Critical Point of a Weakly Interacting Two-Dimensional Bose Gas

We study the Berezinskii-Kosterlitz-Thouless transition in a weakly interacting 2D quantum Bose gas using the concept of universality and numerical simulations of the classical |ψ|⁴ model on a lattice. The critical density and chemical potential are given by relations nc0ex0ex=0ex0ex(mT/2π²)ln(ξ²/mU) and μc0ex0ex=0ex0ex(mTU/π²)ln(ξ_μ²/mU), where T is the temperature, m is the mass, and U is the effective interaction. The dimensionless constant ξ0ex0ex=0ex0ex380±3 is very large and thus any quantitative analysis of the experimental data crucially depends on its value. For ξ_μ our result is ξ_μ0ex0ex=0ex0ex13.2±0.4. We also report the study of the quasicondensate correlations at the critical point.