Abstract-Anisotropy of the infrared-active phonon modes in the mono-domain state of tetragonal SrTiO3 (110)

M. Yazdi-Rizi, P. Marsik, B. P. P. Mallett, C. Bernhard

(Submitted on 8 Aug 2016)

http://arxiv.org/abs/1608.02329

With infrared and terahertz ellipsometry we investigated the anisotropy of the infrared active phonon modes in SrTiO3 (110) single crystals in the tetragonal state below the so-called antiferrodistortive transition at T* = 105 K. In particular, we show that the anisotropy of the oscillator strength of the so-called R-mode, which becomes weakly infrared active below T*, is a valuable indicator for the orientation of the structural domains. Our results reveal that a mono-domain state with the tetragonal axis (c-axis) parallel to the [001] direction can be created by applying a moderate uniaxial stress of about 2.3 MPa along the [1-10] direction (with a mechanical clamp). The resulting, intrinsic splitting of the infrared-active phonon modes is reported.

Abstract-Terahertz ellipsometry study of the soft mode behavior in ultrathin SrTiO3 films

P. Marsik1,a), K. Sen1, J. Khmaladze1, M. Yazdi-Rizi1, B. P. P. Mallett1 and C. Bernhard1

1 Department of Physics and Fribourg Center for Nanomaterials, University of Fribourg, Chemin du Musée 3, CH-1700 Fribourg, Switzerland

a) Electronic mail: premysl.marsik@unifr.ch

Appl. Phys. Lett. 108, 052901 (2016); http://dx.doi.org/10.1063/1.4940976

We present a combined study with time-domain terahertz and conventional far-infrared ellipsometry of the temperature dependent optical response of SrTiO3thin films (82 and 8.5 nm) that are grown by pulsed-laser deposition on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) substrates. We demonstrate that terahertz ellipsometry is very sensitive to the optical response of these thin films, in particular, to the soft mode of SrTiO3. We show that for the 82 nm film the eigenfrequency of the soft mode is strongly reduced by annealing at 1200 °C, whereas for the 8.5 nm film it is hardly affected. For the latter, after annealing the mode remains at 125 cm−1 at 300 K and exhibits only a weak softening to about 90 cm−1 at 10 K. This suggests that this ultrathin film undergoes hardly any relaxation of the compressive strain due to the LSAT substrate.