Ferroelectricity-induced multiorbital odd-frequency superconductivity in SrTiO$_3$

TL;DR

This paper predicts and classifies the emergence of odd-frequency superconductivity in SrTiO$_3$ due to ferroelectricity and multiorbital effects, providing theoretical insights and potential experimental signatures.

Contribution

It introduces a multiorbital model for SrTiO$_3$ near ferroelectricity, demonstrating the generation and classification of odd-frequency pair correlations.

Findings

Odd-frequency pair correlations are generated by LS coupling.

Additional odd-frequency correlations arise from ferroelectric orbital hybridization.

Spectral functions and density of states show signatures of these correlations.

Abstract

We demonstrate that SrTiO$_3$ can be a platform for observing the bulk odd-frequency superconducting state owing to the multiorbital/multiband nature. We consider a three-orbital tight-binding model for SrTiO$_3$ in the vicinity of a ferroelectric critical point. Assuming an intraorbital spin-singlet $s$-wave superconducting order parameter, it is shown that the odd-frequency pair correlations are generated due to the intrinsic LS coupling which leads to the local orbital mixing. Furthermore, we show the existence of additional odd-frequency pair correlations in the ferroelectric phase, which is induced by an odd-parity orbital hybridization term proportional to the ferroelectric order parameter. We also perform a group theoretical classification of the odd-frequency pair amplitudes based on the fermionic and space group symmetries of the system. The classification table enables us to predict dominant components of the odd-frequency pair correlations based on the symmetry of the normal state Hamiltonian that we take into account. Furthermore, we show that experimental signatures of the odd-parity orbital hybridization, which is an essential ingredient for the ferroelectricity-induced odd-frequency pair correlations, can be observed in the spectral functions and density of states.