Electronic Structure and Transport Properties of Superlattices: La(1-X)SrxTiO3 (X =0, 0.20, 0.80, 1)

Abstract

The conventional density functional theory (DFT) and dynamical mean field theory (DMFT) is used to study the structural, electronic and the Mott-Hubbard metal-insulator phase transition of the pristine and superstructures, La_(1-x)Sr_xTiO₃ (x = 0, 0.20, 0.80, 1). The electrical and thermal conductivities, Seebeck coefficient, Figure of merit are calculated using the BoltzTraP codes. The present study reveals that the direct band gap of 2.20 eV and indirect band gap ~2.0 eV at the Γ point in the Brillouin zone of SrTiO₃ is upgraded to 3.423eV by using modified Beck-Johnson (mBJ) interaction potential. The metal-insulator transition (MIT) of LaTiO₃ and the superlattice La_(1-x)Sr_xTiO₃ have been investigated by using conventional density functional theory (DFT) and dynamical mean field theory (DMFT). The Mott-Hubbard metal-insulator transitions for pristine LaTiO₃ for a Coulombian parameter, U = 2.5 eV and the thermodynamic parameter β = 6 (eV)^-1 are consistent with the experimental results. A typical set of these correlation parameters for MIT La_0.20Sr_0.80TiO₃ and La_0.80Sr_0.20TiO₃ systems are found to be U = 3.5 eV and β = 10(eV)^-1 and U = 3.2 eV and β = 10 (eV)^-1 respectively. The characteristic sharp quasi-particle peak for a sample of La_0.80Sr_0.20TiO₃ superlattice systems is obtained correlation parameter U = 3.0 eV and β = 6(eV)^-1. A thermoelectric phase transition is observed for Seebeck Coefficient at temperature 300 K at near chemical potential, μ = 1eV of SrTiO₃. The corresponding figure of merit (ZT) with chemical potential (μ) appears to be unity at near μ = 1eV.