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Physics colloquium-“Reduction of Symmetry and the Return of the War of Currents”
March 12 @ 4:00 pm
University of Nebraska-Lincoln, Dept. of Electrical & Computer Engineering
Abstract: In the late eighteen hundreds, an epic battle raged upon the introduction of electricity and electric energy. Sides were taken and bitterly defended either in favor of direct (DC) or for alternating current (AC) . The winner is known well, and the scores seem to be settled eternally. Yet, most recent breakthrough developments in solid state physics may turn the fate, after all, in favor of DC. A new semiconductor emerges, the monoclinic form of gallium oxide, with potential for electronic power devices capable of switching currents up to ten or even twenty thousands of volts . Thereby, researchers turn their attention to emerging phenomena associated with the reduction in symmetry. In this presentation, I discuss the unusual properties of coupling between free conduction band electrons and transverse and longitudinal optical phonons in crystals with monoclinic lattice symmetry, for gallium oxide as an example. Ellipsometry and optical Hall effect measurements are used, in combination with density functional theory calculations to unravel the behavior of the coupled phonon plasmon modes which change direction and amplitude as a function of free electron density . We measure the effective conduction band mass tensor for low electron densities , and discuss consequences for electric and thermal transport.
 Masataka Higashiwaki and Gregg H. Jesson, Appl. Phys. Lett. GAO2018, 060401 (2018)
 M. Schubert et al., Phys. Rev. B 99, 041201(R) (2019).
 S. Knight et al., Appl. Phys. Lett. 112, 012103 (2018).
Berthoud Hall 241