Multiple quantum phase transitions of different nature in the topological kagome magnet Co3Sn2\u2212xInxS2

Z Guguchia,C Mielke,M Z Hasan,R Khasanov,H Luetkens,T Neupert,C N Wang,A Amato,I Belopolski,S Jia,H Zhou,S S Tsirkin,T A Cochran,S.-S Zhang,J.-X Yin

doi:10.1038/s41535-021-00352-3

Abstract

The exploration of topological electronic phases that result from strong electronic correlations is a frontier in condensed matter physics. One class of systems that is currently emerging as a platform for such studies are so-called kagome magnets based on transition metals. Using muon spin-rotation, we explore magnetic correlations in the kagome magnet Co3Sn2−xInxS2 as a function of In-doping, providing putative evidence for an intriguing incommensurate helimagnetic (HM) state. Our results show that, while the undoped sample exhibits an out-of-plane ferromagnetic (FM) ground state, at 5% of In-doping the system enters a state in which FM and in-plane antiferromagnetic (AFM) phases coexist. At higher doping, a HM state emerges and becomes dominant at the critical doping level of only xcr,1 ≃ 0.3. This indicates a zero temperature first order quantum phase transition from the FM, through a mixed state, to a helical phase at xcr,1. In addition, at xcr,2 ≃ 1, a zero temperature second order phase transition from helical to paramagnetic phase is observed, evidencing a HM quantum critical point (QCP) in the phase diagram of the topological magnet Co3Sn2−xInxS2. The observed diversity of interactions in the magnetic kagome lattice drives non-monotonous variations of the topological Hall response of this system.

Highlights

Layered systems featuring a Kagome lattice provide an ideal playground for discovering and understanding the topological electronic states in strongly correlated materials[1,2,3,4,5,6,7,8,9,10,11,12,13,14]
The HM structure in this system may be interpreted by a competition between dominant Heisenberg-type (FM and AFM) interactions and a weaker antisymmetric Dzyaloshinskii–Moriya (DM) interaction. It seems that In-doping affects the competing interactions such that it promotes the HM state
We note that hydrostatic pressure causes a suppression of both FM and AFM states[41], but a pressure as high as 20 GPa is needed at which both orders are suppressed simultaneously

Summary

Introduction

Layered systems featuring a Kagome lattice provide an ideal playground for discovering and understanding the topological electronic states in strongly correlated materials[1,2,3,4,5,6,7,8,9,10,11,12,13,14]. The crystal structure of the material Co3Sn2S215–18 is layered featuring a kagome lattice of CoSn. It was shown to have an out-of plane ferromagnetic ground state (Curie temperature of TC ≃ 177 K) with a magnetization arising mainly from the cobalt moments. We find a near-perfect correlation between the topological Hall conductivity and the ferromagnetically ordered volume fraction as a function of temperature. Theoretical modelling, considering both localized and itinerant electrons, was recently shown[11] to reproduce the out-of-plane ferromagnetism and 120° antiferromagnetic ordering in the kagome plane, as we observed experimentally[6]. Despite knowing the remarkable thermodynamic response of the magnetic and topological states in

Methods

Results

Conclusion