Regensburg 2013 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 62: Superconductivity: Properties, Electronic Structure, Order Parameter

TT 62.11: Vortrag

Donnerstag, 14. März 2013, 18:00–18:15, H19

Temperature dependence of band gaps in semiconductors: electron-phonon interaction — •Reinhard K. Kremer¹, M. Cardona¹, R. Lauck¹, J. Bhosale², A. K. Ramdas², A. Burger³, A. Muñoz⁴, and A. H. Romero⁵ — ¹MPI for Solid State Research, Stuttgart, Germany — ²Physics Dep., Purdue University, West Lafayette, IN — ³Fisk University, Dep. of Life and Physical Sciences, Nashville, TN, USA — ⁴MALTA Consolider Team, Dep. de Física Fundamental II, and Instituto de Materiales y Nanotecnología, Universidad de La Laguna, La Laguna, Tenerife, Spain — ⁵CINVESTAV, Dep. de Materiales, Unidad Querétaro, Querétaro, Mexico and MPI für Mikrostrukturphysik, Weinberg 2, Halle, Germany

We investigate the temperature dependence of the energy gap of several semiconductors with chalcopyrite structure and re-examine literature data and analyze own high-resolution reflectivity spectra in view of our new ab initio calculations of their phonon properties. This analysis leads us to distinguish between materials with d-electrons in the valence band (e.g. CuGaS₂, AgGaS₂) and those without d-electrons (e.g. ZnSnAs₂). The former exhibit a rather peculiar non-monotonic temperature dependence of the energy gap which, so far, has resisted cogent theoretical description. We demonstrate it can well be fitted by including two Bose-Einstein oscillators with weights of opposite sign leading to an increase at low-T and a decrease at higher T’s. We find that the energy of the former correlates well with characteristic peaks in the phonon density of states associated with low-energy vibrations of the d-electron constituents.