Reconstructing the surface state wavefunction of magnetic topological insulator MnBi₄Te₇

MnBi_2nTe_3n+1 (MBT) compounds were celebrated as the first intrinsic magnetic topological insulators, promising a clean platform for exotic phenomena arising from nontrivial quantum geometry. However, while the quantum anomalous Hall effect has been observed, angle-resolved photoemission spectroscopy (ARPES) consistently reports a surface state exhibiting no gap in the magnetic phase, in contradiction to theory. In general, the electronic structure of MBT remains poorly understood, which hinders research to exploit applications of its unique magnetic topological properties.

Here, we present an experimental methodology to reconstruct the wavefunction of the MnBi₄Te₇ topological surface state using spin- and orbital-resolved ARPES measurements. Based on our methodology, we establish a remarkable connection to circular dichroism measurements. Our results show that the topological surface state is well-described by a single-band picture dominated by p-orbitals, with a sizable contribution of in-plane p orbitals, which deviates from the conventional topological insulator Bi₂Te₃. We discuss our work’s implications on the long-standing puzzle of the gapless Dirac cone in the MBT material family.