Speaker: Erik Henriksen , Washington University in St. Louis
Abstract: Cyclotron resonance—the resonant absorption of infrared light by charge carriers in a strong magnetic field– is one of the more basic measurements that can be made on semiconductors. First demonstrated on germanium in the early ‘50s, CR proved to be enormously useful in determining semiconductor band structures and, from the ‘70s, was instrumental in probing two-dimensional systems in Si and GaAs heterostructures. However, early on W. Kohn pointed out a limitation of the CR technique: in translationally invariant parabolic systems, CR is insensitive to electron-electron interactions, with the consequence that CR has been useless in investigating such remarkable phenomena as the fractional quantum Hall effect. We have performed CR measurements over the past decade that demonstrate how to evade Kohn’s theorem by breaking translational invariance, or working in graphene whose linear dispersion can be viewed as an extreme case of a non-parabolic band structure. In our most recent work we find direct evidence of many-particle physics in the cyclotron resonance of high mobility graphene. This exciting development suggests that infrared spectroscopy will provide a new window on interacting electron phenomena in graphene including (fractional) quantum Hall effects, Hofstadter’s butterfly, hydrodynamic transport, and perhaps even cavity QED.