Dielectric constant measurements of solid ⁴He

Careful measurements of the dielectric properties of solid ⁴He have been carried out down to 35 mK, considerably lower than the temperature range of previous studies. The sample was prepared from high purity gas with ³He concentrations of the order of 200 ppb and were formed by the blocked capillary method. The molar volume of the sample was 20.30 cm ³. The dielectric constant of the samples was found to be independent of temperature down to 120 mK before showing a continuous increase with decreasing temperature and saturating below 50 mK. The total increase in ε is 2 parts in 10 ^-5. The temperature dependence of ε mimics the increase in the resonant frequency found in the torsional oscillator studies and also the increase found in the shear modulus measurements.