Orbital degrees of freedom play a key role in setting out striking effects when dealing with low dimensional noncentrosymmetric superconductors. A relevant concept in this context is represented by the orbital Rashba coupling. I show that, by varying the strength of the orbital Rashba interaction, the superconducting phase can undergo a 0−π transition with the π-phase being marked by a non-trivial sign change of the superconducting order parameter between different orbitals [1] (akin to the s+- phase). Then, I discuss the physical mechanisms for achieving orbital pair-density wave [2]. Breaking of time-reversal and point-group spatial symmetries can have a profound impact on superconductivity. Here, I show that in two-dimensional spin-singlet superconductors with unusually low degree of spatial symmetry content, a vortex state with supercurrents carrying orbital angular momentum around the core can form and be energetically stable [2]. The vortex has zero net magnetic flux since it is made up of counter-propagating Cooper pairs with opposite orbital moments. The orbital vortex has a characteristic pattern with a pronounced angular anisotropy that deviates from the profile of conventional magnetic vortices. Hence, I will discuss the Edelstein effects arising in multiorbital superconductors that lack inversion symmetry. It is known that the flow of supercurrent can induce a nonvanishing magnetization, a phenomenon which is at the heart of nondissipative magnetoelectric effects. For electrons carrying spin and orbital moments, a question of fundamental relevance deals with the orbital nature of magnetoelectric effects in conventional spin-singlet superconductors with Rashba coupling. Remarkably, we find that the supercurrent-induced orbital magnetization is more than one order of magnitude greater than that due to the spin, giving rise to a colossal magnetoelectric effect [3]. An overview on materials which can exhibit these phenomena as well as orbitally driven transport and topological properties are also touched [4,5,6]. Finally, I will make a link between the impact of an electrostatic field on thin film metallic superconductors and the role of crystalline symmetry breaking to assess the observed effects of gate controlled supercurrent [7,8].  This research receives support by the EU’s Horizon 2020 research and innovation program under Grant Agreement nr. 964398 (SUPERGATE).

References

[1] M. T. Mercaldo et al., Phys. Rev. Applied 14, 034041 (2020). 
[2] M. T. Mercaldo et al., Phys. Rev. B 105, L140507 (2022). 
[3] L. Chirolli et al., Phys. Rev. Lett. 128, 217703 (2022). 
[4] Y. Fukaya et al., npj Quantum Materials 7, 99 (2022). 
[5] D. Go et al., EPL 135, 37001 (2021). 
[6] Y. Fukaya et al., arXiv:2209.11077 (2022). 
[7] G. De Simoni et al., Nature Nanotechnology 13, 802 (2018). 
[8] L. Ruf et al., https://arxiv.org/abs/2302.13734.