arXiv subjects
Publications and source records attributed to D. V. Khveshchenko.
We consider electron transport through a quantum point contact between compressible Quantum Hall liquids and derive the contact's impedance function for both diffusive and ballistic regimes of the bulk electron motion. In either regime, the tunneling current deviates from a power-law behavior $I\sim V^{1/ν}$ expected on the basis of the single-mode chiral Luttinger liquid phenomenology.
We elaborate on a single-mode description of the ballistic charge transport through a narrow constriction in a compressible (composite fermion) Quantum Hall liquid. In the presence of long-range Coulomb interactions we find logarithmic deviations from the Luttinger liquid behavior. These extra logarithmic factors are shown to modify the conductance, shot noise spectrum, and other observables.
The temperature dependences of the galvanomagnetic and thermoelectric transport coefficients within a generic hot-spot model are reconsidered. Despite the recent success in explaining ac Hall effect data in YBa_{2}Cu_{3}O_{7}, a general feature of this model is a departure from the approximately universal temperature dependences observed for normal state transport in the optimally doped cuprates. In this paper, we discuss such systematic deviations and illustrate some of their effects through a concrete numerical example using the calculated band structure for YBa_{2}Cu_{3}O_{7}.
We show that gapless plasmons lead to a universal $(δν(ε)/ν\propto |ε|/E_F)$ correction to the tunneling density of states of a clean two dimensional Coulomb interacting electron gas. We also discuss a counterpart of this effect in the "composite fermion metal" which forms in the presence of a quantizing perpendicular magnetic field corresponding to the half-filled Landau level. We argue that the latter phenomenon might be relevant for deviations from a simple scaling observed by A.Chang et al in the tunneling $I-V$ characteristics of Quantum Hall liquids.
We develop a unified treatment of the piesoelectric coupling between two-dimensional electrons and bulk phonons in both cases of zero and strong magnetic fields, the latter corresponding to even denominator filling fractions. In contrast to the case of coupling via the deformation potential, the leading contributions due to impurity-renormalized electron-phonon vertices are not exactly cancelled by processes of inelastic electron-impurity scattering. Electron energy relaxation time, diffusion correction to the conductivity, and phonon emission rate by hot electrons are computed for realistic $GaAs/AlGaAs$ heterostructures.
We study the principal aspects of the interaction between acoustic phonons and two-dimensional electrons in quantizing magnetic fields corresponding to even denominator fractions. Using the composite fermion approach we derive the vertex of the electron-phonon coupling mediated by the Chern-Simons gauge field. We estimate acoustic phonon contribution to electronic mobility, phonon-drag thermopower, and hot electron energy loss rate, which all, depending on the temperature regime, are either proportional to lower powers of T than their zero field counterparts, or enhanced by the same numerical factor as the coefficient of surface acoustic wave attenuation.
Experiments show that at even denominator fractions (EDFs) ($ν=1/2, 3/4, 3/2$,...) the two-dimensional electron gas in a strong magnetic field becomes compressible, has no energy gap, and demonstrates the presence of an ostensible Fermi surface. Since this phenomenon results from a minimization of the interaction, rather than the kinetic energy, the EDF states might well exhibit deviations from a conventional Fermi liquid. We show that impurity scattering at EDFs and its interference with electron-electron and electron-phonon interactions provide examples of intrinsically non-Fermi-liquid transport.
The method of the quantum kinetic equation is applied to the problem of renormalization of the conductivity of normal metals by gauge electron-electron interactions. It is shown that in the three-dimensional case the relativistic electromagnetic interaction (vector interaction of electrons with transverse photons) leads to an unusual temperature dependence, indicating a deviation from the Fermi liquid theory at low temperatures. In two dimensions such corrections are found to result from both the scalar (density-density or Coulomb) and the vector (current-current) gauge interactions.
We compute the electron diffusion thermopower at compressible Quantum Hall states corresponding to even denominator fractions in the framework of the composite fermion approach. It is shown that the deviation from the linear low temperature behavior of the termopower is dominated by the logarithmic temperature corrections to the conductivity and not to the thermoelectric coefficient, although such terms are present in both quantities. The enhanced magnitude of this effect compared to the zero field case may allow its observation with the existing experimental techniques.
We consider both disorder and interaction effects on the magnetoresistance and Hall constant of composite fermions in the vicinity of half filled Landau level. By contrast to the standard case of Coulomb interacting two-dimensional electron gas we find logarithmic temperature corrections to the Hall conductivity and the magnetoresistance of composite fermions whereas the Hall constant acquires no such correction in the lowest order. The theory provides a possible explanation of the resistivity minimum at filling factor $ν=1/2$.
We perform a semiclassical calculation of the magnetoresistance of spinless two-dimensional fermions in a long-range correlated random magnetic field. In the regime relevant for the problem of the half filled Landau level the perturbative Born approximation fails and we develop a new method of solving the Boltzmann equation beyond the relaxation time approximation. In absence of interactions, electron density modulations, in-plane fields, and Fermi surface anisotropy we obtain a quadratic negative magnetoresistance in the weak field limit.
We study temperature dependence of diagonal conductivity at half filled Landau level by means of the theory of composite fermions in the weakly disordered regime $(k_{F}l>>1)$. At low temperatures we find the leading $\log T$ correction resulting from interference between impurity scattering and gauge interactions of composite fermions. The prefactor appears to be strongly enhanced as compared to the standard Altshuler-Aronov term in agreement with recent experimental observations.
We discuss an approach to higher dimensional bosonization of interacting fermion s based on a picture of fluctuating Fermi surface. Compared with the linearized"constructive" approach developed in Refs.[9-11] this method allows an account of the Fermi surface curvature due to nongaussian terms in the bosonized Lagrangian. On the basis of this description we propose a procedure of calculating density response functions beyond the random phase approximation. We also formulate a bosonic theory of the compressible metal-like state at half filled lowest Landau level and check that in gaussian approximation it reproduces RPA results of the gauge theory by Halperin, Lee, and Read.
We demonstrate that the exact form-factors of the Calogero-Sutherland model which were recently found in Ref.[10] in confirmation of the congectures earlier made by Haldane (Ref.[9]) can be reproduced in the framework of some bosonization procedure in momentum space. This observation implies a possibility of an exact bosonization of this model describing one-dimensional anyons.
Recent experiments on inelastic light scattering in a number of insulating cuprates [1] revealed a new excitation appearing in the case of crossed polarizations just below the optical absorption threshold. This observation suggests that there exists a local exciton-like state with an odd parity with respect to a spatial reflection. We present the theory of high energy large shift Raman scattering in Mott insulators and interpret the experiment [1] as an evidence of a chiral bound state of a hole and a doubly occupied site with a topological magnetic excitation. A formation of these composites is a crucial feature of various topological mechanisms of superconductivity. We show that inelastic light scattering provides an instrument for direct measurements of a local chirality and anomalous terms in the electronic current algebra.
Applying the transformation of fermion operators to new fermion quasiparticles introduced by Halperin, Lee, and Read we estimate a scaling behavior of the ground state energy and quasiparticle gaps as a function of filling fraction for a "principal sequence" of FQHE $ν={N\over{2N\pm 1}}$ states converging towards the gapless state at half filling. The exponent describing the shape of the cusp $δE(ν)\sim |δν|^η$ is found to be greater than one and to depend nontrivially on the interaction potential. The dependence of quasiparticle gaps agrees with the results of recent measurements by R.R.Du et al.
We discuss a generalization of the conventional bosonization procedure to the case of current-current interactions which get their natural representation in terms of current instead of fermion number density operators. A consistent bosonization procedure requires a geometrical quantization of the hamiltonian action of $W_\infty$ on its coadjoint orbits. An integrable example of a nontrivial realization of this symmetry is presented by the Calogero-Sutherland model. For an illustrative nonintegrable example we consider transverse gauge interactions and calculate the fermion Green function.
Applying the bosonization procedure to weakly coupled Hubbard chains we discuss the fixed points of the renormalization group flow where all spin excitations are gapful and a singlet pairing becomes the dominant instability.