Survival of itinerant excitations and quantum spin state transitions in YbMgGaO4 with chemical disorder

Xin Rao ,Haidong Zhou ,Tomoya Asaba ,Zhiling Dun ,X Y Yue ,Wangsheng Chu ,Jinguang Cheng ,N N Wang,Xinguo Zhao ,Jun Zhao ,Qing Huang ,L Li,L Chen,Yonghao Gao ,G Hussain,N Li,Eun Sang Choi ,Yao Shen ,G Chen,Xiaofan Sun

doi:10.1038/s41467-021-25247-6

Abstract

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO4, a triangular lattice antiferromagnet with effective spin-1/2 Yb3+ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO4 is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual κ0/T term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO4. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO4.

Highlights

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state
Based on the above comparisons, it is obvious that in zero field the κa behaves as T2 at 200 mK < T < 600 mK with a residual thermal conductivity of κ0/T = 0.0058 W K−2 m−1 and thereafter, the slope change leads to a smaller κ0/T = 0.0016 W K−2 m−1 at T < 200 mK
By comparing YMGO’s phase diagram with B // a to that of Ba3CoSb2O9, we propose a phase I as the canted 120° spin structure, phase II as the UUD phase, and phase III as the oblique phase

Summary

Introduction

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. (whether there is a small gap in this QSL candidate is still under debate); the LiZn2Mo3O8 with breathing kagome lattice has Li+/Zn2+site mixture[10]; the Ca10Cr7O28 with bilayer kagome lattice has disorder among the two different Cr3+positions[11,12], and the H3LiIr2O6 with honeycomb lattice has mobile Hydrogen ions[13] This so-called random-singlet (RS) or valence bond glass state[14,15,16,17,18,19,20,21] seriously prompts re-consideration of the intrinsic magnetic ground state of them: whether they are true gapless QSL or just spin liquid-like?

Methods

Results

Conclusion