Gapless quantum spin liquid in a honeycomb $\Gamma$ magnet

TL;DR

This paper investigates the ground state of the honeycomb Gamma model, revealing a wide gapless quantum spin liquid phase characterized by disordered, gapless, and entanglement properties, despite perturbations favoring magnetic order.

Contribution

It demonstrates the existence of a gapless quantum spin liquid in the honeycomb Gamma model, challenging previous assumptions of magnetic ordering in this system.

Findings

Identification of a wide disordered phase including the Gamma limit

Evidence of a gapless QSL with vanishing energy gap and spectrum collapse

Logarithmic entanglement entropy scaling indicating criticality

Abstract

A family of spin-orbit coupled honeycomb Mott insulators offers a playground to search for quantum spin liquids (QSLs) via bond-dependent interactions. In candidate materials, a symmetric off-diagonal $\Gamma$ term, close cousin of Kitaev interaction, has emerged as another source of frustration that is essential for complete understanding of these systems. However, the ground state of honeycomb $\Gamma$ model remains elusive, with a suggested zigzag magnetic order. Here we attempt to resolve the puzzle by perturbing the $\Gamma$ region with a staggered Heisenberg interaction which favours the zigzag ordering. Despite such favour, we find a wide disordered region inclusive of the $\Gamma$ limit in the phase diagram. Further, this phase exhibits a vanishing energy gap, a collapse of excitation spectrum, and a logarithmic entanglement entropy scaling on long cylinders, indicating a gapless QSL. Other quantities such as plaquette-plaquette correlation are also discussed.