First-order transition in frustrated quantum antiferromagnets

A two-dimensional frustrated quantum Heisenberg model with first-, second- (diagonal), and third-neighbor couplings (J1-J2-J3 model) is studied near the phase boundary of the antiferromagnetic (π,π) phase. It is shown that quantum corrections remove accidental classical degeneracy and ensure a nonzero hysteresis width for the J3=0 transition between commensurate (π,π) and (π,0) phases, so that finite J3 is necessary to produce a continuous transition through the intermediate disordered phase.