Theory of Pines' demon in multiband metals
Dr. Edwin Huang
Gordon and Betty Moore Postdoctoral Research Associate
Department of Physics and Institute for Condensed Matter Theory
University of Illinois, Urbana-Champaign
In 1956, David Pines predicted the existence of an acoustic plasmon, dubbed a "demon", in metals with multiple and sufficiently distinct charge carrier species. Despite extensive searches, demons have not been observed directly until recent momentum-resolved electron energy-loss spectroscopy (M-EELS) experiments on Sr2RuO4. Here, we discuss the theoretical conditions for the existence of demons as a stable collective excitation in multiband metals. We find, without any fitting or tuning of parameters, agreement between experimental M-EELS spectra and multi-orbital random phase approximation (RPA) calculations of the charge susceptibility. A decomposition of the calculation of the susceptibility into intra- and inter-band components provides direct evidence of the out-of-phase character of the demon. Our findings thus demonstrate the utility of numerical calculations for the microscopic interpretation of experimental spectroscopy.
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