We have studied transport properties in a two-dimensional electron gas with equal Rashba and Dresselhaus spin-orbit interactions under a perpendicular magnetic field. By employing the exact solution for this system, we found resonant charge and spin Hall conductances at a certain magnetic field, where all the nearest-neighboring Landau levels cross. Near this value of magnetic field, there exists a resonant spin polarization, which can also induce resonant charge and spin Hall effects.
We study intrinsic spin Hall effect in p-type GaAs quantum well structure described by Luttinger Hamiltonian and a Rashba spin-orbit coupling arising from the structural inversion symmetry breaking. The Rashba term induces an energy level crossing in the lowest heavy hole subband, which gives rise to a resonant spin Hall conductance. The resonance may be used to identify the intrinsic spin Hall effect in experiments.
Following a previous work [Shen, Ma, Xie and Zhang, Phys. Rev. Lett. 92, 256603 (2004)] on the resonant spin Hall effect, we present detailed calculations of the spin Hall conductance in two-dimensional quantum wells in a strong perpendicular magnetic field. The Rashba coupling, generated by spin-orbit interaction in wells lacking bulk inversion symmetry, introduces a degeneracy of Zeeman-split Landau levels at certain magnetic fields. This degeneracy, if occuring at the Fermi energy, will induce a resonance in the spin Hall conductance below a characteristic temperature of order of the Zeeman…
The Spin Hall Effect (SHE) is a promising way for transforming charge currents into spin currents in spintronic devices. Large values of the Spin Hall Angle, the characteristic parameter of the yield of this transformation, have been recently found in noble metals doped with nonmagnetic impurities. We show that this can be explained by resonant scattering off impurity states split by the spin-orbit interaction. We apply our calculation to the interpretation of experiments on copper doped with 5d impurities and we describe the conditions to obtain the largest effects.
Recent experimental observations of unexpectedly large thermal Hall conductivities, $κ_H$, in insulating materials, including the parent compounds of the high temperature superconducting cuprates, likely reflect an extrinsic contribution from a yet to be identified extrinsic source of skew scattering of acoustic phonons. We show that resonant scattering of phonons from a certain class of three-level systems produces strong skew scattering in the presence of a modest magnetic field. We interpret this as a first step towards understanding the experiments.
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 fabrica…
Strong resonant enhancements of inelastic light scattering from the long wavelength inter-Landau level magnetoplasmon and the intra-Landau level spin wave excitations are seen for the fractional quantum Hall state at $ν= 1/3$. The energies of the sharp peaks (FWHM $\lesssim 0.2meV$) in the profiles of resonant enhancement of inelastic light scattering intensities coincide with the energies of photoluminescence bands assigned to negatively charged exciton recombination. To interpret the observed enhancement profiles, we propose three-step light scattering mechanisms in which the intermediate re…
The electric-field-induced resonant spin polarization of a two-dimensional hole gas described by Luttinger Hamiltonian with structural inversion asymmetry and Zeeman splitting in a perpendicular magnetic field was studied. The spin polarization arising from splitting between the light and the heavy hole bands shows a resonant peak at a certain magnetic field. Especially, the competition between the Luttinger term and the structural inversion asymmetry leads to a rich resonant peaks structure, and the required magnetic field for the resonance may be effectively reduced by enlarging the effectiv…
Resonant tunneling through a quantum dot weakly coupled to Tomonaga-Luttinger liquids is discussed. The linear conductance due to sequential tunneling is calculated by solving a master equation for temperatures below and above the average level spacing in the dot. When the parameter g characterizing the Tomonaga-Luttinger liquid is smaller than 1/2, the resonant tunneling process is incoherent down to zero temperature. At low temperature T the height and width of the conductance peaks in the Coulomb blockade oscillations are proportional to T^{(1/g)-2} and T, respectively. The contribution fro…
Spin polarization of the tunnel conductivity has been studied for Fe/GaAs junctions with Schottky barriers. It is shown that band matching of resonant interface states within the Schottky barrier defines the sign of spin polarization of electrons transported through the barrier. The results account very well for experimental results including the tunneling of photo-excited electrons, and suggest that the spin polarization (from -100% to 100%) is dependent on the Schottky barrier height. They also suggest that the sign of the spin polarization can be controlled with a bias voltage.
Giant resonant nonlinear THz valley Hall effect in 2D Dirac semiconductors
Guangdong Technion – Israel Institute of Technology（广东以色列理工学院）；Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Science（俄罗斯科学院西伯利亚分院热诺夫半导体物理研究所）；Novosibirsk State Technical University（新西伯利亚国立技术大学）；Technion – Israel Institute of Technology（以色列理工学院）
We study I-V characteristics of an all-II-VI semiconductor resonant tunneling diode with dilute magnetic impurities in the quantum well layer. Bound magnetic polaron states form in the vicinity of potential fluctuations at the well interface while tunneling electrons traverse these interface quantum dots. The resulting microscopic magnetic order lifts the degeneracy of the resonant tunneling states. Although there is no macroscopic magnetization, the resulting resonant tunneling current is highly spin polarized at zero magnetic field due to the zero field splitting. Detailed modeling demonstra…
We study the spin polarization and its associated spin-Hall current due to EDSR in disordered two-dimensional electron systems. We show that the disorder induced damping of the resonant spin polarization can be strongly reduced by an optimal field configuration that exploits the interference between Rashba and Dresselhaus spin-orbit interaction. This leads to a striking enhancement of the spin susceptibility while the spin-Hall current vanishes at the same time. We give an interpretation of the spin current in geometrical terms which are associated with the trajectories the polarization descri…
It is shown that spin Hall effect creates uniform spin polarization of electrons in semiconductor with a linear in the momentum spin splitting of conduction band. In turn, the profile of the non-uniform spin polarization accumulated at the edge of the sample oscillates in space even in the absence of an external magnetic field.
Using a Hamiltonian formulation of Composite Fermions that I recently developed with R. Shankar, I compute the dependence of the spin polarization on the temperature for the translationally invariant fractional quantum Hall states at $ν=1/3$ and $ν=2/5$. I compare my results to experiments at $ν=1/3$ and find reasonably good agreement.
Electric response of spin polarization in two-dimensional electron gas with structural inversion asymmetry subjected to a magnetic field was studied by means of the linear and non-linear theory and numerical simulation with the disorder effect. It was found by Kubo linear reponse theory that an electric resonant response of spin polarization occurs when the Fermi surface is located near the crossing of two Landau levels, which is induced from the competition between the spin-orbit coupling and Zeeman splitting. The scaling behavior was investigated with a simplified two-level model by non-line…
It is shown that the spin Hall current generates a non-equilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known equilibrium polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.
Using dc excitation to spatially tilt Landau levels, we study resonant acoustic phonon scattering in two-dimensional electron systems. We observe that dc electric field strongly modifies phonon resonances, transforming resistance maxima into minima and back into maxima. Further, phonon resonances are enhanced dramatically in the non-linear dc response and can be detected even at low temperatures. Most of our observations can be explained in terms of dc-induced (de)tuning of the resonant acoustic phonon scattering and its interplay with intra-Landau level impurity scattering. Finally, we observ…
We study the problem of resonant tunneling between a Fermi liquid and the edge of a $ν=1/3$ fractional quantum Hall state. In the limit of weak coupling, the system is adequately described within the sequential tunneling approximation. At low temperatures, however, the system crosses over to a strong coupling phase, which we analyze using renormalization group techniques. We find that at low temperatures a "perfect" can be achieved by tuning two parameters. This resonance has a peak conductance $G = e^2/2h$ and is a realization of the weak backscattering limit of the $g=1/2$ Luttinger liquid, …
We study the disorder effect of resonant spin Hall effect in a two-dimension electron system with Rashba coupling in the presence of a tilted magnetic field. The competition between the Rashba coupling and the Zeeman coupling leads to the energy crossing of the Landau levels, which gives rise to the resonant spin Hall effect. Utilizing the Streda's formula within the self-consistent Born approximation, we find that the impurity scattering broadens the energy levels, and the resonant spin Hall conductance exhibits a double peak around the resonant point, which is recovered in an applied titled …
We have developed a method for electrical polarization of nuclear spins in quantum Hall systems. In a breakdown regime of odd-integer quantum Hall effect (QHE), excitation of electrons to the upper Landau subband with opposite spin polarity dynamically polarizes nuclear spins through the hyperfine interaction. The polarized nuclear spins in turn accelerate the QHE breakdown, leading to hysteretic voltage-current characteristics of the quantum Hall conductor.
At the spin transition point of $ν=2/3$ quantum Hall states, nuclear spins in a two-dimensional electron gas are polarized by an electric current. Using GaAs/AlGaAs double-quantum-well samples, we first observed the spatial diffusion of nuclear spin polarization between the two layers when the nuclear spin polarization is current-induced in one layer. By numerical simulation, we estimated the diffusion constant of the nuclear spin polarization to be $15 \pm 7$\,nm$^2$/s.
Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots lead to nuclear spin polarization that is qualitatively different from the well known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dy…
We study the influence of the phase relaxation process on Hall resistance and spin Hall current of a mesoscopic two-dimensional (2D) four-terminal Hall cross-bar with or without Rashba spin-orbit interaction (SOI) in a perpendicular uniform magnetic field. We find that the plateaus of the Hall resistance with even number of edge states can survive for very strong phase relaxation when the system size becomes much longer than the phase coherence length. On the other hand, the odd integer Hall resistance plateaus arising from the SOI are easily destroyed by the weak phase relaxation during the c…
We study nuclear spin polarization in the quantum Hall regime through the optically pumped electron spin polarization in the lowest Landau level. The nuclear spin polarization is measured as a nuclear magnetic field $B_N$ by means of the sensitive resistive detection. We find the dependence of $B_N$ on filling factor unmonotonous. The comprehensive measurements of $B_N$ with the help of the circularly polarized photoluminescence measurements indicate the participation of the photo-excited complexes i.e., the exciton and trion (charged exciton), in nuclear spin polarization. On the basis of a n…
We investigate the resistance enhancement state (RES) where the magnetoresistance of the $ν= 2/3$ fractional quantum Hall state (FQHS) is increased with dynamic nuclear spin polarization (DNP) induced by a large electric current. After inducing DNP, we measure the temperature dependence of the magnetoresistance by a small current over a short period of time. We find that the FQHS makes a phase transition to an insulating state. By measuring the Hall resistance in the insulating state, we find that the RES exhibits a quantized Hall resistance. We discuss the RES in association with the Anderson…
The parallel field of a full spin polarization of the electron gas in a \Gamma8 conduction band of the HgTe quantum well was obtained from the magnetoresistance by three different ways in a zero and quasi-classical range of perpendicular field component Bper. In the quantum Hall range of Bper the spin polarization manifests in anticrossings of magnetic levels, which were found to strongly nonmonotonously depend on Bper.
We predict theoretically that, when a normal metallic thin film (without bulk spin-orbit coupling, such as Cu or Al) is sandwiched by two insulators, two prominent effects arise due to the interfacial spin-orbit coupling: a giant spin-Hall conductivity due to the surface scattering and a transverse electric polarization due to the spin-dependent phase shift in the spinor wave functions.
In this Letter, a tunable valley polarization is investigated for honeycomb systems with broken inversion symmetry such as transition-metal dichalcogenide MX2 (M = Mo, W; X = S, Se) monolayers through elliptical pumping. As compared to circular pumping, elliptical pumping is more universal and effective method to create coherent valley polarization. When two valleys of MX2 monolayers are doped or polarized, a novel anomalous valley orbital magnetic moment Hall effect driven by opposite Berry curvatures at different valleys is predicted and can generate orbital magnetic moment current without t…
Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly-sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and in particular the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in Q…
Electrical polarization of nuclear spins is studied in a Corbino disk under a breakdown regime of the quantum Hall effect (QHE). Since the edge channels are completely absent in the Corbino disk, we conclude that the electric current flowing in the bulk channel of a quantum Hall conductor is relevant to dynamic nuclear polarization (DNP). A pump and probe measurement demonstrates that DNP emerges near the critical voltage of the QHE breakdown. The agreement of the onset voltage of DNP with that of the QHE breakdown indicates that the underlying origin of DNP is closely related to that of the Q…
A biref review is presented on resonant spin Hall effect, where a tiny external electric field induces a saturated spin Hall current in a 2-dimensional electron or hole gas in a perpendicular magnetic field. The phenomenon is attributted to the energy level crossing associated with the spin-orbit coupling and the Zeeman splitting. We summarize recent theoretical development of the effect in various systems and discuss possible experiments to observe the effect.
This paper presents experimental evidence of the existence of acoustic valley Hall (AVHE) edge states in topological elastic waveguides. The fundamental lattice is assembled based on a non-resonant unit where space inversion symmetry (SIS) is broken by simply perturbing the underlying lattice geometry. This aspect is in net contrast with existing elastic AVHE designs that exploit locally-resonant units and require the addition of masses in order to break SIS. The experimental results presented in this study validate findings so far presented only at theoretical and numerical level. In particul…
We study dynamic nuclear polarization (DNP) induced by breakdown of the fractional quantum Hall (FQH) effect. We find that voltage-current characteristics depend on current sweep rates at the quantum Hall states of Landau level filling factors $ν$ = 1, 2/3, and 1/3. The sweep rate dependence is attributed to DNP occurring in the breakdown regime of FQH states. Results of a pump and probe experiment show that the polarities of the DNP induced in the breakdown regimes of the FQH states is opposite to that of the DNP induced in the breakdown regimes of odd-integer quantum Hall states.
We studied spatial distribution of dynamic nuclear polarization (DNP) in a Hall-bar device in a breakdown regime of the quantum Hall effect (QHE). We detected nuclear magnetic resonance (NMR) signals from the polarized nuclear spins by measuring the Hall voltage $V_{xy}$ using three pairs of voltage probes attached to the conducting channel of the Hall bar. We find that the amplitude of the NMR signal depends on the position of the Hall voltage probes and that the largest NMR signal is obtained from the pair of probes farthest from the electron-injecting electrode. Combined with results on pum…
We investigate dynamic nuclear polarization in quantum point contacts (QPCs) in the integer and fractional quantum Hall regimes. Following the application of a dc bias, fractional plateaus in the QPC shift symmetrically about half filling of the lowest Landau level, ν=1/2, suggesting an interpretation in terms of composite fermions. Polarizing and detecting at different filling factors indicates that Zeeman energy is reduced by the induced nuclear polarization. Mapping effects from integer to fractional regimes extends the composite fermion picture to include hyperfine coupling.
We study theoretically resonant tunneling of composite fermions through their quasi-bound states around a fractional quantum Hall island, and find a rich set of possible transitions of the island state as a function of the magnetic field or the backgate voltage. These considerations have possible relevance to a recent experimental study, and bring out many subtleties involved in deducing fractional braiding statistics.
The concept of fractional charge is central to the theory of the fractional quantum Hall effect (FQHE). Here I use exact diagonalization as well as configuration space renormalization (CSR) to study finite clusters which are large enough to contain two independent edges. I analyze the conditions of resonant tunneling between the two edges. The "computer experiment" reveals a periodic sequence of resonant tunneling events consistent with the experimentally observed fractional quantization of electric charge in units of e/3 and e/5.
The temperature dependence of electron spin polarization for a narrow quantum Hall system shows behavior analogous to that of a two-dimensional system at major filling factors. At the lowest half-filled quantum Hall state for which no two-dimensional analog exists, we find a stable spin partially-polarized system. Periodic Gaussian repulsive impurities (antidots) in such a system leads to novel spin transitions at $ν=\frac13$ and $ν=\frac12$ and the pair-correlation functions provide clues about nature of different ground states in the system. These results can be explored in optical spectrosc…
We study pumping of charge in a 2DEG in the quantum Hall regime at filling factor $ν= 2$ (2 spin-split levels of the lowest Landau level). For pumping frequencies that match the Zeeman energy splitting, quantum pumping together with hyperfine interaction between electrons and nuclei induces transitions between the spin-split levels. These lead to a step-like change in the pumped current and to polarization of the nuclei. We present quantitative predictions for both. Our model provides the first quantitative tool to both control and measure the amount of local nuclear polarization in a 2DEG.
Resonant laser scattering along with photon correlation measurements have established the atom-like character of quantum dots. Here, we present measurements which challenge this identification for a wide range of experimental parameters: the absorption lineshapes that we measure at magnetic fields exceeding 1 Tesla indicate that the nuclear spins polarize by an amount that ensures locking of the quantum dot resonances to the incident laser frequency. In contrast to earlier experiments, this nuclear spin polarization is bi-directional, allowing the electron+nuclear spin system to track the chan…
We report on polarization selection rules of inter-Landau level transitions using reflection-type optical Hall effect measurements from 600 to 4000 cm-1 on epitaxial graphene grown by thermal decomposition of silicon carbide. We observe symmetric and anti-symmetric signatures in our data due to polarization preserving and polarization mixing inter-Landau level transitions, respectively. From field-dependent measurements we identify that transitions in decoupled graphene mono-layers are governed by polarization mixing selection rules, whereas transitions in coupled graphene mono-layers are gove…
We find that the nuclear-spin polarization has not been treated correctly. The references given are those of wrong papers. The credits assigned for discoveries are also not correct. Incorrect theories have been cited. The reference to the correct theory has been neglected. Because there are lots of good people, so they do not want to give reference to my papers even though they have not solved the problem of quantum Hall effect and we have.
Hall effects have been employed as sensitive detectors of magnetic fields and magnetizations. In spintronics, exotic phenomena often emerge from a non-equilibrium spin polarization or magnetization, that is very difficult to measure directly. The challenge is due to the tiny total moment, which is out of reach of superconducting quantum interference devices and vibrating sample magnetometers or spectroscopic methods such as X-ray magnetic circular dichroism. The Kerr effect is sufficiently sensitive only in direct gap semiconductors, in which the Kerr angle can be resonantly enhanced. Here we …
For monolayer transition metal chalcogenides (TMDs), electrons and excitons in different valleys can be driven to opposite directions by the Berry curvature, serving as a valley-dependent effective magnetic field. In addition to monolayer TMDs, Van der Waals heterostructures provide an attractive platform for emerging valley physics and devices with superior physics properties. Interlayer excitons in TMD heterostructures have a long valley lifetime as compared to monolayer intralayer excitons. Here we report an interlayer exciton valley polarization and valley Hall effect in MoS2/WSe2 in room …
We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spi…
The quasiclassical Green function formalism is used to describe charge and spin dynamics in the presence of spin-orbit coupling. We review the results obtained for the spin Hall effect on restricted geometries. The role of boundaries is discussed in the framework of spin diffusion equations.
We apply polarization resolved photoluminescence spectroscopy to measure the spin polarization of a two dimensional electron gas in perpendicular magnetic field. In the vicinity of filling factor nu=5/2, we observe a sharp discontinuity in the energy of the zero Landau level emission line. We find that the splitting between the two circular polarizations exhibits a sharp drop at nu=5/2 and is equal to the bare Zeeman energy, which resembles the behavior at even filling factors. We show that this behavior is consistent with filling factor nu=5/2 being unpolarized.
Determining the detailed spin texture of topological surface states is important when one wants to apply topological insulators in spintronic devices. In principle, the in-plane spin component of the surface states can be measured by a method analogous to the so-called Meservey-Tedrow technique. In the present work we suggest that the out-of-plane spin component can be determined by spin Hall effect tunneling spectroscopy. We derive an analytical formula that allows to extract the out-of-plane spin component from spin Hall effect tunneling spectra. We test our formula using realistic tight-bin…
We have investigated the complex two-dimensional electron system with unequal Rashba and Dresselhaus spin-orbit interactions in the presence of a perpendicular magnetic field. The spin polarizations are obtained in a wide range of magnetic fields. It is shown that such a system is hard to be magnetized. We also find that the resonant charge and spin Hall conductances occurs simultaneously at a certain magnetic field, at which two (nearly) degenerate Landau levels are filled partly. The resonant Hall effects are universal in this type of semiconductor materials, and could have potential applica…
The enhanced spin Hall effect in Au metal due to the resonant skew scattering is studied with first-principles band structure calculations. Especially the gigantic spin Hall angle $γ_S \cong 0.1$ observed recently (T.Seki et al., Nature Materials {\bf 7}, 125 (2008)) is attributed to the orbital-dependent Kondo effect of Fe in the Au host metal, where the $t_{2g}$-orbitals are in the mixed-valence region while $e_g$-orbitals are in the Kondo limit. The enhanced spin-orbit interaction by the electron correlation in the $t_{2g}$-orbitals leads to the gigantic spin Hall effect. Impurities with 5d…
We study transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin orbit coupling competes with Zeeman splitting to introduce additional degeneracies between different Landau levels at certain magnetic fields. This degeneracy, if occuring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as $-\ln T$ at low temperatures. The Hall conductance is unaffected by the Rashba coupling.
We have discussed here the polarization of quantum Hall states in the framework of the hierarchical analysis of IQHE and FQHE in terms of Berry phase. It is observed that we have fully polarized states for the filling factor $ν=1$ as well as $ν=\frac{1}{2m+1}$, $m$ being an integer. However, for $ν=p$ as well as $ν=\frac{p}{q}$, with $p>1$ and odd, $q$ odd we have partially polarized states and for $ν=\frac{p}{q}$, $p$ even, $q$ odd we have unpolarized states. It has been found that skyrmion excitations exist only for fully polarized states and for partially polarized and unpolarized states sk…
A spin-dependent quantum transport is investigated in a paramagnetic resonant tunneling diode (RTD) based on a Zn$_{1-x}$Mn$_x$Se/ZnBeSe heterostructure. Using the Wigner-Poisson method and assuming the two-current model we have calculated the current-voltage characteristics, potential energy profiles and electron density distributions for spin-up and spin-down electron current in an external magnetic field. We have found that -- for both the spin-polarized currents -- two types of the current hysteresis appear on the current-voltage characteristics. The current hysteresis of the first type oc…
We report on our theoretical investigation considering the widths of quantized Hall plateaus (QHPs) depending on the density asymmetry induced by the large current within the out-of-linear response regime. We solve the Schrodinger equation within the Hartree type mean field approximation using Thomas Fermi Poisson nonlinear screening theory. We observe that the two dimensional electron system splits into compressible and incompressible regions for certain magnetic field intervals, where the Hall resistance is quantized and the longitudinal resistance vanishes, if an external current is imposed…
Spin-orbit coupling in semiconductors relates the spin of an electron to its momentum and provides a pathway for electrically initializing and manipulating electron spins for applications in spintronics and spin-based quantum information processing. This coupling can be regulated with quantum confinement in semiconductor heterostructures through band structure engineering. Here we investigate the spin Hall effect and current-induced spin polarization in a two-dimensional electron gas confined in (110) AlGaAs quantum wells using Kerr rotation microscopy. In contrast to previous measurements, th…
Nuclear spins are polarized electrically in a breakdown regime of an odd-integer quantum Hall effect (QHE). Electron excitation to the upper Landau subband with the opposite spin polarity flips nuclear spins through the hyperfine interaction. The polarized nuclear spins reduce the spin-splitting energy and accelerate the QHE breakdown. The Knight shift of the nuclear spins is also measured by tuning electron density during the irradiation of radio-frequency magnetic fields.
Universal properties of spin-Hall effect in ballistic 2D electron systems are addressed. The net spin polarization across the edge of the conductor is second order, ~λ^2, in spin-orbit coupling constant independent of the form of the boundary potential, with the contributions of normal and evanescent modes each being ~ \sqrtλ but of opposite signs. This general result is confirmed by the analytical solution for a hard-wall boundary, which also yields the detailed distribution of the local spin polarization. The latter shows fast (Friedel) oscillations with the spin-orbit coupling entering via …
