Pressure relaxations in solid helium-4

Abstract

Recently, we have used a torsional oscillator to observe supersolid fractions up to 20 % in confined helium samples. To characterize these constrained samples further we measure the solid pressure in a narrow pancake cell. We can fit the pressure data well to the functional form p p0 + aT2 + bT4. The term proportional to the temperature square indicates that crystalline disorder exists in the solid samples. The disorder term in the pressure can be reduced by sample annealing, i.e. holding the sample at a temperature close to the melting temperature. Secondly, when we hold the temperature fixed for an extended period of time, the pressure relaxes in a way similar to an exponential decay. The characteristic time constant of decay rises at low temperatures. The low temperature relaxations also reduce the disorder term in the pressure equation. © 2009 IOP Publishing Ltd.