210 research outputs found
Avalanche statistics of sand heaps
Large scale computer simulations are presented to investigate the avalanche
statistics of sand piles using molecular dynamics. We could show that different
methods of measurement lead to contradicting conclusions, presumably due to
avalanches not reaching the end of the experimental table.Comment: 6 pages, 4 figure
The influence of chiral surface states on the London penetration depth in SrRuO
The London penetration depth for the unconventional superconductor
SrRuO is analyzed assuming an order parameter which breaks time
reversal symmetry and parity simultaneously. Such a superconducting state
possesses chiral quasiparticle states with subgap energies at the surface. We
show that these subgap states can give a significant contribution to the
low-temperature behavior of the London penetration depth yielding a
power-law even though bulk quasiparticle spectrum is gapped. The presence of
several electron bands gives rise to interband transition among the subgap
surface states and influences the properties of the surface impedance.
Furthermore, the surface states lead also to a non-linear Meissner effect.Comment: 4 pages, 1 figure, the definition of the Nambu field operator
introduced, and some typos correcte
Impurity States and the Absence of Quasiparticle Localization in Disordered D-Wave Superconductors
The absence of localization of impurity-induced low-energy quasiparticle
states in a two-dimensional -wave superconductor is argued for any amount of
disorder in the limit of unitary scatterers. This surprising result follows
from the fact that a unitary impurity produces a marginally-bound state at zero
energy which decays as a power-law along the nodes of the -wave energy gap.
Consequently, for finite density of impurities, the impurity-induced states are
coupled by long-range overlaps yielding extended quasiparticle states below a
characteristic energy scale . Simple scaling arguments suggest that
, where is the impurity
density and is a positive constant.Comment: 4 pages, uuencoded postscript fil
Induction of non-d-wave order-parameter components by currents in d-wave superconductors
It is shown, within the framework of the Ginzburg-Landau theory for a
superconductor with d_{x^2-y^2} symmetry, that the passing of a supercurrent
through the sample results, in general, in the induction of order-parameter
components of distinct symmetry. The induction of s-wave and
d_{xy(x^2-y^2)-wave components are considered in detail. It is shown that in
both cases the order parameter remains gapless; however, the structure of the
lines of nodes and the lobes of the order parameter are modified in distinct
ways, and the magnitudes of these modifications differ in their dependence on
the (a-b plane) current direction. The magnitude of the induced s-wave
component is estimated using the results of the calculations of Ren et al.
[Phys. Rev. Lett. 74, 3680 (1995)], which are based on a microscopic approach.Comment: 15 pages, includes 2 figures. To appear in Phys. Rev.
Strong Anisotropy in Spin Suceptibility of Superfluid 3He-B Film Caused by Surface Bound States
Spin susceptibility of superfluid 3He-B film with specular surfaces is
calculated. It is shown that, when the magnetic field is applied in a direction
perpendiculr to the film, the suseptibility is significantly enhanced by the
contribution from the surface bound states. No such enhancement is found for
the magnetic field parallel to the film. A simplified model with spatially
constant order parameter is used to elucidate the magnetic properties of the
surface bound states. The Majorana nature of the zero energy bound state is
also mentioned.Comment: 4 pages, 4 figure
Pinhole calculations of the Josephson effect in 3He-B
We study theoretically the dc Josephson effect between two volumes of
superfluid 3He-B. We first discuss how the calculation of the current-phase
relationships is divided into a mesoscopic and a macroscopic problem. We then
analyze mass and spin currents and the symmetry of weak links. In quantitative
calculations the weak link is assumed to be a pinhole, whose size is small in
comparison to the coherence length. We derive a quasiclassical expression for
the coupling energy of a pinhole, allowing also for scattering in the hole.
Using a selfconsistent order parameter near a wall, we calculate the
current-phase relationships in several cases. In the isotextural case, the
current-phase relations are plotted assuming a constant spin-orbit texture. In
the opposite anisotextural case the texture changes as a function of the phase
difference. For that we have to consider the stiffness of the macroscopic
texture, and we also calculate some surface interaction parameters. We analyze
the experiments by Marchenkov et al. We find that the observed pi states and
bistability hardly can be explained with the isotextural pinhole model, but a
good quantitative agreement is achieved with the anisotextural model.Comment: 20 pages, 21 figures, revtex
Unconventional Pairing in Heavy Fermion Metals
The Fermi-liquid theory of superconductivity is applicable to a broad range
of systems that are candidates for unconventional pairing. Fundamental
differences between unconventional and conventional anisotropic superconductors
are illustrated by the unique effects that impurities have on the
low-temperature transport properties of unconventional superconductors. For
special classes of unconventional superconductors the low-temperature transport
coefficients are {\it universal}, i.e. independent of the impurity
concentration and scattering phase shift. The existence of a universal limit
depends on the symmetry of the order parameter and is achieved at low
temperatures , where is the bandwidth
of the impurity induced Andreev bound states. In the case of UPt thermal
conductivity measurements favor an or ground state.
Measurements at ultra-low temperatures should distinguish different pairing
states.Comment: 8 pages in a LaTex (3.0) file plus 5 Figures in PostScript. To appear
in the Proceedings of the XXI International Conference on Low Temperature
Physics held in Prague, 8-14 August 199
Singular Vortex in Narrow Cylinders of Superfluid 3He-A Phase
Motivated by the on-going rotating cryostat experiments in ISSP, Univ. of
Tokyo, we explore the textures and vortices in superfluid 3He-A phase confined
in narrow cylinders, whose radii are R=50mum and 115mum. The calculations are
based on the Ginzburg-Landau (GL) framework, which fully takes into account the
orbital (l-vector) and spin (d-vector) degrees of freedom for chiral p-wave
pairing superfluid. The GL free energy functional is solved numerically by
using best known GL parameters appropriate for the actual experimental
situations at P=3.2MPa and H=21.6mT. We identify the ground state l-vector
configuration as radial disgyration (RD) texture with the polar core both at
rest and low rotations and associated d-vector textures for both narrow
cylinder systems under high magnetic fields. The RD which has a singularity at
center, changes into Mermin-Ho texture above the critical rotation speed which
is determined precisely, providing an experimental check for own proposal.Comment: 22 pages, 12 figure
Discrete-Lattice Model for Surface Bound States and Tunneling in d-Wave Superconductors
Surface bound states in a discrete-lattice model of a cuprate
superconductor are shown to be, in general, coherent superpositions of an
incoming excitation and more than one outgoing excitation, and a simple
graphical construction based on a surface Brillouin zone is developed to
describe their nature. In addition, a momentum-dependent lifetime contribution
to the width of these bound states as observed in tunneling experiments is
derived and elucidated in physical terms.Comment: 4 pages, 1 figure, revte
Realistic Surface Scattering and Surface Bound State Formation in the High T_c Superconductor YBa_2Cu_3O_{6+x}
Surface Umklapp scattering of quasiparticles, and surface roughness are shown
to play essential roles in the formation of the surface bound states in
realistic models for YBa_2Cu_3O_{6+x}. The results account for the shape, the
impurity dependence of the height, and for a proposed universal width of the
zero bias conductance peak.Comment: 4 pages, 1 figur
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