title: Ising transition in the two-dimensional quantum J1-J2 Heisenberg model.
abstract: We study the thermodynamics of the spin-S two-dimensional quantum Heisenberg antiferromagnet on the square lattice with nearest (J1) and next-nearest (J2) neighbor couplings in its collinear phase (J(2)/J(1)>0.5), using the pure-quantum self-consistent harmonic approximation. Our results show the persistence of a finite-temperature Ising phase transition for every value of the spin, provided that the ratio J(2)/J(1) is greater than a critical value corresponding to the onset of collinear long-range order at zero temperature. We also calculate the spin and temperature dependence of the collinear susceptibility and correlation length, and we discuss our results in light of the experiments on Li2VOSiO4 and related compounds.
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Capriotti
authors.forename: Andrea
authors.initials: A
authors.lastname: Fubini
authors.forename: Tommaso
authors.initials: T
authors.lastname: Roscilde
authors.forename: Valerio
authors.initials: V
authors.lastname: Tognetti