High frequency elastic losses in LaAlO3 and its importance for LaAlO3/SrTiO3 heterojunctions

Cooling heterojunctions on LaAlO3 substrates or thick layers of LaAlO3 on SrTiO3 substrates below 820 K lead to a ferroelastic phase transition Pm (3) over barm -> R (3) over barc in LaAlO3, with extensive twinning and elastic softening. Twin boundaries add to structural disorder near the heterojunction and generate partially localized carriers. Resonant Ultrasound Spectroscopy data relating to the elastic instability in LaAlO3 show that elastic Cole-Cole circles and the background autocorrelation function follow Vogel-Fulcher behaviour, with a Vogel-Fulcher temperature of 230 K. An extremely low activation energy, 0.02 eV, would promote the formation of highly structured, glassy LaAlO3 near the junction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622305]