# Spinon Fermi surface in a cluster Mott insulator model on a triangular lattice and possible application to 1T-TaS$_2$

## TL;DR

This paper models 1T-TaS2 as a spin liquid with a spinon Fermi surface on a triangular lattice, using a derived XXZ model and DMRG simulations, suggesting experimental detection methods.

## Contribution

It introduces a novel effective spin model for 1T-TaS2 and demonstrates the existence of a gapless spin liquid with a spinon Fermi surface through large-scale simulations.

## Key findings

- Identification of a gapless spin liquid phase with spinon Fermi surface
- Static spin structure factor peaks on the '2k_F' surface
- Proposal for experimental detection of the spinon Fermi surface

## Abstract

1T-TaS$_2$ is a cluster Mott insulator on the triangular lattice with 13 Ta atoms forming a star of David cluster as the unit cell. We derive a two dimensional XXZ spin-1/2 model with four-spin ring exchange term to describe the effective low energy physics of a monolayer 1T-TaS$_2$, where the effective spin-1/2 degrees of freedom arises from the Kramers degenerate spin-orbital states on each star of David. A large scale density matrix renormalization group simulation is further performed on this effective model and we find a gapless spin liquid phase with spinon Fermi surface at moderate to large strength region of four-spin ring exchange term. All peaks in the static spin structure factor are found to be located on the "$2k_F$" surface of half-filled spinon on the triangular lattice. Experiments to detect the spinon Fermi surface phase in 1T-TaS$_2$ are discussed.