Course 7: Mott Insulators, Spin Liquids and Quantum Disordered Superconductivity

Matthew P. A. Fisher

George Jackeli

Naoto Nagaosa

Ziyang Meng, Thomas C. Lang, Stefan Weßel +2 more

Abstract In recent years, an increasing number of systems displaying exotic quantum states like unconventional superconductivity, quantum spin‐liquids, or topological states were experimentally found. Here we summarize findings in quantum Monte Carlo simulations of correlated electrons on a honeycomb lattice, the structure of graphene, that revealed an unexpected spin‐liquid emerging between a state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. Moreover, we found that this quantum‐disordered state is a resonating valence‐bond (RVB) liquid, akin to the one proposed for high temperature superconductors. This was the first unbiased determination of a RVB‐liquid in an electronic system.

Joseph C. Szabo, Kyungmin Lee, Vidya Madhavan +1 more

We elucidate the mechanism by which a Mott insulator transforms into a non-Fermi liquid metal upon increasing disorder at half filling. By correlating maps of the local density of states, the local magnetization, and the local bond conductivity, we find a collapse of the Mott gap toward a V-shaped pseudogapped density of states that occurs concomitantly with the decrease of magnetism around the highly disordered sites but an increase of bond conductivity. These metallic regions percolate to form an emergent non-Fermi liquid phase with a conductivity that increases with temperature. Bond conductivity measured via local microwave impedance combined with charge and spin local spectroscopies are ideal tools to corroborate our predictions.

Philip Phillips, Luke Yeo, Edwin W. Huang