New behavior for the density dependence of vacancy formation and mobility in bccHe3at high molar volumes

Abstract

Recent careful measurements of the nuclear spin-lattice relaxation times are reported for bcc $^{3}\mathrm{He}$ at low temperatures and for densities close to the minimum of the melting curve. The results indicate an unexpected density dependence for the formation energy $\ensuremath{\Phi}$ and the mobility $\ensuremath{\mu}$ of delocalized vacancies in bcc $^{3}\mathrm{He}$. For molar volumes ${V}_{m}$ close to the maximum value ${V}_{\mathrm{mc}}$ for the solid phase (near the melting curve minimum), we find that $\ensuremath{\Phi}({V}_{m})$ decreases continuously towards zero as ${V}_{\mathrm{mc}}$ is approached and that $\ensuremath{\mu}$ changes by seven orders of magnitude over the same range of density. Both $\ensuremath{\Phi}({V}_{m})$ and ${log}_{10}\ensuremath{\mu}({V}_{m})$ vary approximately as ${({V}_{\mathrm{mc}}\ensuremath{-}{V}_{m})}^{\frac{1}{2}}$. These results point to new effects as the volume ${V}_{\mathrm{mc}}$ is approached and can be understood qualitatively in terms of density wave fluctuations associated with delocalized vacancies at the highest molar volumes.