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

TL;DR

This paper investigates wetting phase transitions in binary Bose-Einstein condensates at optical walls, revealing that realistic potentials can induce both first-order and critical wetting, with implications for experimental control via Feshbach resonances.

Contribution

It demonstrates that finite-range optical wall potentials can lead to both first-order and critical wetting transitions in binary BEC mixtures, extending previous hard-wall boundary results.

Findings

First-order wetting occurs with realistic exponential potentials.

Critical wetting can also occur under certain conditions.

Exact phase boundary results are derived for the hard-wall limit.

Abstract

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 $\lambda$ 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 the interspecies scattering length $a_{12}$ using Feshbach resonances. In the hard-wall limit, $\lambda \rightarrow 0$, exact results are derived for the prewetting and first-order wetting phase boundaries.