VERY SENSITIVE MICROCALORIMETRY TECHNIQUE FOR MEASURING SPECIFIC-HEATOF MU-G SINGLE-CRYSTALS

A microcalorimetry technique allowing one to measure the specific heat of bulk single crystals of a mass typically 10 mu g, with a relative resolution Delta c/c of 10(-4) is presented. The well known ac steady state technique is employed. The sample holder is a polymer membrane w ith lithographically patterned thermometer and heaters made out of met allic thin films. The diameter of the useful area is 0.6 mm and the sp ecific heat of the addendum is 1.5 mu J/K at 100 K. The sample is ther mally coupled to the membrane through a gold thin film sputtered on it s surface. The thermal coupling time constant of the sample is similar to 5 ms, allowing to work at frequencies of 10 Hz. The method was app lied to small single crystals of YBCO, providing the specific heat jum p at the superconducting transition with a relative resolution of 10(- 2) and a precision of 10(-1). The method is optimized at the temperatu re range 40-160 K, but can easily be modified for lower temperatures. (C) 1997 American Institute of Physics.