arXiv subjects

I. V. Gornyi

Publications and source records attributed to I. V. Gornyi.

At least 109 records · Page 6Linked to original sources

arXiv2006

Electron transport in disordered graphene

We study electron transport properties of a monoatomic graphite layer (graphene) with different types of disorder. We show that the transport properties of the system depend strongly on the character of disorder. Away from half filling, the concentration dependence of conductivity is linear in the case of strong scatterers, in line with recent experimental observations, and logarithmic for weak scatterers. At half filling the conductivity is of the order of e^2/h if the randomness preserves one of the chiral symmetries of the clean Hamiltonian; otherwise, the conductivity is strongly affected by localization effects.

cond-mat.mes-hall↗

arXiv2005

Interaction effects on magnetooscillations in a two-dimensional electron gas

Motivated by recent experiments, we study the interaction corrections to the damping of magnetooscillations in a two-dimensional electron gas (2DEG). We identify leading contributions to the interaction-induced damping which are induced by corrections to the effective mass and quantum scattering time. The damping factor is calculated for Coulomb and short-range interaction in the whole range of temperatures, from the ballistic to the diffusive regime. It is shown that the dominant effect is that of the renormalization of the effective electron mass due to the interplay of the interaction and impurity scattering. The results are relevant to the analysis of experiments on magnetooscillations (in particular, for extracting the value of the effective mass) and are expected to be useful for understanding the physics of a high-mobility 2DEG near the apparent metal-insulator transition.

cond-mat.mes-hall↗

arXiv2005

Interacting electrons in disordered wires: Anderson localization and low-temperature transport

We study transport of interacting electrons in a low-dimensional disordered system at low temperature $T$. In view of localization by disorder, the conductivity $σ(T)$ may only be non-zero due to electron-electron scattering. For weak interactions, the weak-localization regime crosses over with lowering $T$ into a dephasing-induced "power-law hopping". As $T$ is further decreased, the Anderson localization in Fock space crucially affects $σ(T)$, inducing a transition at $T=T_c$, so that $σ(T<T_c)=0$. The critical behavior of $σ(T)$ above $T_c$ is $\lnσ(T)\propto - (T-T_c)^{-1/2}$. The mechanism of transport in the critical regime is many-particle transitions between distant states in Fock space.

cond-mat.dis-nn↗

arXiv2005

Dephasing and weak localization in disordered Luttinger liquid

We study the transport properties of interacting electrons in a disordered quantum wire within the framework of the Luttinger liquid model. The conductivity at finite temperature is nonzero only because of inelastic electron-electron scattering. We demonstrate that the notion of weak localization is applicable to the strongly correlated one-dimensional electron system. We calculate the relevant dephasing rate, which for spinless electrons is governed by the interplay of electron-electron interaction and disorder, thus vanishing in the clean limit.

cond-mat.dis-nn↗

arXiv2004

Quantum corrections to the conductivity and Hall coefficient of a 2D electron gas in a dirty AlGaAs/GaAs/AlGaAs quantum well: transition from diffusive to ballistic regime

We report an experimental study of the quantum corrections to the longitudinal conductivity and the Hall coefficient of a low mobility, high density two-dimensional two-dimensional electron gas in a AlGaAs/GaAs/AlGaAs quantum well in a wide temperature range (1.5 K - 110 K). This temperature range covers both the diffusive and the ballistic interaction regimes for our samples. It was therefore possible to study the crossover region for the longitudinal conductivity and the Hall effect.

cond-mat.mes-hall↗

arXiv2004

Coulomb drag in high Landau levels

Recent experiments on Coulomb drag in the quantum Hall regime have yielded a number of surprises. The most striking observations are that the Coulomb drag can become negative in high Landau levels and that its temperature dependence is non-monotonous. We develop a systematic diagrammatic theory of Coulomb drag in strong magnetic fields explaining these puzzling experiments. The theory is applicable both in the diffusive and the ballistic regimes; we focus on the experimentally relevant ballistic regime (interlayer distance $a$ smaller than the cyclotron radius $R_c$). It is shown that the drag at strong magnetic fields is an interplay of two contributions arising from different sources of particle-hole asymmetry, namely the curvature of the zero-field electron dispersion and the particle-hole asymmetry associated with Landau quantization. The former contribution is positive and governs the high-temperature increase in the drag resistivity. On the other hand, the latter one, which is dominant at low $T$, has an oscillatory sign (depending on the difference in filling factors of the two layers) and gives rise to a sharp peak in the temperature dependence at $T$ of the order of the Landau level width.

cond-mat.mes-hall↗

arXiv2004

Magnetoresistance and dephasing in a two-dimensional electron gas at intermediate conductances

We study, both theoretically and experimentally, the negative magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak transverse magnetic field $B$. The analysis is carried out in a wide range of zero-$B$ conductances $g$ (measured in units of $e^2/h$), including the range of intermediate conductances, $g\sim 1$. Interpretation of the experimental results obtained for a 2D electron gas in GaAs/In$_x$Ga$_{1-x}$As/GaAs single quantum well structures is based on the theory which takes into account terms of higher orders in $1/g$, stemming from both the interference contribution and the mutual effect of weak localization (WL) and Coulomb interaction. We demonstrate that at intermediate conductances the negative MR is described by the standard WL "digamma-functions" expression, but with a reduced prefactor $α$. We also show that at not very high $g$ the second-loop corrections dominate over the contribution of the interaction in the Cooper channel, and therefore appear to be the main source of the lowering of the prefactor, $α\simeq 1-2/πg$. We further analyze the regime of a "weak insulator", when the zero-$B$ conductance is low $g(B=0)<1$ due to the localization at low $T$, whereas the Drude conductance is high, $g_0>>1.$ In this regime, while the MR still can be fitted by the digamma-functions formula, the experimentally obtained value of the dephasing rate has nothing to do with the true one. The corresponding fitting parameter in the low-$T$ limit is determined by the localization length and may therefore saturate at $T\to 0$, even though the true dephasing rate vanishes.

cond-mat.mes-hall↗

arXiv2003

Interaction-induced magnetoresistance in a two-dimensional electron gas

We study the interaction-induced quantum correction δσ_{αβ} to the conductivity tensor of electrons in two dimensions for arbitrary Tτ(where T is the temperature and τthe transport scattering time), magnetic field, and type of disorder. A general theory is developed, allowing us to express δσ_{αβ} in terms of classical propagators (``ballistic diffusons''). The formalism is used to calculate the interaction contribution to the longitudinal and the Hall resistivities in a transverse magnetic field in the whole range of temperature from the diffusive (Tτ<< 1) to the ballistic (Tτ> 1) regime, both in smooth disorder and in the presence of short-range scatterers. Further, we apply the formalism to anisotropic systems and demonstrate that the interaction induces novel quantum oscillations in the resistivity of lateral superlattices.

cond-mat.mes-hall↗

arXiv2003

Transport of interacting electrons through a double barrier in quantum wires

We generalize the fermionic renormalization group method to describe analytically transport through a double barrier structure in a one-dimensional system. Focusing on the case of weakly interacting electrons, we investigate thoroughly the dependence of the conductance on the strength and the shape of the double barrier for arbitrary temperature T. Our approach allows us to systematically analyze the contributions to renormalized scattering amplitudes from different characteristic scales absent in the case of a single impurity, without restricting the consideration to the model of a single resonant level. Both a sequential resonant tunneling for high T and a resonant transmission for T smaller than the resonance width are studied within the unified treatment of transport through strong barriers. For weak barriers, we show that two different regimes are possible. Moderately weak impurities may get strong due to a renormalization by interacting electrons, so that transport is described in terms of theory for initially strong barriers. The renormalization of very weak impurities does not yield any peak in the transmission probability; however, remarkably, the interaction gives rise to a sharp peak in the conductance, provided asymmetry is not too high.

cond-mat.str-el↗

arXiv2003

Interaction-induced magnetoresistance: From the diffusive to the ballistic regime

We study interaction-induced quantum correction to the conductivity tensor of electrons in two dimensions for arbitrary T tau, where T is the temperature and tau the transport mean free time. A general formula is derived, expressing the correction in terms of classical propagators ("ballistic diffusons"). The formalism is used to calculate the interaction contribution to the magnetoresistance in a classically strong transverse field and smooth disorder in the whole range of temperatures from the diffusive (T tau<<1) to the ballistic (T tau>1) regime.

cond-mat.mes-hall↗

arXiv2002

Loschmidt Echo and Lyapunov Exponent in a Quantum Disordered System

We investigate the sensitivity of a disordered system with diffractive scatterers to a weak external perturbation. Specifically, we calculate the fidelity M(t) (also called the Loschmidt echo) characterizing a return probability after a propagation for a time $t$ followed by a backward propagation governed by a slightly perturbed Hamiltonian. For short-range scatterers we perform a diagrammatic calculation showing that the fidelity decays first exponentially according to the golden rule, and then follows a power law governed by the diffusive dynamics. For long-range disorder (when the diffractive scattering is of small-angle character) an intermediate regime emerges where the diagrammatics is not applicable. Using the path integral technique, we derive a kinetic equation and show that M(t) decays exponentially with a rate governed by the classical Lyapunov exponent.

cond-mat.dis-nn↗

arXiv2002

Interacting random Dirac fermions in superconducting cuprates

We study the effects of quasiparticle interactions on disorder-induced localization of Dirac-like nodal excitations in superconducting high-$T_c$ cuprates. As suggested by the experimental ARPES and terahertz conductivity data in $Bi_2Sr_2CaCu_2O_{8+δ}$, we focus on the interactions mediated by the order parameter fluctuations near an incipient second pairing transition $d\to d+is$. We find interaction corrections to the density of states, specific heat, and conductivity as well as phase and energy relaxation rates and assess the applicability of the recent localization scenarios for non-interacting random Dirac fermions to the cuprates.

cond-mat↗

arXiv2001

Cyclotron resonance in antidot arrays

We study the dynamical properties of an electron gas scattered by impenetrable antidots in the presence of a strong magnetic field. We find that the lineshape of the cyclotron resonance is very different from the Lorentzian and is not characterized by the Drude scattering rate. We show that the dissipative dynamical response of skipping orbits, $S_c(ω)$, is broadened on a scale of the cyclotron frequency $ω_c$ and has a sharp dip $\propto |ω-ω_c|$. For small antidots, $S_c(ω)$ is strongly modulated with a period equal to $ω_c$ and has sharp square-root singularities for a series of resonant frequencies. For large antidots, $S_c(ω)$ has a hard gap at $ω<ω_c$ between two sharp peaks, associated respectively with edge states and free cyclotron orbits.

cond-mat.dis-nn↗

arXiv2001

From quantum disorder to quantum chaos

We study the statistics of wave functions in a ballistic chaotic system. The statistical ensemble is generated by adding weak smooth random potential, which allows us to apply the ballistic $σ$-model approach. We analyze conditions of applicability of the $σ$-model, emphasizing the role played by the single-particle mean free path and the Lyapunov exponent due to the random potential. In particular, we present a resolution of the puzzle of repetitions of periodic orbits counted differently by the $σ$-model and by the trace formula.

cond-mat.mes-hall↗

arXiv2001

Nesting symmetries and diffusion in disordered d-wave superconductors

The low-energy density of states (DOS) of disordered 2D d-wave superconductors is extremely sensitive to details of both the disorder model and the electronic band structure. Using diagrammatic methods and numerical solutions of the Bogoliubov-de Gennes equations, we show that the physical origin of this sensitivity is the existence of a novel diffusive mode with momentum close to $(π,π)$ which is gapless only in systems with a global nesting symmetry. We find that in generic situations, the DOS vanishes at the Fermi level. However, proximity to the highly symmetric case may nevertheless lead to observable non-monotonic behavior of the DOS in the cuprates.

cond-mat↗

arXiv2001

Wave function correlations on the ballistic scale: Exploring quantum chaos by quantum disorder

We study the statistics of wave functions in a ballistic chaotic system. The statistical ensemble is generated by adding weak smooth disorder. The conjecture of Gaussian fluctuations of wave functions put forward by Berry and generalized by Hortikar and Srednicki is proven to hold on sufficiently short distances, while it is found to be strongly violated on larger scales. This also resolves the conflict between the above conjecture and the wave function normalization. The method is further used to study ballistic correlations of wave functions in a random magnetic field.

cond-mat.mes-hall↗

arXiv2000

Current correlations and quantum localization in 2D disordered systems with broken time-reversal invariance

We study long-range correlations of equilibrium current densities in a two-dimensional mesoscopic system with the time reversal invariance broken by a random or homogeneous magnetic field. Our result is universal, i.e. it does not depend on the type (random potential or random magnetic field) or correlation length of disorder. This contradicts recent sigma-model calculations of Taras-Semchuk and Efetov (TS&E) for the current correlation function, as well as for the renormalization of the conductivity. We show explicitly that the new term in the sigma-model derived by TS&E and claimed to lead to delocalization does not exist. The error in the derivation of TS&E is traced to an incorrect ultraviolet regularization procedure violating current conservation and gauge invariance.

cond-mat.mes-hall↗

arXiv1999

Statistics of closed paths in two-dimensional systems and negative magnetoresistance studied by computer simulation

Statistics of closed paths in two-dimensional systems, which just determines the interference quantum correction to conductivity and anomalous magnetoconductance, has been studied by computer simulation of a particle motion over the plane with randomly distributed scatters. Both ballistic and diffusion regimes have been considered. The results of simulation have been analyzed in the framework of diffusion approximation. They are used for calculation of the magnetic field dependence of magnetoconductance in the model 2D system. It is shown that the anomalous magnetoconductance can be in principle described by the well known expression, obtained in the diffusion approximation, but with the prefactor less than unity and phase breaking which differs from true value.

cond-mat.stat-mech↗