Structural Tuning Magnetism and Topology in a Magnetic Topological Insulator

To date, the most widely-studied quantum anomalous Hall insulator (QAHI) platform is achieved by dilute doping of magnetic ions into thin films of the alloyed tetradymite topological insulator (TI) (Bi_{1 - x}Sb_x)₂Te₃ (BST). In these films, long-range magnetic ordering of the transition metal substituants opens an exchange gap Δ in the topological surface states, stabilizing spin-polarized, dissipationless edge channels with a nonzero Chern number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>C</mml:mi> <mml:annotation>$\mathcal {C}$</mml:annotation></mml:semantics> </mml:math> . The long-range ordering of the spatially separated magnetic ions is itself mediated by electronic states in the host TI, leading to a sophisticated feedback between magnetic and electronic properties. Here, a study is presented on the electronic and magnetic response of a BST-based QAHI system to structural tuning via hydrostatic pressure. A systematic closure of the topological gap under compressive strain is identified accompanied by a simultaneous enhancement in the magnetic ordering strength. Combining these experimental results with first-principle calculations, structural deformation is identified as a strong tuning parameter to traverse a rich topological phase space and modify magnetism in the magnetically doped BST system.