# Imparting Mass to Zero Relativistic Electrons

**When:**Thursday, February 20, 2014 at 4:00 pm

**Where:**DA 114

**Speaker**: Professor Vidya Madhavan

**Organization**: Boston College

**Sponsor**: Physics Colloquium

Topological crystalline insulators are recently discovered topological materials [1,2] where topology and crystal symmetry intertwine to create massless electrons, which behave like relativistic particles. Among the theoretical predictions for topological crystalline insulators is the possibility of imparting mass to these massless Dirac fermions by breaking crystal symmetry. In this talk I will discuss our recent experimental and theoretical investigations of a topological crystalline insulators, Pb1-xSnxSe [3]. We performed scanning tunneling microscopy (STM) studies at low temperatures and as a function of magnetic field. By analyzing two types of STM data: Fourier transforms of interference patterns and Landau level spectroscopy, we reveal the coexistence of zero mass Dirac fermions protected by crystal symmetry with massive Dirac fermions resulting from crystal symmetry breaking.

[1] L. Fu, Topological Crystalline Insulators. Phys. Rev. Lett. 106, 106802 (2011).

[2] T. H. Hsieh et al., Topological crystalline insulators in the SnTe material class. Nat.Commun. 3, 982 (2012).

[3] Y. Okada, et.al, Observation of Dirac node formation and mass acquisition in a topological crystalline insulator, Science 341, 1496-1499 (2013).

Host: Assistant Professor Meni Wanunu