Insight on Magnetic Topological Insulators by NMR and µSR

by Prof. Roberto Derenzi (University of Parma, Italy)

Friday 6 Sept 2024, 14:00 → 15:00 Europe/Zurich

SZ-WBGB/019

I will describe the work of a large collaboration on the van der Waals family MnPn2Te4 · n(Pn2Te3), with pnictogen Pn = Sb,Bi, MPT for short. These compounds nominally provide the holy grail of a stoichiometric magnetic topological insulator (MTI), where the topologically protected selection of  moment-spin chirality promises novel spintronic functionalities. The MTI concept was demonstrated originally by the presence of the Quantum Anomalous Hall Effect (QAHE)  in diluted magnetic topological insulators. The observation of QAHE in MPT was greeted as a breakthough for their higher crystalline qualities. Unfortunately MPT are not quite as perfect as the formula implies, because of unavoidable Mn,Pn site intermixing. The presence of antisites may be detrimental to the exchange gap at the Dirac point, a key feature in MTIs. I will show that Mn NMR and µSR provide important, clear cut information on the magnetic behavior of the antisites, despite the  large inhomogeneity that dominates the spectra of the two magnetic resonance probes. DFT is crucial in supporting the assignment of the spectra.