109 research outputs found
Electrostatics of Vortices in Type II Superconductors
In a type II superconductor the gap variation in the core of a vortex line
induces a local charge modulation. Accounting for metallic screening, we
determine the line charge of individual vortices and calculate the electric
field distribution in the half space above a field penetrated superconductor.
The resulting field is that of an atomic size dipole , is the Bohr radius, acting
on a force microscope in the pico to femto Newton range.Comment: 9 pages, late
Charge Frustration Effects in Capacitively Coupled Two-Dimensional Josephson-Junction Arrays
We investigate the quantum phase transitions in two capacitively coupled
two-dimensional Josephson-junction arrays with charge frustration. The system
is mapped onto the S=1 and anisotropic Heisenberg antiferromagnets near
the particle-hole symmetry line and near the maximal-frustration line,
respectively, which are in turn argued to be effectively described by a single
quantum phase model. Based on the resulting model, it is suggested that near
the maximal frustration line the system may undergo a quantum phase transition
from the charge-density wave to the super-solid phase, which displays both
diagonal and off- diagonal long-range order.Comment: 6 pages, 6 figures, to appear in Phys. Rev.
Tunnel junctions of unconventional superconductors
The phenomenology of Josephson tunnel junctions between unconventional
superconductors is developed further. In contrast to s-wave superconductors,
for d-wave superconductors the direction dependence of the tunnel matrix
elements that describe the barrier is relevant. We find the full I-V
characteristics and comment on the thermodynamical properties of these
junctions. They depend sensitively on the relative orientation of the
superconductors. The I-V characteristics differ from the normal s-wave RSJ-like
behavior.Comment: 4 pages, revtex, 4 (encapsulated postscript) figures (figures
replaced
The Superconductor-Insulator Transition in a Tunable Dissipative Environment
We study the influence of a tunable dissipative environment on the dynamics
of Josephson junction arrays near the superconductor-insulator transition. The
experimental realization of the environment is a two dimensional electron gas
coupled capacitively to the array. This setup allows for the well-controlled
tuning of the dissipation by changing the resistance of the two dimensional
electron gas. The capacitive coupling cuts off the dissipation at low
frequencies. We determine the phase diagram and calculate the temperature and
dissipation dependence of the array conductivity. We find good agreement with
recent experimental results.Comment: 4 pages, 4 .eps figures, revte
Cluster Monte Carlo Algorithm for the Quantum Rotor Model
We propose a highly efficient "worm" like cluster Monte Carlo algorithm for
the quantum rotor model in the link-current representation. We explicitly prove
detailed balance for the new algorithm even in the presence of disorder. For
the pure quantum rotor model with the new algorithm yields high
precision estimates for the critical point and the correlation
length exponent . For the disordered case, , we
find .Comment: 5 pages, 3 figure
From Effective BCS Action to Vortex Dynamics
The topological term in the effective action for the electrically neutral BCS
system is discussed. It is applied for the calculation of the transverse force
acting on the vortex in the limit of the smooth vortex core and vanishing
interlevel distance in the vortex core. The controversy between the topological
terms in cond-mat/9703124 and cond-mat/9411047 is resolved.Comment: 9 pages, no Figures, inspired by recent preprint by van Otterlo et al
in cond-mat/9703124, corrected after discussion with N.B. Kopni
Nucleation of Stable Superconductivity in YBCO-Films
By means of the linear dynamic conductivity, inductively measured on
epitaxial films between 30mHz and 30 MHz, the transition line to
generic superconductivity is studied in fields between B=0 and 19T. It follows
closely the melting line described recently in terms of a blowout of
thermal vortex loops in clean materials. The critical exponents of the
correlation length and time near , however, seem to be dominated by
some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up
to field-equivalent-doses of lead to a disappointing reduction
of while for the generic line of the pristine film
is recovered. These novel results are also discussed in terms of a loop-driven
destruction of generic superconductivity.Comment: 11 pages including 7 EPS figures, accepted for publication in the
Proceedings of the Spring Meeting of the German Physical Society, Muenster
1999,Festkoerperprobleme/Advances in Solid State Physics 199
Anomalous flux-flow dynamics in layered type-II superconductors at low temperatures
Low-temperature dissipation due to vortex motion in strongly anisotropic
type-II superconductors with a moderate disorder () is shown to be determined by the Zener-type transitions between
the localized electronic states in the vortex core. Statistics of these levels
is described by the random matrix ensemble of the class C defined recently by
Atland and Zirnbauer [cond-mat/9602137], so the vortex motion leads naturally
to the new example of a parametric statistics of energy levels. The flux-flow
conductivity is a bit lower than the quasiclassical one and {\it
grows} slowly with the increase of the electric field.Comment: 4 pages, Revte
Gauge-invariant electromagnetic response of a chiral px+ipy superconductor
We present a gauge-invariant theory of the electromagnetic response of a
chiral px+ipy superconductor in the clean limit. Due to the spontaneously
broken time-reversal symmetry, the effective action of the system contains an
anomalous term not present in conventional superconductors. As a result, the
electromagnetic charge and current responses contain anomalous terms, which
depend explicitly on the chirality of the superconducting order parameter.
These terms lead to a number of unusual effects, such as coupling of the
transverse currents to the collective plasma oscillations and a possibility of
inducing the charge density by the magnetic field perpendicular to the
conducting planes. We calculate the antisymmetric part of the conductivity
tensor (the intrinsic Hall conductivity) and show that it depends on the wave
vector of the electromagnetic field. We also show that the Mermin-Muzikar
magnetization current and the Hall conductivity are strongly suppressed at high
frequencies. Finally, we discuss implications of the theory to the experiments
in Sr2RuO4.Comment: 22 pages, 4 figures, final version as published in PR
Phases of the one-dimensional Bose-Hubbard model
The zero-temperature phase diagram of the one-dimensional Bose-Hubbard model
with nearest-neighbor interaction is investigated using the Density-Matrix
Renormalization Group. Recently normal phases without long-range order have
been conjectured between the charge density wave phase and the superfluid phase
in one-dimensional bosonic systems without disorder. Our calculations
demonstrate that there is no intermediate phase in the one-dimensional
Bose-Hubbard model but a simultaneous vanishing of crystalline order and
appearance of superfluid order. The complete phase diagrams with and without
nearest-neighbor interaction are obtained. Both phase diagrams show reentrance
from the superfluid phase to the insulator phase.Comment: Revised version, 4 pages, 5 figure
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