Ground state of two-dimensional Yukawa bosons: Applications to vortex melting

Using variational and diffusion Monte Carlo techniques, we investigate the ground state of bosons interacting in the continuum through a repulsive modified-Bessel-function potential, εK0(r/σ), in two dimensions. This is a simplified model for flux lines in high-Tc superconductors. A pair-product trial function is first optimized so that its variational energy is very near the ground-state energy, then the diffusion Monte Carlo technqiue is used to calculate the exact ground-state energy. As a function of mass and density, we calculate the region of stability of the solid for densities greater than 0.01/σ2. The quantum crystal melts at high density, due to the potential's soft core, and at low density, due to the exponentially weak interaction. Bosons with Latin small letter h with stroke2/2mσ2ε>0.09 do not crystallize at any density. Within the flux model, we compute the flux-line phase diagram for Bi2Sr2CaCu2O8. Pair-correlation functions, structure factors, and Lindemann ratios at melting are also comptued.