XMCD, reflectometry and multiplet ligand field theory study of the surface properties of the magnetic topological crystalline insulator Cr-(Pb,Sn)Te

Magnetic topological crystalline insulators (MTCI), in which topological surface states are protected by crystalline symmetries, promise the realization of the QAHE and applications in spintronics and lossless transport. MTCIs have hardly been explored by XMCD. Here, we propose to build upon our previous BOREAS work on “conventional”, i.e. time-reversal-symmetry protected, magnetic topological insulators (MTI) and study Cr-doped (Pb,Sn)Te, a MTCI with a very high FM Tc=170 K, much higher than typical in conventional MTIs. The high Tc greatly supports the realization of phenomena and applications. We plan to combine XMCD-TEY and reflectometry data with multiplet ligand field theory calculations to determine the surface magnetic (moments, hystereses) and electronic (orbital occupation, level filling) properties. Knowledge of the surface properties is crucial due to interaction of the magnetic state with the topological surface states and cannot be ob-tained from bulk methods like SQUID.