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Paper   IPM / Physic / 14617
School of Physics
  Title:   Quantum phase diagram of distorted J 1-J 2 Heisenberg S=1/2 antiferromagnet in honeycomb lattice: a modified spin wave study
1.  E. Ghorbani
2.  F. Shahbazi
3.  H. Mosadeq
  Status:   Published
  Journal: J. Physics: Condens. Matter
  No.:  40
  Vol.:  28
  Year:  2016
  Pages:   406001 (11pp)
  Supported by:  IPM
Using the modified spin wave method, we study the ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn003.gif] J1J2 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 ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn004.gif] α=J2/J1 : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn005.gif] 0\leqslant α <~0.207 , (2) a magnetically gapped disordered state for ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn006.gif] 0.207 <~α <~0.369 , 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 ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn007.gif] 0.396 <~α\leqslant 1 . We also explore the phase diagram of a distorted ##IMG## [http://ej.iop.org/images/0953-8984/28/40/406001/cmaa34e4ieqn008.gif] J1J2 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.

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