6,202 research outputs found
Hidden Caldeira-Leggett dissipation in a Bose-Fermi Kondo model
We show that the Bose-Fermi Kondo model (BFKM), which may find applicability
both to certain dissipative mesoscopic qubit devices and to heavy fermion
systems described by the Kondo lattice model, can be mapped exactly onto the
Caldeira-Leggett model. This mapping requires an ohmic bosonic bath and an
Ising-type coupling between the latter and the impurity spin. This allows us to
conclude unambiguously that there is an emergent Kosterlitz-Thouless quantum
phase transition in the BFKM with an ohmic bosonic bath. By applying a bosonic
numerical renormalization group approach, we thoroughly probe physical
quantities close to the quantum phase transition.Comment: Final version appearing in Physical Review Letter
Total electronic Raman scattering in the charge-density-wave phase of the spinless Falicov-Kimball model
The total electronic Raman scattering spectrum, including the nonresonant,
mixed and resonant components, is determined for the charge-density-wave (CDW)
phase of the spinless Falicov-Kimball model at half filling within dynamical
mean-field theory. Its frequency dependence is investigated for different
values of the energy of the incident photons. The spectra reflect the different
structures in the density of states and how they are modified by screening and
resonance effects. The calculations are performed for the , and symmetries (which are typically examined in experiment).
Our results for the resonance effects of the Raman spectra, found by tuning the
energy of the incident photons, give information about the many-body charge
dynamics of the CDW-ordered phase.Comment: 8 pages, contribution to the proceedings of the 3rd Conference
"Statistical Physics: Modern Trends and Applications", June 23-25, 2009 Lviv,
Ukrain
Interaction-induced backscattering in short quantum wires
We study interaction-induced backscattering in clean quantum wires with
adiabatic contacts exposed to a voltage bias. Particle backscattering relaxes
such systems to a fully equilibrated steady state only on length scales
exponentially large in the ratio of bandwidth of excitations and temperature.
Here we focus on shorter wires in which full equilibration is not accomplished.
Signatures of relaxation then are due to backscattering of hole excitations
close to the band bottom which perform a diffusive motion in momentum space
while scattering from excitations at the Fermi level. This is reminiscent to
the first passage problem of a Brownian particle and, regardless of the
interaction strength, can be described by an inhomogeneous Fokker-Planck
equation. From general solutions of the latter we calculate the hole
backscattering rate for different wire lengths and discuss the resulting length
dependence of interaction-induced correction to the conductance of a clean
single channel quantum wire.Comment: 10 pages, 4 figure
Quantum Charge Fluctuations in a Superconducting Grain
We consider charge quantization in a small superconducting grain that is
contacted by a normal-metal electrode and is controlled by a capacitively
coupled gate. At zero temperature and zero conductance between the grain
and the electrode, the charge as a function of the gate voltage
changes in steps. The step height is if , where and
are, respectively, the superconducting gap and the charging energy of the
grain. Quantum charge fluctuations at finite conductance remove the
discontinuity in the dependence of on and lead to a finite step width
. The resulting shape of the Coulomb blockade staircase is
of a novel type. The grain charge is a continuous function of while the
differential capacitance, , has discontinuities at certain values of
the gate voltage. We determine analytically the shape of the Coulomb blockade
staircase also at non-zero temperatures.Comment: 12 pages, 3 figure
Transport through a quantum dot with SU(4) Kondo entanglement
We investigate a mesoscopic setup composed of a small electron droplet (dot)
coupled to a larger quantum dot (grain) also subject to Coulomb blockade as
well as two macroscopic leads used as source and drain. An exotic Kondo ground
state other than the standard SU(2) Fermi liquid unambiguously emerges: an
SU(4) Kondo correlated liquid. The transport properties through the small dot
are analyzed for this regime, through boundary conformal field theory, and
allow a clear distinction with other regimes such as a two-channel spin state
or a two-channel orbital state.Comment: 13 pages, 3 figure
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