The solid helium pressure generation technique

Publisher Summary This chapter focuses on pressure effects in superconductors. The observed effect of pressure on the critical field curve results from a change of superconducting transition temperature, T c , and a change in the molar electronic specific heat constant γ under pressure, and both these effects can be calculated from the observations. There are also closely connected changes in dimensions, elastic constants, and thermal expansion coefficients. The form that the pressure dependence of T c takes under very high pressures is also of current interest, and here there is some controversy as to whether superconductivity can be destroyed by pressure alone without the need for a phase change. Pressure-induced phase changes are found to give rise to abrupt changes in T c, and in a number of cases nonsuperconducting semiconductors are changed to superconducting metals. Quite recently there have been direct measurements of the pressure dependence of the energy gap from tunneling and acoustic attenuation measurements.

Chapter 4 Pressure Effects in Superconductors

The effect of hydrostatic pressures to 3.3 kbar on the superconducting energy gaps in Sn is determined by measuring the longitudinal ultrasonic attenuation for propagation along [110], [100], and [001] directions. The extreme weak-coupling-limit prediction of the BCS theory that the volume dependence of the energy gap at absolute zero is equal to the volume dependence of the transition temperature is experimentally verified for Sn.

A. G. Beattie

Papers

Ultrasonic Determination of the Pressure Dependence of the Superconducting Energy Gap in Tin