Ground State of a Spin System with Two- and Four-spin Exchange Interactions on the Triangular Lattice

We study a spin system with both two- and four-spin exchange interactions on the triangular lattice as a possible model for the nuclear magnetism of solid $^3$He layers adsorbed on grafoil. The ground state is analyzed by the use of the mean-field approximation. It is shown that the four-sublattice state is favored by introduction of the four-spin exchange interaction. A possible phase transition at a finite temperature into a phase with the scalar chirality is predicted. Application of a magnetic field is shown to cause a variety of phase transitions.Comment: 5 pages, Revte

Nematic order in square lattice frustrated ferromagnets

We present a new scenario for the breakdown of ferromagnetic order in a two-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. In this, dynamical effects lead to the formation of two-magnon bound states, which undergo Bose-Einstein condensation, giving rise to bond-centered nematic order. This scenario is explored in some detail for an extended Heisenberg model on a square lattice. In particular, we present numerical evidence confirming the existence of a state with d-wave nematic correlations but no long range magnetic order, lying between the saturated ferromagnetic and collinear antiferromagnetic phases of the ferromagnetic J1-J2 model. We argue by continuity of spectra that this phase is also present in a model with 4-spin cyclic exchange.Comment: 5 pages latex + 5 eps figures, accpeted for publication in Phys. Rev. Let

NMR relaxation rate and dynamical structure factors in nematic and multipolar liquids of frustrated spin chains under magnetic fields

Recently, it has been shown that spin nematic (quadrupolar) or higher multipolar correlation functions exhibit a quasi long-range order in the wide region of the field-induced Tomonaga-Luttinger-liquid (TLL) phase in spin-1/2 zigzag chains. In this paper, we point out that the temperature dependence of the NMR relaxation rate 1/T_1 in these multipolar TLLs is qualitatively different from that in more conventional TLLs of one-dimensional quantum magnets (e.g., the spin-1/2 Heisenberg chain); 1/T_1 decreases with lowering temperature in multipolar TLL. We also discuss low-energy features in spin dynamical structure factors which are characteristic of the multipolar TLL phases.Comment: 4+epsilon pages, 2 figures, published versio

Finite temperature Mott transition in Hubbard model on anisotropic triangular lattice

We investigate the Hubbard model on the anisotropic triangular lattice by means of the cellular dynamical mean field theory. The phase diagram determined in the Hubbard interaction versus temperature plane shows novel reentrant behavior in the Mott transition due to the competition between Fermi-liquid formation and magnetic correlations under geometrical frustration. We demonstrate that the reentrant behavior is characteristic of the Mott transition with intermediate geometrical frustration and indeed consistent with recent experimental results of organic materials.Comment: 5 pages, 6 figure