1,252 research outputs found
Evidence for field-induced excitations in low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8
The thermal conductivity ,, of Bi_2Sr_2CaCu_2O_8 was studied as a
function of magnetic field. Above 5 K, after an initial decrease,
presents a kink followed by a plateau, as recently reported by Krishana et al..
By contrast, below 1K, the thermal conductivity was found to \emph{increase}
with increasing field. This behavior is indicative of a finite density of
states and is not compatible with the existence of a field-induced fully gapped
state which was recently proposed to describe the
plateau regime. Our low-temperature results are in agreement with recent works
predicting a field-induced enhancement of thermal conductivity by Doppler shift
of quasi-particle spectrum.Comment: 4 pages including 4 eps figures, submitted to Phys. Rev. Let
Evidence for Surface Andreev Bound states in Cuprate Superconductors from Penetration Depth Measurements
Tunneling and theoretical studies have suggested that Andreev bound states
form at certain surfaces of unconventional superconductors. Through studies of
the temperature and field dependence of the in-plane magnetic penetration depth
lambda_ab at low temperature, we have found strong evidence for the presence of
these states in clean single crystal YBCO and BSCCO. Crystals cut to expose a
[110] interface show a strong upturn in lambda_ab at around 7K, when the field
is oriented so that the supercurrents flow around this surface. In YBCO this
upturn is completely suppressed by a field of ~0.1 T.Comment: 4 pages 2 column revtex + 4 postscript figures. Submitted to PR
A Cell of One’s Own? Incarceration and Other Turning Points in Women’s Journeys to Desistance
Research has shown the importance of turning points in desistance from criminal behavior. Using qualitative data from a sample of 100 formerly incarcerated mothers interviewed about their criminal behavior, this article explores their descriptions of transition moments and whether and how those moments affected their criminal behavior. The findings indicate that whereas parenting emerges as a turning point, the practical difficulties of reentry may reduce the impact of mothering on women’s desistance. More self-focused turning points, such as those due to incarceration, arrest, and sobriety appeared to be particularly important to the women’s desistance. This article emphasizes the need for research into the subjective and environmental factors that affect women’s desistance behaviors
Josephson scanning tunneling microscopy
We propose a set of scanning tunneling microscopy experiments in which the
surface of superconductor is scanned by a superconducting tip. Potential
capabilities of such experimental setup are discussed. Most important
anticipated results of such an experiment include the position-resolved
measurement of the superconducting order parameter and the possibility to
determine the nature of the secondary component of the order parameter at the
surface. The theoretical description based on the tunneling Hamiltonian
formalism is presented.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Discrete-Lattice Model for Surface Bound States and Tunneling in d-Wave Superconductors
Surface bound states in a discrete-lattice model of a cuprate
superconductor are shown to be, in general, coherent superpositions of an
incoming excitation and more than one outgoing excitation, and a simple
graphical construction based on a surface Brillouin zone is developed to
describe their nature. In addition, a momentum-dependent lifetime contribution
to the width of these bound states as observed in tunneling experiments is
derived and elucidated in physical terms.Comment: 4 pages, 1 figure, revte
Observation of Bound Surface States in Grain Boundary Junctions of High Temperature Superconductors
We have performed a detailed study of the tunneling spectra of bicrystal
grain boundary junctions (GBJs) fabricated from the HTS YBCO, BSCCO, LSCO, and
NCCO. In all experiments the tunneling direction was along the CuO planes. With
the exception of NCCO, for all materials a pronounced zero bias conductance
peak was observed which decreases with increasing temperature and disappears at
the critical temperature. These results can be explained by the presence of a
dominating d-wave symmetry of the order parameter resulting in the formation of
zero energy Andreev bound states at surfaces and interfaces of HTS. The absence
of a ZBCP for NCCO is consistent with a dominating s-wave symmetry of the pair
potential in this material. The observed nonlinear shift of spectral weight to
finite energies by applying a magnetic field is in qualitative agreement with
recent theoretical predictions.Comment: 4 pages, 4 figures, to be published in Phys. Rev.
Tunneling into Current-Carrying Surface States of High T Superconductors
Theoretical results for the ab-plane tunneling conductance in the d-wave
model for high Tc superconductors are presented. The d-wave model predicts
surface bound states below the maximum gap. A sub-dominant order parameter,
stabilized by the surface, leads to a splitting of the zero-bias conductance
peak (ZBCP) in zero external field and to spontaneous surface currents. In a
magnetic field screening currents shift the quasiparticle bound state spectrum
and lead to a voltage splitting of the ZBCP that is linear in H at low fields,
and saturates at a pairbreaking critical field of order 3 Tesla. Comparisons
with recent experimental results on Cu/YBCO junctions are presented.Comment: 4 pages in a RevTex (3.0) file plus 3 Figures in PostScript. To
appear in Phys. Rev. Let
Field induced state and marginal stability of high-Tc superconductors
It is shown that the {\em complex} component is generated in d-wave
superconductor in the magnetic field. As one enters superconducting state at
finite field the normal to superconducting transition occurs into bulk
state . The driving force for the transition is the
linear coupling between magnetic field and non zero magnetization of the
condensate. The external magnetic field violates parity
and time reversal symmetries and the nodal quasiparticle states respond by
generating the component of the order parameter, with the magnitude
estimated to be on the order of few Kelvin. Parity (P) and time reversal (T)
symmetries are violated in this state.Comment: 4 pages, latex file with two eps figure file
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