91 research outputs found
Diamagnetism and Cooper pairing above in cuprates
In the cuprate superconductors, Nernst and torque magnetization experiments
have provided evidence that the disappearance of the Meissner effect at
is caused by the loss of long-range phase coherence, rather than the vanishing
of the pair condensate. Here we report a series of torque magnetization
measurements on single crystals of (LSCO),
(Bi 2201),
(Bi 2212) and optimal
. Some of the measurements were taken to fields as high
as 45 T. Focusing on the magnetization above , we show that the
diamagnetic term appears at an onset temperature high above
. We construct the phase diagram of both LSCO and Bi 2201 and show that
agrees with the onset temperature of the vortex Nernst signal
. Our results provide thermodynamic evidence against a recent
proposal that the high-temperature Nernst signal in LSCO arises from a
quasiparticle contribution in a charge-ordered state.Comment: 10 pages, 11 figures. Final version with revised text and expanded
discussion and 1 new figure (Fig. 10) and 1 modified fig (Fig. 11). Some new
reference
Detection of electronic nematicity using scanning tunneling microscopy
Electronic nematic phases have been proposed to occur in various correlated
electron systems and were recently claimed to have been detected in scanning
tunneling microscopy (STM) conductance maps of the pseudogap states of the
cuprate high-temperature superconductor Bi2Sr2CaCu2O8+x (Bi-2212). We
investigate the influence of anisotropic STM tip structures on such
measurements and establish, with a model calculation, the presence of a
tunneling interference effect within an STM junction that induces
energy-dependent symmetry-breaking features in the conductance maps. We
experimentally confirm this phenomenon on different correlated electron
systems, including measurements in the pseudogap state of Bi-2212, showing that
the apparent nematic behavior of the imaged crystal lattice is likely not due
to nematic order but is related to how a realistic STM tip probes the band
structure of a material. We further establish that this interference effect can
be used as a sensitive probe of changes in the momentum structure of the
sample's quasiparticles as a function of energy.Comment: Accepted for publication (PRB - Rapid Communications). Main text (5
pages, 4 figures) + Supplemental Material (4 pages, 4 figures
Nanoscale Proximity Effect in the High Temperature Superconductor Bi-2212
High temperature cuprate superconductors exhibit extremely local nanoscale
phenomena and strong sensitivity to doping. While other experiments have looked
at nanoscale interfaces between layers of different dopings, we focus on the
interplay between naturally inhomogeneous nanoscale regions. Using scanning
tunneling microscopy to carefully track the same region of the sample as a
function of temperature, we show that regions with weak superconductivity can
persist to elevated temperatures if bordered by regions of strong
superconductivity. This suggests that it may be possible to increase the
maximum possible transition temperature by controlling the distribution of
dopants.Comment: To appear in Physical Review Letter
Electron-boson glue function derived from electronic Raman scattering
Raman scattering cross sections depend on photon polarization. In the
cuprates nodal and antinodal directions are weighted more strongly in
and symmetry, respectively. On the other hand in angle-resolved
photoemission spectroscopy (ARPES), electronic properties are measured along
well-defined directions in momentum space rather than their weighted averages.
In contrast, the optical conductivity involves a momentum average over the
entire Brillouin zone. Newly measured Raman response data on high-quality
BiSrCaCuO single crystals up to high energies have
been inverted using a modified maximum entropy inversion technique to extract
from and Raman data corresponding electron-boson spectral
densities (glue) are compared to the results obtained with known ARPES and
optical inversions. We find that the spectrum agrees qualitatively
with nodal direction ARPES while the looks more like the optical
spectrum. A large peak around meV in , much less prominent
in , is taken as support for the importance of scattering
at this frequency.Comment: 7 pages, 3 figure
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