Path-integral simulation of the superfluid transition in two-dimensional He4

The superfluid transition in a two-dimensional He4 system has been studied using computational-path-integral methods. Thermodynamic and structural properties, the single-particle momentum distribution, the one-particle off-diagonal density matrix (or order-parameter correlation function), the momentum correlations, the superfluid density (based on the winding-number distribution) and the vorticity correlation function were calculated for temperatures above and below the superfluid transition for a film density of 0.0432 A-2 (which corresponds to zero pressure in the ground state). The order-parameter correlation function shows an algebraic decay in good agreement with spin-wave theory. An indirect estimate based on an analysis of finite-size effects using the Kosterlitz-Thouless recursion relations leads to a vortex diameter of 3.70.4 A, a vortex core energy of 2.70.2 K and a critical temperature of 0.720.02 K.