Theory of a quantum spin liquid in hydrogen-intercalated honeycomb iridate, H3LiIr2O6

TL;DR

This paper presents a theoretical model for a gapless quantum spin liquid in hydrogen-intercalated honeycomb iridate, explaining experimental observations through layered Kitaev models with interlayer interactions and Majorana excitations.

Contribution

The authors develop a layered Kitaev honeycomb model with interlayer interactions to explain the observed spin liquid behavior in H3LiIr2O6, highlighting the role of Majorana modes and magnetic field effects.

Findings

The model reproduces the specific heat and NMR relaxation rate behaviors.

Layered structure hosts Majorana modes with quartic dispersion.

Magnetic field splits modes into Majorana cones with velocity scaling as B^{3/4}.

Abstract

We propose a theoretical model for a gapless spin liquid phase that may have been observed in a recent experiment on $\mathrm{H_3Li Ir_2 O_6}$. Despite the insulating and non-magnetic nature of the material, the specific heat coefficient $C/T \sim 1/\sqrt{T}$ in zero magnetic field and $C/T \sim T/ B^{3/2}$ with finite magnetic field $B$ have been observed. In addition, the NMR relaxation rate shows $1/(T_1T) \sim (C/T)^2$. Motivated by the fact that the interlayer/in-plane lattice parameters are reduced/elongated by the hydrogen-intercalation of the parent compound $\mathrm{Li_2 Ir O_3}$, we consider four layers of the Kitaev honeycomb lattice model with additional interlayer exchange interactions. It is shown that the resulting spin liquid excitations reside mostly in the top and bottom layers of such a layered structure and possess a quartic dispersion. In an applied magnetic field, each quartic mode is split into four Majorana cones with the velocity $v \sim B^{3/4}$. We suggest that the spin liquid phase in these "defect" layers, placed between different stacking patterns of the honeycomb layers, can explain the major phenomenology of the experiment, which can be taken as evidence that the Kitaev interaction plays the primary role in the formation of a quantum spin liquid in this material.