213 research outputs found
Local quasiparticle density of states of superconducting SmFeAsOF single crystals: Evidence for spin-mediated pairing
We probe the local quasiparticles density-of-states in micron-sized
SmFeAsOF single-crystals by means of Scanning Tunnelling
Spectroscopy. Spectral features resemble those of cuprates, particularly a
dip-hump-like structure developed at energies larger than the gap that can be
ascribed to the coupling of quasiparticles to a collective mode, quite likely a
resonant spin mode. The energy of the collective mode revealed in our study
decreases when the pairing strength increases. Our findings support
spin-fluctuation-mediated pairing in pnictides.Comment: 11 pages, 4 figure
Two energy gaps in cuprates: pairing and coherence gaps: The interpretation of tunneling and inelastic neutron scattering measurements
Tunneling and inelastic neutron scattering (INS) measurements in cuprates are
discussed. There is a clear discrepancy among energy-gap values for different
90 K cuprates, inferred from tunneling measurements. By using the phase diagram
of hole-doped cuprates we interpret tunneling measurements in 90 K cuprates and
INS data in YBCO.Comment: 2 pages (including 3 figures) Physica C (in press). Proceedings of
M2S-HTSC-VI Conference. Houston, February 20-25, 200
Wang-MacDonald d-wave vortex cores observed in heavily overdoped BiSrCaCuO
Low magnetic field scanning tunneling spectroscopy of individual Abrikosov
vortices in heavily overdoped BiSrCaCuO unveils a
clear d-wave electronic structure of the vortex core, with a zero-bias
conductance peak at the vortex center that splits with increasing distance from
the core. We show that previously reported unconventional electronic
structures, including the low energy checkerboard charge order in the vortex
halo and the absence of a zero-bias conductance peak at the vortex center, are
direct consequences of short inter-vortex distance and consequent vortex-vortex
interactions prevailing in earlier experiments.Comment: Main text : 5 pages, 4 figures Supplemental material : 3 pages, 2
figure
Strong-coupling analysis of scanning tunneling spectra in BiSrCaCuO
We study a series of spectra measured in the superconducting state of
optimally-doped Bi-2223 by scanning tunneling spectroscopy. Each spectrum, as
well as the average of spectra presenting the same gap, is fitted using a
strong-coupling model taking into account the band structure, the BCS gap, and
the interaction of electrons with the spin resonance. After describing our
measurements and the main characteristics of the strong-coupling model, we
report the whole set of parameters determined from the fits, and we discuss
trends as a function of the gap magnitude. We also simulate angle-resolved
photoemission spectra, and compare with recent experimental results.Comment: Published versio
Revisiting the vortex-core tunnelling spectroscopy in YBaCuO
The observation by scanning tunnelling spectroscopy (STS) of Abrikosov vortex
cores in the high-temperature superconductor YBaCuO (Y123)
has revealed a robust pair of electron-hole symmetric states at finite subgap
energy. Their interpretation remains an open question because theory predicts a
different signature in the vortex cores, characterised by a strong zero-bias
conductance peak. We present STS data on very homogeneous Y123 at 0.4 K
revealing that the subgap features do not belong to vortices: they are actually
observed everywhere along the surface with high spatial and energy
reproducibility, even in the absence of magnetic field. Detailed analysis and
modelling show that these states remain unpaired in the superconducting phase
and belong to an incoherent channel which contributes to the tunnelling signal
in parallel with the superconducting density of states.Comment: Final version with supplementary materia
Bound states and extended states around a single vortex in the d-wave superconductors
Making use of the Bogoliubov-de Gennes equation for the d-wave
superconductors, we investigate the quasi-particle spectrum around a single
vortex. Taking , we found that there are bound states which are
localized around the vortex core, and extended states which are rather uniform,
for where is the quasi-particle energy and is the
asymptotic value of the order parameter for away from the vortex.Comment: 4 pages, 6 figure
Polaronic signature in the metallic phase of La0.7Ca0.3MnO3 films detected by scanning tunneling spectroscopy
In this work we map tunnel conductance curves with nanometric spatial
resolution, tracking polaronic quasiparticle excitations when cooling across
the insulator-to-metal transition in La0.7Ca0.3MnO3 films. In the insulating
phase the spectral signature of polarons, a depletion of conductance at low
bias flanked by peaks, is detected all over the scanned surface. These features
are still observed at the transition and persist on cooling into the metallic
phase. Polaron-binding energy maps reveal that polarons are not confined to
regions embedded in a highly-conducting matrix but are present over the whole
field of view both above and below the transition temperature.Comment: 10 pages, 4 figure
Fingerprint of dynamical charge/spin correlations in the tunneling spectra of colossal magnetoresistive manganites
We present temperature-dependent scanning tunneling spectroscopy measurements
on () films with different degrees of biaxial
strain. A depletion in normalized conductance around the Fermi level is
observed both above and below the insulator-to-metal transition temperature
, for weakly as well as highly-strained films. This pseudogap-like
depletion globally narrows on cooling. The zero-bias conductance decreases on
cooling in the insulating phase, reaches a minimum close to and
increases on cooling in the metallic phase, following the trend of macroscopic
conductivity. These results support a recently proposed scenario in which
dynamical short-range antiferromagnetic/charge order correlations play a
preeminent role in the transport properties of colossal magnetoresistive
manganites [R. Yu \textit{et al}., Phys. Rev. B \textbf{77}, 214434 (2008)].Comment: 9 pages, 4 figure
Comment on ``Quasiparticle Spectra around a Single Vortex in a d-wave Superconductor''
In a recent Letter Morita, Kohmoto and Maki analyzed the structure of
quasiparticle states near a single vortex in a d-wave superconductor using an
approximate version of the Bogoliubov - de Gennes theory. Their principal
result is the existence of a bound state within the core region at finite
energy with full rotational symmetry, which they assert explains the recent
scanning tunneling microscopy results on YBCO single crystals. Here we argue
that the approximation used in this work is fundamentally inadequate for the
description of a d-wave vortex and that the obtained circular symmetry of the
local density of states is an unphysical artifact of this approximation.Comment: 1 page REVTeX, to appear in PR
Vortex-core spectroscopy of -wave cuprate high-temperature superconductors
The mechanism of high-temperature superconductivity remains one of the great
challenges of contemporary physics. Here, we review efforts to image the vortex
lattice in copper oxide-based high-temperature superconductors and to measure
the characteristic electronic structure of the vortex core of a -wave
superconductor using scanning tunneling spectroscopy.Comment: Main text : 7 pages, 8 figure
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