Critical wetting, first-order wetting and prewetting phase transitions in binary mixtures of Bose-Einstein condensates

摘要

An ultralow-temperature binary mixture of Bose-Einstein condensates adsorbedat an optical wall can undergo a wetting phase transition in which one of thespecies excludes the other from contact with the wall. Interestingly, whilehard-wall boundary conditions entail the wetting transition to be of firstorder, using Gross-Pitaevskii theory we show that first-order wetting as wellas critical wetting can occur when a realistic exponential optical wallpotential (evanescent wave) with a finite turn-on length $\lambda$ is assumed.The relevant surface excess energies are computed in an expansion in$\lambda/\xi_i$, where $\xi_i$ is the healing length of condensate $i$.Experimentally, the wetting transition may best be approached by varying theinterspecies scattering length $a_{12}$ using Feshbach resonances. In thehard-wall limit, $\lambda \rightarrow 0$, exact results are derived for theprewetting and first-order wetting phase boundaries.