Regensburg 2016 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 3: Optical and nonlinear optical properties, photonic

DF 3.4: Talk

Monday, March 7, 2016, 10:30–10:50, H26

OH⁻ as local, vibrational probe for the inspection ofsmall, strong-coupling polarons — •Felix Freytag, Phillip Booker, and Mirco Imlau — School of Physics, Osnabrueck University,Barbarastr. 7, 49076 Osnabrueck, Germany

A small polaron is defined by the unit of a self-trapped carrier and the associated displacement of atomic equilibrium positions confined to a single lattice site [Emin, Polarons, Cambridge University Press (2013)]. There’s an increasing attention to the structural distortion parameters of small polarons for nonlinear optical processes in polar oxides on the ultrafast time-scale [Imlau et al., Applied Physics Reviews 2, 40606 (2015)]. Even though, a multitude of knowledge has been gathered and a variety of experimental techniques like EPR/NMR measurements were applied, there is still no possibility for direct experimental access to the structural aspects of small polarons within a continuum and at elevated temperatures. Here, we propose a vibrational method to experimentally achieve local information about small polarons at room temperature. The absorption change of the OH⁻ stretching vibration is applied as local probe for optically excited small polarons with lithium niobate as an example; detected by time-resolved mid-infrared pump-probe spectroscopy. The change is explained straightforwardly by a local change of the lattice environment induced by small polaron formation. By analysis of the vibrational potential of the OH⁻-stretching bond, we are able to estimate the polaron induced lattice distortion. Financial support by the DFG (IM 37/5-2, INST 190/165-1 FUGG) is gratefully acknowledged.