Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 28: Correlated Electrons: Spin Systems, Itinerant Magnets 3
TT 28.11: Talk
Tuesday, March 12, 2013, 12:15–12:30, H19
Signature of gap closure in the phonon spectra of FeSi — •Sven Krannich1, Daniel Lamago2, Rolf Heid1, Klaus-Peter Bohnen1, Yvan Sidis2, Jean-Michel Mignot2, Paul Steffens3, Alexander Ivanov3, and Frank Weber1 — 1Karlsruhe Institute of Technology, Institute of Solid State Physics, 76021 Karlsruhe — 2Laboratoire Léon Brillouin, CEA - Saclay, F - 91191 Gif sur Yvette Cedex, France — 3Institut Laue Langevin, F-38042 Grenoble Cedex, France
We report an inelastic neutron scattering study of the lattice degrees of freedom in the narrow gap semiconductor FeSi over a large temperature range 10 K ≤ T ≤ 790 K. In our measurements we observe an unusually strong softening of various phonon modes with some notable exceptions. Calculations based on density-functional-perturbation theory (DFPT) show that only the softening between T = 100 K and room temperature is anomalous, i.e. cannot be explained by normal thermal expansion. Further calculations simulating a vanishing electronic gap at elevated temperatures can account for this anomalous softening and need not involve strong anharmonic lattice effects. Our results support a band-like approach to FeSi where electron-electron correlations are responsible for the gap closure.