Field-driven gapless spin liquid in the spin-1 Kitaev honeycomb model

Ciarán Hickey,Christoph Berke,Panagiotis Peter Stavropoulos,Hae-Young Kee,Simon Trebst

doi:10.1103/physrevresearch.2.023361

Ciarán Hickey, Christoph Berke + Show 3 more

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https://doi.org/10.1103/physrevresearch.2.023361

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Abstract

Recent proposals for spin-1 Kitaev materials, such as honeycomb Ni oxides with heavy elements of Bi and Sb, have shown that these compounds naturally give rise to antiferromagnetic (AFM) Kitaev couplings. Conceptual interest in such AFM Kitaev systems has been sparked by the observation of a transition to a gapless $U(1)$ spin liquid at intermediate field strengths in the AFM spin-1/2 Kitaev model. However, all hitherto known spin-1/2 Kitaev materials exhibit ferromagnetic bond-directional exchanges. Here we discuss the physics of the spin-1 Kitaev model in a magnetic field and show, by extensive numerical analysis, that for AFM couplings it exhibits an extended gapless quantum spin liquid at intermediate field strengths. The close analogy to its spin-1/2 counterpart suggests that this gapless spin liquid is a $U(1)$ spin liquid with a neutral Fermi surface, that gives rise to enhanced thermal transport signatures.

Highlights

Quantum spin liquids (QSL) are disordered phases of matter that exhibit fractionalization of the underlying spin degrees of freedom and an associated emergent gauge structure [1,2,3,4]
We discuss the physics of the spin-1 Kitaev model in a magnetic field and show, by extensive numerical analysis, that for AFM couplings it exhibits an extended gapless quantum spin liquid at intermediate field strengths
By computing a range of static, dynamical, and finite temperature properties we show that the field-driven physics of the spin-1 model bears many striking similarities to the spin-1/2 case

Summary

INTRODUCTION

Quantum spin liquids (QSL) are disordered phases of matter that exhibit fractionalization of the underlying spin degrees of freedom and an associated emergent gauge structure [1,2,3,4]. Dominant Kitaev interactions can be realized, given the right ingredients, in a number of spin-orbit-entangled j = 1/2 Mott insulators [8] These Kitaev materials have been shown to display many properties similar to those theoretically predicted for the Kitaev model, despite the inevitable presence of additional non-Kitaev interactions that drive magnetic order at the lowest temperatures [9,10,11,12,13,14,15,16]. In the absence of an external field, the model has an extensive number of conserved quantities These are given by the plaquette operators Wp = exp [iπ (Six + Syj + Skz + Slx + Smy + Snz )], where Siα is the spin at site i with α the bond not included in the plaquette and with Z2 eigenvalues Wp = ±1.

PHASE DIAGRAM IN FIELD

INTERMEDIATE PHASE

DISCUSSION