Flux flow of Abrikosov-Josephson vortices along grain boundaries in high-temperature superconductors.

Low-angle grain boundaries (GBs) in superconductors exhibit intermediate Abrikosov vortices with Josephson cores, whose length l along GB is smaller than the London penetration depth, but larger than the coherence length. We found an exact solution for a periodic vortex structure moving along GBs in a magnetic field H and calculated the flux flow resistivity R(F)(H), and the nonlinear voltage-current characteristics. The predicted R(F)(H) dependence describes well our experimental data on 7 unirradiated and irradiated YBa(2)Cu(3)O(7) bicrystals, from which the core size l(T), and the intrinsic depairing density J(b)(T) on nanoscales of a few GB dislocations were measured for the first time. The observed J(b)(T) = J(b0)(1-T/T(c))(2) indicates a significant order parameter suppression on GB.

Simultaneous acquisition of photoacoustic and fluorescence spectra at high sensitivity from powdered samples at variable temperature.

An apparatus has been built for simultaneous high-sensitivity photoacoustic and fluorescence studies at temperatures from 4 to 295 K that uses a pulsed tunable dye laser as the excitation light source. A powdered sample, pressed into the pellet, is attached to a coiled fused-silica rod that provides thermal isolation from and good acoustic contact to an ambient temperature acoustic detector. The surface of the rod is roughened, thereby eliminating acoustic interference arising from scattered excitation light. As a test of the apparatus, the absorption spectrum of the (4)F(9/2) state of Nd(3+) in A-phase Nd(2)O(3) powder, dispersed in a KBr pellet, was recorded simultaneously by means of photoacoustic and fluorescence excitation spectroscopies.