B. N. Narozhny

Interaction corrections at intermediate temperatures: Longitudinal conductivity and kinetic equation

temperatures T τ > 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 corrections - electron scattering by Friedel oscillations. However, in this regime the correction is linear in temperature; the value and even the sign of the slope depends on the strength of electron-electron interaction. (This sign change may be relevant for the “metal-insulator” transition observed recently.) 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 ballistic regimes. Finally, we derive the quantum kinetic equation, which describes electron transport for arbitrary value of T τ.

Interaction corrections at intermediate temperatures: Magnetoresistance in a parallel field

We consider the correction to conductivity of a two-dimensional 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 nontrivial 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.

Magnetoresistance in two-component systems

Two-component systems with equal concentrations of electrons and holes exhibit nonsaturating, linear magnetoresistance in classically strong magnetic fields. The effect is predicted to occur in finite-size samples at charge neutrality due to recombination. The phenomenon originates in the excess quasiparticle density developing near the edges of the sample due to the compensated Hall effect. The size of the boundary region is of the order of the electron-hole recombination length that is inversely proportional to the magnetic field. In narrow samples and at strong enough magnetic fields, the boundary region dominates over the bulk leading to linear magnetoresistance. Our results are relevant for two-and three-dimensional semimetals and narrow band semiconductors including most of the topological insulators.

Giant Magnetodrag in Graphene at Charge Neutrality

We report experimental data and theoretical analysis of Coulomb drag between two closely positioned graphene monolayers in a weak magnetic field. Close enough to the neutrality point, the coexistence of electrons and holes in each layer leads to a dramatic increase of the drag resistivity. Away from charge neutrality, we observe nonzero Hall drag. The observed phenomena are explained by decoupling of electric and quasiparticle currents which are orthogonal at charge neutrality. The sign of magnetodrag depends on the energy relaxation rate and geometry of the sample.

Collision-dominated nonlinear hydrodynamics in graphene

We present an effective hydrodynamic theory of electronic transport in graphene in the interaction-dominated regime. We derive the emergent hydrodynamic description from the microscopic Boltzmann kinetic equation taking into account dissipation due to Coulomb interaction and find the viscosity of Dirac fermions in graphene for arbitrary densities. The viscous terms have a dramatic effect on transport coefficients in clean samples at high temperatures. Within linear response, we show that viscosity manifests itself in the nonlocal conductivity as well as dispersion of hydrodynamic plasmons. Beyond linear response, we apply the derived nonlinear hydrodynamics to the problem of hot spot relaxation in graphene.

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.

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 (

Crossover from Poisson to Wigner-Dyson level statistics in spin chains with integrability breaking

\mu_{1(2)}, T\ll v/d

Coulomb drag in graphene near the Dirac point.

) the drag is described by a universal function of the chemical potentials of the layers

Hydrodynamic approach to electronic transport in graphene

\mu_{1(2)}