Spin transport in ferromagnet-InSb nanowire quantum devices

Vlad Pribiag
School of Physics and Astronomy, University of Minnesota
Wednesday, January 22, 2020
4:00 pm
NS2 1201
Topological excitations such as Majorana fermions provide unique pathways to fault-tolerant quantum computing. Recent progress in this direction has been enabled by proximity effects between non-superconducting materials and superconductors; however, further breakthroughs leading to topological quantum computation require developing new material systems that integrate semiconductors not only with superconductors, but also with epitaxial ferromagnets or antiferromagnets. Currently, Majorana devices based on semiconductors require application of an external magnetic field to induce spin splitting and open a helical gap – necessary to realize an odd-parity topological superconductor. However, the presence of this magnetic field limits the robustness of topological properties (by weakening the induced superconductivity). Moreover, the stringent requirements on its orientation with respect to the device greatly restrict the scalability of Majorana-based quantum information systems. A promising path forward is to realize Majorana modes without an applied magnetic field by closely integrating ferromagnets or antiferromagnets with semiconductors and superconductors. With this motivation, we have been studying ballistic InSb nanowire devices with ferromagnetic contacts [1]. I will discuss the results of magneto-transport measurements on these devices spanning from the many-modes regime to few modes, and will show that the magnetoresistance displays hysteretic features across this entire range of conductance regimes. I will discuss possible physical mechanisms underlying these observations, as well as implications for the development of Majorana devices that could operate without the need for external magnetic fields. 
[1] Yang et al., Spin transport in ferromagnet-InSb nanowire quantum devices, arXiv:1909.07431 
Ilya Krivorotov