17 research outputs found
Magnetic field effect in hybrid nanostructures
We examine the effect of the magnetic field on the proximity effect in
nanostructures, self consistently using the Bogoliubov-deGennes formalism
within the two dimensional extended Hubbard model. We calculate the local
density of states and the pair amplitude. We study several nanostructures:
superconductor - two dimensional electron gas, superconductor - ferromagnet. In
these structures the magnetic field can be considered as a modulation parameter
for the proximity effect.Comment: 9 pages, 9 figure
Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters
We study superconductor-ferromagnet bi-layers, not only for s-wave but also
for d-wave superconductors. We observe oscillations of the critical temperature
when varying the thickness of the ferromagnetic layer for both s-wave and
d-wave superconductors. However, for a rotated d-wave order parameter the
critical temperature differs considerably from that for the unrotated case. In
addition we calculate the density of states for different thicknesses of the
ferromagnetic layer; the results reflect the oscillatory behaviour of the
superconducting correlations.Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens.
Matte
Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions
We have performed temperature dependent tunneling conductance spectroscopy on
Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe
counterelectrode was designed to probe the proximity region of the ab-plane of
BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude
and sign dependent on the energy, decaying with increasing distance from the
junction barrier, in conjunction with the theoretical predictions involving
d-wave superconductors coupled with ferromagnets. The conductance oscillates in
antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a
broken time-reversal pairing symmetry are detected and they do not depend on
the geometrical characteristics of the ferromagnetic film.Comment: 4 pages and 4 figures Submitted to Physical Review Letter
Dynamics of the Electro-Optic response of Blue Bronze
We have studied the charge density wave (CDW) repolarization dynamics in blue
bronze by applying square-wave voltages of different frequencies to the sample
and measuring the changes in infrared transmittance, proportional to CDW
strain. The frequency dependence of the electro-transmittance was fit to a
modified harmonic oscillator response and the evolution of the parameters as
functions of voltage, position, and temperature are discussed. Resonant
frequencies decrease with distance from the current contacts, indicating that
the resulting delays are intrinsic to the CDW with the strain effectively
flowing from the contact. For a fixed position, the average relaxation time has
a voltage dependence given by tau_0~V^-p, with 1<p<2. The temperature
dependence of the fitting parameters shows that the dynamics are governed by
both the force on the CDW and the CDW current: for a given force and position,
both the relaxation and delay times are inversely proportional to the CDW
current as temperature is varied. The long relaxation and delay times (~ 1 ms)
suggest that the strain response involves the motion of macroscopic objects,
presumably CDW phase dislocation lines.Comment: 36 pages, including 12 figures, submitted to Phys. Rev.
Temperature and Field Dependence of the Energy Gap of MgB2/Pb planar junction
We have constructed MgB2/Pb planar junctions for both temperature and field
dependence studies. Our results show that the small gap is a true bulk property
of MgB2 superconductor, not due to surface effects. The temperature dependence
of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect
of magnetic field on junctions suggests that the energy gap of MgB2 depends
non-linearly on the magnetic field. Moreover, MgB2 has an upper critical field
of 15 T, in agreement with some reported Hc2 from transport measurements.Comment: 5 pages, 5 figures. Submitted to Phys. Rev.
Dynamics of the electro-optic response of charge-density-wave conductors
We have measured the frequency, voltage, and position
dependence of the electro-optic response of the charge-density-wave (CDW)
conductors TaS and blue bronze at T 80 K. The response,
assumed to be proportional to the local strain of the CDW, is characterized
in terms of a relaxation time and a surprisingly low resonant frequency
(i.e. delay); in some cases, there is also evidence for decay of the
response at long times
Thermodynamic properties of the spin-chain compound PrRuO
We have measured the magnetic susceptibility ( and
specific heat (c of single crystals of PrRuO.
The susceptibility indicates a Neel transition at T
K, with an unusually mean-field specific heat anomaly. While indicates that all intrinsic moments order at T, a
Schottky-like anomaly in c suggests that there remains a
small crystal-field splitting between a magnetic and non-magnetic
state of the rare earth ions