Antiferromagnetic ℤ_2 Topological Metal Near the Metal-Insulator Transition in MnS_2

Antiferromagnetic (AFM) semiconductor MnS_2 possesses both high-spin and low-spin magnetic phases that can be reversibly switched by applying pressure. With increasing pressure, the high-spin state undergoes pressure-induced metalization before transforming into a low-spin configuration, which is then closely followed by a volume collapse and structural transition. We show that the pressure driven band inversion is in fact topological, resulting in an antiferromagnetic ℤ_2 topological metal (Z2AFTM) phase with a small gap and a Weyl metal phase at higher pressures, both of which precede the spin-state crossover and volume collapse. In the Z2AFTM phase, the magnetic order results in a doubling of the periodic unit cell, and the resulting folding of the Brillouin zone leads to a ℤ_2 topological invariant protected by the persisting combined time-reversal and half-translation symmetries. Such a topological phase was proposed theoretically by Mong, Essin, and Moore in 2010 for a system with AFM order on a face-centered cubic (FCC) lattice, which until now has not been found in the pool of real materials. MnS_2 represents a realization of this original proposal through AFM order on the Mn FCC sublattice. A rich phase diagram of topological and magnetic phases tunable by pressure, establishes MnS_2 as a candidate material for exploring magnetic topological phase transitions and for potential applications in AFM spintronics.