STM studies of topological materials

Event Dates: 

Thursday, May 4, 2017 - 12:00pm

CTQM Seminar Type: 

  • Related Seminar Series

Speaker Name(s): 

Jenny Hoffman

Speaker Affiliation(s): 

Harvard University

Abstract, Event Details: 

I will present an informal overview of experiments in progress, using scanning tunneling microscopy to understand several topological materials. We investigate the topological semimetal Sb as a model system with robust, long-lived surface states. We demonstrate new methods to quantify several metrics of interest for spintronics devices: lifetime, spin-orbit coupling, and g-factor. We also find a surprising zero bias conductance state on some Sb surfaces, and we use density functional theory calculations to show how it arises trivially from a structural dislocation - thus introducing a cautionary note in the rush to claim Majorana fermion discovery. We further investigate Sb image potential states as a possible stepping stone to magnetic monopole detection, and suggest the need for ARPES collaboration.

Other topological experiments in progress include: (1) Study of individual vanadium dopants in Sb2Te3 - in which a clean quantum anomalous Hall effect has been measured, but only at surprisingly low temperature. We aim to understand the discrepancy between ferromagnetic transition temperature (~10K) and QAHE temperature (~100 mK). (2) Search for strongly correlated topological surface states in YbB6 - a null result on the topological front, but with potentially interesting surface pn junctions. (3) Search for inversion-symmetry breaking topological surface states on BiTeI - also a null result on the topological front, but also surface pn junctions.