Charge-induced instability and macroscopic quantum nucleation phenomena at a crystalline4He facet

Abstract

The existence of a charge-induced instability is well known for the ${}^{4}$He crystal surface in the rough state. Much less is known about the charge-induced instability at the ${}^{4}$He crystal surface in the smooth well-faceted state below the roughening transition temperature. To meet the lack, we examine here the latter case. As long as the electric field normal to the crystal facet is below the critical value the same as for the rough surface, the crystal faceting remains absolutely stable. Above the critical field, unlike the absolutely unstable state of the rough surface, the crystal facet crosses over to the metastable state separated from the crushed state with a potential barrier proportional to the square of the linear facet step energy. The onset and development of the instability at the charged crystal facet has much in common with the nucleation kinetics of first-order phase transitions. Depending on the temperature, the electric breaking strength is determined either by thermal activation at high temperatures or by quantum tunneling at sufficiently low temperatures.