282 research outputs found
Magnetic field induced enhancement of spin-order peak intensity in La(1.875)Ba(0.125)CuO(4)
We report on neutron-scattering results on the impact of a magnetic field on
stripe order in the cuprate LaBaCuO. It is found that a
7 T magnetic field applied along the {\it c} axis causes a small but finite
enhancement of the spin-order peak intensity and has no observable effect on
the peak width. Inelastic neutron-scattering measurements indicate that the
low-energy magnetic excitations are not affected by the field, within
experimental error. In particular, the small energy gap that was recently
reported is still present at low temperature in the applied field. In addition,
we find that the spin-correlation length along the antiferromagnetic stripes is
greater than that perpendicular to them.Comment: 4 pages, 5 figure
Symmetry Protected Josephson Supercurrents in Three-Dimensional Topological Insulators
Coupling the surface state of a topological insulator (TI) to an s-wave
superconductor is predicted to produce the long-sought Majorana quasiparticle
excitations. However, superconductivity has not been measured in surface states
when the bulk charge carriers are fully depleted, i.e., in the true topological
regime that is relevant for investigating Majorana modes. Here, we report
measurements of DC Josephson effects in TI-superconductor junctions as the
chemical potential is moved from the bulk bands into the band gap, or through
the true topological regime characterized by the presence of only surface
currents. We examine the relative behavior of the system at different
bulk/surface ratios, determining the effects of strong bulk/surface mixing,
disorder, and magnetic field. We compare our results to 3D quantum transport
simulations to conclude that the supercurrent is largely carried by surface
states, due to the inherent topology of the bands, and that it is robust
against disorder
Effect of magnetic field on the spin resonance in FeTe(0.5)Se(0.5) as seen via inelastic neutron scattering
Inelastic neutron scattering and susceptibility measurements have been
performed on the optimally-doped Fe-based superconductor FeTe(0.5)Se(0.5),
which has a critical temperature, Tc of 14 K. The magnetic scattering at the
stripe antiferromagnetic wave-vector Q = (0.5,0.5) exhibits a "resonance" at ~
6 meV, where the scattering intensity increases abruptly when cooled below Tc.
In a 7-T magnetic field parallel to the a-b plane, Tc is slightly reduced to ~
12 K, based on susceptibility measurements. The resonance in the neutron
scattering measurements is also affected by the field. The resonance intensity
under field cooling starts to rise at a lower temperature ~ 12 K, and the low
temperature intensity is also reduced from the zero-field value. Our results
provide clear evidence for the intimate relationship between superconductivity
and the resonance measured in magnetic excitations of Fe-based superconductors.Comment: 4 pages, 3 figure
Short-range incommensurate magnetic order near the superconducting phase boundary in Fe(1+d)Te(1-x)Se(x)
We performed elastic neutron scattering and magnetization measurements on
Fe(1.07)Te(0.75)Se(0.25) and FeTe(0.7)Se(0.3). Short-range incommensurate
magnetic order is observed in both samples. In the former sample with higher Fe
content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature,
while in FeTe(0.7)Se(0.3) the broad magnetic peak is found to be closer to the
antiferromagnetic (AFM) wave-vector (0.5,0,0.5). The incommensurate peaks are
only observed on one side of the AFM wave-vector for both samples, which can be
modeled in terms of an imbalance of ferromagnetic/antiferromagnetic
correlations between nearest-neighbor spins. We also find that with higher Se
(and lower Fe) concentration, the magnetic order becomes weaker while the
superconducting temperature and volume increase.Comment: Version as appeared in PR
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
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