Andreev reflection spectroscopy of high-T-c superconductors at high pressures

Andreev reflection effect has allowed one to determine the anisotropy of en ergy gap Delta(phi) in high-T-c superconductors and its pressure response. The values of Delta(phi) in the ab plane are found to be Delta(max) = 42 mV , Delta(max) = 19.5 mV ((BiPb)2223 phase, T-c = 110 K. dT(c)/d P = 0.16 K/k bar); Delta(max) = 44 mV, Delta(min) = 12.5 mV, dT(c)/d P = 0.28 K/kbar (Hg Pb)2223 phase, T-c = 133 K). A rise in r = 2 Delta(max)/kT(c) with pressure is found: for Bi2223 dr/dP approximate to 0.03 kbar(-1), and for Hg2223 dr /dP approximate to 0.06 kbar(-1). (C) 1999 Published by Elsevier Science B. V. All rights reserved.