669 research outputs found
Photocurrent in a visible-light graphene photodiode
We calculate the photocurrent in a clean graphene sample normally irradiated
by a monochromatic electromagnetic field and subject to a step-like
electrostatic potential. We consider the photon energies that
significantly exceed the height of the potential barrier, as is the case in the
recent experiments with graphene-based photodetectors. The photocurrent comes
from the resonant absorption of photons by electrons and decreases with
increasing ratio . It is weakly affected by the background
gate voltage and depends on the light polarization as ,
being the angle between the potential and the polarization plane.Comment: 5 pages, 3 figure
Induced Ferromagnetism due to Superconductivity in Superconductor-Ferromagnet structures
We consider a superconductor-ferromagnet (S/F) structure and assume that
above the superconducting transition temperature the magnetic moment
exists only in F. {In a simple model of the ferromagnet (the exchange field is
of the ferromagnetic type for all energies)}we show by an explicit calculation
that below the magnetic moment may penetrate the superconductor. {In
this model} its direction in S is opposite {to the magnetization of free
electrons} in the ferromagnet. The magnetization spreads over a large distance
which is of the order of the superconducting coherence length and can
much exceed the ferromagnet film thickness. At the same time the magnetic
moment in the ferromagnet is reduced. This inverse proximity effect may explain
the reduction in magnetization observed in recent experiments and may lead to a
strong interaction between the ferromagnetic layers in F/S/F structures.Comment: 5 pages, 2 figures. revised and longer version. to be published in
Phys. Rev.
Nonperturbative interaction effects in the thermodynamics of disordered wires
We study nonperturbative interaction corrections to the thermodynamic
quantities of multichannel disordered wires in the presence of the Coulomb
interactions. Within the replica nonlinear -model (NLM)
formalism, they arise from nonperturbative soliton saddle points of the
NLM action. The problem is reduced to evaluating the partition function
of a replicated classical one dimensional Coulomb gas. The state of the latter
depends on two parameters: the number of transverse channels in the wire,
N_{ch}, and the dimensionless conductance, G(L_T), of a wire segment of length
equal to the thermal diffusion length, L_T. At relatively high temperatures,
, the gas is dimerized, i.e. consists of bound
neutral pairs. At lower temperatures, ,
the pairs overlap and form a Coulomb plasma. The crossover between the two
regimes occurs at a parametrically large conductance ,
and may be studied independently from the perturbative effects. Specializing to
the high temperature regime, we obtain the leading nonperturbative correction
to the wire heat capacity. Its ratio to the heat capacity for noninteracting
electrons, C_0, is .Comment: 18 page
Role of the impurity-potential range in disordered d-wave superconductors
We analyze how the range of disorder affects the localization properties of
quasiparticles in a two-dimensional d-wave superconductor within the standard
non-linear sigma-model approach to disordered systems. We show that for purely
long-range disorder, which only induces intra-node scattering processes, the
approach is free from the ambiguities which often beset the disordered
Dirac-fermion theories, and gives rise to a Wess-Zumino-Novikov-Witten action
leading to vanishing density of states and finite conductivities. We also study
the crossover induced by internode scattering due to a short range component of
the disorder, thus providing a coherent non-linear sigma-model description in
agreement with all the various findings of different approaches.Comment: 38 pages, 1 figur
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