575 research outputs found
Vorticity and vortex-core states
The origin of the vortex-core states in s-wave and d_{x^2-y^2}-wave
superconductors is investigated by means of some selected numerical
experiments. By relaxing the self-consistency condition in the Bogoliubov-de
Gennes equations and tuning the order parameter in the core region, it is shown
that the suppression of the superfluid density in the core is not a necessary
condition for the core states to form. This excludes ``potential well'' types
of interpretations for the core states. The topological defect in the phase of
the order parameter, however, plays a crucial role. This observation is
explained by considering the effect of the vortex supercurrent on the
Bogoliubov quasiparticles, and illustrated by comparing conventional vortices
with multiply-quantized vortices and vortex-antivortex pairs. The core states
are also found to be extremely robust against random phase disorder.Comment: REVTeX 4, 11 pages, 8 EPS figure
Gorkov equations for a pseudo-gapped high temperature superconductor
A theory of superconductivity based on the two-body Cooperon propagator is
presented. This theory takes the form of a modified Gorkov equation for the
Green's function and allows one to model the effect of local superconducting
correlations and long range phase fluctuations on the spectral properties of
high temperature superconductors, both above and below Tc. A model is proposed
for the Cooperon propagator, which provides a simple physical picture of the
pseudo-gap phenomenon, as well as new insights into the doping dependence of
the spectral properties. Numerical calculations of the density of states and
spectral functions based on this model are also presented, and compared with
the experimental STM and ARPES data. It is found, in particular, that the
sharpness of the peaks in the density of states is related to the strength and
the range of the superconducting correlations and that the apparent pseudo-gap
in STM and ARPES can be different, although the underlying model is the same.Comment: REVTEX 3.1, 8 pages, 5 EPS figures, submitted to Phys. Rev.
Interplay of the pseudogap and the BCS gap for heteropairs in K-Li mixture
The description of heteropairs like K-Li near and in the
superconducting state requires a fully selfconsistent theory [see Hanai and
Ohashi, Phys. Rev. A 90, 043622 (2014)]. We derive analytic pseudogap Green's
functions for the "normal" and superconducting states from the Luttinger-Ward
theory with the T-matrix in the static separable approximation. The
self-consistency in the closing loop of self-energy has two pronounced effects
on the single-particle spectrum. First, the single-particle excitations decay
before the asymptotic quasiparticle propagation is established, therefore the
normal state is not a Fermi liquid. Second, the pseudogap has a V shape even
for s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere
resulting in slope breaks of the gap walls and the in-gap states in the density
of states. Various consequences of an incomplete self-consistency are
demonstrated.Comment: Published versio
Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core
In copper- and iron-based unconventional superconductors, the Bogoliubov
quasiparticles interact with a spin resonance at momentum . This
interaction is revealed by specific signatures in the quasiparticle
spectroscopies, like kinks in photoemission and dips in tunneling. We study
these signatures, as they appear inside and around a vortex core in the local
density of states (LDOS), a property accessible experimentally by scanning
tunneling spectroscopy. Our model retains the whole nonlocal structure of the
self-energy in space and time and is therefore not amenable to a Hamiltonian
treatment using Bogoliubov-de Gennes equations. The interaction with the spin
resonance does not suppress the zero-bias peak at the vortex center, although
it reduces its spectral weight; neither does it smear out the vortex LDOS, but
rather it adds structure to it. Some of the signatures we find may have been
already measured in FeSe, but remained unnoticed. We compare the LDOS as a
function of both energy and position with and without coupling to the spin
resonance and observe, in particular, that the quasiparticle interference
patterns around the vortex are strongly damped by the coupling. We study in
detail the transfer of spectral weight induced both locally and globally by the
interaction and also by the formation of the vortex. Finally, we introduce a
new way of imaging the quasiparticles in real space, which combines locality
and momentum-space sensitivity. This approach allows one to access
quasiparticle properties that are not contained in the LDOS.Comment: Published versio
Periodicity of superconducting shape resonances in thin films
The pairing temperature of superconducting thin films is expected to display,
within the Bardeen-Cooper-Schrieffer theory, oscillations as a function of the
film thickness. We show that the pattern of these oscillations switches between
two different periodicities at a density-dependent value of the superconducting
coupling. The transition is most abrupt in the anti-adiabatic regime, where the
Fermi energy is less than the Debye energy. To support our numerical data, we
provide new analytical expressions for the chemical potential and the pairing
temperature as a function of thickness, which only differ from the exact
solution at weak coupling by exponentially-small corrections.Comment: Published versio
Cooperon propagator description of high temperature superconductivity
A phenomenological description of the high-Tc superconductors based on the
Cooperon propagator is presented. This model allows one to study the effects of
local pairing correlations and long-range phase fluctuations on the same
footing, both above and below Tc. Based on numerical calculations, it is shown
that the two types of correlations contribute to the gap/pseudogap in the
single-particle excitation spectra. The concourse of these two effects can
induce low energy states, which should be observable in underdoped materials at
very low temperature.Comment: LaTeX, 6 pages, 2 EPS figures; paper presented at New^3SC-3, Hawaii,
01/2001. To appear in Physica
Large modulation of the Shubnikov-de Haas oscillations by the Rashba interaction at the LaAlO/SrTiO interface
We investigate the 2-dimensional Fermi surface of high-mobility
LaAlO/SrTiO interfaces using Shubnikov-de Haas oscillations. Our
analysis of the oscillation pattern underscores the key role played by the
Rashba spin-orbit interaction brought about by the breaking of inversion
symmetry, as well as the dominant contribution of the heavy /
orbitals on electrical transport. We furthermore bring into light the complex
evolution of the oscillations with the carrier density, which is tuned by the
field effect
Optical Response of SrRuO Reveals Universal Fermi-liquid Scaling and Quasiparticles Beyond Landau Theory
We report optical measurements demonstrating that the low-energy relaxation
rate () of the conduction electrons in SrRuO obeys scaling
relations for its frequency () and temperature () dependence in
accordance with Fermi-liquid theory. In the thermal relaxation regime,
1/\tau\propto (\hbar\omega)^2 + (p\pi\kB T)^2 with , and
scaling applies. Many-body electronic structure calculations using dynamical
mean-field theory confirm the low-energy Fermi-liquid scaling, and provide
quantitative understanding of the deviations from Fermi-liquid behavior at
higher energy and temperature. The excess optical spectral weight in this
regime provides evidence for strongly dispersing "resilient" quasiparticle
excitations above the Fermi energy
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