Two-dimensional quantum spin liquid with S=1/2 spins interacting with acoustic phonons

The spin density of states of a two-dimensional antiferromagnet in magnetic field having spins-1/2 and interacting with acoustic phonons is investigated in the nonadiabatic approximation using the quantum Monte Carlo method. It is found the gap energy A in the single particle spin excitations spectrum closes at magnetic field Delta similar or equal to H-c, W-ph < W-s and Delta similar or equal to (1/2)H-c, W-ph > W-s, where W-ph and W-s are the bandwidths of phonon and spin excitations in antiferromagnet. (C) 2004 Elsevier B.V All rights reserved.