Condensed-Matter Physics & Materials Science Seminar

"Towards the Lifshitz transition in elemental bismuth: Light electrons gone heavy at the metal-insulator transition?"

Presented by N. Peter Armitage, Johns Hopkins University

Thursday, October 30, 2008, 1:30 pm — Small Seminar Room, Bldg. 510

Since the seminal work of Wigner in 1930's, it has been believed that the diverging electron-electron interactions found in low density electron gases can manifest in a variety of novel phases like electronic crystals or correlated heavy electron fluids. In principle elemental semi-metal Bismuth presents a model system to investigate such physics as the application of modest pressure is believed to drive electron and hole bands apart resulting in a semi-metal/semiconductor transition. Within a non-interacting purely band point of view this is an electronic topological transition of the Lifshitz variety, which is of order 2.5 in the Eherenfest classification. It is unclear however the role which electronic correlations play on the approach to the transition. Do interaction effects dominate result in a strongly correlated liquid state? Perhaps the topological transition is actually superseded by an exotic phase like an electron crystal or excitonic insulator? I present the results of our detailed optical study investigating these issues and trying to answer these questions. In the ambient pressure spectra correlations manifest themselves in a novel fashion by the observation of a strong coupling of conduction electrons to a plasmon collective mode. The observation of a ``plasmaron'' as such is made possible by the exceptional properties of semi-metal bismuth, but it is also likely relevant to the low energy transport and thermodynamic properties of other semi-metals, like graphite and graphene. As a function of pressure, we observe massive changes in bismuth's optical conductivity as the material approaches the Lifshitz-like metal/insulator transition. In the transition region we find evidence for an exotic correlated fluid regime, which is likely driven by a pairwise electron-hole interaction.

Hosted by: Cedomir Petrovic

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