6,382 research outputs found
Asymmetric Zero-Bias Anomaly for Strongly Interacting Electrons in One Dimension
We study a system of one-dimensional electrons in the regime of strong
repulsive interactions, where the spin exchange coupling J is small compared
with the Fermi energy, and the conventional Tomonaga-Luttinger theory does not
apply. We show that the tunneling density of states has a form of an asymmetric
peak centered near the Fermi level. In the spin-incoherent regime, where the
temperature is large compared to J, the density of states falls off as a power
law of energy \epsilon measured from the Fermi level, with the prefactor at
positive energies being twice as large as that at the negative ones. In
contrast, at temperatures below J the density of states forms a split peak with
most of the weight shifted to negative \epsilon.Comment: 4 pages, 2 figure
Zeros of the Partition Function for Higher--Spin 2D Ising Models
We present calculations of the complex-temperature zeros of the partition
functions for 2D Ising models on the square lattice with spin , 3/2, and
2. These give insight into complex-temperature phase diagrams of these models
in the thermodynamic limit. Support is adduced for a conjecture that all
divergences of the magnetisation occur at endpoints of arcs of zeros protruding
into the FM phase. We conjecture that there are such arcs for , where denotes the integral part of .Comment: 8 pages, latex, 3 uuencoded figure
Universal low-temperature crossover in two-channel Kondo models
An exact expression is derived for the electron Green function in two-channel
Kondo models with one and two impurities, describing the crossover from
non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi
liquid (FL) physics at low temperatures. Symmetry-breaking perturbations
generically present in experiment ensure the standard low-energy FL
description, but the full crossover is wholly characteristic of the unstable
NFL state. Distinctive conductance lineshapes in quantum dot devices should
result. We exploit a connection between this crossover and one occurring in a
classical boundary Ising model to calculate real-space electron densities at
finite temperature. The single universal finite-temperature Green function is
then extracted by inverting the integral transformation relating these Friedel
oscillations to the t matrix. Excellent agreement is demonstrated between exact
results and full numerical renormalization group calculations.Comment: 26 pages, 14 figures: updated version including new a section and
figure comparing exact results to finite-temperature numerical
renormalization group calculation
Dynamical conductance in the two-channel Kondo regime of a double dot system
We study finite-frequency transport properties of the double-dot system
recently constructed to observe the two-channel Kondo effect [R. M. Potok et
al., Nature 446, 167 (2007)]. We derive an analytical expression for the
frequency-dependent linear conductance of this device in the Kondo regime. We
show how the features characteristic of the 2-channel Kondo quantum critical
point emerge in this quantity, which we compute using the results of conformal
field theory as well as numerical renormalization group methods. We determine
the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid
cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma
Smearing of Coulomb Blockade by Resonant Tunneling
We study the Coulomb blockade in a grain coupled to a lead via a resonant
impurity level. We show that the strong energy dependence of the transmission
coefficient through the impurity level can have a dramatic effect on the
quantization of the grain charge. In particular, if the resonance is
sufficiently narrow, the Coulomb staircase shows very sharp steps even if the
transmission through the impurity at the Fermi energy is perfect. This is in
contrast to the naive expectation that perfect transmission should completely
smear charging effects.Comment: 4 pages, 3 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
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
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