , which has been definitively observed, is one of the last fractions for which no viable explanation has so far been demonstrated. Our detailed study suggests that it belongs to a new class of exotic states described by the Bonderson-Slingerland wave function. Its excitations are non-Abelian anyons similar to those of the well studied Pfaffian state at 5/2, but its wave function has a more complex structure. Using the effective edge theory, we make predictions for various measurable quantities that should enable a confirmation of the underlying topological order of this state.
Leder, Martin; Grossert, Christopher; Sitta, Lukas; Genske, Maximilian; Rosch, Achim; Weitz, Martin
2016-10-01
To describe a mobile defect in polyacetylene chains, Su, Schrieffer and Heeger formulated a model assuming two degenerate energy configurations that are characterized by two different topological phases. An immediate consequence was the emergence of a soliton-type edge state located at the boundary between two regions of different configurations. Besides giving first insights in the electrical properties of polyacetylene materials, interest in this effect also stems from its close connection to states with fractional charge from relativistic field theory. Here, using a one-dimensional optical lattice for cold rubidium atoms with a spatially chirped amplitude, we experimentally realize an interface between two spatial regions of different topological order in an atomic physics system. We directly observe atoms confined in the edge state at the intersection by optical real-space imaging and characterize the state as well as the size of the associated energy gap. Our findings hold prospects for the spectroscopy of surface states in topological matter and for the quantum simulation of interacting Dirac systems.
Charge metastability and hysteresis in the quantum Hall regime
Pollanen, J.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
2016-12-01
We report simultaneous quasi-dc magnetotransport and high-frequency surface acoustic wave measurements on bilayer two-dimensional electron systems in GaAs. Near strong integer quantized Hall states, a strong magnetic-field-sweep hysteresis in the velocity of the acoustic waves is observed at low temperatures. This hysteresis indicates the presence of a metastable state with anomalously high conductivity in the interior of the sample. This nonequilibrium state is not revealed by conventional low-frequency transport measurements which are dominated by dissipationless transport at the edge of the two-dimensional system. We find that a field-cooling technique allows the equilibrium charge configuration within the interior of the sample to be established. A simple model for this behavior is discussed.
Maximilien Brice
2002-01-01
Since 1992, after its move from the 600 MeV SC, ISOLDE is a customer of the Booster (then 1 GeV, now 1.4 GeV). The intense Booster beam (some 3E13 protons per pulse) is directed onto a target, from which a mixture of isotopes emanates. After ionization and electrostatic acceleration to 60 keV, they enter one of the 2 spectrometers (General Purpose Separator: GPS, and High Resolution Separator: HRS) from which the selected ions are directed to the experiments. The photos show: the REX-ISOLDE post accelerator; the mini-ball experiment; an overview of the ISOLDE hall. In the picture (_12) of the hall, the separators are behind the wall. From either of them, beams can be directed into any of the many beamlines towards the experiments, some of which are visible in the foreground. The elevated cubicle at the left is EBIS (Electron Beam Ion Source), which acts as a charge-state multiplier for the REX facility. The ions are further mass analzyzed and passed on to the linac which accelerates them to higher energies. T...
Integer quantum Hall effect in graphene
Jellal, Ahmed, E-mail: ahmed.jellal@gmail.com [Saudi Center for Theoretical Physics, Dhahran (Saudi Arabia); Theoretical Physics Group, Faculty of Sciences, Chouaïb Doukkali University, 24000 El Jadida (Morocco)
2016-04-08
We study the quantum Hall effect in a monolayer graphene by using an approach based on thermodynamical properties. This can be done by considering a system of Dirac particles in an electromagnetic field and taking into account of the edges effect as a pseudo-potential varying continuously along the x direction. At low temperature and in the weak electric field limit, we explicitly determine the thermodynamical potential. With this, we derive the particle numbers in terms of the quantized flux and therefore the Hall conductivity immediately follows.
The Quantum Spin Hall Effect: Theory and Experiment
Konig, Markus; Buhmann, Hartmut; Molenkamp, Laurens W.; /Wurzburg U.; Hughes, Taylor L.; /Stanford U., Phys. Dept.; Liu, Chao-Xing; /Tsinghua U., Beijing /Stanford U., Phys. Dept.; Qi, Xiao-Liang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-19
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Recently, a new class of topological insulators has been proposed. These topological insulators have an insulating gap in the bulk, but have topologically protected edge states due to the time reversal symmetry. In two dimensions the helical edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. Here we review a recent theory which predicts that the QSH state can be realized in HgTe/CdTe semiconductor quantum wells. By varying the thickness of the quantum well, the band structure changes from a normal to an 'inverted' type at a critical thickness d{sub c}. We present an analytical solution of the helical edge states and explicitly demonstrate their topological stability. We also review the recent experimental observation of the QSH state in HgTe/(Hg,Cd)Te quantum wells. We review both the fabrication of the sample and the experimental setup. For thin quantum wells with well width d{sub QW} < 6.3 nm, the insulating regime shows the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d{sub QW} > 6.3 nm), the nominally insulating regime shows a plateau of residual conductance close to 2e{sup 2}/h. The residual conductance is independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance is destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d{sub c} = 6.3 nm, is also independently determined from the occurrence of a magnetic field induced insulator to metal transition.
Li, Yuanchang
2016-07-01
It is generally believed that the interedge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of interedge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the nontrivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one maintains the edge state feature. We attribute such an anomalous behavior to the orbital-dependent decay of edge states into the bulk, which allows the interedge coupling between just one pair of edge states rather than two.
Edge state tunneling in a point contact at filling fraction ν=5/2
Radu, Iuliana P.; Miller, J. B.; Dillard, C. R.; Marcus, C. M.; Kastner, M. A.; Pfeiffer, L. N.; West, K. W.
2008-03-01
We investigate low temperature transport properties of quantum point contacts (QPCs) fabricated in a GaAs/AlGaAs 2-dimensional electron gas (2-DEG) with mobility 2000 m^2/Vs in a perpendicular magnetic field. The 2-DEG exhibits fractional quantum Hall effect, including a well-quantized plateau at ν=5/2. We study the temperature and DC current bias dependence of the transport through the QPC at ν=5/2 while preserving the same filling number in both the QPC and the bulk of the sample. We compare our results to theoretical predictions for quasi-particle tunneling in the weak coupling regime, and extract the quasi-particle charge and the strength of the Coulomb interaction, as reflected by the Luttinger liquid parameter g. This work was partially supported by ARO (W911NF-05-1-0062), by the NSEC program of NSF (PHY-0117795), by NSF (DMR-0353209) at MIT and by Project Q of Microsoft Corporation at Harvard University.
Huang Yifan
2016-12-01
Full Text Available Three-dimensional (3D finite element analyses (FEA are performed to simulate the local compression (LC technique on the clamped single-edge notched tension (SE(T specimens. The analysis includes three types of indenters, which are single pair of cylinder indenters (SPCI, double pairs of cylinder indenters (DPCI and single pair of ring indenters (SPRI. The distribution of the residual stress in the crack opening direction in the uncracked ligament of the specimen is evaluated. The outcome of this study can facilitate the use of LC technique on SE(T specimens.
Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors
Moroz, Sergej; Gurarie, Victor; Radzihovsky, Leo
2016-01-01
Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for $s$-wave, $d+id$, and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of low-energy excitations and incorporate global continuous symmetries - specifically, spin rotation and conservation of magnetic flux - present in all singlet superconductors. We compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly-coupled phase of a chiral state paired in the even $k^{\\text{th}}$ partial wave has a spin Hall coefficient $\
Hotta, Chisa; Nishimoto, Satoshi; Shibata, Naokazu
2013-03-01
The grand canonical numerical analysis recently developed for quantum many-body systems on a finite cluster [C. Hotta and N. Shibata, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.86.041108 86, 041108(R) (2012)] is the technique to efficiently obtain the physical quantities in an applied field. There, the observables are the continuous and real functions of fields, mimicking their thermodynamic limit, even when a small cluster is adopted. We develop a theory to explain the mechanism of this analysis based on the deformation of the Hamiltonian. The deformation spatially scales down the energy unit from the system center toward zero at the open edge sites, which introduces the renormalization of the energy levels in a way reminiscent of Wilson's numerical renormalization group. However, compared to Wilson's case, our deformation generates a number of far well-localized edge states near the chemical potential level, which are connected via a very small quantum fluctuation in k space with the “bulk” states which spread at the center of the system. As a response to the applied field, the particles on the cluster are self-organized to tune the particle number of the bulk states to their thermodynamic limit by using the “edges” as a buffer. We demonstrate the present analysis in two-dimensional quantum spin systems on square and triangular lattices, and determine the smooth magnetization curve with a clear (1)/(3) plateau structure in the latter.
Takagaki, Y. [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)
2015-08-07
The helical edge states of two-dimensional topological insulators (TIs) experience appreciable quantum mechanical scattering in narrow channels when the width changes abruptly. The interference of the geometry scattering in narrow-wide-narrow waveguide structures is shown to give rise to the strong suppression of transmission when the incident energy is barely above the propagation threshold. Periodic resonant transmission takes place in this high reflection regime while the length of the wide section is varied. The resonance condition is governed by the transverse confinement in the wide section, where the form of quantization is manifested to differ for the two orthogonal directions. The confined energy levels in TI quantum dots are derived based on this observation. In addition, the off-diagonal spin-orbit term is found to produce an anomalous resonance state, which merges with the bottom ordinary resonance state to annihilate.
MAGNETORESISTANCE AND HALL EFFECT IN SINGLE CRYSTALS OF ALUMINUM
ALUMINUM, *SINGLE CRYSTALS, CRYSTALS, HALL EFFECT , IMPURITIES, LOW PRESSURE, MAGNETIC FIELDS, MAGNETIC PROPERTIES, PARTICLE TRAJECTORIES, ELECTRICAL RESISTANCE, SOLID STATE PHYSICS, SURFACE PROPERTIES.
Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material
Reis, F.; Li, G.; Dudy, L.; Bauernfeind, M.; Glass, S.; Hanke, W.; Thomale, R.; Schäfer, J.; Claessen, R.
2017-07-01
Quantum spin Hall materials hold the promise of revolutionary devices with dissipationless spin currents but have required cryogenic temperatures owing to small energy gaps. Here we show theoretically that a room-temperature regime with a large energy gap may be achievable within a paradigm that exploits the atomic spin-orbit coupling. The concept is based on a substrate-supported monolayer of a high-atomic number element and is experimentally realized as a bismuth honeycomb lattice on top of the insulating silicon carbide substrate SiC(0001). Using scanning tunneling spectroscopy, we detect a gap of ~0.8 electron volt and conductive edge states consistent with theory. Our combined theoretical and experimental results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance.
Mesoscopic spin Hall effect in semiconductor nanostructures
Zarbo, Liviu
The spin Hall effect (SHE) is a name given to a collection of diverse phenomena which share two principal features: (i) longitudinal electric current flowing through a paramagnetic semiconductor or metallic sample leads to transverse spin current and spin accumulation of opposite sign at opposing lateral edges; (ii) SHE does not require externally applied magnetic field or magnetic ordering in the equilibrium state of the sample, instead it relies on the presence of spin-orbit (SO) couplings within the sample. This thesis elaborates on a new type of phenomenon within the SHE family, predicted in our recent studies [Phys. Rev. B 72, 075361 (2005); Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 72, 075335 (2005); Phys. Rev. B 73 , 075303 (2006); and Europhys. Lett. 77, 47004 (2007)], where pure spin current flows through the transverse electrodes attached to a clean finitesize two-dimensional electron gas (2DEG) due to unpolarized charge current injected through its longitudinal leads. If transverse leads are removed, the effect manifests as nonequilibrium spin Hall accumulation at the lateral edges of 2DEG wires. The SO coupling driving this SHE effect is of the Rashba type, which arises due to structural inversion asymmetry of semiconductor heterostructure hosting the 2DEG. We term the effect "mesoscopic" because the spin Hall currents and accumulations reach optimal value in samples of the size of the spin precession length---the distance over which the spin of an electron precesses by an angle pi. In strongly SO-coupled structures this scale is of the order of ˜100 nm, and, therefore, mesoscopic in the sense of being much larger than the characteristic microscopic scales (such as the Fermi wavelength, screening length, or the mean free path in disordered systems), but still much smaller than the macroscopic ones. Although the first theoretical proposal for SHE, driven by asymmetry in SO-dependent scattering of spin-up and spin-down electrons off impurities
X-ray absorption near-edge structure and valence state of Mn in (Ga,Mn)N
Titov, A.; Biquard, X.; Halley, D.; Kuroda, S.; Bellet-Amalric, E.; Mariette, H.; Cibert, J.; Merad, A. E.; Merad, G.; Kanoun, M. B.; Kulatov, E.; Uspenskii, Yu. A.
2005-09-01
The band structure of the diluted magnetic semiconductor (Ga,Mn)N, and the x-ray absorption near-edge structure (XANES) at the K edge of Mn, were calculated using the linearized augmented plane wave method. The calculated K-edge spectra fit well with experimental data obtained on samples of Ga1-xMnxN with a wide range of Mn content, from x=0.3% to 5.7%. These samples were grown by molecular beam epitaxy. X-ray diffraction measurements and extended x-ray absorption fine structure studies were used to confirm the wurtzite structure of the samples, the absence of any secondary phase, and the substitutional position of Mn in the gallium sublattice of GaN. The shape of the measured XANES spectra does not depend on the Mn content, implying the same valence state and local atomic structure around the Mn atom in all samples. The comparison between the measured spectra and the results of the ab initio calculation offers a clear interpretation of the preedge structure: It is mainly due to dipolar transitions, with a single peak in the case of Mn2+ and an additional peak for Mn3+ . Such a behavior of the XANES preedge of Mn2+ was confirmed experimentally on (Ga,Mn)As and (Zn,Mn)Te. We conclude that the valence state of Mn in wurtzite (Ga,Mn)N is 3+ , a conclusion which is also supported by infrared optical transmission and magnetization data obtained on the same samples.
E. Kalesaki
2014-01-01
Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.
Chung, Chung-Hou; Lee, Der-Hau; Chao, Sung-Po
2014-07-01
We study the quantum phases and phase transitions of the Kane-Mele Hubbard (KMH) model on a zigzag ribbon of honeycomb lattice at a finite size via the weak-coupling renormalization group (RG) approach. In the noninteracting limit, the Kane-Mele (KM) model is known to support topological edge states where electrons show helical property with orientations of the spin and momentum being locked. The effective interedge hopping terms are generated due to finite-size effect. In the presence of an on-site Coulomb (Hubbard) interaction and the interedge hoppings, special focus is put on the stability of the topological edge states (TI phase) in the KMH model against (i) the charge and spin gaped (II) phase, (ii) the charge gaped but spin gapless (IC) phase, and (iii) the spin gaped but charge gapless (CI) phase depending on the number (even/odd) of the zigzag ribbons, doping level (electron filling factor) and the ratio of the Coulomb interaction to the interedge tunneling. We discuss different phase diagrams for even and odd numbers of zigzag ribbons. We find the TI-CI, II-IC, and II-CI quantum phase transitions are of the Kosterlitz-Thouless (KT) type. By computing various correlation functions, we further analyze the nature and leading instabilities of these phases. The relevance of our results for graphene is discussed.
Optical Hall effect in strained graphene
Nguyen, V. Hung; Lherbier, A.; Charlier, J.-C.
2017-06-01
When passing an optical medium in the presence of a magnetic field, the polarization of light can be rotated either when reflected at the surface (Kerr effect) or when transmitted through the material (Faraday rotation). This phenomenon is a direct consequence of the optical Hall effect arising from the light-charge carrier interaction in solid state systems subjected to an external magnetic field, in analogy with the conventional Hall effect. The optical Hall effect has been explored in many thin films and also more recently in 2D layered materials. Here, an alternative approach based on strain engineering is proposed to achieve an optical Hall conductivity in graphene without magnetic field. Indeed, strain induces lattice symmetry breaking and hence can result in a finite optical Hall conductivity. First-principles calculations also predict this strain-induced optical Hall effect in other 2D materials. Combining with the possibility of tuning the light energy and polarization, the strain amplitude and direction, and the nature of the optical medium, large ranges of positive and negative optical Hall conductivities are predicted, thus opening the way to use these atomistic thin materials in novel specific opto-electro-mechanical devices.
The state-of-the-art of emergency contraception with the cutting edge drug
Sarkar, Narendra Nath
2011-01-01
Full Text Available The objective of this study is to evaluate and elucidated the potential of selective progesterone receptor modulators (SPRMs to be an effective emergency contraception (EC. The data are extracted from the literature through the MEDLINE database service from 2000–2010. The SPRMs are in fact progesterone receptor ligands that could bind to progesterone receptor (PR and exert antagonistic, agonistic or mixed agonist-antagonistic effects. These SPRMs are mifepristone, onapristone, asoprisnil, ulipristal, proellex among other compounds. Currently developed SPRMs may exert contraceptive effects by inhibiting ovulation and retarding endometrial synchronization. Low-doses of progesterone antagonists retard endometrial maturation without affecting ovulation. Mifepristone being a SPRM is effective for prevention of pregnancy but with prostaglandin acts as an excellent abortifacient; yet could not compete with levonorgestrel as EC. However, a single dose of 30 mg ulipristal acetate, another SPRM with similar effectiveness and side effect profiles as 1.5 mg levonorgestrel EC, has shown wider ‘window of effect’ by inhibition of the LH peak even if administered at the advanced pre-ovulatory phase, a time when use of levonorgestrel EC is no longer effective. Thus, ulipristal acetate goes one-step ahead of levonorgestrel in the field of emergency contraception treatment. Further studies are needed to explore the potential of other SPRMs to be cutting edge emergency contraceptive drugs.
Fresno State joins CERN-related program to explore cutting edge physics
2008-01-01
California State University, Fresno has joined a collaboration of top physicists to work with what scientists believe will be the driving force behind high-energy physics for the foreseeable future. The program is the ATLAS (an acronym for A Toroidal LHC ApparatuS) experiment, which makes use of the Large Hadron Collider under construction at the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. Fresno State says it is the only one of the 23 California State University system schools participating in the LHC program and CERN.
Kim, Bom Soo; Shapere, Alfred D.
2016-09-01
We derive a generalized set of Ward identities that captures the effects of topological charge on Hall transport. The Ward identities follow from the (2 +1 )-dimensional momentum algebra, which includes a central extension proportional to the topological charge density. In the presence of topological objects like Skyrmions, we observe that the central term leads to a direct relation between the thermal Hall conductivity and the topological charge density. We extend this relation to incorporate the effects of a magnetic field and an electric current. The topological charge density produces a distinct signature in the electric Hall conductivity, which is identified in existing experimental data and yields further novel predictions. For insulating materials with translation invariance, the Hall viscosity can be directly determined from the Skyrmion density and the thermal Hall conductivity to be measured as a function of momentum.
Kharitonov, Maxim; Juergens, Stefan; Trauzettel, Björn
2016-07-01
We consider a class of quantum Hall topological insulators: topologically nontrivial states with zero Chern number at finite magnetic field, in which the counterpropagating edge states are protected by a symmetry (spatial or spin) other than time-reversal. HgTe-type heterostructures and graphene are among the relevant systems. We study the effect of electron interactions on the topological properties of the system. We particularly focus on the vicinity of the topological phase transition, marked by the crossing of two Landau levels, where the system is a strongly interacting quantum Hall ferromagnet. We analyze the edge properties using the formalism of the nonlinear σ -model. We establish the symmetry requirement for the topological protection in this interacting system: effective continuous U(1) symmetry with respect to uniaxial isospin rotations must be preserved. If U(1) symmetry is preserved, the topologically nontrivial phase persists; its edge is a helical Luttinger liquid with highly tunable effective interactions. We obtain explicit analytical expressions for the parameters of the Luttinger liquid in the quantum-Hall-ferromagnet regime. However, U(1) symmetry may be broken, either spontaneously or by U(1)-asymmetric interactions. In either case, interaction-induced transitions occur to the respective topologically trivial phases with gapped edge charge excitations.
On the impact of multi-axial stress states on trailing edge bondlines in wind turbine rotor blades
Noever Castelos, Pablo; Balzani, Claudio
2016-09-01
For a reliable design of wind turbine systems all of their components have to be designed to withstand the loads appearing in the turbine's lifetime. When performed in an integral manner this is called systems engineering, and is exceptionally important for components that have an impact on the entire wind turbine system, such as the rotor blade. Bondlines are crucial subcomponents of rotor blades, but they are not much recognized in the wind energy research community. However, a bondline failure can lead to the loss of a rotor blade, and potentially of the entire turbine, and is extraordinarily relevant to be treated with strong emphasis when designing a wind turbine. Modern wind turbine rotor blades with lengths of 80 m and more offer a degree of flexibility that has never been seen in wind energy technology before. Large deflections result in high strains in the adhesive connections, especially at the trailing edge. The latest edition of the DNV GL guideline from end of 2015 demands a three-dimensional stress analysis of bondlines, whereas before an isolated shear stress proof was sufficient. In order to quantify the lack of safety from older certification guidelines this paper studies the influence of multi-axial stress states on the ultimate and fatigue load resistance of trailing edge adhesive bonds. For this purpose, detailed finite element simulations of the IWES IWT-7.5-164 reference wind turbine blades are performed. Different yield criteria are evaluated for the prediction of failure and lifetime. The results show that the multi-axial stress state is governed by span-wise normal stresses. Those are evidently not captured in isolated shear stress proofs, yielding non-conservative estimates of lifetime and ultimate load resistance. This finding highlights the importance to include a three-dimensional stress state in the failure analysis of adhesive bonds in modern wind turbine rotor blades, and the necessity to perform a three-dimensional characterization
van Zyl, Henry; Powell, Albert, Jr.
2012-01-01
Thomas Edison State College (TESC) and Colorado State University (CSU) offer significant contrasts in institutional culture, student demographics, faculty and institutional priorities and approaches to distance education course development and delivery. This article offers case studies showing that widely disparate program design and delivery…
Unconventional quantum Hall effect in Floquet topological insulators
Tahir, M.
2016-07-27
We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the lights polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity αyx = 0 at zero Fermi energy, to a Hall insulator state with αyx = e2/2h. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaus at (±1/2,±3/2,±5/2, ...)e2/h. © 2016 IOP Publishing Ltd Printed in the UK.
Unconventional quantum Hall effect in Floquet topological insulators.
Tahir, M; Vasilopoulos, P; Schwingenschlögl, U
2016-09-28
We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the light's polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity [Formula: see text] at zero Fermi energy, to a Hall insulator state with [Formula: see text]. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaus at [Formula: see text].
Crossed Andreev effects in two-dimensional quantum Hall systems
Hou, Zhe; Xing, Yanxia; Guo, Ai-Min; Sun, Qing-Feng
2016-08-01
We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.
Edge Reduction for EVMDDs to Speed Up Analysis of Multi-State Systems
2015-01-01
for two-variable numeric function generators using multiple-valued decision diagrams,” IEICE Trans. on Information and Systems, Vol. E93-D, No. 8, pp...of multi-state systems,” IEICE Transactions on Information and Systems, Vol.E97-D, No.9, pp.2234–2242, Sept. 2014. [16] J. E. Ramirez-Marquez and D. W
Nelson, George; Harris, William; Izzo, John; Grew, Kyle N. (Connecticut); (USARL)
2012-01-20
Reduction-oxidation (redox) cycling of the nickel electrocatalyst phase in the solid oxide fuel cell (SOFC) anode can lead to performance degradation and cell failure. A greater understanding of nickel redox mechanisms at the microstructural level is vital to future SOFC development. Transmission x-ray microscopy (TXM) provides several key techniques for exploring oxidation states within SOFC electrode microstructure. Specifically, x-ray nanotomography and x-ray absorption near edge structure (XANES) spectroscopy have been applied to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct regions of the materials in question. XANES spectra presented for the individual materials provide a basis for the further processing and analysis of mixed samples. Images of composite samples obtained are segmented, and the distinct nickel and nickel oxide phases are uniquely identified using full field XANES spectroscopy. Applications to SOFC analysis are discussed.
Spectroscopic signature for bundling, edge states and impurities in 1D and 0D materials
Lingam, Kiran Kumar
Study of nanomaterials has gained interest of researchers from various fields of science and technology due to their unique electronic and vibrational properties as compared to their bulk counterparts. In particular, carbon nanotechnology has evolved rapidly over the past few decades and nowadays, carbon nanotubes are used in various fields such as energy storage, electronics etc. However, the quest for new properties of this material is never ending and the invention of graphene generated enormous interest in the scientific community due to its excellent properties such as strength, high electron mobility, thermal conductivity etc. In this thesis, I aim at gaining better understanding of the electronic properties of carbon nanostructures and also discuss the effect of impurities on the vibrational properties of Bismuth nanorods. In the case of SWNTs, I have studied the effect of surrounding environment on their electronic properties, in particular Sub-nm SWNTs. Due to their unique electronic and vibrational properties, single walled carbon nanotubes (SWNTs) with sub-nanometer diameters d ˜ 0.5-0.9 nm have recently gained interest in the carbon community. Using UV-Vis-NIR spectroscopy and ultra-centrifugation, we have conducted a detailed study of the π plasmon energy (present at˜5-7 eV) in sub-nm SWCNTs as a function of the size of the bundle. We find that the energy of the π plasmon peak E varies with the bundle diameter Dh as E = (0.023 eV )*ln(Dh/do) + 5.3 7 eV, where do = 0.5 nm and corresponds to the smallest tube diameter. This is compared with the same data for HiPCo and Carbolex SWCNTs of larger diameter (1-1.4 nm) confirming a clear dependence of E on the bundle size, which is present in addition to the previously reported dependence of E on SWCNT diameter d. In case of graphene, the carbon atoms at the edges of graphene sheet contribute to its electronic properties. This effect becomes more prominent in confined structures such as graphene
The effect of dephasing on edge state transport through p-n junctions in HgTe/CdTe quantum wells.
Zhang, Ying-Tao; Song, Juntao; Sun, Qing-Feng
2014-02-26
Using the Landauer-Büttiker formula, we study the effect of dephasing on the transport properties of the HgTe/CdTe p-n junction. It is found that in the HgTe/CdTe p-n junction the topologically protected gapless helical edge states manifest a quantized 2e²/h plateau robust against dephasing, in sharp contrast to the case for the normal HgTe/CdTe quantum well. This robustness of the transport properties of the edge states against dephasing should be attributed to the special construction of the HgTe/CdTe p-n junction, which limits the gapless helical edge states to a very narrow region and thus weakens the influence of the dephasing on the gapless edge states to a large extent. Our results demonstrate that the p-n junction could be a substitute device for use in experimentally observing the robust edge states and quantized plateau. Finally, we present a feasible scheme based on current experimental methods.
Matthes, L.; Küfner, S.; Furthmüller, J.; Bechstedt, F.
2016-08-01
Ab initio relativistic band structure calculations are performed for the frequency-dependent spin Hall conductivity of three- (3D), two- (2D) and one-dimensional (1D) materials such as bulk semiconductors, atomically thin crystals, and their nanoribbons. Besides the influence of the dimensionality we also study differences between trivial and topological insulators (TIs). The frequency dependence of the conductivity is governed by the band-structure details, while its static value scales with the spin-orbit interaction in 3D but is quantized in units of e2/h for 2D TIs. 1D topological edge states influence the conductivity mainly for vanishing frequencies.
Novel roles for protein disulphide isomerase in disease states: a double edged sword?
Sonam eParakh
2015-05-01
Full Text Available Protein disulphide isomerase (PDI is a multifunctional redox chaperone of the endoplasmic reticulum (ER. Since it was first discovered 40 years ago the functions ascribed to PDI have evolved significantly and recent studies have recognized its distinct functions, with adverse as well as protective effects in disease. Furthermore, post translational modifications of PDI abrogate its normal functional roles in specific disease states. This review focusses on recent studies that have identified novel functions for PDI relevant to specific diseases.
SINTEF Building and Infrastructure; Norwegian University of Science and Technology (NTNU); Bergh, Sofie Van Den; Hart, Robert; Jelle, Bjrn Petter; Gustavsen, Arild
2013-01-31
Insulating glass (IG) units typically consist of multiple glass panes that are sealed and held together structurally along their perimeters. This report describes a study of edge seals in IG units. First, we summarize the components, requirements, and desired properties of edge construction in IG units, based on a survey of the available literature. Second, we review commercially available window edge seals and describe their properties, to provide an easily accessible reference for research and commercial purposes. Finally, based on the literature survey and review of current commercial edge seal systems, we identify research opportunities for future edge seal improvements and solutions.
Observation of the Spin Hall Effect in Semiconductors
Kato, Y. K.; Myers, R. C.; Gossard, A. C.; Awschalom, D. D.
2004-12-01
Electrically induced electron-spin polarization near the edges of a semiconductor channel was detected and imaged with the use of Kerr rotation microscopy. The polarization is out-of-plane and has opposite sign for the two edges, consistent with the predictions of the spin Hall effect. Measurements of unstrained gallium arsenide and strained indium gallium arsenide samples reveal that strain modifies spin accumulation at zero magnetic field. A weak dependence on crystal orientation for the strained samples suggests that the mechanism is the extrinsic spin Hall effect.
Hamiltonian theory of the FQHE edge: Collective modes
Nguyen, Hoang; Joglekar, Yogesh; Murthy, Ganpathy
2003-03-01
We study the collective modes of the fractional quantum Hall edge states using the Hamiltonian formalism [1]. While most theoretical approaches start with an effective bosonic theory [2] in which all fermions are integrated out (an exception is the approach based on Chern-Simons theory [3]), the Hamiltonian theory treats the composite fermions as fully interacting. We obtain the gapless edge-modes using a conserving approximation which respects the constraints [4]. The implications of our study to the tunneling experiments into the edge of a fractional quantum Hall system [5] are discussed. [1] R.Shankar and G.Murthy, Phys.Rev.Lett. 79, 4437 (1997). [2] X.-G.Wen, Phys.Rev.Lett. 64, 2206 (1990); D.-H.Lee and X.-G.Wen, cond-mat/9809160; A.Lopez and E.Fradkin, Phys.Rev.B 59, 15323 (1999); U. Zulicke and A.H.MacDonald, Phys.Rev.B 60, 1837 (1999); V.J.Goldman and E.V.Tsiper, Phys.Rev.Lett. 86, 5841 (2001); S.S.Mandal and J.K.Jain, Phys.Rev.Lett. 89, 096801 (2002). [3] L.S.Levitov, A.V.Shytov, and B.I.Halperin, Phys. Rev. B 64, 075322 (2001). [4] N. Read, Phys.Rev.B 58, 16262 (1998); G. Murthy, Phys.Rev.B 64, 195310 (2001). [5] A.M.Chang et.al., Phys.Rev.Lett. 86, 143 (2000).
Fermion-Parity Anomaly of the Critical Supercurrent in the Quantum Spin-Hall Effect
Beenakker, C. W. J.; Pikulin, D. I.; Hyart, T.; Schomerus, H.; Dahlhaus, J. P.
2013-01-01
The helical edge state of a quantum spin-Hall insulator can carry a supercurrent in equilibrium between two superconducting electrodes (separation L, coherence length ξ). We calculate the maximum (critical) current Ic that can flow without dissipation along a single edge, going beyond the short-junction restriction L≪ξ of earlier work, and find a dependence on the fermion parity of the ground state when L becomes larger than ξ. Fermion-parity conservation doubles the critical current in the low-temperature, long-junction limit, while for a short junction Ic is the same with or without parity constraints. This provides a phase-insensitive, dc signature of the 4π-periodic Josephson effect.
Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors
Moroz, Sergej; Prem, Abhinav; Gurarie, Victor; Radzihovsky, Leo
2017-01-01
Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for s -wave, d +i d , and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of Bogoliubov quasiparticles and vortices and incorporate global continuous symmetries—specifically, spin rotation and conservation of magnetic flux—present in all singlet superconductors. For all such systems, we compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly coupled phase of a chiral d +i d chiral state has a spin Hall coefficient νs=2 and a vanishing Hall response for the magnetic flux symmetry. We argue that the latter is a generic result for two-dimensional superconductors with gapped photons, thereby demonstrating the absence of a spontaneous magnetic field in the ground state of chiral superconductors. It is also shown that the Chern-Simons theories of chiral spin-singlet superconductors derived here fall into Kitaev's 16-fold classification of topological superconductors.
A Holographic Quantum Hall Ferromagnet
Kristjansen, C; Semenoff, G W
2013-01-01
A detailed numerical study of a recent proposal for exotic states of the D3-probe D5 brane system with charge density and an external magnetic field is presented. The state has a large number of coincident D5 branes blowing up to a D7 brane in the presence of the worldvolume electric and magnetic fields which are necessary to construct the holographic state. Numerical solutions have shown that these states can compete with the the previously known chiral symmetry breaking and maximally symmetric phases of the D3-D5 system. Moreover, at integer filling fractions, they are incompressible with integer quantized Hall conductivities. In the dual superconformal defect field theory, these solutions correspond to states which break the chiral and global flavor symmetries spontaneously. The region of the temperature-density plane where the D7 brane has lower energy than the other known D5 brane solutions is identified. A hypothesis for the structure of states with filling fraction and Hall conductivity greater than on...
National Oceanic and Atmospheric Administration, Department of Commerce — Salt marsh habitats along the shoreline of Halls Lake are threatened by wave erosion, but the reconstruction of barrier islands to reduce this erosion will modify or...
General footage ISOLDE experimental hall
2016-01-01
Overview of the ISOLDE experimental hall. Equipment and experiments. Taken from the WITCH / EBIS platform: ISOLDE hall infrastructure, GHM line, LA1, LA2, LA0, central beamline, COLLAPS experiment, CRIS experiment, ISOLTRAP experiment, laser guidance from building 508 into the hall for laser spectroscopy COLLAPS and CRIS. Taken from the HIE ISOLDE shielding tunnel roof: ISOLDE hall infrastructure, WITCH experiment, VITO line, TAS experiment. General footage: High Tension room entrance and EBIS platform, staircases and passages in the experimental hall.
The study of below and above band-edge imperfection states in In2S3 solar energy materials
Ho, Ching-Hwa
2012-08-01
β-In2S3 is a nontoxic buffer layer material usually used in a thin-film solar cell due to a lot of vacancies and surface states naturally existing in the crystal to assist in photoelectric conversion. Transition metal (TM)-incorporated β-In2S3 has also been proposed to increase conversion efficiency in In2S3 since multi-photons absorption by intermediate band (IB) would happen in the sulfide. In this paper, single crystals of undoped and Nb-doped β-In2S3 have been grown by the chemical vapor transport (CVT) method using ICl3 as a transport agent. Optical properties of the imperfection states of the crystals are probed by thermoreflectance (TR), photoconductivity (PC), photoluminescence (PL), surface photoconductive response (SPR), optical absorption and photo-voltage-current (photo V-I) measurements. The TR and optical-absorption measurements confirmed that the undoped and Nb-doped β-In2S3 are direct semiconductors with energy gap of 1.935 eV for undoped β-In2S3, 1.923 eV for β-In2S3:Nb0.005, and 1.901 eV for β-In2S3:Nb0.01. For undoped β-In2S3, PC and PL measurements are used to characterize defect transitions below band gap. The above band-edge transitions of undoped β-In2S3 have also been evaluated using PL, PC, and SPR measurements. For the evaluation of Nb-doped β-In2S3, an intermediate band with energy of ∼0.4 eV below the conduction band edge has been detected in the TR measurements in both β-In2S3:Nb0.005 and β-In2S3:Nb0.01. The photo V-I measurements also verified that the photoelectric-conversion efficiency would be enhanced in the β-In2S3 with higher niobium content. Based on the experimental analyses, the optical behavior of the defects, surface states, and IB (formed by Nb) in the In2S3 crystals is thus explored.
Zhang, Ying-Tao; Deng, Xinzhou; Sun, Qing-Feng; Qiao, Zhenhua
2015-01-01
The quantum entanglement between two qubits is crucial for applications in the quantum communication. After the entanglement of photons was experimentally realized, much effort has been taken to exploit the entangled electrons in solid-state systems. Here, we propose a Cooper-pair splitter, which can generate spatially-separated but entangled electrons, in a quantum anomalous Hall insulator proximity-coupled with a superconductor. After coupling with a superconductor, the chiral edge states of the quantum anomalous Hall insulator can still survive, making the backscattering impossible. Thus, the local Andreev reflection becomes vanishing, while the crossed Andreev reflection becomes dominant in the scattering process. This indicates that our device can serve as an extremely high-efficiency Cooper-pair splitter. Furthermore, because of the chiral characteristic, our Cooper-pair splitter is robust against disorders and can work in a wide range of system parameters. Particularly, it can still function even if the system length exceeds the superconducting coherence length.
Dynamic Feedback in Ferromagnet-Spin Hall Metal Heterostructures
Cheng, Ran; Zhu, Jian-Gang; Xiao, Di
2016-08-01
In ferromagnet-normal-metal heterostructures, spin pumping and spin-transfer torques are two reciprocal processes that occur concomitantly. Their interplay introduces a dynamic feedback effect interconnecting energy dissipation channels of both magnetization and current. By solving the spin diffusion process in the presence of the spin Hall effect in the normal metal, we show that the dynamic feedback gives rise to (i) a nonlinear magnetic damping that is crucial to sustain uniform steady-state oscillations of a spin Hall oscillator at large angles and (ii) a frequency-dependent spin Hall magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc limit.
Wallace-Williams, Stacie E.; Møller, Søren; Goldbeck, Robert A.;
1993-01-01
The shapes of the fluorescence emission and lowest excited singlet-state absorption spectra of all-trans-1,4- diphenylbutadiene (DPB) in hydrocarbon solvents vary with excitation wavelength when exciting on the extreme red edge of the ground-state absorption spectrum. This contrasts with the wave......The shapes of the fluorescence emission and lowest excited singlet-state absorption spectra of all-trans-1,4- diphenylbutadiene (DPB) in hydrocarbon solvents vary with excitation wavelength when exciting on the extreme red edge of the ground-state absorption spectrum. This contrasts...... changes in DPB can be explained in terms of an excitation wavelength-dependent production of s-cis and s-trans rotamer populations in the excited state. The DPB fluorescence emission spectrum was resolved into s-cis and s-trans components. The vibronic structure of the s-cis fluorescence spectrum...
Formulation of the Relativistic Quantum Hall Effect and "Parity Anomaly"
Yonaga, Kouki; Shibata, Naokazu
2016-01-01
We present a relativistic formulation of the quantum Hall effect on a Riemann sphere. An explicit form of the pseudopotential is derived for the relativistic quantum Hall effect with/without mass term.We clarify particular features of the relativistic quantum Hall states with use of the exact diagonalization study of the pseudopotential Hamiltonian. Physical effects of the mass term to relativistic quantum Hall states are investigated in detail.The mass term acts as an interporating parameter between the relativistic and non-relativistic quantum Hall effects. It is pointed out that the mass term inequivalently affects to many-body physics of the positive and negative Landau levels and brings instability of the Laughlin state of the positive first relativistic Landau level as a consequence of the "parity anomaly".
Effective Field Theory of Fractional Quantized Hall Nematics
Mulligan, Michael; /MIT, LNS; Nayak, Chetan; /Station Q, UCSB; Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC
2012-06-06
We present a Landau-Ginzburg theory for a fractional quantized Hall nematic state and the transition to it from an isotropic fractional quantum Hall state. This justifies Lifshitz-Chern-Simons theory - which is shown to be its dual - on a more microscopic basis and enables us to compute a ground state wave function in the symmetry-broken phase. In such a state of matter, the Hall resistance remains quantized while the longitudinal DC resistivity due to thermally-excited quasiparticles is anisotropic. We interpret recent experiments at Landau level filling factor {nu} = 7/3 in terms of our theory.
Nonlocal Anomalous Hall Effect
Zhang, Steven S.-L.; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect—the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt /YIG structures.
Conducting Wall Hall Thrusters
Goebel, Dan M.; Hofer, Richard R.; Mikellides, Ioannis G.; Katz, Ira; Polk, James E.; Dotson, Brandon
2013-01-01
A unique configuration of the magnetic field near the wall of Hall thrusters, called Magnetic Shielding, has recently demonstrated the ability to significantly reduce the erosion of the boron nitride (BN) walls and extend the life of Hall thrusters by orders of magnitude. The ability of magnetic shielding to minimize interactions between the plasma and the discharge chamber walls has for the first time enabled the replacement of insulating walls with conducting materials without loss in thruster performance. The boron nitride rings in the 6 kW H6 Hall thruster were replaced with graphite that self-biased to near the anode potential. The thruster efficiency remained over 60% (within two percent of the baseline BN configuration) with a small decrease in thrust and increase in Isp typical of magnetically shielded Hall thrusters. The graphite wall temperatures decreased significantly compared to both shielded and unshielded BN configurations, leading to the potential for higher power operation. Eliminating ceramic walls makes it simpler and less expensive to fabricate a thruster to survive launch loads, and the graphite discharge chamber radiates more efficiently which increases the power capability of the thruster compared to conventional Hall thruster designs.
Nonlocal Anomalous Hall Effect.
Zhang, Steven S-L; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect-the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt/YIG structures.
Inertial-Hall effect: the influence of rotation on the Hall conductivity
Brandão, Julio E.; Moraes, F.; Cunha, M. M.; Lima, Jonas R. F.; Filgueiras, C.
Inertial effects play an important role in classical mechanics but have been largely overlooked in quantum mechanics. Nevertheless, the analogy between inertial forces on mass particles and electromagnetic forces on charged particles is not new. In this paper, we consider a rotating non-interacting planar two-dimensional electron gas with a perpendicular uniform magnetic field and investigate the effects of the rotation in the Hall conductivity. The rotation introduces a shift and a split in the Landau levels. As a consequence of the break of the degeneracy, the counting of the states fully occupied below the Fermi energy increases, tuning the Hall quantization steps. The rotation also changes the quantum Hall plateau widths. Additionally, we find the Hall quantization steps as a function of rotation at a fixed value of the magnetic field.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-05-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Guterding, Daniel; Jeschke, Harald O; Valentí, Roser
2016-05-17
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Inertial-Hall effect: the influence of rotation on the Hall conductivity
Julio E. Brandão
2015-01-01
Full Text Available Inertial effects play an important role in classical mechanics but have been largely overlooked in quantum mechanics. Nevertheless, the analogy between inertial forces on mass particles and electromagnetic forces on charged particles is not new. In this paper, we consider a rotating non-interacting planar two-dimensional electron gas with a perpendicular uniform magnetic field and investigate the effects of the rotation in the Hall conductivity. The rotation introduces a shift and a split in the Landau levels. As a consequence of the break of the degeneracy, the counting of the states fully occupied below the Fermi energy increases, tuning the Hall quantization steps. The rotation also changes the quantum Hall plateau widths. Additionally, we find the Hall quantization steps as a function of rotation at a fixed value of the magnetic field.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-01-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions. PMID:27185665
Orbitronics: the Intrinsic Orbital Hall Effect in p-Doped Silicon
Bernevig, B.Andrei; Hughes, Taylor L.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-01-15
The spin Hall effect depends crucially on the intrinsic spin-orbit coupling of the energy band. Because of the smaller spin-orbit coupling in silicon, the spin Hall effect is expected to be much reduced. We show that the electric field in p-doped silicon can induce a dissipationless orbital current in a fashion reminiscent of the spin Hall effect. The vertex correction due to impurity scattering vanishes and the effect is therefore robust against disorder. The orbital Hall effect can lead to the accumulation of local orbital momentum at the edge of the sample, and can be detected by the Kerr effect.
ZHOU Xiang; HU Cheng-zheng; GONG Ping; WANG Ai-jun
2005-01-01
The relations between Hall effect and symmetry are discussed for all 2- and 3 dimensional quasicrystals with crystallographically forbidden symmetries. The results show that the numbers of independent components of the Hall coefficient (RH) are one for 3-dimensional quasicrystals, two for those 2 dimensional quasicrystals whose symmetry group is non-Abelian, and three for those 2-dimensional quasicrystals whose symmetry group is Abelian, respectively. The quasicrystals with the same number of independent components have the same form of the components of RH.
78 FR 19799 - National Baseball Hall of Fame Commemorative Coin Program Design Competition
2013-04-02
... United States Mint National Baseball Hall of Fame Commemorative Coin Program Design Competition ACTION: Notification of the Opening of the National Baseball Hall of Fame Commemorative Coin Program Design Competition... (heads side) of the 2014 National Baseball Hall of Fame Commemorative Coins. The competition, which...
A New Definition in Atlanta: Q&A with Beverly Hall
Crow, Tracy
2010-01-01
Beverly Hall has been superintendent of Atlanta Public Schools since 1999. Before coming to Atlanta, Hall was state district superintendent of Newark Public Schools, deputy chancellor for instruction of New York City Public Schools, superintendent of Community School District 27 in New York City, and a principal in Brooklyn. Hall chairs Harvard…
Avdonin, A., E-mail: avdonin@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa (Poland); Skupiński, P. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa (Poland); Grasza, K. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa (Poland); Institute of Electronic Materials Technology, ul. Wólczyńska 133, 01-919 Warszawa (Poland)
2016-02-15
A simple description of the Hall effect in the hopping regime of conductivity in semiconductors is presented. Expressions for the Hall coefficient and Hall mobility are derived by considering averaged equilibrium electron transport in a single triangle of localization sites in a magnetic field. Dependence of the Hall coefficient is analyzed in a wide range of temperature and magnetic field values. Our theoretical result is applied to our experimental data on temperature dependence of Hall effect and Hall mobility in ZnO. - Highlights: • Expressions for Hall coefficient and mobility for hopping conductivity are derived. • Theoretical result is compared with experimental curves measured on ZnO. • Simultaneous action of free and hopping conduction channels is considered. • Non-linearity of hopping Hall coefficient is predicted.
Kunkel, W. B.
1981-01-01
Describes an apparatus and procedure for conducting an undergraduate laboratory experiment to quantitatively study the Hall effect in a plasma. Includes background information on the Hall effect and rationale for conducting the experiment. (JN)
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
Access to a New Plasma Edge State with High Density and Pressures using Quiescent H-mode
Solomon, Wayne M. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Snyder, P. B. [General Atomics, San Diego, CA (United States); Burrell, K. H. [General Atomics, San Diego, CA (United States); Fenstermacher, M. E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Garofalo, A. M. [General Atomics, San Diego, CA (United States); Grierson, B. A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Loarte, A. [ITER Organization, St. Paul Lez Durance (France); McKee, G. R. [Univ. of Wisconsin, Madison, WI (United States); Nazikian, R [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Osborne, T. H. [General Atomics, San Diego, CA (United States)
2014-07-01
A path to a new high performance regime has been discovered in tokamaks that could improve the attractiveness of a fusion reactor. Experiments on DIII-D using a quiescent H-mode edge have navigated a valley of improved edge peeling-ballooning stability that opens up with strong plasma shaping at high density, leading to a doubling of the edge pressure over standard edge localized mode (ELM)ing H-mode at these parameters. The thermal energy confinement time increases both as a result of the increased pedestal height and improvements in the core transport and reduced low-k turbulence. Calculations of the pedestal height and width as a function of density using constraints imposed by peeling-ballooning and kinetic-ballooning theory are in quantitative agreement with the measurements.
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
U.S. Environmental Protection Agency — This EnviroAtlas dataset categorizes land cover into structural elements (e.g. core, edge, connector, etc.). It depicts core areas of natural land cover, core...
Zhou, Liujiang; Shao, Bin; Shi, Wujun; Sun, Yan; Felser, Claudia; Yan, Binghai; Frauenheim, Thomas
2016-09-01
We report the existence of the quantum spin Hall effect (QSHE) in monolayers of transition-metal carbides MC (M = Zr, Hf). Under ambient conditions, the ZrC monolayer exhibits QSHE with an energy gap of 54 meV, in which topological helical edge states exist. Enhanced d xy -d xy interaction induces band inversion, resulting in nontrivial topological features. By applying in-plane strain, the HfC monolayer can be tuned from a trivial insulator to a quantum spin Hall insulator with an energy gap of 170 meV, three times that of the ZrC monolayer. The strong stability of MC monolayers provides a new platform for QSHE and spintronic applications.
Fractional Quantization of the Hall Effect
Laughlin, R. B.
1984-02-27
The Fractional Quantum Hall Effect is caused by the condensation of a two-dimensional electron gas in a strong magnetic field into a new type of macroscopic ground state, the elementary excitations of which are fermions of charge 1/m, where m is an odd integer. A mathematical description is presented.
Mesoscopic effects in the quantum Hall regime
R N Bhatt; Xin Wan
2002-02-01
We report results of a study of (integer) quantum Hall transitions in a single or multiple Landau levels for non-interacting electrons in disordered two-dimensional systems, obtained by projecting a tight-binding Hamiltonian to the corresponding magnetic subbands. In ﬁnite-size systems, we ﬁnd that mesoscopic effects often dominate, leading to apparent non-universal scaling behavior in higher Landau levels. This is because localization length, which grows exponentially with Landau level index, exceeds the system sizes amenable to the numerical study at present. When band mixing between multiple Landau levels is present, mesoscopic effects cause a crossover from a sequence of quantum Hall transitions for weak disorder to classical behavior for strong disorder. This behavior may be of relevance to experimentally observed transitions between quantum Hall states and the insulating phase at low magnetic ﬁelds.
Silicon-based chalcogenide: Unexpected quantum spin Hall insulator with sizable band gap
Zhang, Run-wu; Zhang, Chang-wen; Ji, Wei-xiao; Li, Ping; Wang, Pei-ji; Li, Sheng-shi; Yan, Shi-shen
2016-10-01
Searching for two-dimensional (2D) silicon-based topological materials is imperative for the development of various innovative devices. Here, by using first-principles calculations, we discover the silicon-based chalcogenide Si2Te2 film to be a 2D quantum spin Hall (QSH) insulator with a fundamental band gap of 0.34 eV, which can be tunable under external strain. This nontrivial topological phase stems from band inversion between the Si-px,y and Te-px,y orbitals, demonstrated by a single pair of topologically protected helical edge states with Dirac point located in the bulk gap. Notably, the characteristic properties of edge states, such as the Fermi velocity and edge shape, can be engineered by edge modifications. Additionally, the BN sheet is an ideal substrate for the experimental realization of Si2Te2 films, without destroying its nontrivial topology. Our works open a meaningful route for designing topological spintronics devices based on 2D silicon-based films.
Coxon, Bruce
2011-01-01
An account is given of the life, scientific contributions, and passing of Laurance David Hall (1938-2009), including his early history and education at the University of Bristol, UK, and the synthesis and NMR spectroscopy of carbohydrates and other natural products during ∼20 years of research and teaching at the University of British Columbia in Vancouver, Canada. Lists of graduate students, post-doctoral fellows, and sabbatical visitors are provided for this period. Following a generous endowment by Dr. Herchel Smith, Professor Hall built a new Department of Medicinal Chemistry at Cambridge University, UK, and greatly expanded his researches into the technology and applications of magnetic resonance imaging (MRI) and zero quantum NMR. MRI technology was applied both to medical problems such as the characterization of cartilage degeneration in knee joints, the measurement of ventricular function, lipid localization in animal models of atherosclerosis, paramagnetic metal complexes of polysaccharides as contrast agents, and studies of many other anatomical features, but also to several aspects of materials analysis, including food analyses, process control, and the elucidation of such physical phenomena as the flow of liquids through porous media, defects in concrete, and the visualization of fungal damage to wood. Professor Hall's many publications, patents, lectures, and honors and awards are described, and also his successful effort to keep the Asilomar facility in Pacific Grove, California as the alternating venue for the annual Experimental NMR Conference. Two memorial services for Professor Hall are remembered.
Milovanović, S. P.; Peeters, F. M.
2017-02-01
The effects of strain, induced by a Gaussian bump, on the magnetic field dependent transport properties of a graphene Hall bar are investigated. The numerical simulations are performed using both classical and quantum mechanical transport theory and we found that both approaches exhibit similar characteristic features. The effects of the Gaussian bump are manifested by a decrease of the bend resistance, R B, around zero-magnetic field and the occurrence of side-peaks in R B. These features are explained as a consequence of bump-assisted scattering of electrons towards different terminals of the Hall bar. Using these features we are able to give an estimate of the size of the bump. Additional oscillations in R B are found in the quantum description that are due to the population/depopulation of Landau levels. The bump has a minor influence on the Hall resistance even for very high values of the pseudo-magnetic field. When the bump is placed outside the center of the Hall bar valley polarized electrons can be collected in the leads.
Crisp, D J; W Moran; Pollington, A. D.
2012-01-01
We show that the inhomogenous approximation spectrum, associated to an irrational number \\alpha\\ always has a Hall's Ray; that is, there is an \\epsilon>0 such that [0,\\epsilon) is a subset of the spectrum. In the case when \\alpha\\ has unbounded partial quotients we show that the spectrum is just a ray.
Oguntoyinbo, Lekan
2011-01-01
Many urban and commuter universities have their sights set on students who are unlikely to connect with the college and likely to fail unless the right strategies are put in place to help them graduate. In efforts to improve retention rates, commuter colleges are looking to an unusual suspect: residence halls. The author discusses how these…
Ben-Abdallah, Philippe
2015-01-01
A near-field thermal Hall effect (i.e.Righi-Leduc effect) in lattices of magneto-optical particles placed in a constant magnetic field is predicted. This effect is related to a symetry breaking in the system induced by the magnetic field which gives rise to preferential channels for the heat-transport by photon tunneling thanks to the particles anisotropy tuning.
Barteld Kooi, [No Value
2006-01-01
Samenvatting: In het begin van de jaren negentig brak een wereldwijde discussie los over een probleem dat in het Engels 'The Monty Hall Dilemma' wordt genoemd. Marilyn vos Savant, die in het Guinness Book of World Records wordt genoemd als degene met het
The local nature of incompressibility of quantum Hall effect
Kendirlik, E. M.; Sirt, S.; Kalkan, S. B.; Ofek, N.; Umansky, V.; Siddiki, A.
2017-01-01
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry. Here, by our magneto-transport measurements performed on GaAs/AlGaAs high purity Hall bars with two inner contacts we show that incompressible strips formed at the edges result in Hall quantization, even if the bulk is compressible. Consequently, the relationship between the quantum Hall effect and topological bulk insulator breaks for specific field intervals within the plateaus. The measurement of conducting bulk, strongly challenges all existing single-particle theories. PMID:28071652
The local nature of incompressibility of quantum Hall effect
Kendirlik, E. M.; Sirt, S.; Kalkan, S. B.; Ofek, N.; Umansky, V.; Siddiki, A.
2017-01-01
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry. Here, by our magneto-transport measurements performed on GaAs/AlGaAs high purity Hall bars with two inner contacts we show that incompressible strips formed at the edges result in Hall quantization, even if the bulk is compressible. Consequently, the relationship between the quantum Hall effect and topological bulk insulator breaks for specific field intervals within the plateaus. The measurement of conducting bulk, strongly challenges all existing single-particle theories.
Plasma Relaxation in Hall Magnetohydrodynamics
Shivamoggi, B K
2011-01-01
Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient alpha in the Hall MHD Beltrami condition turns out now to be proportional to the "potential vorticity." The Hall MHD Beltrami condition becomes equivalent to the "potential vorticity" conservation equation in two-dimensional hydrodynamics if the Hall MHD Lagrange multiplier beta is taken to be proportional to the "potential vorticity" as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as "potential vorticity" lines in 2D hydrodynamics.
Probing bulk physics in the 5/2 fractional quantum Hall effect using the Corbino geometry
Schmidt, Benjamin; Bennaceur, Keyan; Bilodeau, Simon; Gaucher, Samuel; Lilly, Michael; Reno, John; Pfeiffer, Loren; West, Ken; Reulet, Bertrand; Gervais, Guillaume
We present two- and four-point Corbino geometry transport measurements in the second Landau level in GaAs/AlGaAs heterostructures. By avoiding edge transport, we are able to directly probe the physics of the bulk quasiparticles in fractional quantum Hall (FQH) states including 5/2. Our highest-quality sample shows stripe and bubble phases in high Landau levels, and most importantly well-resolved FQH minima in the second Landau level. We report Arrhenius-type fits to the activated conductance, and find that σ0 agrees well with theory and existing Hall geometry data in the first Landau level, but not in the second Landau level. We will discuss the advantages the Corbino geometry could bring to various experiments designed to detect the non-Abelian entropy at 5/2, and our progress towards realizing those schemes. The results of these experiments could complement interferometry and other edge-based measurements by providing direct evidence for non-Abelian behaviour of the bulk quasiparticles. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL8500.
Geometric spin Hall effect of light with inhomogeneous polarization
Ling, Xiaohui; Zhou, Xinxing; Yi, Xunong
2017-01-01
The spin Hall effect of light originates from spin-orbit interaction of light, which manifests two types of geometric phases. In this paper, we report the observation of a geometric spin Hall effect by generating a light beam with inhomogeneous polarization distribution. Unlike the previously reported geometric spin Hall effect observed in a tilted beam-detector system, which is believed to result from an effective spin-redirection Berry geometric phase, the geometric spin Hall effect demonstrated here is attributed to an effective, spatially varying Pancharatnam-Berry geometric phase generated by the inhomogeneous polarization geometry. Our further experiments show that the geometric spin Hall effect can be tuned by tailoring the polarization geometry of light, demonstrating the spin states of photons can be steered with a great flexibility.
Cylindrical geometry hall thruster
Raitses, Yevgeny; Fisch, Nathaniel J.
2002-01-01
An apparatus and method for thrusting plasma, utilizing a Hall thruster with a cylindrical geometry, wherein ions are accelerated in substantially the axial direction. The apparatus is suitable for operation at low power. It employs small size thruster components, including a ceramic channel, with the center pole piece of the conventional annular design thruster eliminated or greatly reduced. Efficient operation is accomplished through magnetic fields with a substantial radial component. The propellant gas is ionized at an optimal location in the thruster. A further improvement is accomplished by segmented electrodes, which produce localized voltage drops within the thruster at optimally prescribed locations. The apparatus differs from a conventional Hall thruster, which has an annular geometry, not well suited to scaling to small size, because the small size for an annular design has a great deal of surface area relative to the volume.
Bliokh, Konstantin Y
2011-01-01
We consider the relativistic deformation of quantum waves and mechanical bodies carrying intrinsic angular momentum (AM). When observed in a moving reference frame, the centroid of the object undergoes an AM-dependent transverse shift. This is the relativistic analogue of the spin Hall effect, which occurs in free space without any external fields. Remarkably, the shifts of the geometric and energy centroids differ by a factor of 2, and both centroids are crucial for the correct Lorentz transformations of the AM tensor. We examine manifestations of the relativistic Hall effect in quantum vortices, mechanical flywheel, and discuss various fundamental aspects of the phenomenon. The perfect agreement of quantum and relativistic approaches allows applications at strikingly different scales: from elementary spinning particles, through classical light, to rotating black-holes.
Nobili, Andrea; Radi, Enrico; Lanzoni, Luca
2017-08-01
The problem of a rectilinear crack propagating at constant speed in an elastically supported thin plate and acted upon by an equally moving load is considered. The full-field solution is obtained and the spotlight is set on flexural edge wave generation. Below the critical speed for the appearance of travelling waves, a threshold speed is met which marks the transformation of decaying edge waves into edge waves propagating along the crack and dying away from it. Yet, besides these, and for any propagation speed, a pair of localized edge waves, which rapidly decay behind the crack tip, is also shown to exist. These waves are characterized by a novel dispersion relation and fade off from the crack line in an oscillatory manner, whence they play an important role in the far field behaviour. Dynamic stress intensity factors are obtained and, for speed close to the critical speed, they show a resonant behaviour which expresses the most efficient way to channel external work into the crack. Indeed, this behaviour is justified through energy considerations regarding the work of the applied load and the energy release rate. Results might be useful in a wide array of applications, ranging from fracturing and machining to acoustic emission and defect detection.
Zeuthen, Helene; Kudernatsch, Wilhelmine; Merte, Lindsay Richard
2015-01-01
reaction environments we studied pristine, oxidized, and reduced FeO islands. Oxidation of the FeO islands by O2 exposure led to the formation of two types of O adatom dislocations and to a restructuring of the FeO islands, creating long O-rich edges and few short Fe terminated edges. In contrast, reducing...... FeO films and geometrical considerations we unraveled the atomic structure of the predominant FeO boundaries of pristine, oxidized, and reduced FeO islands. The results indicate an astonishing flexibility of the FeO islands on Pt(111), since the predominant edge termination and the island shape......We used high-resolution scanning tunneling microscopy to study the structure of ultrathin FeO islands grown on Pt(111). Our focus is particularly on the edges of the FeO islands that are important in heterogeneous catalysis, as they host the active sites on inversed catalysts. To imitate various...
Co K-edge magnetic circular dichroism across the spin state transition in LaCoO3 single crystal
Efimov, V.; Ignatov, A.; Troyanchuk, I. O.; Sikolenko, V. V.; Rogalev, A.; Wilhelm, F.; Efimova, E.; Tiutiunnikov, S. I.; Karpinsky, D.; Kriventsov, V.; Yakimchuk, E.; Molodtsov, S.; Sainctavit, P.; Prabhakaran, D.
2016-05-01
We report on Co K-edge x-ray magnetic circular dichroism (XMCD) measurements of LaCoO3 single crystal in temperature range from 5 to 300 K and external magnetic field of 17 T. The response consists of pre-edge (at 7712 eV) and bi-polar peak (up at 7727, down at 7731 eV) with amplitudes, respectively, less than 10-3 and 10-2 of the Co K-edge jump. Using the sum rule the orbital magnetic moment of 4p Co is evaluated. Its temperature dependence reaches a maximum of (2.7 ± 0.9) x10-3 μB at 120 K, following the trend for the total magnetic moment on the Co obtained from the superconducting quantum interference device measurements. However, on warming from 25 to 120 K, the orbital magnetic moment of the 4p Co doubles while total magnetic moment of Co increases 10 times. First principle calculations are in order to relate the Co K-edge XMCD results to the orbital and spin moment of 3d Co.
Bason, Y.; Klein, L.; Yau, J. -B.; Hong, X.; Hoffman, J.; Ahn, C. H.
2005-01-01
We suggest a new type of magnetic random access memory (MRAM) that is based on the phenomenon of the planar Hall effect (PHE) in magnetic films, and we demonstrate this idea with manganite films. The PHE-MRAM is structurally simpler than currently developed MRAM that is based on magnetoresistance tunnel junctions (MTJ), with the tunnel junction structure being replaced by a single layer film.
EL CROWN HALL. CONTEXTO Y PROYECTO
Laura Lizondo Sevilla
2010-05-01
Full Text Available RESUMEN El artículo enmarca el edificio del Crown Hall en el contexto docente y arquitectónico de Mies van der Rohe. Revisa sus inicios en la Bauhaus con su primera intervención en un espacio docente para la Bauhaus de Berlín en 1932, así como su marcha a Estados Unidos, los planteamientos arquitectónicos del campus del IIT y el proyecto del Crown Hall. El texto incide en el estudio del proceso proyectual del Crown Hall analizando la evolución de su concepción arquitectónica a través de las diferentes versiones del proyecto. Se constata la transición desde los primeros planteamientos arquitectónicos de los edificios del campus del IIT proyectados por Mies hacia el planteamiento del gran espacio unitario del Crown Hall. Este proyecto se puede entender desde la creciente importancia de la estructura, la claridad constructiva y el manejo del acero y vidrio como únicos materiales de la imagen del edificio y el carácter flexible y unitario del espacio. Finalmente se hace referencia al concepto del "espacio universal" en la arquitectura de Mies, como un concepto abstracto que supera los de flexibilidad de uso o unidad espacial, insinuando, a modo de reflexión, las principales variables que definirían el espacio universal miesiano.SUMMARY The article showcases the Crown Hall building in the educational and architectural context of Mies van der Rohe. It reviews his beginnings in the Bauhaus with his first intervention in an educational space for the Bauhaus of Berlin in 1932, as well as his sojourn to the United States, and the architectural approaches to the IIT campus and the Crown Hall project. The text touches on the study of the planning process for the Crown Hall, analysing the evolution of its architectural conception, through the different versions of the project. The article covers the transition from the first architectural approaches for the IIT campus buildings, planned by Mies, to the approach of the large unitary space of
Correlated Electrons in Two Dimensions: The Fractional Quantum Hall Effect and More
Eisenstein, James
2014-03-01
A collection of electrons confined to move on a plane surface is surely one of the simplest many-body systems imaginable. But in spite of this apparent simplicity, a strong magnetic field applied perpendicular to the plane opens a door to a complex and beautiful world filled with many-body exotica. The magnetic field quenches the kinetic energy, leaving Coulomb interactions in control of the physics. The result has been a revolution in many-body physics comparable to that created by the discovery of superconductivity. Incompressible liquid ground states with fractionally charged quasiparticle excitations exhibit the quantized Hall effect at numerous discrete partial fillings of the lowest and first excited Landau level. The first examples of topological condensed matter, these many-body bulk insulators possess complex families of both conducting and neutral edge states at their boundaries. Highly correlated compressible phases of composite fermions also exist and may be viewed as progenitors of the various families of incompressible states. Multi-component two-dimensional systems with active discrete internal degrees of freedom (spin, layer, valley, etc.) display a wide array of broken symmetry states including ferromagnetism and exciton condensation. Now thirty years old, the field generically dubbed ``the fractional quantum Hall effect,'' remains extraordinarily vibrant. Once confined largely to GaAs/AlGaAs heterostructures, the fractional quantum Hall effect and its many relatives and offspring are now pursued in graphene, various oxide interfaces, and other materials. Some of the most fundamental aspects, including the exotic non-abelian quasiparticle statistics expected of some of the more subtle phases, have hardly been touched experimentally even as their potential for applications to quantum computation is alluring. In this talk, I will try to give a flavor of this enormous field, emphasizing current topics and possible future directions.
Earon, Ofri
2013-01-01
the building. The research explores and develops the architectural characteristics of correlations between the resident, the singular unit, the building and the given location at the edge zone. It approaches the edge zone of the urban house as a platform for dynamic interactions between these behaviours....... The following text includes the first draft of the first two chapters: introduction and theory. The chapters are not written completely, and some parts are written only as headlines. These headlines and other comments are marked in red. The text is on working progress and far from being finished...
Earon, Ofri
2014-01-01
of the involved actors at the border. By doing so, the study underlines a forgotten, yet important, role of this edge zone – being a zone of commonality between the house and city, between indoors and outdoors, between the man at home and the man at the street. The city of Copenhagen promotes porous borders...... is a collection of material from the case study of an ongoing PhD study titled: LIVING EDGE - The Architectural and Urban Prospect of Domestic Borders. The paper includes a description of the problem analysis, research question, method, discussion and conclusion....
Wheel of concert hall acoustics
Kuusinen, A.; Lokki, T.
2017-01-01
More than a hundred years of research on concert hall acoustics has provided an extensive list of attributes to describe and evaluate the perceptual aspects of sound in concert halls. This brief overview discusses the current knowledge, and presents a "wheel of concert hall acoustics" in which the main aspects are gathered together with the descriptive attributes that are commonly encountered in the research literature. Peer reviewed
Thermal Hall Effect of Magnons
Murakami, Shuichi; Okamoto, Akihiro
2017-01-01
We review recent developments in theories and experiments on the magnon Hall effect. We derive the thermal Hall conductivity of magnons in terms of the Berry curvature of magnonic bands. In addition to the Dzyaloshinskii-Moriya interaction, we show that the dipolar interaction can make the Berry curvature nonzero. We mainly discuss theoretical aspects of the magnon Hall effect and related theoretical works. Experimental progress in this field is also mentioned.
The transport mechanism of the integer quantum Hall effect
LiMing, W
2016-01-01
The integer quantum Hall effect is analysed using a transport mechanism with a semi-classic wave packages of electrons in this paper. A strong magnetic field perpendicular to a slab separates the electron current into two branches with opposite wave vectors $({\\it k})$ and locating at the two edges of the slab, respectively, along the current. In this case back scattering of electrons ($k\\rightarrow -k$) is prohibited by the separation of electron currents. Thus the slab exhibits zero longitudinal resistance and plateaus of Hall resistance. When the Fermi level is scanning over a Landau level when the magnetic field increases, however, the electron waves locate around the central axis of the slab and overlap each other thus back scattering of electrons takes place frequently. Then longitudinal resistance appears and the Hall resistance goes up from one plateau to a new plateau.
Tripartite composite fermion states
Sreejith, G. J.; Wu, Ying-Hai; Wójs, A.; Jain, J. K.
2013-06-01
The Read-Rezayi wave function is one of the candidates for the fractional quantum Hall effect at filling fraction ν=2+⅗, and thereby also its hole conjugate at 2+⅖. We study a general class of tripartite composite fermion wave functions, which reduce to the Rezayi-Read ground state and quasiholes for appropriate quantum numbers, but also allow a construction of wave functions for quasiparticles and neutral excitations by analogy to the standard composite fermion theory. We present numerical evidence in finite systems that these trial wave functions capture well the low energy physics of a four-body model interaction. We also compare the tripartite composite fermion wave functions with the exact Coulomb eigenstates at 2+⅗, and find reasonably good agreement. The ground state as well as several excited states of the four-body interaction are seen to evolve adiabatically into the corresponding Coulomb states for N=15 particles. These results support the plausibility of the Read-Rezayi proposal for the 2+⅖ and 2+⅗ fractional quantum Hall effect. However, certain other proposals also remain viable, and further study of excitations and edge states will be necessary for a decisive establishment of the physical mechanism of these fractional quantum Hall states.
Modelling of micro-Hall sensors for magnetization imaging
Manzin, A.; Nabaei, V.
2014-05-01
This paper presents a numerical model for the study of micro-Hall magnetometry applications, aiming at evaluating the sensitivity of semiconductor miniaturized devices to the stray field of permalloy nanostructures with ring and disk geometry. The procedure couples a micromagnetic code, for the calculation of the stray field generated by the nanomagnet, to a 2D classical transport model for the determination of the electric potential distribution inside the Hall plate. The model is applied to study the sensitivity of a micro-Hall device in the detection of magnetization switching processes characterized by vortex state, focusing on the influence of magnetic nanostructure position.
Hall effect in CNT doped YBCO high temperature superconductor
S Dadras
2010-09-01
Full Text Available In order to study Hall effect in pure and CNT doped YBCO polycrystalline samples, we have measured longitudinal and transverse voltages at the different magnetic field (0-9T in the vortex state. We found a sign reversal for pure sample near 3T and double sign reversal of the Hall coefficient for CNT doped sample near 3 and 5T. It can be deduced that CNT doping caused strong flux pinning and Hall double sign reversal in this compound.
Protected Edge Modes without Symmetry
Michael Levin
2013-05-01
Full Text Available We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, K_{H}≠0, support such modes, here we show that robust modes can also occur when K_{H}=0—if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and K_{H}=0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle types M such that (1 all the quasiparticles in M have trivial mutual statistics, and (2 every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems.
Szabo, James J.
2015-01-01
This Phase II project is developing a magnesium (Mg) Hall effect thruster system that would open the door for in situ resource utilization (ISRU)-based solar system exploration. Magnesium is light and easy to ionize. For a Mars- Earth transfer, the propellant mass savings with respect to a xenon Hall effect thruster (HET) system are enormous. Magnesium also can be combusted in a rocket with carbon dioxide (CO2) or water (H2O), enabling a multimode propulsion system with propellant sharing and ISRU. In the near term, CO2 and H2O would be collected in situ on Mars or the moon. In the far term, Mg itself would be collected from Martian and lunar regolith. In Phase I, an integrated, medium-power (1- to 3-kW) Mg HET system was developed and tested. Controlled, steady operation at constant voltage and power was demonstrated. Preliminary measurements indicate a specific impulse (Isp) greater than 4,000 s was achieved at a discharge potential of 400 V. The feasibility of delivering fluidized Mg powder to a medium- or high-power thruster also was demonstrated. Phase II of the project evaluated the performance of an integrated, highpower Mg Hall thruster system in a relevant space environment. Researchers improved the medium power thruster system and characterized it in detail. Researchers also designed and built a high-power (8- to 20-kW) Mg HET. A fluidized powder feed system supporting the high-power thruster was built and delivered to Busek Company, Inc.
Fractional quantum Hall effect in the absence of Landau levels.
Sheng, D N; Gu, Zheng-Cheng; Sun, Kai; Sheng, L
2011-07-12
It is well known that the topological phenomena with fractional excitations, the fractional quantum Hall effect, will emerge when electrons move in Landau levels. Here we show the theoretical discovery of the fractional quantum Hall effect in the absence of Landau levels in an interacting fermion model. The non-interacting part of our Hamiltonian is the recently proposed topologically non-trivial flat-band model on a checkerboard lattice. In the presence of nearest-neighbouring repulsion, we find that at 1/3 filling, the Fermi-liquid state is unstable towards the fractional quantum Hall effect. At 1/5 filling, however, a next-nearest-neighbouring repulsion is needed for the occurrence of the 1/5 fractional quantum Hall effect when nearest-neighbouring repulsion is not too strong. We demonstrate the characteristic features of these novel states and determine the corresponding phase diagram.
2008-09-23
in Fig. 1. An alternating current source operating at frequency f1 is attached to contacts B and D with a respective lock-in amplifier monitoring...that floats the signal and a transconductance amplifier . The input voltage of each lock-in amplifier is composed of two signals: the Hall voltage at...alternating current sources operating at frequencies f1 and f2 respectively. VAC and VDB are lock-in amplifiers set for the reference frequencies f2 and f1
2015-01-01
This paper describes a simple microwave apparatus to measure the Hall effect in semiconductor wafers. The advantage of this technique is that it does not require contacts on the sample or the use of a resonant cavity. Our method consists of placing the semiconductor wafer into a slot cut in an X-band (8 - 12 GHz) waveguide series tee, injecting microwave power into the two opposite arms of the tee, and measuring the microwave output at the third arm. A magnetic field applied perpendicular to ...
Li, Yuanchang
2016-01-01
It is generally believed that the inter-edge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of inter-edge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the non-trivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one m...
Fuzzy spaces, the M(atrix) model and the quantum Hall effect
Karabali, D; Randjbar-Daemi, S; Karabali, Dimitra
2004-01-01
This is a short review of recent work on fuzzy spaces in their relation to the M(atrix) theory and the quantum Hall effect. We give an introduction to fuzzy spaces and how the limit of large matrices is obtained. The complex projective spaces ${\\bf CP}^k$, and to a lesser extent spheres, are considered. Quantum Hall effect and the behavior of edge excitations of a droplet of fermions on these spaces and their relation to fuzzy spaces are also discussed.
New resistivity for high-mobility quantum Hall conductors
Mceuen, P. L.; Szafer, A.; Richter, C. A.; Alphenaar, B. W.; Jain, J. K.
1990-01-01
Measurements showing dramatic nonlocal behavior in the four-terminal resistances of a high-mobility quantum Hall conductor are presented. These measurements illustrate that the standard definition of the resistivity tensor is inappropriate, but they are in excellent agreement with a new model of the conductor that treats the edge and bulk conducting pathways independently. This model uses a single intensive parameter, analogous to a local resistivity for the bulk channel only, to characterize the system.
Cosmopolitanism - Conversation with Stuart Hall
Hall, Stuart
2006-01-01
Forty minute conversation between Stuart Hall and Pnina Werbner, filmed and edited by Haim Bresheeth. Synopsis by Sarah Harrison. Conversation between Stuart Hall and Pnina Werbner on the theme of Cosmopolitanism (to be shown at the Association of Social Anthropologists Silver Jubilee conference in 2006), in March 2006
Zhou, Liujiang; Shi, Wujun; Sun, Yan; Shao, Bin; Felser, Claudia; Yan, Binghai; Frauenheim, Thomas
2016-09-01
Quantum spin Hall (QSH) insulates exist in special two-dimensional (2D) semiconductors, possessing the quantized spin-Hall conductance that are topologically protected from backscattering. Based on the first-principles calculations, we predict a novel family of QSH insulators in 2D tantalum carbide halides TaCX (X = Cl, Br, and I) with unique rectangular lattice and large direct energy gaps. The mechanism for 2D QSH effect originates from an intrinsic d-d band inversion in the process of chemical bonding. Further, stain and intrinsic electric field can be used to tune the electronic structure and enhance the energy gap. TaCX nanoribbon, which has the single-Dirac-cone edge states crossing the bulk band gap, exhibits a linear dispersion with a high Fermi velocity comparable to that of graphene. These 2D materials with considerable nontrivial gaps promise great application potential in the new generation of dissipationless electronics and spintronics.
Khaibrakhmanov, Sergey A; Parfenov, Sergey Yu; Sobolev, Andrey M
2016-01-01
We investigate the fossil magnetic field in the accretion and protoplanetary discs using the Shakura and Sunyaev approach. The distinguishing feature of this study is the accurate solution of the ionization balance equations and the induction equation with Ohmic diffusion, magnetic ambipolar diffusion, buoyancy and the Hall effect. We consider the ionization by cosmic rays, X-rays and radionuclides, radiative recombinations, recombinations onto dust grains, and also thermal ionization. The buoyancy appears as the additional mechanism of magnetic flux escape in the steady-state solution of the induction equation. Calculations show that Ohmic diffusion and magnetic ambipolar diffusion constraint the generation of the magnetic field inside the `dead' zones. The magnetic field in these regions is quasi-vertical. The buoyancy constraints the toroidal magnetic field strength close to the disc inner edge. As a result, the toroidal and vertical magnetic fields become comparable. The Hall effect is important in the re...
Watashige, Tatsuya; Arsenijević, Stevan; Yamashita, Takuya; Terazawa, Daiki; Onishi, Takafumi; Opherden, Lars; Kasahara, Shigeru; Tokiwa, Yoshifumi; Kasahara, Yuichi; Shibauchi, Takasada; von Löhneysen, Hilbert; Wosnitza, Jochen; Matsuda, Yuji
2017-01-01
There is growing evidence that the superconducting semimetal FeSe (Tc ˜ 8 K) is in the crossover regime between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits. We report on longitudinal and transverse thermal conductivities, κxx and κxy, respectively, in magnetic fields up to 20 T. The field dependences of κxx and κxy imply that a highly anisotropic small superconducting gap forms at the electron Fermi-surface pocket whereas a more isotropic and larger gap forms at the hole pocket. Below ˜1.0 K, both κxx and κxy exhibit distinct anomalies (kinks) at the upper critical field Hc2 and at a field H* slightly below Hc2. The analysis of the thermal Hall angle (κxy/κxx) indicates a change of the quasiparticle scattering rate at H*. These results provide strong support to the previous suggestion that above H* a distinct field-induced superconducting phase emerges with an unprecedented large spin imbalance.
Topologically protected quantum state transfer in a chiral spin liquid.
Yao, N Y; Laumann, C R; Gorshkov, A V; Weimer, H; Jiang, L; Cirac, J I; Zoller, P; Lukin, M D
2013-01-01
Topology plays a central role in ensuring the robustness of a wide variety of physical phenomena. Notable examples range from the current-carrying edge states associated with the quantum Hall and the quantum spin Hall effects to topologically protected quantum memory and quantum logic operations. Here we propose and analyse a topologically protected channel for the transfer of quantum states between remote quantum nodes. In our approach, state transfer is mediated by the edge mode of a chiral spin liquid. We demonstrate that the proposed method is intrinsically robust to realistic imperfections associated with disorder and decoherence. Possible experimental implementations and applications to the detection and characterization of spin liquid phases are discussed.
Maximilien Brice
2011-01-01
8 April 2011 - Brazilian Minister of State for Science and Technology A. Mercadante Oliva signing the guest book with CERN Director-General R. Heuer and Head of International Relations F. Pauss; in the ATLAS visitor centre with Collaboration Former Spokesperson P. Jenni; visiting LHC superconducting magnet test hall with J.M. Jimenez.
Maximilien Brice; SM18
2009-01-01
William Brinkman (centre), Director of the Department of Energy, U.S.A. at the superconducting magnet test hall SM18 with (from left to right) Coordinator for External Relations F. Pauss, Advisor for Non-Member States J. Ellis, J. Strait from Fermilab and Deputy Head of Technology Department L. Rossi on 13 November 2009.
Benoît Jeannet
2011-01-01
Austrian state secretary for foreign affairs, Wolfgang Waldner, left, was welcomed to CERN by Felicitas Pauss, head of international relations at CERN, on 19 September. While at CERN, he toured the CMS control room and underground experimental service cavern, the LHC superconducting magnet test hall, and the Universe of Particles exhibition in the Globe of Science and Innovation.
The Evolution of College Residence Halls in the United States%美国高校宿舍教育的历史分析：宿舍与人才培养
徐波; 苍玉权
2014-01-01
美国高校学生宿舍从早期承担的生活功能、管理功能，到近50年才开拓的教育功能，走过了漫长的历史。殖民时期，受英国牛津剑桥模式的影响，采用住宿学院制，宿舍主要作用是代替父母监督；内战结束后至19世纪后期，受德国大学影响，认为为学生提供宿舍没有意义；19世纪后期至20世纪中期，伴随赠地学院的发展，宿舍建设再次兴起，这个时期宿舍主要作用是为学生提供生活服务；20世纪60年代以后，宿舍教育功能被广泛认可，开始有目的地设计宿舍教育环境，宿舍成为学生课堂教育与非课堂教育的衔接，成为促进学生全面发展的教育资源。%Collegiate housing has been in existence for more than 300 years in the United States. During the early period, American residence halls followed the English residential college model of Oxford and Cambridge with the function of supervision. Between 1850 and the late nineteenth century, influenced by the German university model, residence halls were denounced as inappropriate and a waste of money in American universities. Between the late nineteenth century and the mid-twentieth century, trends in American higher education once again encouraged the construction of residence halls. Since 1960s, to extend learning outside of the classroom, student affairs educators have infused programmatic curriculums and strategic management techniques into the residential experience.
New type of quantum spin Hall insulators in hydrogenated PbSn thin films
Liu, Liang; Qin, Hongwei; Hu, Jifan
2017-01-01
The realization of a quantum spin Hall (QSH) insulator working at high temperature is of both scientific and technical interest since it supports spin-polarized and dssipationless edge states. Based on first-principle calculations, we predicted that the two-dimensional (2D) binary compound of lead and tin (PbSn) in a buckled honeycomb framework can be tuned into a topological insulator with huge a band gap and structural stability via hydrogenation or growth on special substrates. This heavy-element-based structure is sufficiently ductile to survive the 18 ps molecular dynamics (MD) annealing to 400 K, and the band gap opened by strong spin-orbital-coupling (SOC) is as large as 0.7 eV. These characteristics indicate that hydrogenated PbSn (H-PbSn) is an excellent platform for QSH realization at high temperature. PMID:28218297
Robust large-gap quantum spin Hall insulators in chemically decorated arsenene films
Wang, Dongchao; Chen, Li; Shi, Changmin; Wang, Xiaoli; Cui, Guangliang; Zhang, Pinhua; Chen, Yeqing
2016-03-01
Based on first-principles calculations, we propose one new category of two-dimensional topological insulators (2D TIs) in chemically functionalized (-CH3 and -OH) arsenene films. The results show that the surface decorated arsenene (AsCH3 and AsOH) films are intrinsic 2D TIs with sizeable bulk gap. The bulk energy gaps are 0.184 eV, and 0.304 eV in AsCH3 and AsOH films, respectively. Such large bulk gaps make them suitable to realize quantum spin Hall effect in an experimentally accessible temperature regime. Topologically helical edge states in these systems are desirable for dissipationless transport. Moreover, we find that the topological properties in these systems are robust against mechanical deformation by exerting biaxial strain. These novel 2D TIs with large bulk gaps are potential candidate in future electronic devices with ultralow dissipation.
Quantum spin Hall effect and spin-charge separation in a kagome lattice
Wang Zhigang; Zhang Ping, E-mail: zhang_ping@iapcm.ac.c [LCP, Institute of Applied Physics and Computational Mathematics, PO Box 8009, Beijing 100088 (China)
2010-04-15
A two-dimensional kagome lattice is theoretically investigated within a simple tight-binding model, which includes the nearest-neighbor hopping term and the intrinsic spin-orbit interaction between the next nearest neighbors. By using the topological winding properties of the spin-edge states on the complex-energy Riemann surface, the spin Hall conductance is obtained to be quantized as -e/2{pi} (e/2{pi}) in insulating phases. This result is consistent with the numerical linear-response calculation and the Z{sub 2} topological invariance analysis. When the sample boundaries are connected in twist, by which two defects with {pi} flux are introduced, we obtain the spin-charge separated solitons at 1/3 (or 2/3) filling.
1985-09-01
PROJECT. T ASK0 Artificial Inteligence Laboratory AREA It WORK UNIT NUMBERS V 545 Technology Square ( Cambridge, HA 02139 I I* CONTOOL1LIN@4OFFICE NAME...ARD-A1t62 62 EDGE DETECTION(U) NASSACNUSETTS INST OF TECH CAMBRIDGE 1/1 ARTIFICIAL INTELLIGENCE LAB E C HILDRETH SEP 85 AI-M-8 N99SI4-8S-C-6595...used to carry out this analysis. cce~iO a N) ’.~" D LI’BL. P p ------------ Sj. t i MASSACHUSETTS INSTITUTE OF TECHNOLOGY i ARTIFICIAL INTELLIGENCE
Hall Effect Gyrators and Circulators
Viola, Giovanni; DiVincenzo, David P.
2014-04-01
The electronic circulator and its close relative the gyrator are invaluable tools for noise management and signal routing in the current generation of low-temperature microwave systems for the implementation of new quantum technologies. The current implementation of these devices using the Faraday effect is satisfactory but requires a bulky structure whose physical dimension is close to the microwave wavelength employed. The Hall effect is an alternative nonreciprocal effect that can also be used to produce desired device functionality. We review earlier efforts to use an Ohmically contacted four-terminal Hall bar, explaining why this approach leads to unacceptably high device loss. We find that capacitive coupling to such a Hall conductor has much greater promise for achieving good circulator and gyrator functionality. We formulate a classical Ohm-Hall analysis for calculating the properties of such a device, and show how this classical theory simplifies remarkably in the limiting case of the Hall angle approaching 90°. In this limit, we find that either a four-terminal or a three-terminal capacitive device can give excellent circulator behavior, with device dimensions far smaller than the ac wavelength. An experiment is proposed to achieve GHz-band gyration in millimeter (and smaller) scale structures employing either semiconductor heterostructure or graphene Hall conductors. An inductively coupled scheme for realizing a Hall gyrator is also analyzed.
Diagnostics Systems for Permanent Hall Thrusters Development
Ferreira, Jose Leonardo; Soares Ferreira, Ivan; Santos, Jean; Miranda, Rodrigo; Possa, M. Gabriela
-Effect Thruster (PMHET), developed at the Plasma Physics Laboratory of UnB. The idea of using an array of permanent magnets, instead of an electromagnet, to produce a radial magnetic field inside the cylindrical plasma drift channel of the thruster is very attractive, especially because of the possibility of developing a HET with power consumption low enough to be used in small satellites or medium-size satellites with low on board power. Hall-Effect Thrusters are now a very good option for spacecraft primary propulsion and also for station-keeping of medium and large satellites. This is because of their high specific impulse, efficient use of propellant mass and combined low and precise thrust capabilities, which are related to an economy in terms of propellant mass utilization , longer satellite lifetime and easier spacecraft maneuvering in microgravity environment. The first HETs were developed in the mid 1950’s, and they were first called Closed Drift Thrusters. Today, the successful use of electric thrusters for attitude control and orbit modification on hundreds of satellites shows the advanced stage of development of this technology. In addition to this, after the success of space missions such as Deep Space One and Dawn (NASA), Hayabusa (JAXA) and Smart-1 (ESA), the employment of electric thrusters is also consolidated for the primary propulsion of spacecraft. This success is mainly due to three factors: reliability of this technology; efficiency of propellant utilization, and therefore reduction of the initial mass of the ship; possibility of operation over long time intervals, with practically unlimited cycling and restarts. This thrusting system is designed to be used in satellite attitude control and long term space missions. One of the greatest advantage of this kind of thruster is the production of a steady state magnetic field by permanent magnets providing electron trapping and Hall current generation within a significant decrease on the electric energy supply
Edge phonons in black phosphorus
Ribeiro, H. B.; Villegas, C. E. P.; Bahamon, D. A.; Muraca, D.; Castro Neto, A. H.; de Souza, E. A. T.; Rocha, A. R.; Pimenta, M. A.; de Matos, C. J. S.
2016-07-01
Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.
Topological Hall and spin Hall effects in disordered skyrmionic textures
Ndiaye, Papa Birame
2017-02-24
We carry out a thorough study of the topological Hall and topological spin Hall effects in disordered skyrmionic systems: the dimensionless (spin) Hall angles are evaluated across the energy-band structure in the multiprobe Landauer-Büttiker formalism and their link to the effective magnetic field emerging from the real-space topology of the spin texture is highlighted. We discuss these results for an optimal skyrmion size and for various sizes of the sample and find that the adiabatic approximation still holds for large skyrmions as well as for nanoskyrmions. Finally, we test the robustness of the topological signals against disorder strength and show that the topological Hall effect is highly sensitive to momentum scattering.
Tuning giant anomalous Hall resistance ratio in perpendicular Hall balance
Zhang, J. Y.; Yang, G. [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wang, S. G., E-mail: sgwang@iphy.ac.cn, E-mail: ghyu@mater.ustb.edu.cn [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Liu, J. L. [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Department of Physics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Wang, R. M. [Department of Physics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Amsellem, E.; Kohn, A. [Department of Materials Engineering, Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Yu, G. H., E-mail: sgwang@iphy.ac.cn, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)
2015-04-13
Anomalous Hall effect at room temperature in perpendicular Hall balance with a core structure of [Pt/Co]{sub 4}/NiO/[Co/Pt]{sub 4} has been tuned by functional CoO layers, where [Pt/Co]{sub 4} multilayers exhibit perpendicular magnetic anisotropy. A giant Hall resistance ratio up to 69 900% and saturation Hall resistance (R{sub S}{sup P}) up to 2590 mΩ were obtained in CoO/[Pt/Co]{sub 4}/NiO/[Co/Pt]{sub 4}/CoO system, which is 302% and 146% larger than that in the structure without CoO layers, respectively. Transmission electron microscopy shows highly textured [Co/Pt]{sub 4} multilayers and oxide layers with local epitaxial relations, indicating that the crystallographic structure has significant influence on spin dependent transport properties.
Ward Identities for Hall Transport
Hoyos, Carlos; Oz, Yaron
2014-01-01
We derive quantum field theory Ward identities based on linear area preserving and conformal transformations in 2+1 dimensions. The identities relate Hall viscosities, Hall conductivities and the angular momentum. They apply both for relativistic and non relativistic systems, at zero and at finite temperature. We consider systems with or without translation invariance, and introduce an external magnetic field and viscous drag terms. A special case of the identities yields the well known relation between the Hall conductivity and half the angular momentum density.
Olsen, Thomas
2016-12-01
Interfaces between normal and topological insulators are bound to host metallic states that are protected by time-reversal symmetry and are therefore robust against disorder and interface reconstruction. Two-dimensional topological insulators (quantum spin Hall insulators) offer a unique opportunity to change the local topology by adsorption of atoms or molecules and thus comprise an ideal platform for designing topological heterostructures. Here we apply first-principles calculations to show that the quantum spin Hall insulator 1 T'-MoS2 exhibits a phase transition to a trivial insulator upon adsorption of various atoms. It is then demonstrated that one-dimensional metallic states indeed arise at the boundary of regions with and without adsorbed oxygen and that these boundary states generically constitute simple linear connections between valence and conduction bands in reciprocal space. This is in sharp contrast to topological edge states, which typically exhibit strong dispersion that are sensitive to a particular edge termination. The heterostructure is also suggestive of a simple design of one-dimensional metallic networks in sheets of 1 T'-MoS2 .
Planar Hall effect bridge magnetic field sensors
Henriksen, A.D.; Dalslet, Bjarke Thomas; Skieller, D.H.
2010-01-01
Until now, the planar Hall effect has been studied in samples with cross-shaped Hall geometry. We demonstrate theoretically and experimentally that the planar Hall effect can be observed for an exchange-biased ferromagnetic material in a Wheatstone bridge topology and that the sensor signal can...... Hall effect bridge sensors....
Sengupta, Parijat; Kubis, Tillmann; Tan, Yaohua; Klimeck, Gerhard
2014-01-01
Bi$_{2}$Te$_{3}$ and Bi$_{2}$Se$_{3}$ are well known 3D-topological insulators. Films made of these materials exhibit metal-like surface states with a Dirac dispersion and possess high mobility. The high mobility metal-like surface states can serve as channel material for TI-based field effect transistors. While such a transistor offers superior terminal characteristics, they suffer from an inherent zero band gap problem. The absence of a band gap for the surface states prevents an easy turn-...
Vetrov, S. Ya.; Bikbaev, R. G.; Timofeev, I. V.
2017-07-01
The optical Tamm states localized at the edges of a photonic crystal bounded by a nanocomposite on its one or both sides are investigated. The nanocomposite consists of metal nanoinclusions with an orientation-ordered spheroidal shape, which are dispersed in a transparent matrix, and is characterized by the effective resonance permittivity. The spectrum of transmission of the longitudinally and transversely polarized waves by such structures at the normal incidence of light was calculated. The spectral manifestation of the Tamm states caused by negative values of the real part of the effective permittivity in the visible spectral range was studied. Features of the spectral manifestation of the optical Tamm states for different degrees of extension of spheroidal nanoparticles and different periods of a photonic crystal were investigated. It is demonstrated that splitting of the frequency due to elimination of degeneracy of the Tamm states localized at the interfaces between the photonic crystal and nanocomposite strongly depends on the volume fraction of the spheroids in the nanocomposite and on the ratio between the polar and equatorial semiaxes of the spheroid. Each of the two orthogonal polarizations of the incident wave has its own dependence of splitting on the nanoparticle density, which makes the transmission spectra polarization-sensitive. It is shown that the Tamm state is affected by the size-dependent permittivity of anisotropic nanoparticles.
Shared Magnetics Hall Thruster Project
National Aeronautics and Space Administration — In the proposed Phase II program, Busek Co. will demonstrate an innovative methodology for clustering Hall thrusters into a high performance, very high power...
Shared Magnetics Hall Thruster Project
National Aeronautics and Space Administration — In the proposed Phase I program, Busek Co. will demonstrate an innovative methodology for clustering Hall thrusters into a high performance, very high power...
"Hall mees" Linnateatris / Triin Sinissaar
Sinissaar, Triin
1999-01-01
Tallinn Linnateatri ja Raadioteatri ühislavastus "Hall mees" Gill Adamsi näidendi järgi, lavastaja Eero Spriit, osades Helene Vannari ja Väino Laes, kunstnik Kustav - Agu Püüman. Esietendus 22. okt
"Hall mees" Linnateatris / Triin Sinissaar
Sinissaar, Triin
1999-01-01
Tallinn Linnateatri ja Raadioteatri ühislavastus "Hall mees" Gill Adamsi näidendi järgi, lavastaja Eero Spriit, osades Helene Vannari ja Väino Laes, kunstnik Kustav - Agu Püüman. Esietendus 22. okt
Hall measurements on InAs nanowires
Bloemers, Christian; Grap, Thomas; Lepsa, Mihail I.; Gruetzmacher, Detlev; Lueth, Hans [Peter Gruenberg Institut (PGI-9), Forschungszentrum Juelich GmbH, 52425 Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany); Trellenkamp, Stefan [Peter Gruenberg Institut (PGI-8), Forschungszentrum Juelich GmbH, 52425 Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany); Schaepers, Thomas [Peter Gruenberg Institut (PGI-9), Forschungszentrum Juelich GmbH, 52425 Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany); II. Physikalisches Institut, RWTH Aachen, 52074 Aachen (Germany)
2012-07-01
In search of novel concepts for the realization of nanoelectronic devices, semiconductor nanowires grown by ''bottom-up'' techniques have shown great promise. Without any doubt, the knowledge about the free carrier concentration n{sub el} is crucial for the fabrication of such devices on the nanometer scale. The most common method to determine n{sub el} in nanowires is to utilize the field effect in a gate measurement setup. However, within this method, uncertainties such as the density of surface states between the nanowire and the dielectric material or the resulting nanowire capacitance influence results. Additionally, source and drain electrodes tend to screen the gate potential in devices of small size. Here we report on Hall measurements on InAs nanowires as an alternative method to determine n{sub el}. By electron beam lithography we are able to fabricate side contacts to single nanowires to realize a Hall-measurement geometry. The side contacts allow us to measure a Hall-voltage, from which we deduce the carrier concentration in the wires.
Tunnelling anomalous and planar Hall effects (Conference Presentation)
Matos-Abiague, Alex; Scharf, Benedikt; Han, Jong E.; Hankiewicz, Ewelina M.; Zutic, Igor
2016-10-01
We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow[1]. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices. [1] B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).
The quantum Hall's effect:A quantum electrodynamic phenomenon
A.I. Arbab
2012-01-01
We have applied Maxwell's equations to study the physics of quantum Hall's effect.The electromagnetic properties of this system are obtained.The Hall's voltage,VH =2πh2ns/e rn,where ns is the electron number density,for a 2-dimensional system,and h =2πh is the Planck's constant,is found to coincide with the voltage drop across the quantum capacitor.Consideration of the cyclotronic motion of electrons is found to give rise to Hall's resistance.Ohmic resistances in the horizontal and vertical directions have been found to exist before equilibrium state is reached.At a fundamental level,the Hall's effect is found to be equivalent to a resonant LCR circuit with LH =2π m/e2ns and CH =me2/2πh2ns satisfying the resonance condition with resonant frequency equal to the inverse of the scattering (relaxation) time,Ts.The Hall's resistance is found to be RH =√LH/CH.The Hall's resistance may be connected with the impedance that the electron wave experiences when it propagates in the 2-dimeasional gas.
The spin Hall effect in a quantum gas.
Beeler, M C; Williams, R A; Jiménez-García, K; LeBlanc, L J; Perry, A R; Spielman, I B
2013-06-13
Electronic properties such as current flow are generally independent of the electron's spin angular momentum, an internal degree of freedom possessed by quantum particles. The spin Hall effect, first proposed 40 years ago, is an unusual class of phenomena in which flowing particles experience orthogonally directed, spin-dependent forces--analogous to the conventional Lorentz force that gives the Hall effect, but opposite in sign for two spin states. Spin Hall effects have been observed for electrons flowing in spin-orbit-coupled materials such as GaAs and InGaAs (refs 2, 3) and for laser light traversing dielectric junctions. Here we observe the spin Hall effect in a quantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz forces to realize a cold-atom spin transistor. By engineering a spatially inhomogeneous spin-orbit coupling field for our quantum gas, we explicitly introduce and measure the requisite spin-dependent Lorentz forces, finding them to be in excellent agreement with our calculations. This 'atomtronic' transistor behaves as a type of velocity-insensitive adiabatic spin selector, with potential application in devices such as magnetic or inertial sensors. In addition, such techniques for creating and measuring the spin Hall effect are clear prerequisites for engineering topological insulators and detecting their associated quantized spin Hall effects in quantum gases. As implemented, our system realizes a laser-actuated analogue to the archetypal semiconductor spintronic device, the Datta-Das spin transistor.
General footage ISOLDE experimental hall HD
2016-01-01
Overview of the ISOLDE experimental hall. Equipment and experiments. Taken from the WITCH / EBIS platform: ISOLDE hall infrastructure, GHM line, LA1, LA2, LA0, central beamline, COLLAPS experiment, CRIS experiment, ISOLTRAP experiment, laser guidance from building 508 into the hall for laser spectroscopy COLLAPS and CRIS. Taken from the HIE ISOLDE shielding tunnel roof: ISOLDE hall infrastructure, WITCH experiment, VITO line, TAS experiment. General footage: High Tension room entrance and EBIS platform, staircases and passages in the experimental hall.
Magnetic Topological Insulators and Quantum Anomalous Hall Effect
Kou, Xufeng
The engineering of topological surface states is a key to realize applicable devices based on topological insulators (TIs). Among various proposals, introducing magnetic impurities into TIs has been proven to be an effective way to open a surface gap and integrate additional ferromagnetism with the original topological order. In this Dissertation, we study both the intrinsic electrical and magnetic properties of the magnetic TI thin films grown by molecular beam epitaxy. By doping transition element Cr into the host tetradymite-type V-VI semiconductors, we achieve robust ferromagnetic order with a strong perpendicular magnetic anisotropy. With additional top-gating capability, we realize the electric-field-controlled ferromagnetism in the magnetic TI systems, and demonstrate such magneto-electric effects can be effectively manipulated, depending on the interplays between the band topology, magnetic exchange coupling, and structural engineering. Most significantly, we report the observation of quantum anomalous Hall effect (QAHE) in the Cr-doped (BiSb)2Te3 samples where dissipationless chiral edge conduction is realized in the macroscopic millimeter-size devices without the presence of any external magnetic field, and the stability of the quantized Hall conductance of e2/h is well-maintained as the film thickness varies across the 2D hybridization limit. With additional quantum confinement, we discover the metal-to-insulator switching between two opposite QAHE states, and reveal the universal QAHE phase diagram in the thin magnetic TI samples. In addition to the uniform magnetic TIs, we further investigate the TI/Cr-doped TI bilayer structures prepared by the modulation-doped growth method. By controlling the magnetic interaction profile, we observe the Dirac hole-mediated ferromagnetism and develop an effective way to manipulate its strength. Besides, the giant spin-orbit torque in such magnetic TI-based heterostructures enables us to demonstrate the current
Nonlinear transport of graphene in the quantum Hall regime
Tian, Shibing; Wang, Pengjie; Liu, Xin; Zhu, Junbo; Fu, Hailong; Taniguchi, Takashi; Watanabe, Kenji; Chen, Jian-Hao; Lin, Xi
2017-03-01
We have studied the breakdown of the integer quantum Hall (QH) effect with fully broken symmetry, in an ultra-high mobility graphene device sandwiched between two single crystal hexagonal boron nitride substrates. The evolution and stabilities of the QH states are studied quantitatively through the nonlinear transport with dc Hall voltage bias. The mechanism of the QH breakdown in graphene and the movement of the Fermi energy with the electrical Hall field are discussed. This is the first study in which the stabilities of fully symmetry broken QH states are probed all together. Our results raise the possibility that the ν = ±6 states might be a better target for the quantum resistance standard.
Bamshad Michael J
2009-03-01
Full Text Available Abstract Sheldon-Hall syndrome (SHS is a rare multiple congenital contracture syndrome characterized by contractures of the distal joints of the limbs, triangular face, downslanting palpebral fissures, small mouth, and high arched palate. Epidemiological data for the prevalence of SHS are not available, but less than 100 cases have been reported in the literature. Other common clinical features of SHS include prominent nasolabial folds, high arched palate, attached earlobes, mild cervical webbing, short stature, severe camptodactyly, ulnar deviation, and vertical talus and/or talipes equinovarus. Typically, the contractures are most severe at birth and non-progressive. SHS is inherited in an autosomal dominant pattern but about half the cases are sporadic. Mutations in either MYH3, TNNI2, or TNNT3 have been found in about 50% of cases. These genes encode proteins of the contractile apparatus of fast twitch skeletal muscle fibers. The diagnosis of SHS is based on clinical criteria. Mutation analysis is useful to distinguish SHS from arthrogryposis syndromes with similar features (e.g. distal arthrogryposis 1 and Freeman-Sheldon syndrome. Prenatal diagnosis by ultrasonography is feasible at 18–24 weeks of gestation. If the family history is positive and the mutation is known in the family, prenatal molecular genetic diagnosis is possible. There is no specific therapy for SHS. However, patients benefit from early intervention with occupational and physical therapy, serial casting, and/or surgery. Life expectancy and cognitive abilities are normal.
Nontrivial topological states on a Möbius band
Beugeling, W.; Quelle, A.; Morais Smith, C.
2014-06-01
In the field of topological insulators, the topological properties of quantum states in samples with simple geometries, such as a cylinder or a ribbon, have been classified and understood during the past decade. Here we extend these studies to a Möbius band and argue that its lack of orientability prevents a smooth global definition of parity-odd quantities such as pseudovectors. In particular, the Chern number, the topological invariant for the quantum Hall effect, lies in this class. The definition of spin on the Möbius band translates into the idea of the orientable double cover, an analogy used to explain the possibility of having the quantum spin Hall effect on the Möbius band. We also provide symmetry arguments to show the possible lattice structures and Hamiltonian terms for which topological states may exist in a Möbius band, and we locate our systems in the classification of topological states. Then, we propose a method to calculate Möbius dispersions from those of the cylinder, and we show the results for a honeycomb and a kagome Möbius band with different types of edge termination. Although the quantum spin Hall effect may occur in these systems when intrinsic spin-orbit coupling is present, the quantum Hall effect is more intricate and requires the presence of a domain wall in the sample. We propose an experimental setup which could allow for the realization of the elusive quantum Hall effect in a Möbius band.
Dalal, Vikram L.; Knox, Ralph D.; Moradi, Behnam
1990-01-01
A technique for measuring the Urbach energy of valence band tail states and midgap defect densities in a-Si:H and a-(Si,Ge):H devices is described. The Urbach energy is determined by measuring the quantum efficiency (QE) of delocalized holes in the devices, whereas the midgap state density (DOS) is estimated by measuring the QE of localized holes. The distinction between delocalized and localized holes is obtained from the behavior of the QE upon the application of reverse bias to the device. The QE of holes localized in midgap states increases significantly upon the application of reverse bias because of Frenkel-Poole tunneling, whereas the QE of holes in tail states does not show such an increase. It is shown that upon light soaking the Urbach edge does not change, but the midgap DOS does increase significantly. A primary consequence of the increase in DOS is a decrease in electric field in the low-field middle i region of the p-i-n cell. The decrease in electric field is experimentally estimated by fitting the increase in the reverse bias QE to Frenkel-Poole tunneling.
Danielson, L. R.; Righter, K.; Sutton, S.; Newville, M.
2008-01-01
Tungsten is important in constraining core formation of the Earth because this element is a moderately siderophile element (depleted 10 relative to chondrites) and, as a member of the Hf-W isotopic system, it is useful in constraining the timing of core formation. A number of previous experimental studies have been carried out to determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies are inconsistent on whether W occurs as W(4+) or W(6+). It is assumed that W(4+) is the cation valence relevant to core formation. Given the sensitivity to silicate composition of high valence cations, knowledge of the oxidation state of W over a wide range of fO2 is critical to understanding the oxidation state of the mantle and core formation processes. This study seeks to measure the W valence and change in valence state over the range of fO2 most relevant to core formation, around IW-2.
Anomalous Suppression of the Vortex Hall Current in Underdoped YBa2Cu3Ox
许祝安; 黄有兴; 赵彦立; 张宣嘉; 焦正宽
2001-01-01
The transport properties of underdoped YBa2 Cu3 Ox (YBCO) crystals with x = 6.95, 6.80 and 6.66 were measured and the effect of the pseudogap on the Hall conductivity was studied. In the normal state, the Hall angle remains unperturbed at the crossover temperature of resistivity for the underdoped samples. An anomalous suppression of the vortex Hall current was observed near Tc and the contribution of the vortices to the Hall current is absent above 40 K in 60 K YBCO (x = 6.66).
Extrinsic spin Hall effect induced by resonant skew scattering in graphene.
Ferreira, Aires; Rappoport, Tatiana G; Cazalilla, Miguel A; Castro Neto, A H
2014-02-14
We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging.
On transport in quantum Hall systems with constrictions
Lal, S.
2007-10-01
We study edge transport in a simple model of a constricted quantum Hall system with a lowered local filling factor. The current backscattered from the constriction is explained from a matching of the properties of the edge-current excitations in the constriction (ν2) and bulk (ν1) regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model, finding that a competition between two tunneling process, related by a quasiparticle-quasihole symmetry, determines the fate of the low-bias transmission conductance. A novel generalisation of the Kane-Fisher quantum impurity model is found, describing transitions from a weak-coupling theory at partial transmission to strong-coupling theories for perfect transmission and reflection as well as a new symmetry dictated fixed point. These results provide satisfactory explanations for recent experimental results at filling factors of 1/3 and 1.
The Quantum Hall Effect in Supersymmetric Chern-Simons Theories
Tong, David
2015-01-01
In d=2+1 dimensions, there exist gauge theories which are supersymmetric but non-relativistic. We solve the simplest U(1) gauge theory in this class and show that the low-energy physics is that of the fractional quantum Hall effect, with ground states given by the Laughlin wavefunctions. We do this by quantising the vortices and relating them to the quantum Hall matrix model. We further construct coherent state representations of the excitations of vortices. These are quasi-holes. By an explicit computation of the Berry phase, without resorting to a plasma analogy, we show that these excitations have fractional charge and spin.
CaFeAs2: A staggered intercalation of quantum spin Hall and high-temperature superconductivity
Wu, Xianxin; Qin, Shengshan; Liang, Yi; Le, Congcong; Fan, Heng; Hu, Jiangping
2015-02-01
We predict that CaFeAs2, a newly discovered iron-based high-temperature (Tc) superconductor, is a staggered intercalation compound that integrates topological quantum spin Hall (QSH) and superconductivity (SC). CaFeAs2 has a structure with staggered CaAs and FeAs layers. While the FeAs layers are known to be responsible for high Tc superconductivity, we show that with spin orbital coupling each CaAs layer is a Z2 topologically nontrivial two-dimensional QSH insulator and the bulk is a three-dimensional weak topological insulator. In the superconducting state, the edge states in the CaAs layer are natural one-dimensional topological superconductors. The staggered intercalation of QSH and SC provides us a unique opportunity to realize and explore physics, such as Majorana modes and Majorana fermion chains.
Szabo, James
2015-01-01
Iodine enables dramatic mass and cost savings for lunar and Mars cargo missions, including Earth escape and near-Earth space maneuvers. The demonstrated throttling ability of iodine is important for a singular thruster that might be called upon to propel a spacecraft from Earth to Mars or Venus. The ability to throttle efficiently is even more important for missions beyond Mars. In the Phase I project, Busek Company, Inc., tested an existing Hall thruster, the BHT-8000, on iodine propellant. The thruster was fed by a high-flow iodine feed system and supported by an existing Busek hollow cathode flowing xenon gas. The Phase I propellant feed system was evolved from a previously demonstrated laboratory feed system. Throttling of the thruster between 2 and 11 kW at 200 to 600 V was demonstrated. Testing showed that the efficiency of iodine fueled BHT-8000 is the same as with xenon, with iodine delivering a slightly higher thrust-to-power (T/P) ratio. In Phase II, a complete iodine-fueled system was developed, including the thruster, hollow cathode, and iodine propellant feed system. The nominal power of the Phase II system is 8 kW; however, it can be deeply throttled as well as clustered to much higher power levels. The technology also can be scaled to greater than 100 kW per thruster to support megawatt-class missions. The target thruster efficiency for the full-scale system is 65 percent at high specific impulse (Isp) (approximately 3,000 s) and 60 percent at high thrust (Isp approximately 2,000 s).
Edge instabilities of topological superconductors
Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.
2016-05-01
Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.
Quantum spin Hall effect in α -Sn /CdTe(001 ) quantum-well structures
Küfner, Sebastian; Matthes, Lars; Bechstedt, Friedhelm
2016-01-01
The electronic and topological properties of heterovalent and heterocrystalline α -Sn/CdTe(001) quantum wells (QWs) are studied in dependence on the thickness of α -Sn by means of ab initio calculations. We calculate the topological Z2 invariants of the respective bulk crystals, which identify α -Sn as strong three-dimensional (3D) topological insulators (TIs), whereas CdTe is a trivial insulator. We predict the existence of two-dimensional (2D) topological interface states between both materials and show that a topological phase transition from a trivial insulating phase into the quantum spin Hall (QSH) phase in the QW structures occurs at much higher thicknesses than in the HgTe case. The QSH effect is characterized by the localization, dispersion, and spin polarization of the topological interface states. We address the distinction of the 3D and 2D TI characters of the studied QW structures, which is inevitable for an understanding of the underlying quantum state of matter. The 3D TI nature is characterized by two-dimensional topological interface states, while the 2D phase exhibits one-dimensional edge states. The two different state characteristics are often intermixed in the discussion of the topology of 2D QW structures, especially, the comparison of ab initio calculations and experimental transport studies.
Sellmer, Christian
2012-08-31
The electronic properties of amorphous and microcrystalline silicon layers in thin-film solar cells significantly affect the efficiency of solar cells. An important property of the individual layer is the electronic transport, which is described by the variables conductivity, photoconductivity, mobility, and carrier concentration. In the past, individual characterization methods were typically used to determine the electronic properties. Using the combination of Hall effect, conductivity, and thermoelectric power measurements additional variables can be derived, such as the effective density of states at the valence and conduction band edge, making a more detailed description of the material possible. To systematically study the electronic properties - in particular carrier mobility and carrier concentration - various series of silicon films are prepared for this work including microcrystalline silicon layers of different doping and crystallinity and a series of silicon films where the Fermi level is moved by irradiation with high energy electrons on one and the same sample. The results show that the transition from amorphous to microcrystalline transport is relatively abrupt. If the electron transport takes place in only amorphous regions, it is marked by the sign anomaly of the Hall effect. If a continuous crystalline path exists, the electronic properties are dominated by the crystalline volume fraction. The results of the measurements of silicon layers are compared with those of microcrystalline silicon carbide samples. Silicon carbide is especially interesting for future applications in thin-film solar cells due to high transparency and high conductivity. It is shown that the effective density of states at the valence and conduction band edge as a function of temperature in p- and n-type microcrystalline silicon and silicon carbide samples largely coincide with those of crystalline silicon or silicon carbide. A square root shaped profile of the density of
2013-04-04
... Culturally Significant Objects Imported for Exhibition Determinations: ``Hall of Ancient Egypt'' SUMMARY... objects to be included in the exhibition ``Hall of Ancient Egypt,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to...
Thickness Dependence of the Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films.
Feng, Xiao; Feng, Yang; Wang, Jing; Ou, Yunbo; Hao, Zhenqi; Liu, Chang; Zhang, Zuocheng; Zhang, Liguo; Lin, Chaojing; Liao, Jian; Li, Yongqing; Wang, Li-Li; Ji, Shuai-Hua; Chen, Xi; Ma, Xucun; Zhang, Shou-Cheng; Wang, Yayu; He, Ke; Xue, Qi-Kun
2016-08-01
The evolution of the quantum anomalous Hall effect with the thickness of Cr-doped (Bi,Sb)2 Te3 magnetic topological insulator films is studied, revealing how the effect is caused by the interplay of the surface states, band-bending, and ferromagnetic exchange energy. Homogeneity in ferromagnetism is found to be the key to high-temperature quantum anomalous Hall material.
The Alberta Jubilee Halls reborn with up-to-date acoustics
Jordan, Niels V.; Rindel, Jens Holger
2006-01-01
acoustical knowledge of that time, it had become clear that the halls suffered by several acoustical problems, and thus the government of Alberta wanted the halls to be brought up-to-date for the 100 years jubilee of the state. The Canadian architect Fred Valentine together with other North American...
Duality in the quantum Hall system
Lütken, C. A.; Ross, G. G.
1992-05-01
We suggest that a unified description of the integer and fractional phases of the quantum Hall system may be possible if the scaling diagram of transport coefficients is invariant under linear fractional (modular) transformations. In this model the hierarchy of states, as well as the observed universality of critical exponents, are consequences of a discrete SL(2,openZ) symmetry acting on the parameter space of an effective quantum-field theory. Available scaling data on the position of delocalization fixed points in the integer case and the position of mobility fixed points in the fractional case agree with the model within experimental accuracy.
Twisted CFT and bilayer Quantum Hall systems
Cristofano, G; Naddeo, A
2003-01-01
We identify the impurity interactions of the recently proposed CFT description of a bilayer Quantum Hall system at filling nu =m/(pm+2) in Mod. Phys. Lett. A 15 (2000) 1679. Such a CFT is obtained by m-reduction on the one layer system, with a resulting pairing symmetry and presence of quasi-holes. For the m=2 case boundary terms are shown to describe an impurity interaction which allows for a localized tunnel of the Kondo problem type. The presence of an anomalous fixed point is evidenced at finite coupling which is unstable with respect to unbalance and flows to a vacuum state with no quasi-holes.
Supercurrent in the quantum Hall regime
Amet, F.; Ke, C. T.; Borzenets, I. V.; Wang, J.; Watanabe, K.; Taniguchi, T.; Deacon, R. S.; Yamamoto, M.; Bomze, Y.; Tarucha, S.; Finkelstein, G.
2016-05-01
A promising route for creating topological states and excitations is to combine superconductivity and the quantum Hall (QH) effect. Despite this potential, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has been challenging to observe. We demonstrate the existence of a distinct supercurrent mechanism in encapsulated graphene samples contacted by superconducting electrodes, in magnetic fields as high as 2 tesla. The observation of a supercurrent in the QH regime marks an important step in the quest for exotic topological excitations, such as Majorana fermions and parafermions, which may find applications in fault-tolerant quantum computing.
Excitons in the Fractional Quantum Hall Effect
Laughlin, R. B.
1984-09-01
Quasiparticles of charge 1/m in the Fractional Quantum Hall Effect form excitons, which are collective excitations physically similar to the transverse magnetoplasma oscillations of a Wigner crystal. A variational exciton wavefunction which shows explicitly that the magnetic length is effectively longer for quasiparticles than for electrons is proposed. This wavefunction is used to estimate the dispersion relation of these excitons and the matrix elements to generate them optically out of the ground state. These quantities are then used to describe a type of nonlinear conductivity which may occur in these systems when they are relatively clean.
1993-01-01
Direction Switching A state machine for CREQ and CACK handling was written in Altera Hard- ware Description Language ( AHDL ) (see [4]). The corresponding...34, Issue 1.32. Spectrum Signal Process- ing Inc.. Burnaby. B.C.. Canada, Nov. 1991. [4] "’MAX+plusII Text Editor & AHDL ". Altera Corporation. version 1.0
Precise quantization of anomalous Hall effect near zero magnetic field
Bestwick, A. J. [Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Fox, E. J. [Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Kou, Xufeng [Univ. of California, Los Angeles, CA (United States); Pan, Lei [Univ. of California, Los Angeles, CA (United States); Wang, Kang L. [Univ. of California, Los Angeles, CA (United States); Goldhaber-Gordon, D. [Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
2015-05-04
In this study, we report a nearly ideal quantum anomalous Hall effect in a three-dimensional topological insulator thin film with ferromagnetic doping. Near zero applied magnetic field we measure exact quantization in the Hall resistance to within a part per 10,000 and a longitudinal resistivity under 1 Ω per square, with chiral edge transport explicitly confirmed by nonlocal measurements. Deviations from this behavior are found to be caused by thermally activated carriers, as indicated by an Arrhenius law temperature dependence. Using the deviations as a thermometer, we demonstrate an unexpected magnetocaloric effect and use it to reach near-perfect quantization by cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration.
THE CALCULATION OF STRESS-STRAIN STATE OF THREE-LAYER BEAM TAKING INTO ACCOUNT EDGE EFFECTS
Kh. M. Muselemov
2015-01-01
Full Text Available The work is dedicated to the calculation of the stress-strain state (SSS of the three-layer beam (TLB subject to boundary effects.In this paper, a system of differential equations of equilibrium of the threelayer beam. To solve these equations, it is necessary to know the 12 boundary conditions, co-which depend on support conditions and loading of sandwich beams under study. This system of equations is solved by the application package of mathematical modeling "Maple 5.4." The solution of this system we obtain expressions for determining de-formations and stress all components (bearing layers and filler, a three-layer beam anywhere under specified conditions of fastening the ends of the beam and its loading.
Ho, Ching-Hwa, E-mail: chho@mail.ntust.edu.tw [Graduate Institute of Engineering, Graduate Institute of Applied Science and Engineering, and Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China)
2012-08-01
{beta}-In{sub 2}S{sub 3} is a nontoxic buffer layer material usually used in a thin-film solar cell due to a lot of vacancies and surface states naturally existing in the crystal to assist in photoelectric conversion. Transition metal (TM)-incorporated {beta}-In{sub 2}S{sub 3} has also been proposed to increase conversion efficiency in In{sub 2}S{sub 3} since multi-photons absorption by intermediate band (IB) would happen in the sulfide. In this paper, single crystals of undoped and Nb-doped {beta}-In{sub 2}S{sub 3} have been grown by the chemical vapor transport (CVT) method using ICl{sub 3} as a transport agent. Optical properties of the imperfection states of the crystals are probed by thermoreflectance (TR), photoconductivity (PC), photoluminescence (PL), surface photoconductive response (SPR), optical absorption and photo-voltage-current (photo V-I) measurements. The TR and optical-absorption measurements confirmed that the undoped and Nb-doped {beta}-In{sub 2}S{sub 3} are direct semiconductors with energy gap of 1.935 eV for undoped {beta}-In{sub 2}S{sub 3}, 1.923 eV for {beta}-In{sub 2}S{sub 3}:Nb{sub 0.005}, and 1.901 eV for {beta}-In{sub 2}S{sub 3}:Nb{sub 0.01}. For undoped {beta}-In{sub 2}S{sub 3}, PC and PL measurements are used to characterize defect transitions below band gap. The above band-edge transitions of undoped {beta}-In{sub 2}S{sub 3} have also been evaluated using PL, PC, and SPR measurements. For the evaluation of Nb-doped {beta}-In{sub 2}S{sub 3}, an intermediate band with energy of {approx}0.4 eV below the conduction band edge has been detected in the TR measurements in both {beta}-In{sub 2}S{sub 3}:Nb{sub 0.005} and {beta}-In{sub 2}S{sub 3}:Nb{sub 0.01}. The photo V-I measurements also verified that the photoelectric-conversion efficiency would be enhanced in the {beta}-In{sub 2}S{sub 3} with higher niobium content. Based on the experimental analyses, the optical behavior of the defects, surface states, and IB (formed by Nb) in the In
Non-abelian fractional quantum hall effect for fault-resistant topological quantum computation.
Pan, Wei; Thalakulam, Madhu; Shi, Xiaoyan; Crawford, Matthew; Nielsen, Erik; Cederberg, Jeffrey George
2013-10-01
Topological quantum computation (TQC) has emerged as one of the most promising approaches to quantum computation. Under this approach, the topological properties of a non-Abelian quantum system, which are insensitive to local perturbations, are utilized to process and transport quantum information. The encoded information can be protected and rendered immune from nearly all environmental decoherence processes without additional error-correction. It is believed that the low energy excitations of the so-called =5/2 fractional quantum Hall (FQH) state may obey non-Abelian statistics. Our goal is to explore this novel FQH state and to understand and create a scientific foundation of this quantum matter state for the emerging TQC technology. We present in this report the results from a coherent study that focused on obtaining a knowledge base of the physics that underpins TQC. We first present the results of bulk transport properties, including the nature of disorder on the 5/2 state and spin transitions in the second Landau level. We then describe the development and application of edge tunneling techniques to quantify and understand the quasiparticle physics of the 5/2 state.
Ansari, R.; Gholami, R.
2016-09-01
Considering the small scale effect together with the influences of transverse shear deformation, rotary inertia and the magneto-electro-thermo-mechanical coupling, the linear free vibration of magneto-electro-thermo-elastic (METE) rectangular nanoplates with various edge supports in pre- and post-buckled states is investigated herein. It is assumed that the METE nanoplate is subjected to the external in-plane compressive loads in combination with magnetic, electric and thermal loads. The Mindlin plate theory, von Kármán hypothesis and the nonlocal theory are utilized to develop a size-dependent geometrically nonlinear plate model for describing the size-dependent linear and nonlinear mechanical characteristics of moderately thick METE rectangular nanoplates. The nonlinear governing equations and the corresponding boundary conditions are derived using Hamilton’s principle which are then discretized via the generalized differential quadrature method. The pseudo-arc length continuation approach is used to obtain the equilibrium postbuckling path of METE nanoplates. By the obtained postbuckling response, and taking a time-dependent small disturbance around the buckled configuration, and inserting them into the nonlinear governing equations, an eigenvalue problem is achieved from which the frequencies of pre- and post-buckled METE nanoplates can be calculated. The effects of nonlocal parameter, electric, magnetic and thermal loadings, length-to-thickness ratio and different boundary conditions on the free vibration response of METE rectangular nanoplates in the pre- and post-buckled states are highlighted.
Jia, Chuankun; Liu, Qi; Sun, Cheng-Jun; Yang, Fan; Ren, Yang; Heald, Steve M; Liu, Yadong; Li, Zhe-Fei; Lu, Wenquan; Xie, Jian
2014-10-22
Synchrotron-based in situ X-ray near-edge absorption spectroscopy (XANES) has been used to study the valence state evolution of the vanadium ion for both the catholyte and anolyte in all-vanadium redox flow batteries (VRB) under realistic cycling conditions. The results indicate that, when using the widely used charge-discharge profile during the first charge process (charging the VRB cell to 1.65 V under a constant current mode), the vanadium ion valence did not reach V(V) in the catholyte and did not reach V(II) in the anolyte. Consequently, the state of charge (SOC) for the VRB cell was only 82%, far below the desired 100% SOC. Thus, such incompletely charged mix electrolytes results in not only wasting the electrolytes but also decreasing the cell performance in the following cycles. On the basis of our study, we proposed a new charge-discharge profile (first charged at a constant current mode up to 1.65 V and then continuously charged at a constant voltage mode until the capacity was close to the theoretical value) for the first charge process that achieved 100% SOC after the initial charge process. Utilizing this new charge-discharge profile, the theoretical charge capacity and the full utilization of electrolytes has been achieved, thus having a significant impact on the cost reduction of the electrolytes in VRB.
Displacement ventilation in lecture halls
Egorov, Artem
2013-01-01
This thesis considers several important goals. The main purpose is to see how displacement ventilation sys-tem works in the lecture hall of M-building and compare obtained results with D2 and Indoor Climate Classi-fication. The second one is to analyze the function of the ventilation system. The last one is to realize when displacement ventilation is preferable to mixing ventilation. Analysis of the system was carried out with instruments from MUAS HVAC laboratory. In lecture hall were me...
Edge conduction in monolayer WTe2
Fei, Zaiyao; Palomaki, Tauno; Wu, Sanfeng; Zhao, Wenjin; Cai, Xinghan; Sun, Bosong; Nguyen, Paul; Finney, Joseph; Xu, Xiaodong; Cobden, David H.
2017-07-01
A two-dimensional topological insulator (2DTI) is guaranteed to have a helical one-dimensional edge mode in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe2 was predicted to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that, at temperatures below about 100 K, monolayer WTe2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by an in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly, which reduces the linear-response conductance. Bilayer WTe2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe2 being a 2DTI. However, the low-temperature edge conductance, for contacts spacings down to 150 nm, never reaches values higher than ~20 μS, about half the predicted value of e2/h, suggesting significant elastic scattering in the edge.
Fluctuations and topological transitions of quantum Hall stripes: Nematics as anisotropic hexatics
Ettouhami, A. M.; Doiron, C. B.; Côté, R.
2007-10-01
We study fluctuations and topological melting transitions of quantum Hall stripes near half filling of intermediate Landau levels. Taking the stripe state to be an anisotropic Wigner crystal (AWC) allows us to identify the quantum Hall nematic state conjectured in previous studies of the two-dimensional (2D) electron gas as an anisotropic hexatic. The transition temperature from the AWC to the quantum Hall nematic state is explicitly calculated, and a tentative phase diagram for the 2D electron gas near half filling is suggested.
Bound values for Hall conductivity of heterogeneous medium under quantum Hall effect conditions
V E Arkhincheev
2008-02-01
Bound values for Hall conductivity under quantum Hall effect (QHE) conditions in inhomogeneous medium has been studied. It is shown that bound values for Hall conductivity differ from bound values for metallic conductivity. This is due to the unusual character of current percolation under quantum Hall effect conditions.
Few-body, hyperspherical treatment of the quantum Hall effect
Wooten R. E.
2016-01-01
Full Text Available The quantum Hall effect arises from the quantum behavior of two-dimensional, strongly-interacting electrons exposed to a strong, perpendicular magnetic field [1, 2]. Conventionally treated from a many-body perspective, we instead treat the system from the few-body perspective using collective coordinates and the hyperspherical adiabatic technique developed originally for atomic systems [3]. The grand angular momentum K from K-harmonic few-body theory, is shown to be an approximate good collective quantum number in this system, and is shown to correlate with known fractional quantum Hall (FQH states at experimentally observed filling factors.
Stability of Hall equilibria in neutron star crusts
Marchant, Pablo; Valdivia, Juan Alejandro; Hoyos, Jaime H
2014-01-01
In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which Ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria", i.e., field configurations that are unaffected by Hall drift. Here, we address the crucial question of the stability of these equilibria through axially symmetric (2D) numerical simulations of Hall drift and Ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D-stability of a purely poloidal equilibrium, for which Ohmic dissipation makes the field evolve towards an attractor state through adjacent stab...
Transport studies on Cr-doped (Bi,Sb)2Te3 thin films with nearly quantized anomalous Hall effect
Liu, Minhao; Richardella, Anthony; Kandala, Abhinav; Wang, Wudi; Yazdani, Ali; Samarth, Nitin; Ong, N. Phuan
2015-03-01
We describe measurements of the quantum anomalous Hall effect in ferromagnetic Cr-doped (Bi,Sb)2Te3 thin films (6-8 QL thickness) grown on (111) SrTiO3 (STO) substrates by molecular beam epitaxy. The Fermi level is tuned close to the neutral point by tuning the growth flux ratios of Cr, Bi and Sb. Transport measurements were carried out in a dilution fridge at a base temperature of 20 mK. By tuning the chemical potential with a back gate on the STO substrate, we observed an anomalous Hall effect as high as 0.95h/e2, with a coercive field ~ 0.15 T and a narrow transition between positive/negative Hall plateaus. Transport measurements in a non-local configuration showed a Hall-effect-like non-local resistance with a systematic dependence on the back gate voltage and with pronounced peaks which resembled the non-local resistance of the quantum Hall effect. The non-local signal has a maximum that coincides with the maximum in Hall conductivity, indicating the edge channel as its origin. Our results show that the edge channel manifests itself in various transport properties even though the Hall resistance is not perfectly quantized. Supported by DARPA SPAWAR Grant No. N66001-11-1-4110 and MURI grant on Topological Insulators (ARO W911NF-12-1-0461).
Quantum Hall fluids in the presence of topological defects
Iacomino, Patrizia; Naddeo, Adele
2013-01-01
We review our recent results on the physics of quantum Hall fluids at Jain and non conventional fillings within a general field theoretic framework. We focus on a peculiar conformal field theory (CFT), the one obtained by means of the m-reduction technique, and stress its power in describing strongly correlated low dimensional condensed matter systems in the presence of localized impurities or topological defects. By exploiting the notion of Morita equivalence for field theories on noncommutative two-tori and choosing rational values of the noncommutativity parameter, we find a general one-to-one correspondence between the m-reduced conformal field theory describing the quantum Hall fluid and an Abelian noncommutative field theory. As an example of application of the formalism, we study a quantum Hall bilayer at nonconventional fillings in the presence of a localized topological defect and briefly recall its boundary state structure corresponding to two different boundary conditions, the periodic as well as t...
Hall coefficient of insulating n-type CdSe
Roy, A.; Levy, M.; Guo, X.M.; Sarachik, M.P.; Ledesma, R.; Isaacs, L.L.
1989-05-15
We report measurements of the conductivity and Hall coefficient of insulating n-type CdSe with dopant concentrations near the critical concentration for the metal-insulator transition. In the temperature range 1.2--4.2 K, where the resistivity is consistent with variable-range hopping, the Hall coefficient is finite and observable and follows an analogous temperature dependence, R/sub H//similar to/exp(K/sub H/(T/sub 0//T)/sup n/). We find n<1, so that the observed Hall coefficient is not due to carriers activated to extended states; the data are consistent instead with an exponent n = 1/4 or 1/2. We compare this result with previous experiments and with current theory.