58 research outputs found
Hydrodynamic Approach to Electronic Transport in Graphene: Energy Relaxation
In nearly compensated graphene, disorder-assisted electron-phonon scattering or “supercollisions” are responsible for both quasiparticle recombination and energy relaxation. Within the hydrodynamic approach, these processes contribute weak decay terms to the continuity equations at local equilibrium, i.e., at the level of “ideal” hydrodynamics. Here we report the derivation of the decay term due to weak violation of energy conservation. Such terms have to be considered on equal footing with the well-known recombination terms due to nonconservation of the number of particles in each band. At high enough temperatures in the “hydrodynamic regime” supercollisions dominate both types of the decay terms (as compared to the leading-order electron-phonon interaction). We also discuss the contribution of supercollisions to the heat transfer equation (generalizing the continuity equation for the energy density in viscous hydrodynamics)
Counterflows in viscous electron-hole fluid
In ultra-pure conductors, collective motion of charge carriers at relatively
high temperatures may become hydrodynamic such that electronic transport may be
described similarly to a viscous flow. In confined geometries (e.g., in
ultra-high quality nanostructures), the resulting flow is Poiseuille-like. When
subjected to a strong external magnetic field, the electric current in
semimetals is pushed out of the bulk of the sample towards the edges. Moreover,
we show that the interplay between viscosity and fast recombination leads to
the appearance of counterflows. The edge currents possess a non-trivial spatial
profile and consist of two stripe-like regions: the outer stripe carrying most
of the current in the direction of the external electric field and the inner
stripe with the counterflow.Comment: 10 pages, 5 figure
Nonmonotonic magnetoresistance of a two-dimensional viscous electron-hole fluid in a confined geometry
Ultra-pure conductors may exhibit hydrodynamic transport where the collective
motion of charge carriers resembles the flow of a viscous fluid. In a confined
geometry (e.g., in ultra-high quality nanostructures) the electronic fluid
assumes a Poiseuille-like flow. Applying an external magnetic field tends to
diminish viscous effects leading to large negative magnetoresistance. In
two-component systems near charge neutrality the hydrodynamic flow of charge
carriers is strongly affected by the mutual friction between the two
constituents. At low fields, the magnetoresistance is negative, however at high
fields the interplay between electron-hole scattering, recombination, and
viscosity results in a dramatic change of the flow profile: the
magnetoresistance changes its sign and eventually becomes linear in very high
fields. This novel non-monotonic magnetoresistance can be used as a fingerprint
to detect viscous flow in two-component conducting systems.Comment: 10 pages, 8 figure
Magnetoresistance of compensated semimetals in confined geometries
Two-component conductors -- e.g., semi-metals and narrow band semiconductors
-- often exhibit unusually strong magnetoresistance in a wide temperature
range. Suppression of the Hall voltage near charge neutrality in such systems
gives rise to a strong quasiparticle drift in the direction perpendicular to
the electric current and magnetic field. This drift is responsible for a strong
geometrical increase of resistance even in weak magnetic fields. Combining the
Boltzmann kinetic equation with sample electrostatics, we develop a microscopic
theory of magnetotransport in two and three spatial dimensions. The compensated
Hall effect in confined geometry is always accompanied by electron-hole
recombination near the sample edges and at large-scale inhomogeneities. As the
result, classical edge currents may dominate the resistance in the vicinity of
charge compensation. The effect leads to linear magnetoresistance in two
dimensions in a broad range of parameters. In three dimensions, the
magnetoresistance is normally quadratic in the field, with the linear regime
restricted to rectangular samples with magnetic field directed perpendicular to
the sample surface. Finally, we discuss the effects of heat flow and
temperature inhomogeneities on the magnetoresistance.Comment: 22 pages, 7 figures, published versio
Magnetoresistance in two-component systems
Two-component systems with equal concentrations of electrons and holes
exhibit non-saturating, linear magnetoresistance in classically strong magnetic
fields. The effect is predicted to occur in finite-size samples at charge
neutrality in both disorder- and interaction-dominated regimes. 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 semimetals and narrow-band
semiconductors including most of the topological insulators.Comment: 11 pages, 3 figure
Linear magnetoresistance in compensated graphene bilayer
We report a nonsaturating linear magnetoresistance in charge-compensated
bilayer graphene in a temperature range from 1.5 to 150 K. The observed linear
magnetoresistance disappears away from charge neutrality ruling out the
traditional explanation of the effect in terms of the classical random resistor
network model. We show that experimental results qualitatively agree with a
phenomenological two-fluid model taking into account electron-hole
recombination and finite-size sample geometry
Ballistic transport in disordered graphene
An analytic theory of electron transport in disordered graphene in a
ballistic geometry is developed. We consider a sample of a large width W and
analyze the evolution of the conductance, the shot noise, and the full
statistics of the charge transfer with increasing length L, both at the Dirac
point and at a finite gate voltage. The transfer matrix approach combined with
the disorder perturbation theory and the renormalization group is used. We also
discuss the crossover to the diffusive regime and construct a ``phase diagram''
of various transport regimes in graphene.Comment: 23 pages, 10 figure
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.Comment: 4 page
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