School of Physics Hard Condensed Matter & AMO Seminar: Jonathan Ludwig, Florida State University

Dirac materials can be broadly defined as systems with the electronic structure that can be described by a Dirac equation for massless or massive fermions. Graphene is arguably the most well known Dirac material where the low-energy states behave as relativistic massless particles. Other examples of “graphene-inspired” 2D Dirac materials include HgTe quantum wells near the transition between trivial semiconductor and quantum spin Hall states and monolayers of semiconducting transition metal dichalcogenides (TMDs). In this talk, I will discuss our recent optical magneto spectroscopy studies of these novel 2D electronic materials. The use of complementary optical techniques (infrared, photoluminescence, Raman scattering, photo-conductivity spectroscopy) combined with high magnetic fields offers exceptionally sensitive and selective experimental probes to explore and control their electronic structure through Zeeman and orbital quantization effects. Specifically, I will discuss cyclotron resonance of single-valley Dirac fermions in nearly gapless HgTe quantum wells [1], valley-selective Zeeman effect in monolayer TMDs [2], and photoconductivity probe of the Hofstadter spectrum in BN encapsulated graphene.

"Helvetica Neue"">  mso-bidi-font-size:12.0pt;font-family:"Helvetica Neue"">[1] J. Ludwig, Y.B. Vasilyev, N.N. Mikhailov, J.M. Poumirol, Z. Jiang, O. Vafek, and D. Smirnov. Cyclotron resonance of single-valley Dirac fermions in nearly gapless HgTe quantum wells. Phys. Rev. B 89, 241406(R) (2014).