Pressure‐Driven Magneto‐Topological Phase Transition in a Magnetic Weyl Semimetal

Abstract

The co-occurrence of phase transitions with local and global order parameters, such as entangled magnetization and topological invariants, is attractive but seldom realized experimentally. In this study, a magneto-topological phase transition (magneto-TPT), that is, the phenomenon of magnetic materials undergoing different magnetic and topological phases during pressure loading, is investigated. By considering both out-of-plane ferromagnetic and in-plane antiferromagnetic components, it is discovered that the calculated results fit well with the experimental data. The calculation results further reveal a pristine Weyl phase with four additional pairs of Weyl nodes under low pressure, and a generally defined Z 2 topological insulator phase after the restoration of time-reversal symmetry at 40.4 GPa. The transport measurements performed at 5 K reveal that the magnetic order almost vanishes at 40.3 GPa, which is consistent with the theoretical prediction. Moreover, the present magneto-TPT involves the degeneration of a pair of crossing bands of two spin channels. Hence, all the chiral Weyl nodes annihilate with their counterparts from another spin channel, in contrast to the typical intraband annihilation of Weyl pairs in inversion-asymmetric systems. The study reveals a method for realizing diverse topological states by modulating exchange splitting by external physical knobs such as pressure in topological magnets.

Pressure driven Weyl-topological insulator phase transition in Weyl semimetal SrSi2

“…Topological order may be tuned via changing the chemical composition and thereby modifying both the strength of spin orbit coupling (SOC) and the lattice parameters. Another strategy is to apply external strain [30,31] which has been theoretically shown for a number of narrow band gap cubic semiconductors such as grey tin (𝛼-Sn) [32] and HgTe [32,33], InSb [34], KNa 2 Bi [35], TaAs [36], Co 3 Sn 2 S 2 [37]. (Colour online) Weyl-TI TPT in a non-magnetic system with intraband annihilation of chiral Weyl node [37] Hence, compressive/tensile strain is utilised to close/reopen the bandgap in some topological materials, which may be accompanied by strain-induced topological phase transitions [30,[38][39][40].…”

“…Another strategy is to apply external strain [30,31] which has been theoretically shown for a number of narrow band gap cubic semiconductors such as grey tin (𝛼-Sn) [32] and HgTe [32,33], InSb [34], KNa 2 Bi [35], TaAs [36], Co 3 Sn 2 S 2 [37]. (Colour online) Weyl-TI TPT in a non-magnetic system with intraband annihilation of chiral Weyl node [37] Hence, compressive/tensile strain is utilised to close/reopen the bandgap in some topological materials, which may be accompanied by strain-induced topological phase transitions [30,[38][39][40]. Recent studies indicate that SrSi 2 is a robust double-Weyl semimetal due to the absence of inversion symmetry.…”

“…Here, we consider the new Weyl-TI phase transition which includes two separate topological non-trivial phases as well as the metal-insulator transition. The chiral Weyl nodes annihilate in pairs during phase transition if time-reversal symmetry is preserved [37] (figure 1). We predict a new d-p band inversion in SrSi 2 using band structure calculations.…”

“…Figure 1. (Colour online) Weyl-TI TPT in a non-magnetic system with intraband annihilation of chiral Weyl node[37] …”

Tuning the anomalous Nernst and Hall effects with shifting the chemical potential in Fe-doped and Ni-doped Co3Sn2S2

“…Calculations and experiments indicated the presence of Weyl points located at 60 meV above the Fermi level [14][15][16][17]. This allows to adjust the topological property easily through doping [18][19][20][21][22] or by applying pressure [23][24][25]. The cobalt site can be doped by either nickel or iron.…”