Effects of spin-orbit interaction and electron correlations in strontium titanate

Abstract

We show that the bottom of the conduction band in SrTiO3 is formed by the Kramers doublet of states with finite angular momentum involving a spin-orbit-coupled superposition of all three t2g orbitals of Ti. Analysis of electron correlations based on the Hubbard model shows that superconductivity may be mediated by the orbital entanglement of electrons due to the Mott-Hund's coupling between t2g orbitals. The proposed mechanism is likely relevant to other multiband superconductors.

Chiral superconductivity in cuprates mediated by spin-orbit coupling to spinon superfluidity

“…Spinon entanglement then effectively "rectifies" the circulating orbital currents, resulting in a macroscopic supercurrent. This mechanism is similar to the one recently proposed for STO, and is likely relevant to other unconventional superconductors [22].…”

“…Recent analysis of the electronic properties of STO showed that the bottom of the conduction band in this material is formed by a Kramers doublet of states with unquenched orbital moments and maximal total angular momentum j = 5/2 minimizing the spin-orbit coupling (SOC) energy [22]. Coulomb interaction dominant at small carrier density was shown to stabilize a spin-orbit liquid characterized by polaronic-like electron localization.…”