arXiv subjects

B. N. Narozhny

Publications and source records attributed to B. N. Narozhny.

At least 37 records · Page 2Linked to original sources

arXiv2012

Coulomb drag in graphene near the Dirac point

We study Coulomb drag in double-layer graphene near the Dirac point. A particular emphasis is put on the case of clean graphene, with transport properties dominated by the electron-electron interaction. Using the quantum kinetic equation framework, we show that the drag becomes $T$-independent in the clean limit, $Tτ\to \infty$, where $T$ is temperature and $1/τ$ impurity scattering rate. For stronger disorder (or lower temperature), $Tτ\ll 1/α^2$, where $α$ is the interaction strength, the kinetic equation agrees with the leading-order ($α^2$) perturbative result. At still lower temperatures, $Tτ\ll 1$ (diffusive regime) this contribution gets suppressed, while the next-order ($α^3$) contribution becomes important; it yields a peak centered at the Dirac point with a magnitude that grows with lowering $Tτ$.

cond-mat.mes-hall↗

arXiv2012

Coulomb drag in graphene: perturbation theory

We study the effect of Coulomb drag between two closely positioned graphene monolayers. In the limit of weak electron-electron interaction and small inter-layer spacing ($μ_{1(2)}, T\ll v/d$) the drag is described by a universal function of the chemical potentials of the layers $μ_{1(2)}$ measured in the units of temperature $T$. When both layers are tuned close to the Dirac point, then the drag coefficient is proportional to the product of the chemical potentials $ρ_D\proptoμ_1μ_2$. In the opposite limit of low temperature the drag is inversely proportional to both chemical potentials $ρ_D\propto T^2/(μ_1μ_2)$. In the mixed case where the chemical potentials of the two layers belong to the opposite limits $μ_1\ll T\llμ_2$ we find $ρ_D\propto μ_1/μ_2$. For stronger interaction and larger values of $d$ the drag coefficient acquires logarithmic corrections and can no longer be described by a power law. Further logarithmic corrections are due to the energy dependence of the impurity scattering time in graphene (for $μ_{1(2)}\gg T$ these are small and may be neglected). In the case of strongly doped (or gated) graphene $μ_{1(2)}\gg v/d\gg T$ the drag coefficient acquires additional dependence on the inter-layer spacing and we recover the usual Fermi-liquid result if the screening length is smaller than $d$.

cond-mat.mes-hall↗

arXiv2010

Electron-electron interactions in the conductivity of graphene

The effect of electron-electron interaction on the low-temperature conductivity of graphene is investigated experimentally. Unlike in other two-dimensional systems, the electron-electron interaction correction in graphene is sensitive to the details of disorder. A new temperature regime of the interaction correction is observed where quantum interference is suppressed by intra-valley scattering. We determine the value of the interaction parameter, F_0 ~ -0.1, and show that its small value is due to the chiral nature of interacting electrons.

cond-mat.mes-hall↗

arXiv2007

Coulomb drag as a measure of trigonal warping in doped graphene

I suggest to use the effect of Coulomb drag between two closely positioned graphite monolayers (graphene sheets) for experimental measurement of the strength of weak non-linearities of the spectrum in graphene. I consider trigonal warping as a representative mechanism responsible for the drag effect. Since graphene is relatively defect-free, I evaluate the drag conductivity in the ballistic regime and find that it is proportional to the fourth power of the warping strength.

cond-mat.mes-hall↗

arXiv2007

Giant Fluctuations of Coulomb Drag in a Bilayer System

We have observed reproducible fluctuations of the Coulomb drag, both as a function of magnetic field and electron concentration, which are a manifestation of quantum interference of electrons in the layers. At low temperatures the fluctuations exceed the average drag, giving rise to random changes of the sign of the drag. The fluctuations are found to be much larger than previously expected, and we propose a model which explains their enhancement by considering fluctuations of local electron properties.

cond-mat.mes-hall↗

arXiv2006

Quantum Correction to Conductivity Close to Ferromagnetic Quantum Critical Point in Two Dimensions

We study the temperature dependence of the conductivity due to quantum interference processes for a two-dimensional disordered itinerant electron system close to a ferromagnetic quantum critical point. Near the quantum critical point, the cross-over between diffusive and ballistic regimes of quantum interference effects occurs at a temperature $ T^{\ast}=1/τγ(E_{F}τ)^{2}$, where $γ$ is the parameter associated with the Landau damping of the spin fluctuations, $τ$ is the impurity scattering time, and $E_{F}$ is the Fermi energy. For a generic choice of parameters, $T^{\ast}$ is smaller than the nominal crossover scale $1/τ$. In the ballistic quantum critical regime, the conductivity behaves as $T^{1/3}$.

cond-mat.str-el↗

arXiv2004

Fractional charge excitations in fermionic ladders

The system of interacting spinless fermions hopping on a two-leg ladder in the presence of an external magnetic field is shown to possess a long range order: the bond density wave or the staggered flux phase. In both cases the elementary excitations are $Z_2$ kinks and carry one half the charge of an electron.

cond-mat.str-el↗

arXiv2003

Crossover from Poisson to Wigner-Dyson Level Statistics in Spin Chains with Integrability Breaking

We study numerically the evolution of energy-level statistics as an integrability-breaking term is added to the XXZ Hamiltonian. For finite-length chains, physical properties exhibit a cross-over from behavior resulting from the Poisson level statistics characteristic of integrable models to behavior corresponding to the Wigner-Dyson statistics characteristic of the random-matrix theory used to describe chaotic systems. Different measures of the level statistics are observed to follow different crossover patterns. The range of numerically accessible system sizes is too small to establish with certainty the scaling with system size, but the evidence suggests that in a thermodynamically large system an infinitesimal integrability breaking would lead to Wigner-Dyson behavior.

cond-mat↗

arXiv2003

Two dimensional electron gas near full polarization

We establish the consistency of the Fermi liquid description and find a relation between Fermi liquid constants for the two dimensional electron system near the point of full polarization due to a parallel magnetic field $H$. Our results enable us to predict connections between different thermodynamic properties of the system. In particular, we find that near the point of full polarization $H_c$, the thermodynamic compressibility of the system experiences a jump with the subleading $(H_c-H)^{1/2}$ dependence on the magnetic field. Also, the magnetization has a cusp with the dependence of the type $(H-H_c) + (H_c-H)^{3/2}$ at $H<H_c$.

cond-mat.mes-hall↗

arXiv2002

In-plane Magnetoconductivity of Si-MOSFET's: A Quantitative Comparison between Theory and Experiment

For densities above $n=1.6 \times 10^{11}$ cm$^{-2}$ in the strongly interacting system of electrons in two-dimensional silicon inversion layers, excellent agreement between experiment and the theory of Zala, Narozhny and Aleiner is obtained for the response of the conductivity to a magnetic field applied parallel to the plane of the electrons. However, the Fermi liquid parameter $F_0^σ(n)$ and the valley splitting $Δ_V(n)$ obtained from fits to the magnetoconductivity, although providing qualitatively correct behavior (including sign), do not yield quantitative agreement with the temperature dependence of the conductivity in zero magnetic field. Our results suggest the existence of additional scattering processes not included in the theory in its present form.

cond-mat.str-el↗

arXiv2002

Interaction corrections at intermediate temperatures: dephasing time

We calculate the temperature dependence of the weak localization correction in a two dimensional system at arbitrary relation between temperature, $T$ and the elastic mean free time. We describe the crossover in the dephasing time ${τ_ϕ(T)}$ between the high temperature, $1/τ_ϕ\simeq T^2 \ln T$, and the low temperature $1/τ_ϕ\simeq T$ behaviors. The prefactors in these dependences are not universal, but are determined by the Fermi liquid constant characterising the spin exchange interaction.

cond-mat.dis-nn↗

arXiv2001

Interaction corrections at intermediate temperatures: magneto-resistance in parallel field

We consider the correction to conductivity of a 2D electron gas due to electron-electron interaction in the parallel magnetic field at arbitrary relation between temperature and the elastic mean free time. The correction exhibits non-trivial dependence on both temperature and the field. This dependence is determined by the Fermi liquid constant, which accounts for the spin-exchange interaction. In particular, the sign of the slope of the temperature dependence is not universal and can change with the increase of the field.

cond-mat.dis-nn↗

arXiv2001

Interaction corrections at intermediate temperatures: I. Longitudinal conductivity and kinetic equation

It is well known that electron-electron interaction in disordered systems leads to logarithmically divergent Altshuler-Aronov corrections to conductivity at low temperatures ($Tτ\ll 1$; $τ$ is the elastic mean-free time). This paper is devoted to the fate of such corrections at intermediate temperatures $Tτ\ge 1$. We show that in this (ballistic) regime the temperature dependence of conductivity is still governed by the same physical processes as the Altshuler-Aronov correction - scattering by Friedel oscillations. However, in this regime the correction is linear in temperature; the value and even the {\em sign} of the slope depends on the strength of electron-electron interaction. We show that the slope is directly related to the renormalization of the spin susceptibility and grows as the system approaches the ferromagnetic Stoner instability. Also, we obtain the temperature dependence of the conductivity in the cross-over region between the diffusive and the ballistic regimes. Finally, we derive the quantum kinetic equation, which describes electron transport for arbitrary value of $Tτ$.

cond-mat↗

arXiv2001

Interaction corrections to the Hall coefficient at intermediate temperatures

We investigate the effect of electron-electron interaction on the temperature dependence of the Hall coefficient of 2D electron gas at arbitrary relation between the temperature $T$ and the elastic mean-free time $τ$. At small temperature $Tτ\ll \hbar$ we reproduce the known relation between the logarithmic temperature dependences of the Hall coefficient and of the longitudinal conductivity. At higher temperatures, this relation is violated quite rapidly; correction to the Hall coefficient becomes $\propto 1/T$ whereas the longitudinal conductivity becomes linear in temperature.

cond-mat.dis-nn↗

arXiv2000

Mesoscopic fluctuations of the Coulomb drag at $ν$=1/2

We consider mesoscopic fluctuations of Coulomb drag transresistivity between two layers at a Landau level filling factor $ν=1/2$ each. We find that at low temperature sample to sample fluctuations exceed both the ensemble average and the corresponding fluctuations at B=0. At the experimentally relevant temperatures, the variance of the transresistivity is proportional to $T^{-1/2}$. We find the dependence of this variance on density and magnetic field to reflect the attachment of two flux quanta to each electron.

cond-mat.mes-hall↗

arXiv2000

Magnetic fluctuations in 2D metals close to the Stoner instability

We consider the effect of potential disorder on magnetic properties of a two-dimensional metallic system (with conductance $g\gg 1$) when interaction in the triplet channel is so strong that the system is close to the threshold of the Stoner instability. We show, that under these conditions there is an exponentially small probability for the system to form local spin droplets which are local regions with non zero spin density. Using a non-local version of the optimal fluctuation method we find analytically the probability distribution and the typical spin of a local spin droplet (LSD). In particular, we show that both the probability to form a LSD and its typical spin are independent of the size of the droplet (within the exponential accuracy). The LSDs manifest themselves in temperature dependence of observable quantities. We show, that below certain cross-over temperature the paramagnetic susceptibility acquires the Curie-like temperature dependence, while the dephasing time (extracted from magneto-resistance measurements) saturates.

cond-mat.dis-nn↗

arXiv1999

Effect of Time Reversal Symmetry Breaking on the Density of States in Small Superconducting Grains

We show that in ultra-small superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states. Instead, though exponentially suppressed at low energies, the tunneling density of states exhibits the ``soft gap'' behavior, vanishing linearly with excitation energy, as the energy approaches zero.

cond-mat↗

arXiv1999

Mesoscopic fluctuations of the Coulomb drag

We consider mesoscopic fluctuations of the Coulomb drag coefficient $ρ_D$ in the system of two separated two-dimensional electron gases. It is shown that at low temperatures sample to sample fluctuations of $ρ_D$ exceed its ensemble average. It means that in such a regime the sign of $ρ_D$ is random and the temperature dependence almost saturates $ρ_D \sim 1/\sqrt{T}$.

cond-mat↗