Ultra-high magnetoresistance and field-induced Fermi surface reconstruction in a topological magnet*

Square lattice compounds have attracted much attention in the field of topological materials and complex magnetism. Recently it has been established that many different types of square-net materials, beyond nonsymmorphic space groups, can host Dirac fermions coming from band folding and electron count. In this talk I will discuss our recent results on a layered square lattice compound where ultra-high magnetoresistance (> 200,000%, T = 2 K, H = 14 T) is observed when magnetic order sets in. Through ARPES measurement and DFT calculation we identify a symmetry protected Dirac cone near the Fermi level, which we expect to be responsible for the observed high magnetoresistance and high carrier mobility. We also studied the field induced Fermi surface reconstruction across the magnetic transition. The interplay of magnetism and band topology point to rich physics in this material system.