Multiple quantum phase transitions of different nature in the topological kagome magnet Co3Sn2−xInxS2

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.

Magnetic competition in topological kagome magnets

“…The in-plane AFM experimentally observed in Co 3 Sn 2 S 2 is the 1 × 1 one [12,13]. > the in-plane 1 × 1 AFM is stable, because their grand potential has a lowest value.…”

“…The kagome magnets have a layered crystal structure with stacked quasi-two-dimensional kagome layers [10][11][12][13]. We focus on the two-dimensional kagome lattice, where the magnetic atoms are located in the kagome lattice sites (see figure 1).…”

“…The present work is motivated by the striking effects observed in the kagome magnets, and in particular, the magnetic competition between the out-of-plane FM and the in-plane AFM [9][10][11][12][13]. We propose a minimal model, which can qualitatively describe the observed effects.…”

“…With the inclusion of electron correlations and spin-orbit coupling (SOC), the kagome lattice engenders a rich interplay between unconventional magnetism, electron correlations and nontrivial topology. Recently, experiments observed striking effects including large anomalous Hall effect and unusual magnetic tunability in magnetic kagome materials [9][10][11][12][13]. In particular, the kagome magnet Co 3 Sn 2 S 2 exhibits an out-ofplane ferromagnetic (FM) ground state, but at a finite temperature before reaching the paramagnetic (PM) state an in-plane antiferromagnetism (AFM) appears and coexists with the out-of-plane FM [12,13].…”

“…Recently, experiments observed striking effects including large anomalous Hall effect and unusual magnetic tunability in magnetic kagome materials [9][10][11][12][13]. In particular, the kagome magnet Co 3 Sn 2 S 2 exhibits an out-ofplane ferromagnetic (FM) ground state, but at a finite temperature before reaching the paramagnetic (PM) state an in-plane antiferromagnetism (AFM) appears and coexists with the out-of-plane FM [12,13]. The competition between these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure [12,13].…”