422 research outputs found
Dissipation in a superconducting artificial atom due to a single non-equilibrium quasiparticle
We study a superconducting artificial atom which is represented by a single
Josephson junction or a Josephson junction chain, capacitively coupled to a
coherently driven transmission line, and which contains exactly one residual
quasiparticle (or up to one quasiparticle per island in a chain). We study the
dissipation in the atom induced by the quasiparticle tunneling, taking into
account the quasiparticle heating by the drive. We calculate the transmission
coefficient in the transmission line for drive frequencies near resonance and
show that, when the artificial atom spectrum is nearly harmonic, the intrinsic
quality factor of the resonance increases with the drive power. This
counterintuitive behavior is due to the energy dependence of the quasiparticle
density of states
Effect of Coulomb interaction on current noise in open quantum dots
We analyze the effect of Coulomb interaction on the noise of electric current
through an open quantum dot. We demonstrate that the ensemble average value of
the noise power acquires an interaction correction even for a dot coupled to
the leads by reflectionless point contacts, when the ensemble average
conductance is known to have no interaction corrections. To leading order, the
correction to the noise originates from the formation of a nonequilibrium state
of the Coulomb field describing the interaction between electrons. We find the
dependence of the current noise power on the electron temperature, the applied
voltage bias, and the strength of the Coulomb interaction.Comment: 4.5 pages, 2 figure
Design and implementation of an automatic measurement system for the characterization of power MOSFETs
Peer Reviewe
Interaction corrections: temperature and parallel field dependencies of the Lorentz number in two-dimensional disordered metals
The electron-electron interaction corrections to the transport coefficients
are calculated for a two-dimensional disordered metal in a parallel magnetic
field via the quantum kinetic equation approach. For the thermal transport,
three regimes (diffusive, quasiballistic and truly ballistic) can be identified
as the temperature increases. For the diffusive and quasiballistic regimes, the
Lorentz number dependence on the temperature and on the magnetic field is
studied. The electron-electron interactions induce deviations from the
Wiedemann-Franz law, whose sign depend on the temperature: at low temperatures
the long-range part of the Coulomb interaction gives a positive correction,
while at higher temperature the inelastic collisions dominate the negative
correction. By applying a parallel field, the Lorentz number becomes a
non-monotonic function of field and temperature for all values of the
Fermi-liquid interaction parameter in the diffusive regime, while in the
quasiballistic case this is true only sufficiently far from the Stoner
instability.Comment: 11 pages, 5 figures. Appendix A revised, notes adde
Orbital Response of Evanescent Cooper Pairs in Paramagnetically Limited Al Films
We report a detailed study of the pairing resonance via tunneling density of
states in ultra-thin superconducting Al films in supercritical magnetic fields.
Particular emphasis is placed on effects of the perpendicular component of the
magnetic field on the resonance energy and magnitude. Though the resonance is
broadened and attenuated by as expected, its energy is shifted upward
linearly with . Extension of the original theory of the resonance to
include strong perpendicular fields shows that at sufficiently large
the overlap of the broadened resonance tail with the underlying degenerate
Fermi sea alters the spectral distribution of the resonance via the exclusion
principle. This leads to the shift of the the resonance feature to higher
energy.Comment: 8 pages, 4 figure
The AdS/CFT correspondence in two dimensions
We review recent progress in understanding the anti-de Sitter/conformal field
theory correspondence in the context of two-dimensional dilaton gravity theory.Comment: Contribution to the Proceedings of the Euroconference on "Brane New
World and Noncommutative Geometry", Turin, October 200
Density of States, Entropy, and the Superconducting Pomeranchuk Effect in Pauli-Limited Al Films
We present low temperature tunneling density of states measurements of
Pauli-limited Al films in which the Zeeman and orbital contributions to the
critical field are comparable. We show that films in the thickness range of 6-7
nm exhibit a reentrant parallel critical field transition which is associated
with a high entropy superconducting phase, similar to the high entropy solid
phase of 3He responsible for the Pomeranchuk effect. This phase is
characterized by an excess of states near the Fermi energy so long as the
parallel critical field transition remains second order. Theoretical fits to
the zero bias tunneling conductance are in good agreement with the data well
below the transition but theory deviates significantly near the transition. The
discrepancy is a consequence of the emergence of e-e interaction correlations
as one enters the normal state.Comment: 9 pages, 5 figures; to be published in Phys. Rev.
Temperature dependence of the superheating field for superconductors in the high-k London limit
We study the metastability of the superheated Meissner state in type II
superconductors with k >> 1 beyond Ginzburg-Landau theory, which is applicable
only in the vicinity of the critical temperature. Within Eilenberger's
semiclassical approximation, we use the local electrodynamic response of the
superconductor to derive a generalized thermodynamic potential valid at any
temperature. The stability analysis of this functional yields the temperature
dependence of the superheating field. Finally, we comment on the implications
of our results for superconducting cavities in particle accelerators.Comment: 7.5 pages, 2 figure
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