Metal-insulator transition and robust thermoelectricity via strain-tuned interplay between structural and electronic properties in (SrVO3)1/(SrTiO3)1(001) superlattices
Exploring the origin of the metal-to-insulator transition (MIT) in transition metal oxide heterostructures is of high interest in current condensed matter physics research. Here based on density functional theory calculations with the meta-GGA exchange correlation functional SCAN, we find distinct mechanisms of MIT in (SrVO3)1/(SrTiO3)1(001) superlattices (SLs). The SCAN functional is sufficient to determine the ground state structure and possible symmetry breaking at a given lateral lattice constant and best describes the electronic and magnetic properties of the weakly correlated (SrRuO3)1/(SrTiO3)1(001) SL and its constituents by minimizing the self-interaction error. However, an additional Hubbard U term is necessary for the strongly correlated (SrVO3)1/(SrTiO3)1(001)SLs. We show that SCAN + U always favors the monoclinic (P21/c) symmetry in (SrXO3)1/(SrTiO3)1(001)SLs, X=V and Ru, irrespective of the in-plane lattice constant and X. For the orthorhombic (SrVO3)1/(SrTiO3)1(001)SL(Cmmm) at aSTO (tensile strain +1.7%), we report strong correlation and confinement driven Mott-Hubbard type MIT via long-range stripe antiferromagnetic ordering, whereas, under compressive strain (−3.6%) at aYAO, the interplay of confinement, correlation, and finite octahedral tilts and rotations lead to monoclinic (P21/c) symmetry, which drives an orbital reconstruction and a concomitant MIT with ferromagnetic spin alignment. Lastly, using Boltzmann transport theory within the constant relaxation time approximation, for (SrVO3)1/(SrTiO3)1(001)SL at aSTO, we obtain large n-type Seebeck coefficients S of −566 (in-plane) and −454 μV/K (cross-plane), respectively, along with an in-plane (cross-plane) power factor of 31.4 (8.5) μWK−2cm−1 (assuming τ=4 fs) at 300 K. These values directly categorize (SrVO3)1/(SrTiO3)1(001)SL as a promising oxide thermoelectric material.
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