Theory of a Competitive Spin Liquid State for Weak Mott Insulators on the Triangular Lattice

Abstract

We propose a novel quantum spin liquid state that can explain many of the intriguing experimental properties of the low-temperature phase of the organic spin liquid candidate materials κ-(BEDT-TTF)[subscript 2] Cu[subscript 2](CN)[subscript 3] and EtMe[subscript 3] Sb[Pd(dmit)[subscript 2]][subscript 2]. This state of paired fermionic spinons preserves all symmetries of the system, and it has a gapless excitation spectrum with quadratic bands that touch at momentum k⃗ = 0. This quadratic band touching is protected by symmetries. Using variational Monte Carlo techniques, we show that this state has highly competitive energy in the triangular lattice Heisenberg model supplemented with a realistically large ring-exchange term.