863 research outputs found
Role of electronic correlations in the Fermi surface formation of NaCoO
Band structure of metallic sodium cobaltate NaCoO (=0.33, 0.48,
0.61 0.72) has been investigated by local density approximation+Hubbard
(LDA+) method and within Gutzwiller approximation for the Co-
manifold. Correlation effects being taken into account results in suppression
of the hole pockets at the Fermi surface in agreement with recent
angle-resolved photo-emission spectroscopy (ARPES) experiments. In the
Gutzwiller approximation the bilayer splitting is significantly reduced due to
the correlation effects. The formation of high spin (HS) state in Co -shell
was shown to be very improbable.Comment: 6 pages, 2 figure
Coulomb Blockade with Dispersive Interfaces
What quantity controls the Coulomb blockade oscillations if the dot--lead
conductance is essentially frequency--dependent ? We argue that it is the ac
dissipative conductance at the frequency given by the effective charging
energy. The latter may be very different from the bare charging energy due to
the interface--induced capacitance (or inductance). These observations are
supported by a number of examples, considered from the weak and strong coupling
(perturbation theory vs. instanton calculus) perspectives.Comment: 4 page
Electron Transport in Granular Metals
We consider thermodynamic and transport properties of a long granular array
with strongly connected grains (inter-grain conductance g>>1.) We find that the
system exhibits activated behavior of conductance and thermodynamic density of
states ~exp(-T*/T) where the gap, T*, is parametrically larger than the energy
at which conventional perturbation theory breaks down. The scale T* represents
energy needed to create a long single-electron charge soliton propagating
through the array.Comment: 4 pages, 1 figur
Charge relaxation resistance in the Coulomb blockade problem
We study the dissipation in a system consisting of a small metallic island
coupled to a gate electrode and to a massive reservoir via single tunneling
junction. The dissipation of energy is caused by a slowly oscillating gate
voltage. We compute it in the regimes of weak and strong Coulomb blockade. We
focus on the regime of not very low temperatures when electron coherence can be
neglected but quantum fluctuations of charge are strong due to Coulomb
interaction. The answers assume a particularly transparent form while expressed
in terms of specially chosen physical observables. We discovered that the
dissipation rate is given by a universal expression in both limiting cases.Comment: 21 pages, 12 figure
Fractional-flux vortices and spin superfluidity in triplet superconductors
We discuss a novel type of fractional flux vortices along with integer flux
vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We
show that under certain conditions a spin-triplet superconductor should exhibit
a novel state of {\it spin superfluidity} without superconductivity.Comment: Physical Review Lettes, in print. v2: references added, v3:
discussion of several points extended according to referee request. Latest
updates and links to related papers are available at my homepage
http://people.ccmr.cornell.edu/~egor
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
Two-instanton approximation to the Coulomb blockade problem
We develop the two-instanton approximation to the current-voltage
characteristic of a single electron transistor within the
Ambegaokar-Eckern-Sch\"on model. We determine the temperature and gate voltage
dependence of the Coulomb blockade oscillations of the conductance and the
effective charge. We find that a small (in comparison with the charging energy)
bias voltage leads to significant suppression of the Coulomb blockade
oscillations and to appearance of the bias-dependent phase shift
Simplicity out of complexity: band structure for WO superconductor
The band structure, density of states, and the Fermi surface of a recently
discovered superconductor, oxygen-deficient tungsten oxide WO that is
equivalent to WO, studied within the density functional theory
(DFT) in the generalized gradient approximation (GGA). Here we show that
despite the extremely complicated structure containing 78 atoms in the unit
cell, the low-energy band structure is quite feasible. Fermi level is crossed
by no more than 10 bands per one spin projection (and even 9 bands per
pseudospin projection when the spin-orbit coupling is considered) originating
from the -orbitals of tungsten atoms forming zigzag chains.Comment: 6 pages, 5 figure
Itinerant in-plane magnetic fluctuations and many-body correlations in NaCoO
Based on the {\it ab-initio} band structure for NaCoO we derive the
single-electron energies and the effective tight-binding description for the
bands using projection procedure. Due to the presence of the
next-nearest-neighbor hoppings a local minimum in the electronic dispersion
close to the point of the first Brillouin zone forms. Correspondingly,
in addition to a large Fermi surface an electron pocket close to the
point emerges at high doping concentrations. The latter yields the new
scattering channel resulting in a peak structure of the itinerant magnetic
susceptibility at small momenta. This indicates dominant itinerant in-plane
ferromagnetic fluctuations above certain critical concentration , in
agreement with neutron scattering data. Below the magnetic susceptibility
shows a tendency towards the antiferromagnetic fluctuations. We further analyze
the many-body effects on the electronic and magnetic excitations using various
approximations applicable for different ratio.Comment: 10 page
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