Variational study of triangular lattice spin-1/2 model with ring exchanges and spin liquid state in \kappa-(ET)_2 Cu_2 (CN)_3

TL;DR

This paper investigates a triangular lattice spin-1/2 model with ring exchanges, proposing a Gutzwiller-projected Fermi sea spin liquid as a candidate for the nonmagnetic insulating phase in -(ET)_2 Cu_2 (CN)_3, supported by variational energetics.

Contribution

It introduces a variational approach to identify a spin liquid state with a spinon Fermi surface in a triangular lattice model with ring exchanges, linking it to experimental observations.

Findings

Gutzwiller-projected Fermi sea state is energetically favorable in certain ring exchange regimes.

Proposes the spinon Fermi surface spin liquid as a candidate for the observed nonmagnetic insulator.

Provides experimental predictions consistent with the proposed spin liquid state.

Abstract

We study triangular lattice spin-1/2 system with antiferromagnetic Heisenberg and ring exchanges using variational approach focusing on possible realization of spin liquid states. Trial spin liquid wave functions are obtained by Gutzwiller projection of fermionic mean field states and their energetics is compared against magnetically ordered trial states. We find that in a range of the ring exchange coupling upon destroying the antiferromagnetic order, the best such spin liquid state is essentially a Gutzwiller-projected Fermi sea state. We propose this spin liquid with spinon Fermi surface as a candidate for the nonmagnetic insulating phase observed in the organic compound \kappa-(ET)_2 Cu_2 (CN)_3, and describe some experimental consequences of this proposal.