1301.3107 (Gang Chen et al.)

Anomalous enhancement of the Wilson ratio in a quantum spin liquid:
Na$_4$Ir$_3$O$_8$    [PDF]

Gang Chen, Yong Baek Kim

We present a theory for recent experiments on the quantum spin liquid candidate material Na$_4$Ir$_3$O$_8$. In particular, we provide an explanation of large enhancement and high sensitivity of the Wilson ratio and magnetic susceptibility across the metal-insulator transition (MIT). We consider an extended Hubbard model on a hyperkagome lattice, which incorporates atomic spin-orbit coupling (SOC) and multi-orbital interactions of Ir 5d electrons. We analyze the model near MIT and study thermodynamic properties across the MIT. We propose that the system on the insulating side is a U(1) quantum spin liquid with spinon Fermi surfaces. We further show that, the magnetic susceptibility experiences multiple enhancements from the strong SOC, reduced bandwidth and onsite spin-orbital exchange, while the heat capacity does not. Understanding of the currently available experiments and suggestions for future experiments are discussed.

View original: http://arxiv.org/abs/1301.3107