Bose-Einstein condensation in two dimensions: A quantum Monte Carlo study

A path-integral quantum Monte Carlo method is used to calculate finite temp erature properties of up to 1000 hard-core bosons in a two-dimensional isot ropic harmonic-oscillator potential. If the interatomic repulsions are suff iciently short range, an abrupt increase in the condensate fraction and a h ump in the specific heat occur close to the critical temperature of ideal b osons. The critical temperature and the condensate fraction are in general lowered by an increase in the hard-core radius a. If a is decreased below a certain level, the condensate fraction becomes indistinguishable from the corresponding value of the ideal bosons. For up to 1000 particles. this occ urs when ln(-1)(1/na(2))less than or similar to 0.1, where n is the average particle density. [S1050-2947(98)04812-4].