Spin liquid versus long range magnetic order in the frustrated   body-centered tetragonal lattice
  The quantum Heisenberg model is studied in the geometrically frustrated body-centered tetragonal lattice(BCT lattice) with antiferromagnetic interlayer coupling J1 and intralayer first and second neighbor coupling J2 and J3. We introduce a variational method: each interaction term can be decoupled partially in the purely magnetic Weiss and in the spin-liquid (SL) mean-field channels. We find that the most stable variational solutions correspond to the three different possible long range magnetic orders that are respectively governed by J1, J2, and J3. We characterize three different purely SL non-magnetic solutions that are variationally the second most stable states after the purely magnetic ones. This suggests that quantum fluctuations induced by the frustration between J1-J2-J3 coupling should destroy magnetic orders and stabilize the formation of SL in large areas of parameters. The SL solution governed by J1 breaks the lattice translation symmetry. This Modulated SL is associated to a commensurate ordering wave vector (1,1,1). We discuss the relevance of our results for heavy fermion Uru2Si2 and cuprate superconductors that have a BCT lattice structure. Also, the general variational method introduced here can be applied to any other system where interaction terms can be decoupled in two different mean-field channels. 
S\'ebastien Burdin, Christopher Thomas, Catherine P\'epin, Alvaro   Ferraz, Claudine Lacroix
cond-mat.str-el