Quantum phase diagram of distorted J1 − J2 Heisenberg S = 1/2 antiferromagnet in honeycomb lattice: a modified spin wave study

Abstract

Using the modified spin wave method, we study the Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for , (2) a magnetically gapped disordered state for , preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for . We also explore the phase diagram of a distorted model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.