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 adsorbed at an optical wall can undergo a wetting phase transition in which one of the species excludes the other from contact with the wall. Interestingly, while hard-wall boundary conditions entail the wetting transition to be of first order, using Gross-Pitaevskii theory we show that first-order wetting as well as critical wetting can occur when a realistic exponential optical wall potential (evanescent wave) with a finite turn-on length. 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 the interspecies scattering length a(12) using Feshbach resonances. In the hard-wall limit, lambda -> 0, exact results are derived for the prewetting and first-order wetting phase boundaries.