Charge-induced instability and macroscopic quantum nucleation phenomena at the crystal 4He facet

TL;DR

This paper investigates charge-induced instability phenomena at the smooth, well-faceted surface of helium-4 crystals, revealing a metastable state and quantum nucleation effects below the roughening transition temperature.

Contribution

It provides the first analysis of charge-induced instability at the well-faceted helium-4 crystal surface, highlighting the metastable state and quantum tunneling effects.

Findings

Below critical electric field, the crystal surface remains stable.

Above critical field, a metastable state forms with a potential barrier.

Instability onset involves thermal activation or quantum tunneling depending on temperature.

Abstract

An existence of the charge-induced instability is well known for the 4He crystal surface in the rough state. Much less is known about charge-induced instability at the 4He 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 same as for the rough surface, the crystal faceting remains absolutely stable. Above the critical field, unlike absolutely unstable state of the rough surface, the crystal facet crosses over to the metastable state separated from new 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.