Two spin liquid phases in the spatially anisotropic triangular Heisenberg model

TL;DR

This study identifies two distinct spin liquid phases in the anisotropic triangular Heisenberg model, revealing their properties and stability regions, and supports their relevance to real materials through quantum Monte Carlo simulations.

Contribution

The paper provides the first detailed quantum Monte Carlo analysis revealing two separate spin liquid phases in the anisotropic triangular Heisenberg model, with specific stability regions and properties.

Findings

First spin liquid phase is gapless and fractionalized for J'/J < 0.65.

Second spin liquid phase has a small spin gap and is stable for 0.65 < J'/J < 0.8.

No evidence of broken translation or reflection symmetry in either phase.

Abstract

The quantum spin-1/2 antiferromagnetic Heisenberg model on a two dimensional triangular lattice geometry with spatial anisotropy is relevant to describe materials like ${\rm Cs_2 Cu Cl_4}$ and organic compounds like {$\kappa$-(ET)$_2$Cu$_2$(CN)$_3$}. The strength of the spatial anisotropy can increase quantum fluctuations and can destabilize the magnetically ordered state leading to non conventional spin liquid phases. In order to understand these intriguing phenomena, quantum Monte Carlo methods are used to study this model system as a function of the anisotropic strength, represented by the ratio $J'/J$ between the intra-chain nearest neighbor coupling $J$ and the inter-chain one $J'$. We have found evidence of two spin liquid regions. The first one is stable for small values of the coupling $J'/J \alt 0.65$, and appears gapless and fractionalized, whereas the second one is a more conventional spin liquid with a small spin gap and is energetically favored in the region $0.65\alt J'/J \alt 0.8$. We have also shown that in both spin liquid phases there is no evidence of broken translation symmetry with dimer or spin-Peirls order or any broken spatial reflection symmetry of the lattice. The various phases are in good agreement with the experimental findings, thus supporting the existence of spin liquid phases in two dimensional quantum spin-1/2 systems.