Limit of Stability of Crystalline Helium

摘要

The mobility of a vacancy in a crystal at the absolute zero of temperature is investigated. In this minimum energy configuration movement of the vacancy to an adjacent lattice site occurs by tunneling, the rate being determined by an approximation in which the barrier and adjacent potential wells are formed by nearest neighbor interactions only. There is found a critical volume at which the vacancy begins to move rapidly through the barrier. Identifying this increased mobility with the beginning of the melt, a criterion for stability of the crystalline structure is deduced. On applying this criterion to helium at the absolute zero, general agreement with experimental critical volumes is obtained.