Halperin-Saslow modes as the origin of the low temperature anomaly in NiGa2S4NiGa_2S_4

The absence of magnetic long range order in the triangular lattice spin-1 antiferromagnet $NiGa$_2$S$_4$has prompted the search for a novel quantum ground state. In particular, several experiments suggest the presence of a linearly dispersing mode despite no long-range magnetic order. We show that the anomalous low temperature properties of NiGa$_2$S$_4$ can naturally be explained by the formulation developed by Halperin and Saslow where the linearly dispersing Halperin-Saslow mode may exist in the background of frozen spin moments and zero net magnetization. We provide highly non-trivial consistency checks on the existing experimental data and suggest future experiments that can further confirm the existence of the Halperin-Saslow mode. Our results place strong constraints on any microscopic theory of this material.Comment: 5 pages, 1 figur

Spin-orbit coupling in the metallic and spin-liquid phases of Na4Ir3O8

It has recently been proposed that Na4Ir3O8 is a weak Mott insulator at ambient pressure, supporting a three-dimensional spin liquid phase with a spinon Fermi surface. This proposal is consistent with recent experimental findings that the material becomes a metal upon increasing pressure or doping. In this work, we investigate the effect of the spin-orbit coupling arising from 5d Ir moments both in the metallic and spin liquid phases of Na4Ir3O8. The effective Hubbard model in terms of pseudospin j=1/2 Ir states is derived and its consequences to both metallic and spin liquid phases are studied. In particular, the model leads to enhanced Wilson ratio and strong temperature dependence of the Hall coefficient.Comment: 8 pages, 9 figure

Nernst effect and diamagnetism in phase fluctuating superconductors

When a superconductor is warmed above its critical temperature $T_c$, long range order is destroyed by fluctuations in the order parameter. These fluctuations can be probed by measurements of conductivity, diamagnetism, and of the Nernst effect. Here, we study a regime where superconductivity is destroyed by phase fluctuations arising from a dilute liquid of mobile vortices. We find that the Nernst effect and diamagnetic response differ significantly from Gaussian fluctuations -- in particular, a much sharper decay with temperature is obtained. We predict a rapid onset of Nernst signal at a temperature T$_{\rm onset}$ that tracks $T_c$, rather than the pairing temperature. We also predict a close quantitative connection with diamagnetism -- the ratio of magnetization to transverse thermoelectric conductivity $\alpha_{xy}$ reaches a universal value at high temperatures. We interpret Nernst effect measurements on the underdoped cuprates in terms of a dilute vortex liquid over a wide temperature range above $T_c$.Comment: 4 pages, 4 figures; (v2) acknowledgments adde

Topological Order in an Antiferomagnetic Tetratic

We study lattice melting in two dimensional antiferromagnets. We argue that, for strong enough magnetic interactions, single lattice dislocations are prohibitive due to magnetic frustration. This leads to a melting scenario in which a tetratic phase, composed of free dislocation pairs and bound disclinations, separates the solid from the liquid phases. We demonstrate this phase numerically in a system of hard spheres confined between parallel plates, where spins are represented by the the heights of the spheres. We find that, in the tetratic phase, the spins are as antiferromagnetically ordered as allowed by their spatial configuration