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Origins of bad metal conductivity and the insulator-metal transition in the rare-earth nickelates (RNiO3, R = rare earth)

Event Details

Event Dates: 

Thursday, January 23, 2014 - 12:00pm

Seminar Location: 

  • JILA X317

Speaker Name(s): 

Rafael Jaramillo

Speaker Affiliation(s): 

MIT
Seminar Type/Subject

Scientific Seminar Type: 

  • Condensed Matter Seminar

Event Details & Abstract: 

For most metals increasing temperature (T) or disorder quickens electron scattering. This scattering time hypothesis informs the Drude model of electronic conductivity (\sigma). However, for so-called bad metals with very low \sigma this hypothesis predicts scattering times so short as to conflict with Heisenberg’s uncertainty principle. Bad metal conductivity has remained a puzzle since its discovery in the 1980s in high T superconductors.Here we introduce the rare-earth nickelates (RNiO3, R = rare earth) as a class of bad metals. We study SmNiO3 thin films using infrared (IR) spectroscopy while varying T and disorder. We show that the interaction between lattice distortions and Ni-O bond covalence explains both the bad metal conductivity and the insulator-metal transition (IMT) in the nickelates. It does so by shifting spectral weight over the large energy scale established by the Ni-O orbital interaction, thus enabling very low \sigma while preserving the Drude model and without violating the uncertainty principle.