## "Resonant x-ray spectroscopy of topological semimetals"

**Speaker:**Stefanos Kourtis, Boston University, Physics Department

**When:**September 15, 2017 (Fri), 12:00PM to 01:30PM (add to my calendar)

**Location:**SCI 352

*This event is part of the Condensed Matter Theory Seminar Series. *

Angle-resolved photoemission spectroscopy (ARPES) has so far been the definitive method for the characterization of materials as topological Weyl or Dirac semimetals, via direct visualization of band touchings in the bulk and nontrivial states at the boundary. However, the unconventional and potentially useful properties of these materials are a consequence of a singular Berry curvature distribution, which cannot be resolved in ARPES. Furthermore, control over the number and position of Weyl nodes -- the most important property from an application standpoint -- can only be achieved with sizable electromagnetic fields, which curtail the resolving power of ARPES, thereby rendering the band structure inaccessible to this technique. We show how resonant x-ray scattering (RXS) offers a viable path for (a) deducing the band structure of materials in arbitrarily large magnetic fields and (b) visualizing the Berry curvature distribution in momentum space via polarization control of incoming and outgoing x-ray beams. By low-energy modeling of specific material candidates based on ab initio band structure calculations, we derive the corresponding RXS spectra and highlight the salient features stemming from topological nontriviality. The proposed measurements are within the resolving capabilities of current instrumentation.