Effect of annealing on the temperature-dependent dielectric properties of LaAlO3 at terahertz frequencies

Xingquan Zou, Mi He, Daniel Springer, Dongwook Lee, Saritha K. Nair, Siew Ann Cheong, Tom Wu, C. Panagopoulos, D. Talbayev, and Elbert E. M. Chia

Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore 

Department of Physics and Engineering Physics, 2001 Percival Stern Hall, 6400 Freret street, New Orleans, Louisiana 70118, USA  

AIP Advances 2, 012120 (2012); http://dx.doi.org/10.1063/1.3679725

Abstract

We present THz conductivity of LaAlO3 (LAO) as a function of temperature and annealing, using terahertz time-domain spectroscopy (THz-TDS). We observed that, after annealing, spectral weight redistribution occurs, such that the real conductivity σ1(ω) changed from a featureless and almost frequency-independent spectrum, into one where peaks occur near the phonon frequencies. These phonon frequencies increase with increasing temperature. We attribute the appearance of these absorption peaks to the diffusion and relocation of oxygen vacancies. The dielectric functions of annealed LAO are well fitted with the Drude-Lorentz model.

from the paper

"........Our work fills this gap in knowledge, enabling future researchers to use the temperature-dependent refractive index of LAO to characterize their thin films more accurately. Here we report the temperature-dependent (10 K ‐ 300 K) dielectric response of LAO by terahertz time-domain spectroscopy (THz-TDS) from 0.2 THz − 3 THz. After annealing, strong absorption peaks appear in k(ω), with peak positions shifting to higher frequencies with increasing temperature.

Our investigated samples are single crystals of (100) LAO: a 10×10×1 mm³ piece from CrysTec GmbH (Berlin, Germany), and a 10×10×0.5 mm³ piece from SWI (Hsinchu, Taiwan). Since both samples give the similar results, we only show data from the CrysTec sample. The dielectric response of LAO was measured by a commercial THz-TDS system (TeraView Spectra 3000). .........."

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