KOSTERLITZ-THOULESS TRANSITION IN A DILUTE BOSE-GAS

We study the two-dimensional dilute Bose gas using the ladder or T-matrix approximation, which is valid if ln(1/na2) >> 1, and show that this approximation can describe also the critical region of the Kosterlitz-Thouless transition accurately. In particular, we consider the superfluid properties of the gas and find that the superfluid density shows the square-root cusp together with the universal jump at the critical temperature. The theory is applied to spin-polarized atomic hydrogen adsorbed on a superfluid helium film, since this appears to be one of the most promising experimental setups to achieve the Kosterlitz-Thouless transition in a weakly interacting Bose gas.