16 research outputs found
Quantum interference between non-magnetic impurities in d_x2-y2-wave superconductors
We study quantum interference of electronic waves that are scattered by
multiple non-magnetic impurities in a d_x2-y2-wave superconductor. We show that
the number of resonance states in the density-of-states (DOS), as well as their
frequency and spatial dependence change significantly as the distance between
the impurities or their orientation relative to the crystal lattice is varied.
Since the latter effect arises from the momentum dependence of the
superconducting gap, we argue that quantum interference is a novel tool to
identify the symmetry of unconventional superconductors.Comment: 4 pages, 4 figure
Note on a sigma model connection with instanton dynamics
It is well known that the instanton approach to QCD generates an effective
term which looks like a three flavor determinant of quark bilinears. This has
the right behavior to explain the unusual mass and mixing of the
meson, as is often simply illustrated with the aid of a linear SU(3) sigma
model. It is less well known that the instanton analysis generates another term
which has the same transformation property but does not have a simple
interpretation in terms of this usual linear sigma model. Here we point out
that this term has an interpretation in a generalized linear sigma model
containing two chiral nonets. The second chiral nonet is taken to correspond to
mesons having two quarks and two antiquarks in their makeup. The generalized
model seems to be useful for learning about the spectrum of low lying scalar
mesons which have been emerging in the last few years. The physics of the new
term is shown to be related to the properties of an "excited" state
present in the generalized model and for which there are some experimental
candidates.Comment: reference added, minor typos correcte
Checkerboard local density of states in striped domains pinned by vortices
Within a Green's function formalism we calculate the electronic structure
around static extended magnetic and non-magnetic perturbations in a d-wave
superconductor. In partucular, we discuss recent elastic neutron scattering and
scanning tunneling experiments on High-T_c cuprates exposed to an applied
magnetic field. A physical picture consisting of antiferromagnetic vortex cores
operating as pinning centers for surrounding stripes is qualitatively
consistent with the neutron data provided the stripes have the usual antiphase
modulation. The low energy electronic structure in such a region reveals a
checkerboard interference pattern consistent with recent scanning tunneling
experiments.Comment: 5 pages, 4 figure
Quantum Interference between Impurities: Creating Novel Many-Body States in s-wave Superconductors
We demonstrate that quantum interference of electronic waves that are
scattered by multiple magnetic impurities in an s-wave superconductor gives
rise to novel bound states. We predict that by varying the inter-impurity
distance or the relative angle between the impurity spins, the states' quantum
numbers, as well as their distinct frequency and spatial dependencies, can be
altered. Finally, we show that the superconductor can be driven through
multiple local crossovers in which its spin polarization, , changes
between and 1.Comment: 4 pages, 4 figure
Quantum interference between multiple impurities in anisotropic superconductors
We study the quantum interference between impurities in d-wave
superconductors within a potential scattering formalism that easily applies to
multiple impurities. The evolution of the low-energy local density of states
for both magnetic and nonmagnetic short-ranged scatterers are studied as a
function of the spatial configuration of the impurities. Further we discuss the
influence of subdominant bulk superconducting order parameters on the
interference pattern from multiple impurities.Comment: 4 pages, 6 figure
Quasiparticle Scattering Interference in High Temperature Superconductors
We propose that the energy-dependent spatial modulation of the local density
of states seen by Hoffman, et al [hoff2] is due to the scattering interference
of quasiparticles. In this paper we present the general theoretical basis for
such an interpretation and lay out the underlying assumptions. As an example,
we perform exact T-matrix calculation for the scattering due to a single
impurity. The results of this calculation is used to check the assumptions, and
demonstrate that quasiparticle scattering interference can indeed produce
patterns similar to those observed in Ref. [hoff2].Comment: RevTex4 twocolumn, 4 pages, 3 figures. Figs.2-3 virtually embedded
(bacause of too big size) while jpg files available in the postscript/source
package. Further polishe
Spin injection through the depletion layer: a theory of spin-polarized p-n junctions and solar cells
A drift-diffusion model for spin-charge transport in spin-polarized {\it p-n}
junctions is developed and solved numerically for a realistic set of material
parameters based on GaAs. It is demonstrated that spin polarization can be
injected through the depletion layer by both minority and majority carriers,
making all-semiconductor devices such as spin-polarized solar cells and bipolar
transistors feasible. Spin-polarized {\it p-n} junctions allow for
spin-polarized current generation, spin amplification, voltage control of spin
polarization, and a significant extension of spin diffusion range.Comment: 4 pages, 3 figure
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
Impurity state in the vortex core of d-wave superconductors: Anderson impurity model versus unitary impurity model
Using an extended Anderson/Kondo impurity model to describe the magnetic
moments around an impurity doped in high- d-wave cuprates and in
the framework of the slave-boson meanfield approach, we study numerically the
impurity state in the vortex core by exact diagonalization of the
well-established Bogoliubov-de Gennes equations. The low-energy impurity state
is found to be good agreement with scanning tunnelingmicroscopy observation.
After pinning a vortex on the impurity site, we compare the unitary impurity
model with the extended Anderson impurity model by examining the effect of the
magnetic field on the impurity state. We find that the impurity resonance in
the unitary impurity model is strongly suppressed by the vortex; while it is
insensitive to the field in the extended Anderson impurity model.Comment: 8 pages, 3 figure
Effect of magnetic field on impurity bound states in high-temperature superconductors
We consider the influence of a magnetic field H on the quasiparticle bound
states near scalar impurities in d-wave superconductors. A ``Doppler shift'' in
the excitation energies induced by the supercurrent leads to several important
effects. At large but finite impurity strength, there are corrections to the
energy and width of the impurity-induced resonance, proportional to H^2. On the
other hand, in the limit of very strong impurity potential (unitary limit), the
bound state is destroyed and acquires a finite width proportional to H/ln H.
There are also considerable changes in the asymptotic behaviour of the bound
state wave functions.Comment: RevTeX, 5 pages, 2 figure