Experimental data available in the literature for peak values of the diagonal resistivity in the transitions between fractional quantum Hall states are compared with the theoretical predictions. It is found that the majority of the peak values are close to the theoretical values for two-dimensional systems with moderate mobilities.
We consider the effect of microwave radiation on the Hall resistivity in two-dimension electron systems. It is shown that the photon-assisted impurity scattering of electrons can result in oscillatory dependences of both dissipative and Hall components of the conductivity and resistivity tensors on the ratio of radiation frequency to cyclotron frequency. The Hall resistivity can include a component induced by microwave radiation which is an even function of the magnetic field. The phase of the dissipative resistivity oscillations and the polarization dependence of their amplitude are compared …
We present a direct numerical evidence for reflection symmetry of longitudinal resistivity $ρ_{xx}$ and quantized Hall resistivity $ρ_{xy}$ near the transition between $ν=1$ quantum Hall state and insulator, in accord with the recent experiments. Our results show that a universal scaling behavior of conductances, $σ_{xx}$ and $σ_{xy}$, in the transition regime decide the reflection symmetry of $ρ_{xx}$ and quantization of $ρ_{xy}$, independent of particle-hole symmetry. We also find that in insulating phase away from the transition region $ρ_{xy}$ deviates from the quantization and diverges wi…
The longitudinal resistivity at transitions between integer quantum Hall states in two-dimensional electrons confined to AlAs quantum wells is found to depend on the spin orientation of the partially-filled Landau level in which the Fermi energy resides. The resistivity can be enhanced by an order of magnitude as the spin orientation of this energy level is aligned with the majority spin. We discuss possible causes and suggest a new explanation for spike-like features observed at the edges of quantum Hall minima near Landau level crossings.
The critical resistivity measured along the quantum Hall liquid--insulator transition line indicates a pronounced peak at a critical filling factor close to 1, which marks the crossover from the high to low magnetic field regime in the phase diagram. The origin of this behavior is explained in the framework of classical transport in a puddle network model. The proposed scenario is also consistent with the behavior of the critical Hall resistance along the transition line. In addition, a formula is suggested as a fit for isotherms ($ρ_{xx}$ vs. $ν$) in the moderately high field regime, which ex…
Hall effect of two-dimensional holes that are spin-polarized by a strong parallel magnetic field was explored with a small tilt angle. The Hall resistivity increases nonlinearly with the magnetic field and exhibits negative corrections. The anomalous negative corrections increase with the perpendicular magnetization of the two-dimensional hole system. We attribute this to the anomalous Hall effect of spin-polarized carriers in a nonmagnetic system. The anomalous corrections to the conductivity exhibit non-monotonic dependence on the magnetic field.
We show that when bulk graphene breaks into n-type and p-type puddles, the in-plane resistivity becomes strongly field dependent in the presence of a perpendicular magnetic field, even if homoge- neous graphene has a field-independent resistivity. We calculate the longitudinal resistivity ρ_{xx} and Hall resistivity ρ_{xy} as a function of field for this system, using the effective-medium approximation. The conductivity tensors of the individual puddles are calculated using a Boltzmann approach suit- able for the band structure of graphene near the Dirac points. The resulting resistivity agree…
Robustness of quantized Hall resistivity under cavity coupling at zero temperature
Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza(阿拉贡纳米科学与材料研究所);Departamento de Física de la Materia Condensada, Universidad de Zaragoza(萨拉戈萨大学凝聚态物理系);International Center for Quantum Materials, Peking University(北京大学量子材料中心);Beijing Key Laboratory of Quantum Devices, Peking University(北京量子器件重点实验室);Max Planck Institute for the Structure and Dynamics of Matter(马普物质结构与动力学研究所);The Flatiron Institute(平顿研究所);Villanova University(维拉诺瓦大学)
Based on a thermodynamic approach, we have calculated the resistivity of a 2D electron gas, assumed $dissipationless$ in a strong quantum limit. Standard measurements, with extra current leads, define the resistivity caused by a combination of Peltier and Seebeck effects. The current causes heating(cooling) at the first(second) sample contacts, due to the Peltier effect. The contact temperatures are different. The measured voltage is equal to the Peltier effect-induced thermoemf which is linear in current. As a result, the resistivity is non-zero as $I\to 0$. The resistivity is a universal fun…
Following recent experiments, we consider current flow in two dimensional electronic systems in the quantum Hall regime where a gradient in the electron density induces a spatial variation in the Hall resistivity. Describing the system in terms of a spatially varying local resistivity tensor, we show that in such a system the current density is generically non-uniform, with the current being pushed towards one side of the sample. We show that, for sufficiently large density gradient, the voltage along that side is determined by the change of the Hall resistivity, and is independent of the micr…
The energy efficiency of the spin Hall effects (SHE) can be enhanced if the electrical conductivity is decreased without sacrificing the spin Hall conductivity. The resistivity of Pt films can be increased to 150-300 μΩ*cm by mesoscopic lateral confinement, thereby decreasing the conductivity. The SHE and inverse spin Hall effects (ISHE) in these mesoscopic Pt films are explored at 10 K by using the nonlocal spin injection/detection method. All relevant physical quantities are determined in-situ on the same substrate, and a quantitative approach is developed to characterize all processes effec…
Quantum Hall stripe phases near half-integer filling factors $ν\ge 9/2$ were predicted by Hartree-Fock (HF) theory and confirmed by discoveries of giant resistance anisotropies in high-mobility two-dimensional electron gases. A theory of such anisotropy was proposed by MacDonald and Fisher, although they used parameters whose dependencies on the filling factor, electron density, and mobility remained unspecified. Here, we fill this void by calculating the hard-to-easy resistivity ratio as a function of these three variables. Quantitative comparison with experiment yields very good agreement wh…
We theoretically analyzed the microwave-induced modification of the Hall magnetoresistivity in high mobility two-dimensional electron systems. These systems present diagonal magnetoresistivity oscillations and zero-resistance states when are subjected to microwave radiation. The most surprising modification of the Hall magnetoresistivity is a periodic reduction which correlates with a periodic increase in the diagonal resistivity. We present a model that explains the experimental results considering that radiation affects directly only the diagonal resistivity and the observed Hall resistivity…
We analyzed the magnetoresistivity of a two-dimensional electron system excited by microwave radiation in a regime of high intensities and low frequencies. In such a regime, recent experiments show that different features appear in the magnetoresistivity response which suggest an anharmonic behavior. These features consist mainly in distorted oscillations and new resonance peaks at the subharmonics of the cyclotron frequency. We follow the model of microwave-driven electron orbits motion which become anharmonic when the ratio of microwave intensity to microwave frequency is large enough.
We report measurements of the spin torque efficiencies in perpendicularly-magnetized Pt/Co bilayers where the Pt resistivity $ρ_{Pt}$ is strongly dependent on thickness $t_{Pt}$ . The damping-like spin Hall torque efficiency per unit current density, $ξ^j_{DL}$ , varies significantly with $t_{Pt}$, exhibiting a peak value $ξ^j_{DL}=0.12$ at $t_{Pt} = 2.8 - 3.9$ nm. In contrast, $ξ^j_{DL}/ρ_{Pt}$ increases monotonically with $t_{Pt}$ and saturates for $t_{Pt} > 5$ nm, consistent with an intrinsic spin Hall effect mechanism, in which $ξ^j_{DL}$ is enhanced by an increase in $ρ_{Pt}$ . Assuming t…
Transport measurements indicate strong oscillations in the Hall-,$R_{xy}$, and the diagonal-, $R_{xx}$, resistances and exhibit Hall plateaus at the lowest temperatures, in three-dimensional Highly Oriented Pyrolytic Graphite (HOPG). At the same time, a comparative Shubnikov-de Haas-oscillations-based Berry's phase analysis indicates that graphite is unlike the GaAs/AlGaAs 2D electron system, the 3D n-GaAs epilayer, semiconducting $Hg_{0.8}Cd_{0.2}Te$, and some other systems. Finally, we observe the transport data to follow $B\times dR_{xy}/dB \approx - ΔR_{xx}$. This feature is consistent wit…
The longstanding problem of the Hall resistivity rho(x,y) in the Hall insulator phase is addressed using four-lead Chalker-Coddington networks. Electron interaction effects are introduced via a finite dephasing length. In the quantum coherent regime, we find that rho(x,y) scales with the longitudinal resistivity rho(x,x), and they both diverge exponentially with dephasing length. In the Ohmic limit, (dephasing length shorter than Hall puddles' size), rho(x,y) remains quantized and independent of rho(x,x). This suggests a new experimental probe for dephasing processes.
We report that the rate of field sweep is important for the observation of the zeroes in the transverse resistivity in the quantum Hall effect. The resistivity also shows resonances at the nuclear magnetic resonance (NMR) frequencies when the r.f. coil is placed along the x direction. The relationship of the eigen values with the resistivity is pointed out which shows that even if the eigen values are largely corresponding to that of the single-particle, the plateau widths, shifts and shape require many-body interactions.
The resistivity minima of the quantum Hall effect arise due to the localization of the electron states at the Fermi energy, when it is positioned between adjacent Landau levels. In this paper we calculate the localization length $ξ$ of such states at even filling factors $ν= 2 N$. The calculation is done for several models of disorder (``white-noise,'' short-range, and long-range random potentials). We find that the localization length has a power-law dependence on the Landau level index, $ξ\propto N^α$ with the exponent $α$ between one and ${10/3}$, depending on the model. In particular, for …
Experimental studies of the transitions from a primary quantum Hall (QH) liquid at filling factor 1/k (with k an odd integer) to the insulator have indicated a ``quantized Hall insulator'' (QHI) behavior: while the longitudinal resistivity diverges with decreasing temperature and current bias, the Hall resistivity remains quantized at the value $k h/ e^2$. We review the experimental results and the theoretical studies addressing this phenomenon. In particular, we discuss a theoretical approach which employs a model of the insulator as a random network of weakly coupled puddles of QH liquid at …
We present a systematic study of the corrections to both the longitudinal conductivity and Hall resistivity due to electron-electron interactions in high quality GaAs systems using the recent theory of Zala et al. [Phys. Rev. B 64, 214204 (2001)]. We demonstrate that the interaction corrections to the longitudinal conductivity and Hall resistivity predicted by the theory are consistent with each other. This suggests that the anomalous metallic drop in resistivity at B=0 is due to interaction effects and supports the theory of Zala et al.
Recently, Tieke et al (to be published in PRL) have observed the relation S_{yx} = alpha B dS_{xx}/dB for the components of the thermopower tensor in the quantum Hall regime, where alpha is a constant and B is the magnetic field. Simon and Halperin (PRL 73, 3278 (1994)) have suggested that an analogous relation observed for the resistivity tensor R_{xx} = αB dR_{xy}/dB can be explained with a model of classical transport in an inhomogeneous medium where the local Hall resistivity is a function of position and the local dissipative resistivity is a small constant. In the present paper, we show …
Quasiparticles with fractional charge and fractional statistics are key features of the fractional quantum Hall effect. We discuss in detail the definitions of fractional charge and statistics and the ways in which these properties may be observed. In addition to theoretical foundations, we review the present status of the experiments in the area. We also discuss the notions of non-Abelian statistics and attempts to find experimental evidence for the existence of non-Abelian quasiparticles in certain quantum Hall systems.
We give a brief introduction to the phenomenon of the Fractional Quantum Hall effect, whose discovery was awarded the Nobel prize in 1998. We also explain the composite fermion picture which describes the fractional quantum Hall effect as the integer quantum Hall effect of composite fermions.
A fractional quantization in a two dimensional space is proposed. The angular momenta of the two dimensional electrons are quantized in fractional numbers by the boundary conditions on a multi-layered Riemann surface. Extended wave functions for the incompressible quantum fluid states are presented and the cohesive and the excitation energies are given.
Two kinds of topological excitations, vortices and skyrmions, are studied in the frame of Ginzburg-Landau theory. We obtain the rigorous relation between the topological excitation and the order parameters in the fractional quantum Hall systems. We also discuss the evolution of the vortices in fractional quantum Hall systems.
A wide variation in the disorder strength, as inferred from an order of magnitude variation in the longitudinal resistivity of Co2FeSi (CFS) Huesler alloy thin films of fixed (50 nm) thickness, has been achieved by growing these films on Si(111) substrates at substrate temperatures ranging from room temperature (RT) to 600 C. An in-depth study of the influence of disorder on anomalous Hall resistivity,longitudinal resistivity(LR) and magnetoresistance, enabled by this approach, reveals the following. The side-jump mechanism gives a dominant contribution to anomalous Hall resistivity (AHR) in t…
We calculate the Hall conductivity $\sig_{xy}$ and resistivity $ρ_{xy}$ of a granular system at large tunneling conductance $g_{T}\gg 1$. We show that in the absence of Coulomb interaction the Hall resistivity depends neither on the tunneling conductance nor on the intragrain disorder and is given by the classical formula $ρ_{xy}=H/(n^* e c)$, where $n^*$ differs from the carrier density $n$ inside the grains by a numerical coefficient determined by the shape of the grains. The Coulomb interaction gives rise to logarithmic in temperature $T$ correction to $ρ_{xy}$ in the range $\Ga \lesssim T …
We obtain a ``mean field'' scaling flow of the longitudinal and the Hall conductivities in the fractional quantum Hall regime. Using the composite fermion picture and assuming that the composite fermions follow the Khmelnitskii-Pruisken scaling flow for the integer quantum Hall effect, the unstable fixed points which govern the transitions between different fractional quantum Hall states are identified. Distributions of the critical longitudinal and Hall conductivities at the unstable fixed points are obtained and implications of the results for the experiments on mesoscopic quantum Hall syste…
The true nature of the lowest-energy, long-wavelength neutral excitation of the fractional quantum Hall effect has been a long outstanding problem. In this Letter, we establish that it is a two-roton bound state.
We constructed a Hall resistance formula for the fractional quantum Hall effect by analyzing the experimental data reported in [J. P. Eisenstein and H. L. Stormer, {Science} {\bf 248}, 1510 (1990)]. The formula is given as a function of magnetic induction, chemical potential and temperature. The Hall resistance function contains a single-electron energy spectrum, which has phenomenological perturbation terms with three tunable parameters. The formula yields 12 plateaus that are consistent with the experiment. The perturbations can be interpreted as precession or nutation of a Landau orbital in…
The quantum magnetotransport properties of a monolayer of molybdenum disulfide are derived using linear response theory. Especially, the effect of topological terms on longitudinal and Hall conductivity is analyzed. The Hall conductivity exhibits fractional steps in the integer quantum Hall regime. Further complete spin and valley polarization of the longitudinal conductivity is seen in presence of these topological terms. Finally, the Shubnikov-de Hass oscillations are suppressed or enhanced contingent on the sign of these topological terms.
Quasielectrons and quasiholes in the fractional quantum Hall liquids obey fractional (including nontrivial mutual) exclusion statistics. Their statistics matrix can be determined from several possible state-counting scheme, involving different assumptions on statistical correlations. Thermal activation of quasiparticle pairs and thermodynamic properties of the fractional quantum Hall liquids near fillings $1/m$ ($m$ odd) at low temperature are studied in the approximation of generalized ideal gas. The existence of hierarchical states in the fractional quantum Hall effect is shown to be a manif…
We argue that dynamics of gapless Fractional Quantum Hall Edge states is essentially non-linear and that it features fractionally quantized solitons propagating along the edge. Observation of solitons would be a direct evidence of fractional charges. We show that the non-linear dynamics of the Laughlin's FQH state is governed by the quantum Benjamin-Ono equation. Non-linear dynamics of gapless edge states is determined by gapped modes in the bulk of FQH liquid. The dispersion of edge modes is traced to the double boundary layer of FQH states.
We report on a systematic study of Hall effect using high quality single crystals of type-II Weyl semimetal WTe2 with the applied magnetic field B//c. The residual resistivity ratio of 1330 and the large magnetoresistance of 1.5\times10^6 % in 9 T at 2 K, being in the highest class in the literature, attest to their high quality. Based on a simple two-band model, the densities (n_e and n_h) and mobilities (μ_e and μ_h) for electron and hole carriers have been uniquely determined combining both Hall- and electrical-resistivity data. The difference between ne and nh is ~1% at 2 K, indicating tha…
We consider interacting bosonic atoms in an optical lattice subject to a large simulated magnetic field. We develop a model similar to a bilayer fractional quantum Hall system valid near simple rational numbers of magnetic flux quanta per lattice cell. Then we calculate its ground state, magnetic lengths, fractional fillings, and find unexpected sign changes in the Hall current. Finally we study methods for detecting these novel features via shot noise and Hall current measurements.
The activation energy measured in transport experiments in the fractional Hall regime corresponds to the energy required to create a far separated particle hole pair. We calculate, for several fractional quantum Hall states, the energy gaps for the excitation in which the excited composite fermion reverses its spin quantum number. Our results indicate that such spin reversed excitations may be relevant in experimentally accessible regimes.
In the fractional quantum Hall effect regime we measure diagonal ($ρ_{xx}$) and Hall ($ρ_{xy}$) magnetoresistivity tensor components of two-dimensional electron system (2DES) in gated GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions, together with capacitance between 2DES and the gate. We observe 1/3- and 2/3-fractional quantum Hall effect at rather low magnetic fields where corresponding fractional minima in the thermodynamical density of states have already disappeared manifesting complete suppression of the quasiparticle energy gaps.
With the recent observation of graphene-like Landau levels at the surface of topological insulators, the possibility of fractional quantum Hall effect, which is a fundamental signature of strong correlations, has become of interest. Some experiments have reported intra-Landau level structure that is suggestive of fractional quantum Hall effect. This paper discusses the feasibility of fractional quantum Hall effect from a theoretical perspective, and argues that while this effect should occur, ideally, in the $n=0$ and $|n|=1$ Landau levels, it is ruled out in higher $|n|$ Landau levels. Unlike…
It is shown that the description of the FQHE as condensation of the electron system into a ground state with fractionally charged excitations is incompatible with experimental observations. The nature of the Hall voltage in fractional plateaux as a chemical potential difference eliminates the condensate as current carrier and the temperature dependence of longitudinal conductance eliminates the excitation picture of charge carriers.
Two dimensional electron systems exhibiting the 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 present. We present a {\it microscopic} calculation of the edge states in the fractional quantum Hall systems at various filling factors using the extended Hamiltonian theory of the fractional quantum Hall effect. We find that at $ν=1/3$ the quantum Hall edge undergoes a reconstruction as the background potential softens, whereas quantum Hall edges at hi…
We generalize the fractional quantum Hall hierarchy picture to apply to arbitrary, possibly non-Abelian, fractional quantum Hall states. Applying this to the nu = 5/2 Moore-Read state, we construct new explicit trial wavefunctions to describe the fractional quantum Hall effect in the second Landau level. The resulting hierarchy of states, which reproduces the filling fractions of all observed Hall conductance plateaus in the second Landau level, is characterized by electron pairing in the ground state and an excitation spectrum that includes non-Abelian anyons of the Ising type. We propose thi…
Previously we have demonstrated that, on a torus, the abelian quantum hall liquid is adiabatically connected to a charge density wave as the smaller dimension of the torus is varied. In this work we extend this result to the non-abelian bosonic Hall state. The outcome of these works is the realization that the paradigms of quantum number fractionalization in one dimension (polyacetylene) and two dimensions (fractional quantum Hall effect) are in fact equivalent.
We have experimentally identified fractional quasiparticle creation in a tunneling process through a local fractional quantum Hall (FQH) state. The local FQH state is prepared in a low-density region near a quantum point contact (QPC) in an integer quantum Hall (IQH) system. Shot-noise measurements reveal a clear transition from elementary-charge tunneling at low bias to fractional-charge tunneling at high bias. The fractional shot noise is proportional to T1(1 ? T1) over a wide range of T1, where T1 is the transmission probability of the IQH edge channel. This binomial distribution indicates …
Most of the fractions observed to date belong to the sequences $ν=n/(2pn\pm 1)$ and $ν=1-n/(2pn\pm 1)$, $n$ and $p$ integers, understood as the familiar {\em integral} quantum Hall effect of composite fermions. These sequences fail to accommodate, however, many fractions such as $ν=4/11$ and 5/13, discovered recently in ultra-high mobility samples at very low temperatures. We show that these "next generation" fractional quantum Hall states are accurately described as the {\em fractional} quantum Hall effect of composite fermions.
Magnetic skyrmions are knot-like quasiparticles. They are candidates for non-volatile data storage in which information is moved between fixed read and write terminals. Read-out operation of skyrmion-based spintronic devices will rely upon electrical detection of a single magnetic skyrmion within a nanostructure. Here, we present Pt/Co/Ir nanodiscs which support skyrmions at room temperature. We measured the Hall resistivity whilst simultaneously imaging the spin texture using magnetic scanning transmission x-ray microscopy (STXM). The Hall resistivity is correlated to both the presence and si…
Edge states of the quantum Hall fluid provide an opportunity to study mesoscopic effects in a highly correlated electron system that is both experimentally accessible and theoretically tractable. In this paper we review recent work on the persistent current and Aharonov-Bohm magnetoconductance oscillations in the fractional quantum Hall effect regime.
At sufficiently low temperatures, many quantum effects, such as weak localization, electron-electron interaction (EEI), and Kondo screening, can lead to pronounced corrections to the semiclassical electron transport. Although low temperature corrections to longitudinal resistivity, ordinary Hall resistivity, or anomalous Hall resistivity are often observed, the corrections to three of them have never been simultaneously detected in a single sample. Here, we report on the observation of $\sqrt T$-type temperature dependences of the longitudinal, ordinary Hall and AH resistivities at temperature…
We derive the effective field theory from the microscopic Hamiltonian of interacting two-dimensional (pseudo) Dirac electrons by performing a statistic gauge transformation. The quantized Hall conductance are expected to be $σ_{xy}=\frac{e^2}{h}(2k-1)$ with $k$ is arbitrary integer. There are also topological excitations which have fractional charge and obey fractional statistics.
We study the behavior of two-dimensional electron gas in the fractional quantum Hall regime in the presence of finite layer thickness and correlated disordered potential. Generalizing the Chern number calculation to many-body systems, we determine the mobility gaps of fractional quantum Hall states based on the distribution of Chern numbers in a microscopic model. We find excellent agreement between experimentally measured activation gaps and our calculated mobility gaps, when combining the effects of both disordered potential and layer thickness. We clarify the difference between mobility gap…
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.
Hall experiments in chiral magnets are often analyzed as the sum of an anomalous Hall effect, dominated by momentum-space Berry curvature, and a topological Hall effect, arising from the real-space Berry curvature in the presence of skyrmions, in addition to the ordinary Hall resistivity. This raises the questions of how one can incorporate, on an equal footing, the effects of the anomalous velocity and the real space winding of the magnetization, and when such a decomposition of the resistivity is justified. We provide definitive answers to these questions by including the effects of all phas…
We report a simple route to generate magnetotransport data that results in fractional quantum Hall plateaus in the conductance. Ingredients to the generating model are conducting tiles with integer quantum Hall effect and metallic linkers, further Kirchhoff rules. When connecting few identical tiles in a mosaic, fractional steps occur in the conductance values. Richer spectra representing several fractions occur when the tiles are parametrically varied. Parts of the simulation data are supported with purposefully designed graphene mosaics in high magnetic fields. The findings emphasize that th…
We calculate the classic Hall conductivity and mobility of the undoped and doped (or in the gate voltage) graphene as a function of temperature, magnetic field, and carrier concentration. Carrier collisions with defects and acoustic phonons are taken into account. The Hall resistivity varies almost linearly with temperature. The magnetic field dependence of resistivity and mobility is anomalous in weak magnetic fields. There is the square root contribution from the field in the resistivity. The Hall mobility diverges logarithmically with the field for low doping.