Giulia Venditti (Department of Quantum Matter Physics, University of Geneva)
Titre : Filamentary superconductivity and odd-parity coupling in oxide interfaces
Institut Néel, Salle E424 (Salle Louis Weil)
Résumé : In low-dimensional superconductors, the ideal picture of a uniform condensate often breaks down, as mesoscopic inhomogeneities can dominate the physics and give rise to filamentary superconductivity (FSC).
Such percolative behavior naturally explains several exotic transport features (such as broad resistive transitions, non-linear I-V curves, unusual superfluid stiffnesses, and significant residual resistivity) that cannot be easily reconciled with quantum fluctuations [1,2]. SrTiO₃ (STO)-based interfaces provide a paradigmatic platform where these effects can be disentangled from intrinsic quantum phenomena [3].
In contrast, KTaO₃ (KTO) heterostructures display a remarkably clean Berezinskii–Kosterlitz–Thouless transition [4], with critical temperatures reaching values one order of magnitude larger than their STO counterparts and a strong dependence from crystallographic orientation [5]. We investigate a pairing mechanism based on spin–orbit-assisted coupling between the t2g conduction electrons and the soft ferroelectric tranverse optical (TO) modes, which generates a Rashba-like, odd-parity interaction [5]. In bulk KTO, we find that this Rashba-like coupling exhibits a strong angular dependence in momentum space and comparable intra- and interband contributions. Notably, non-spin-conserving EPC matrix elements are observed to be mode dependent, and dominating in the case of the soft TO mode [7,8].
In this talk, I will give an overview of filamentary superconductivity: what are its general phenomenological feature and possible microscopic origins of condensate breaking. I will then discuss the spin-orbit-assisted electron-polar-phonon coupling that may account for superconductivity in these systems with such low density of states.
[1] G. Venditti, et al., Phys. Rev. B 100 (2019) 064506.
[2] G. Venditti, et al., SciPost Phys. 15 239 (2023).
[3] G. Venditti, et al., Phys. Rev. B 105, 064512 (2022).
[4] S. Mallik et al., Nat Commun 13, 4625 (2022).
[5] Changjiang Liu, et al., Nat. Comm., 14, 951 (2023); X. Chen, et al., Nat. Commun. 15, 7704 (2024).
[6] M. N. Gastiasoro, et al, Phys. Rev. B 105 224503 (2022); Phys. Rev. R., 5(2), 023177 (2023).
[7] G. Venditti, et al., J. of Phys: Mater., 6(1), 014007 (2023).
[8] G. Venditti, F. Macheda, P. Barone, J. Lorenzana, and M. N. Gastiasoro, Spin-dependent anisotropic electron-phonon coupling in KTaO3, In preparation (2025).
