SFB Seminar

This talk will deal with the analysis of quantum materials platforms with potential impact in the area of spinorbitronics and superconducting spintronics which combine spin-orbit coupling, superconductivity and topological effects.

Topological states of matter are at present one of the most challenging and active fields in condensed matter physics and low-dimensional semiconducting nanomaterials are certainly key players. In this context, apart from the conventional material geometries the most recent advances in nanotechnology have made it possible to have at hand an entirely novel family of low-dimensional nanostructures: flexible semiconductor nanomaterials which are bent into curved, deformable objects ranging from semiconductor nanotubes, to nanohelices. Motivated by the excitement in both topological states of matter and novel shape deformed nanostructures, we have theoretically considered the possible interplay between curvature effects [1] on the electronic properties and the topological properties of the quantum states in low-dimensional nanomaterials. In this talk, I will firstly discuss how geometric effects in low-dimensional nanomaterials can lead to metal-insulator transition and promote the generation of topological states of matter by considering the paradigmatic example of quantum wires with RSOC coupling, which are periodically corrugated at the nanometer scale [2].  Remarkably, we demonstrate that a semiconductor wire patterned in a mesoscale serpentine shape upon the application of a rotating magnetic field, serving as the external ac perturbation, and in cooperation with the RSOC, which is modulated by the geometric curvature of the patterned wire, can realize the topological pumping protocol originally introduced by Thouless in an entirely novel fashion [3]. Then, I will present the intricate twist between spin texture and spin transport in shape deformed nanostructures. Non-uniform RSOC in shape deformed nanostructures drives spin textures with a tunable topological character having windings around the radial and the out-of-plane directions. These topologically non trivial spin patterns affect the electron spin interference in the deformed quantum ring, thereby resulting in a novel geometry-driven electronic transport behavior [4].

Finally, when considering the nature of the superconducting state in curved nanostructures we find a local enhancement or suppression of the superconducting order parameter, with the effect that can be tailored by tuning either the RSOC strength or the carrier density. Apart from the local superconducting spin-singlet amplitude control, the geometric curvature is shown to generate non-trivial textures of the spin-triplet pairs through a spatial variation of the d-vector.

In the second part of the talk, I will consider the interplay of superconductivity and magnetism in heterostructures with a special focus on topological superconductors. Within the superconducting systems, a notable case of superconductor with non-trivial topological number is the two dimensional (p+i p)-wave superconductor with time reversal symmetry breaking,   which has in the single layer SrRuO its leading candidate.

In this context I will shortly present various remarkable effects occurring at the interface/edge of chiral and helical spin-triplet superconductors: i) the spin-orbital coupling emerging at the interface with a ferromagnet (FM) [6,7], ii) the occurrence of magnetic Andreev states at their edge if the system allows for mixed singlet-triplet configurations [8,9,10], and iii) the control of spin- and charge currents at the interface between helical spin-triplet and ferromagnets [11], iv) as well as the possibility of having a magnetic field driven topological reorganization [12].

[Acknowledgements –EU- FET OPEN project “CNTQC” , grant agreement N. 618083 (http://www.nano2qc.eu/) ]

1) P. Gentile, M. Cuoco, C. Ortix, SPIN, Vol. 3, No. 2, 1340002 (2013).

2) P. Gentile, M. Cuoco, C. Ortix, Phys. Rev. Lett. 115, 256801 (2015).

3) S. Pandey, N. Scopigno, P. Gentile, M. Cuoco, C. Ortix, arXiv:1707.08773 (2017).

4) Z.-J. Ying, P. Gentile, C. Ortix, and M. Cuoco, Phys. Rev. B 94, 081406(R) (2016).

5) Z.-J. Ying, M. Cuoco, C. Ortix, and P. Gentile,  Phys. Rev. B 96, 100506(R) (2017).

6)  P. Gentile, M. Cuoco, A. Romano, C. Noce, D. Manske, P. M. R. Brydon, Phys. Rev. Lett. 111, 097003 (2013).

7)  D. Terrade, P. Gentile, M. Cuoco, and D. Manske, Phys. Rev. B 88, 054516 (2013). 

8) A. Romano, P. Gentile, C. Noce, I. Vekhter, M. Cuoco, Phys. Rev. Lett. 110, 267002 (2013).

9) A. Romano, P. Gentile, C. Noce, I. Vekhter, and M. Cuoco, Phys. Rev. B 93, 014510 (2016).

10) A. Romano, C. Noce, I. Vekhter, and M. Cuoco, Phys. Rev. B 96, 054512 (2017).

11) D. Terrade, D. Manske, and M. Cuoco, Phys. Rev. B 93, 104523 (2016).

12) M. T. Mercaldo, M. Cuoco, P. Kotetes, Phys. Rev. B 94, 140503(R) (2016)