13 research outputs found
Local density of states in the vortex lattice in a type II superconductor
Local density of states (LDOS) in the triangular vortex lattice is
investigated based on the quasi-classical Eilenberger theory. We consider the
case of an isotropic s-wave superconductor with the material parameter
appropriate to NbSe_2. At a weak magnetic field, the spatial variation of the
LDOS shows cylindrical structure around a vortex core. On the other hand, at a
high field where the core regions substantially overlap each other, the LDOS is
sixfold star-shaped structure due to the vortex lattice effect. The orientation
of the star coincides with the experimental data of the scanning tunneling
microscopy. That is, the ray of the star extends toward the nearest-neighbor
(next nearest-neighbor) vortex direction at higher (lower) energy.Comment: 10 pages, RevTex, 32 figure
Coherence in the Quasi-Particle 'Scattering' by the Vortex Lattice in Pure Type-II Superconductors
The effect of quasi-particle (QP) 'scattering' by the vortex lattice on the
de-Haas van-Alphen oscillations in a pure type-II superconductor is
investigated within mean field,asymptotic perturbation theory. Using a 2D
electron gas model it is shown that, due to a strict phase coherence in the
many-particle correlation functions, the 'scattering' effect in the asymptotic
limit () is much weaker than what is predicted
by the random vortex lattice model proposed by Maki and Stephen, which destroys
this coherence . The coherent many particle configuration is a collinear array
of many particle coordinates, localized within a spatial region with size of
the order of the magnetic length. The amplitude of the magnetization
oscillations is sharply damped just below because of strong
out of phase magnetic oscillations in the superconducting
condensation energy ,which tend to cancel the normal electron oscillations.
Within the ideal 2D model used it is found, however, that because of the
relative smallness of the quartic and higher order terms in the expansion, the
oscillations amplitude at lower fields does not really damp to zero, but only
reverses sign and remains virtually undamped well below . This
conclusion may be changed if disorder in the vortex lattice, or vortex lines
motion will be taken into account. The reduced QP 'scattering' effect may be
responsible for the apparent crossover from a strong damping of the dHvA
oscillations just below to a weaker damping at lower fields observed
experimentally in several 3D superconductors.Comment: 26 pages, Revtex no Figure
The Current Carried by Bound States of a Superconducting Vortex
We investigate the spectrum of quasiparticle excitations in the core of
isolated pancake vortices in clean layered superconductors. Analysis of the
spectral current density shows that both the circular current around the vortex
center as well as any transport current through the vortex core is carried by
localized states bound to the core by Andreev scattering. Hence the physical
properties of the core are governed in clean high- superconductors
(e.g. the cuprate superconductors) by the Andreev bound states, and not by
normal electrons as it is the case for traditional (dirty) high-
superconductors.Comment: 17 pages in a RevTex (3.0) file plus 5 Figures in PostScript.
Submitted to Physical Review
Field dependence of the vortex structure in chiral p-wave superconductors
To investigate the different vortex structure between two chiral pairing p_x
+(-) i p_y, we calculate the pair potential, the internal field, the local
density of states, and free energy in the vortex lattice state based on the
quasiclassical Eilenberger theory, and analyze the magnetic field dependence.
The induced opposite chiral component of the pair potential plays an important
role in the vortex structure. It also produces H^{1/2}-behavior of the
zero-energy density of states at higher field. These results are helpful when
we understand the vortex states in Sr2RuO4.Comment: 11 pages, 10 figures, to be published in Phys. Rev.
Effects of gap anisotropy upon the electronic structure around a superconducting vortex
An isolated single vortex is considered within the framework of the
quasiclassical theory. The local density of states around a vortex is
calculated in a clean type II superconductor with an anisotropy. The anisotropy
of a superconducting energy gap is crucial for bound states around a vortex. A
characteristic structure of the local density of states, observed in the
layered hexagonal superconductor 2H-NbSe2 by scanning tunneling microscopy
(STM), is well reproduced if one assumes an anisotropic s-wave gap in the
hexagonal plane. The local density of states (or the bound states) around the
vortex is interpreted in terms of quasiparticle trajectories to facilitate an
understanding of the rich electronic structure observed in STM experiments. It
is pointed out that further fine structures and extra peaks in the local
density of states should be observed by STM.Comment: 11 pages, REVTeX; 20 PostScript figures; An Animated GIFS file for
the star-shaped vortex bound states is available at
http://mp.okayama-u.ac.jp/~hayashi/vortex.htm
Superconductivity in High Magnetic Field:Excitation Spectrum and Tunneling Properties
The quasiparticle excitation spectrum of a type-II superconductor placed in
high magnetic field is shown to be gapless. The gap turns to zero at the points
in the MBZ which are in correspondence with the vortex lattice in real space.
When the field decreases below certain critical value, branch crossing occur
and gaps starts opening up at the Fermi surface.The strong dispersion around
gapless points leads to algebraic temperature dependence in the thermodynamic
functions and the algebraic voltage dependence in the tunneling conductance
between the microscope tip and superconductor in an STM experiment.Comment: 16 pages+$figures (on request), REVTE