First-principles calculation of polarizability in (LaAlO3)n/(SrTiO3)n (n = 1-5) superlattices
نویسندگان
چکیده
Although both LaAlO3 (LAO) and SrTiO3 (STO) are insulators, at the interface of LAO/STO [001] stacking structures, formation of two-dimensional electronic gas with high mobility was reported [1]. Associated with this, a problem concerning divergence of electrostatic potential was also pointed out [2]. We performed first-principles calculations on LAO/STO [001] stacking thin films and investigated carefully how ionic and electronic relaxation occurs, and how carriers are created at the interface [3]. Another interesting aspect is also expected. For LAO/STO [001] stacking, there is no mirror symmetry along the [001] direction and the second nonlinear coefficient of electronic polarizability may have a significant value. In the present study, for LAO/STO [001] superlattices, we have calculated electronic polarizability including nonlinear terms as a function of superlattice period. By utilizing the computational method proposed by Souza et al. [4], we have performed electronic structure calculations under static electric field and obtained induced polarization. With polynomial fitting, linear and nonlinear polarizabilities up to third order have been evaluated. All the calculations have been performed with our in-house computational code QMAS (Quantum MAterials Simulator) [5]. The obtained linear and third-order-nonlinear polarizabilities show small variations against the superlattice period. In contrast with this, the secondorder-nonlinear polarizability changes systematically with the superlattice period. The origin of this systematic change is discussed relating to the ionic relaxation and the band alignment.
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تاریخ انتشار 2010