Ground-state phase diagram and magnetic properties of a tetramerized pin-1/2 J(1)-J(2) model: BEC of bound magnons and absence of the transverse magnetization

[摘要] We study the ground state and the magnetization process of a spin-1/2 J(1)-J(2) model with a plaquette structure by using various methods. For small interplaquette interaction, this model is expected to have a spin gap and we computed the first and the second excitation energies. If the gap of the lowest excitation closes, the corresponding particle condenses to form magnetic orders. By analyzing the quintet gap and magnetic interactions among the quintet excitations, we find a spin-nematic phase around J(1)/J(2) similar to-2 due to the strong frustration and the quantum effect. When high magnetic moment is applied, not the spin-1 excitations but the spin-2 ones soften and dictate the magnetization process. We apply a mean-field approximation to the effective Hamiltonian to find three different types of phases (a conventional BEC phase, striped supersolid phases, and a 1/2 plateau). Unlike the BEC in spin-dimer systems, this BEC phase is not accompanied by transverse magnetization. Possible connection to the recently discovered spin-gap compound (CuCl)LaNb2O7 is discussed.

[发布日期] 2007-12-01

[关键词] FRUSTRATED SQUARE-LATTICE;QUANTUM HEISENBERG-ANTIFERROMAGNET;SHASTRY-SUTHERLAND MODEL;DIMER ORDER;SRCU2(BO3)(2);(CUCL)LANB2O7;TRANSITIONS;SUPERSOLIDS;EXCITATION;SPECTRUM