A very sensitive microcalorimetry technique for measuring specific heat of μg single crystals

Abstract

A microcalorimetry technique allowing one to measure the specific heat of bulk single crystals of a mass typically 10 μ g , with a relative resolution Δc/c of 10 −4 is presented. The well known ac steady state technique is employed. The sample holder is a polymer membrane with lithographically patterned thermometer and heaters made out of metallic thin films. The diameter of the useful area is 0.6 mm and the specific heat of the addendum is 1.5 μ J / K at 100 K. The sample is thermally coupled to the membrane through a goldthin filmsputtered on its surface. The thermal coupling time constant of the sample is ∼5 ms , allowing to work at frequencies of 10 Hz. The method was applied to small single crystals of YBCO, providing the specific heat jump at the superconducting transition with a relative resolution of 10 −2 and a precision of 10 −1 . The method is optimized at the temperature range 40–160 K, but can easily be modified for lower temperatures.