[Talk] Shota Kanasugi – Spin-orbit-coupled ferroelectric superconductivityand multiorbital effects in SrTiO3

Speaker: Shota Kanasugi
Affiliation: Kyoto University

Title: Spin-orbit-coupled ferroelectric superconductivityand multiorbital effects in SrTiO3

Abstract: A lot of exotic superconducting statesemerge close to other ordered phases, such as anisotropic superconductivity in cuprates. Although previous studies have mainly focused on the superconductivityclose to magnetic instability, the ferroelectric (FE) counterpart is recently receiving increased attention since such superconductivity was reported in doped SrTiO3(STO). STO is a unique compound which exhibits both quantum paraelectricity and superconductivity. The superconducting transition temperature is enhanced in the vicinity of the FE quantum critical point [1-4]. Moreover, recent experiments suggest the coexistence ofsuperconductivity and ferroelectricity in doped STO [2]. These results imply a cooperative correlation between superconductivity and ferroelectricity against a long-held belief that they should be incompatible.In this talk, we present that aFE-like polar inversion symmetry breaking order can be controlled by the superconductivityin spin-orbit coupled systems. We introduce a model of electron-lattice coupled two-dimensional superconductor,in which the ferroelectricity-induced Rashba spin-orbit coupling [5]is included. It is shown that the FE superconductivity,which is characterized by a FE structural transition in the superconducting state,is realized through two different mechanisms [6]. First, the FE superconducting state is stabilized by the Lifshitz transition of the Rashba split bandsin lowcarrier density regimes.Second, the FE superconductingstate is stabilized under a Zeeman magnetic field, thanksto the suppressionof the Pauli depairingeffect in the FE phase. Furthermore, we show that the FE superconductivity in bulk STO is strongly affected by the multiorbital effectoft2gelectrons[7]. Then, we predict a topologicalWeyl superconducting state in the FE superconducting phase of bulk STO.

References
[1] A. Stucky et al., Sci. Rep. 6,37582 (2016).
[2] C. W. Rischau et al., Nat. Phys. 13, 643 (2017).
[3] Y. Tomioka et al., Nat. Commun. 10, 738 (2019).
[4] K. Ahadi et al., Sci. Adv. 5, eaaw0120 (2019).
[5] G. Khalsa, B. Lee, and A. H. MacDonald, Phys. Rev. B 88, 041302 (2013).
[6] S. Kanasugi and Y. Yanase, Phys. Rev. B 98, 024521 (2018).
[7] S. Kanasugi and Y. Yanase, arXiv: 1904.11113 (2019)