Anisotropic vortex squeezing and supercurrent diode effect in non-centrosymmetric Rashba superconductors

Denis Kochan^1*

¹Department of Physics, Slovak Academy of Sciences, Bratislava, Slovak Republic

* Presenter:Denis Kochan, email:denis.kochan@gmail.com

Superconductivity in materials with broken inversion symmetry has been a subject of theoretical and experimental studies from the early 90's. It was understood that unlike symmetric spin-orbit coupling found in centrosymmetric metals, spin-orbit coupling in non-centrosymmetric materials has a spectacular influence on the electronic bands through a specific spin splitting of the quasiparticle states. Superconductivity as a Fermi-surface instability towards pairing of electrons with opposite momenta and spins is naturally influenced by such a modification of the electronic states. The removal of inversion symmetry and also of time-reversal, e.g. by an applied external magnetic field, promotes a novel form of electron pairing–the so-called helical phase, in which Cooper pairs acquire a finite center of mass momentum. The latter gives rise to several interesting magneto-electric or magneto-chiral effects, like the enhancement of Tc in the presence of magnetic fields, the supercurrent diode effect, magneto-chiral inductance anisotropy, zero-pi-like transitions, the anomalous Josephson effect, as well as, unusual vortex squeezing and engendered London physics in the Meissner state. The last decade witnessed a renewed interest in superconductors with broken inversion symmetry by using the so-called synthetic superconductors, e.g. 2DEG with a strong Rashba spin-orbit-coupling in a proximity of conventional superconductors, in a pursuit to find or engineer topologically non-trivial superconducting states with non-Abelian (Majorana) excitations.
In the talk I will discuss general properties of the non-centrosymmetric superconductors summarizing the main theoretical and phenomenological concepts standing behind. Apart of that, I will present exciting experimental evidences showing the emergence of i) supercurrent diode effect and Josephson inductance anisotropy [1] in the synthetic Josephson junctions incorporating proximitized 2DEG formed in InAs-quantum wells that possess strong Rashba coupling and large g-factor, ii) zero-pi-like transitions and anomalous Josephson effect [2] in such non-centrosymmetric systems, and, last but not least, also iii) an unexpected enhancement of pinning and squeezing of Abrikosov vortices when probed in such Rashba-based superconductors in a Meissner phase [3]. I will elucidate these phenomena from the microscopic point of view, but as well as, phenomenologically–as a direct manifestation of the Lifshitz invariant that is allowed in the Ginzburg-Landau free energy when the underlying Cooper pairs acquire a finite center of mass momentum.

References:
[1] C. Baumgartner, L. Fuchs, A. Costa, S. Reinhardt, S. Gronin, G. Gardner, T. Lindemann, M. Manfra, P. Faria Junior, D. Kochan, J. Fabian, N. Paradiso, C. Strunk; Nature Nanotechnology 17 (1), 39 (2022).

[2] A. Costa, C. Baumgartner, S. Reinhardt, J. Berger, S. Gronin, G. Gardner, T. Lindemann, M. Manfra, J. Fabian, D. Kochan, N. Paradiso, C. Strunk; Nature Nanotechnology (2023), https://doi.org/10.1038/s41565-023-01451-x

[3] L. Fuchs, D. Kochan, C. Baumgartner, S. Reinhardt, S. Gronin, G. Gardner, T. Lindemann, M. Manfra, C. Strunk, N. Paradiso; Physical Review X 12 (4), 041020 (2022).

Keywords: synthetic Rashba superconductors, non-centrosymmetric superconductors, vortex dynamics