Visual Observations of Disordered Solid Helium

Abstract

We report visual observations of solid helium from experiments conducted near the melting curve in the vicinity of 1.65 K. Given the recent interest in solid helium and the possible role of disorder, these observations conducted in 1974, but never reported in the literature, may be of some current interest. We show an image and sketches from the laboratory notebook from 1974 that document that solid helium can be milky (i.e. cloudy) in appearance and that this behavior persists for lengths of time longer than thirty minutes. We also report differences in the appearance of hcp and bcc solid ⁴He, with the bcc appearing more lumpy and disturbed by cracks, but also cloudy. These observations suggest that disorder, at least on the length scale of visible light, can be present in solid ⁴He and can persist for extended periods of time near the melting curve in the vicinity of 1.65 K.