375 research outputs found
Reply to ``Comment on `Magnetic field effects on neutron diffraction in the antiferromagnetic phase of '''
Fak, van Dijk and Wills (FDW) question our interpretation of elastic
neutron-scattering experiments in the antiferromagnetic phase of UPt_3. They
state that our analysis is incorrect because we average over magnetic
structures that are disallowed by symmetry. We disagree with FDW and reply to
their criticism. FDW also point out that we have mistaken the magnetic field
direction in the experiment reported by N. H. van Dijk et al. [Phys. Rev. B 58,
3186 (1998)]. We correct this error and note that our previous conclusion is
also valid for the correct field orientation.Comment: 3 page
Nonlocality in mesoscopic Josephson junctions with strip geometry
We study the current in a clean superconductor-normal-metal-superconductor
junction of length d and width w in the presence of an applied magnetic field
H. We show that both the geometrical pattern of the current density and the
critical current as a function of the total flux in the junction, depend on the
ratio of the Josephson vortex distance a_0 and the range r of the nonlocal
electrodynamics. In particular, the critical current has the periodicity of the
superconducting flux quantum only for r<a_0 and acquires, due to boundary
effects, the double (pseudo-) periodicity for strong nonlocality, r>a_0.
Comparing our results to recent experiments of Heida et al. [Phys. Rev. B 57,
R5618 (1998)] we find good agreement.Comment: 4 pages, 5 figures, to be published in the RC section of Phys. Rev.
Stability of junction configurations in ferromagnet-superconductor heterostructures
We investigate the stability of possible order parameter configurations in
clean layered heterostructures of the type, where is a
superconductor and a ferromagnet. We find that for most reasonable values
of the geometric parameters (layer thicknesses and number) and of the material
parameters (such as magnetic polarization, wavevector mismatch, and oxide
barrier strength) several solutions of the {\it self consistent} microscopic
equations can coexist, which differ in the arrangement of the sequence of ``0''
and ``'' junction types (that is, with either same or opposite sign of the
pair potential in adjacent layers). The number of such coexisting self
consistent solutions increases with the number of layers. Studying the relative
stability of these configurations requires an accurate computation of the small
difference in the condensation free energies of these inhomogeneous systems. We
perform these calculations, starting with numerical self consistent solutions
of the Bogoliubov-de Gennes equations. We present extensive results for the
condensation free energies of the different possible configurations, obtained
by using efficient and accurate numerical methods, and discuss their relative
stabilities. Results for the experimentally measurable density of states are
also given for different configurations and clear differences in the spectra
are revealed. Comprehensive and systematic results as a function of the
relevant parameters for systems consisting of three and seven layers (one or
three junctions) are given, and the generalization to larger number of layers
is discussed.Comment: 17 pages, including 14 Figures. Higher resolution figures available
from the author
Magnetic field influence on the proximity effect in semiconductor - superconductor hybrid structures and their thermal conductance
We show that a magnetic field can influnce the proximity effect in NS
junctions via diamagnetic screening current flowing in the superconductor.
Using ballistic quasi-one-dimensional (Q1D) electron channels as an example, we
show that the supercurrent flow shifts the proximity-induced minigap in the
excitation spectrum of a Q1D system from the Fermi level to higher
quasiparticle energies. Thermal conductance of a Q1D channel (normalized by
that of a normal Q1D ballistic system) is predicted to manifest such a spectral
feature as a nonmonotonic behavior at temperatures corresponding to the energy
of excitation into the gapful part of the spectrum.Comment: 5 pages, 3 figures, revised version with a new titl
Tunnelling defect nanoclusters in hcp 4He crystals: alternative to supersolidity
A simple model based on the concept of resonant tunnelling clusters of
lattice defects is used to explain the low temperature anomalies of hcp 4He
crystals (mass decoupling from a torsional oscillator, shear modulus anomaly,
dissipation peaks, heat capacity peak). Mass decoupling is a result of an
internal Josephson effect: mass supercurrent inside phase coherent tunnelling
clusters. Quantitative results are in reasonable agreement with experiments.Comment: 13 pages, 5 figure
Conductivity of the classical two-dimensional electron gas
We discuss the applicability of the Boltzmann equation to the classical
two-dimensional electron gas. We show that in the presence of both the
electron-impurity and electron-electron scattering the Boltzmann equation can
be inapplicable and the correct result for conductivity can be different from
the one obtained from the kinetic equation by a logarithmically large factor.Comment: Revtex, 3 page
Phase coherence phenomena in superconducting films
Superconducting films subject to an in-plane magnetic field exhibit a gapless
superconducting phase. We explore the quasi-particle spectral properties of the
gapless phase and comment on the transport properties. Of particular interest
is the sensitivity of the quantum interference phenomena in this phase to the
nature of the impurity scattering. We find that films subject to columnar
defects exhibit a `Berry-Robnik' symmetry which changes the fundamental
properties of the system. Furthermore, we explore the integrity of the gapped
phase. As in the magnetic impurity system, we show that optimal fluctuations of
the random impurity potential conspire with the in-plane magnetic field to
induce a band of localized sub-gap states. Finally, we investigate the
interplay of the proximity effect and gapless superconductivity in thin normal
metal-superconductor bi-layers.Comment: 13 pages, 8 figures include
Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers
We study non-equilibrium Josephson effect and phase-dependent conductance in
three-terminal diffusive interferometers with short arms. We consider strong
proximity effect and investigate an interplay of dissipative and Josephson
currents co-existing within the same proximity region. In junctions with
transparent interfaces, the suppression of the Josephson current appears at
rather large voltage, , and the current vanishes at
. Josephson current inversion becomes possible in junctions with
resistive interfaces, where the inversion occurs within a finite interval of
the applied voltage. Due to the presence of considerably large and
phase-dependent injection current, the critical current measured in a current
biased junction does not coincide with the maximum Josephson current, and
remains finite when the true Josephson current is suppressed. The voltage
dependence of the conductance shows two pronounced peaks, at the bulk gap
energy, and at the proximity gap energy; the phase oscillation of the
conductance exhibits qualitatively different form at small voltage ,
and at large voltage .Comment: 11 pages, 9 figures, revised version, to be published in Phys. Rev.
Magnetoconductance Oscillations in Ballistic Semiconductor-Superconductor Junctions
The mechanism of the magnetoconductance oscillations in junctions of a
ballistic semiconductor and a superconductor is discussed. The oscillations
appear when both the normal and the Andreev reflection occur at the interface.
The interplay between the classical cyclotron motion of a quasiparticle and the
phase shift caused by the magnetic field is the origin of the conductance
oscillations.Comment: 4 pages, 4 figure
Observation of non-classical rotational inertia in bulk solid 4He
In recent torsional oscillator experiments by Kim and Chan (KC), a decrease
of rotational inertia has been observed in solid 4He in porous materials and in
a bulk annular channel. This observation strongly suggests the existence of
"non-classical rotational inertia" (NCRI), i.e. superflow, in solid 4He. In
order to study such a possible "supersolid" phase, we perform torsional
oscillator experiments for cylindrical solid 4He samples. We have observed
decreases of rotational inertia below 200 mK for two solid samples (pressures P
= 4.1 and 3.0 MPa). The observed NCRI fraction at 70 mK is 0.14 %, which is
about 1/3 of the fraction observed in the annulus by KC. Our observation is the
first experimental confirmation of the possible supersolid finding by KC.Comment: 6 pages, 3 firures, submitted to J. Low Temp. Phys. (Proceedings of
QFS2006
- …