25 research outputs found
Distribution of the area enclosed by a 2D random walk in a disordered medium
The asymptotic probability distribution for a Brownian particle wandering in
a 2D plane with random traps to enclose the algebraic area A by time t is
calculated using the instanton technique.Comment: 4 pages, ReVTeX. Phys. Rev. E (March 1999), to be publishe
Possible symmetries of the superconducting order parameter in a hexagonal ferromagnet
We study the order parameter symmetry in a hexagonal crystal with co-existing
superconductivity and ferromagnetism. An experimental example is provided by
carbon-based materials, such as graphite-sulfur composites, in which an
evidence of such co-existence has been recently discovered. The presence of a
non-zero magnetization in the normal phase brings about considerable changes in
the symmetry classification of superconducting states, compared to the
non-magnetic case.Comment: 4 pages, REVTe
On the theory of superconductivity in ferromagnetic superconductors with triplet pairing
We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.Comment: 8 pages, no figure; important changes with respect to the previous
versions due to the correction of a mistake: in this new version, a more
general form is considered for the order parameter (the two-components of the
order parameter were considered before as equal, which is in general not
true) ; submitted to Physical Review
Effect of diffusive boundaries on surface superconductivity in unconventional superconductors
Boundary conditions for a superconducting order parameter at a diffusive
scattering boundary are derived from microscopic theory. The results indicate
that for all but isotropic gap functions the diffusive boundary almost
completely suppresses surface superconductivity in the Ginzburg-Landau regime.
This indicates that in anisotropic superconductors surface superconductivity
can only be observed for surface normals along high symmetry directions where
atomically clean surfaces can be cleaved.Comment: Latex File, 12 pages, 2 Postscript figures, to appear in Phys. Rev. B
(June 1 1996
Localized surface states in HTSC: Alternative mechanism of zero-bias conductance peaks
It is shown that the quasiparticle states localized in the vicinity of
surface imperfections of atomic size can be responsible for the zero-bias
tunneling conductance peaks in high-Tc superconductors. The contribution from
these states can be easily separated from other mechanisms using their
qualitatively different response on an external magnetic field.Comment: REVTeX, 4 pages, 2 figs; to be published in PR
Magnetic Properties of a Superconductor with no Inversion Symmetry
We study the magnetic properties of a superconductor in a crystal without symmetry, in particular how the lack of this symmetry exhibits itself.
We show that, though the penetration depth itself shows no such effect, for
suitable orientation of magnetic field, there is a magnetic field discontinuity
at the interface which shows this absence of symmetry. The magnetic field
profile of a vortex in the plane is shown to be identical to that of an
ordinary anisotropic superconductor except for a shift in the direction by
(see errata). For a vortex along , there is an
induced magnetization along the radial direction.Comment: J. Low Temp. Physics, 140, 67 (2005); with Errat
Spin-orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals
Spin-orbit coupling of electrons with the crystal lattice plays a crucial
role in materials without inversion symmetry, lifting spin degeneracy of the
Bloch states and endowing the resulting nondegenerate bands with complex spin
textures and topologically nontrivial wavefunctions. We present a detailed
symmetry-based analysis of the spin-orbit coupling and the band degeneracies in
noncentrosymmetric metals. We systematically derive the semiclassical equations
of motion for fermionic quasiparticles near the Fermi surface, taking into
account both the spin-orbit coupling and the Zeeman interaction with an applied
magnetic field. Some of the lowest-order quantum corrections to the equations
of motions can be expressed in terms of a fictitious "magnetic field" in the
momentum space, which is related to the Berry curvature of the band
wavefunctions. The band degeneracy points or lines serve as sources of a
topologically nontrivial Berry curvature. We discuss the observable effects of
the wavefunction topology, focusing, in particular, on the modifications to the
Lifshitz-Onsager semiclassical quantization condition and the de Haas-van
Alphen effect in noncentrosymmetric metals.Comment: 38 LaTeX page
Area distribution of two-dimensional random walks on a square lattice
The algebraic area probability distribution of closed planar random walks of
length N on a square lattice is considered. The generating function for the
distribution satisfies a recurrence relation in which the combinatorics is
encoded. A particular case generalizes the q-binomial theorem to the case of
three addends. The distribution fits the L\'evy probability distribution for
Brownian curves with its first-order 1/N correction quite well, even for N
rather small.Comment: 8 pages, LaTeX 2e. Reformulated in terms of q-commutator
Order parameter symmetry in ferromagnetic superconductors
We analyze the symmetry and the nodal structure of the superconducting order
parameter in a cubic ferromagnet, such as ZrZn. We demonstrate how the
order parameter symmetry evolves when the electromagnetic interaction of the
conduction electrons with the internal magnetic induction and the spin-orbit
coupling are taken into account. These interactions break the cubic symmetry
and lift the degeneracy of the order parameter. It is shown that the order
parameter which appears immediately below the critical temperature has two
components, and its symmetry is described by {\em co-representations} of the
magnetic point groups. This allows us to make predictions about the location of
the gap nodes.Comment: 12 pages, ReVTeX, submitted to PR
Recent developments in unconventional superconductivity theory
The review of recent developments in the unconventional superconductivity
theory is given. In the fist part I consider the physical origin of the Kerr
rotation polarization of light reflected from the surface of superconducting
. Then the comparison of magneto-optical responses in
superconductors with orbital and spin spontaneous magnetization is presented.
The latter result is applied to the estimation of the magneto-optical
properties of neutral superfluids with spontaneous magnetization. The second
part is devoted to the natural optical activity or gyrotropy properties of
noncentrosymmetric metals in their normal and superconducting states. The
temperature behavior of the gyrotropy coefficient is compared with the
temperature behavior of paramagnetic susceptibility determining the noticeable
increase of the paramagnetic limiting field in noncentrosymmetric
superconductors. In the last chapter I describe the order parameter and the
symmetry of superconducting state in the itinerant ferromagnet with
orthorhombic symmetry. Finally the Josephson coupling between two adjacent
ferromagnet superconducting domains is discussed.Comment: 15 page