Ballistic super-semi gate-defined nanowires based on Ge quantum wells

Majorana zero mode (MZM) is a promising candidate to realize the topological quantum computation, which is naturally immune to both decoherence and unitary error. Existence of MZMs in the semiconductor-superconductor hybrid nanowire depends on gap-to-disorder ratio. It is theoretically predicted that although the topological gap of Ge-based hybrid nanowire is smaller compared to the conventional InAs-based device, extremely high material quality of Ge quantum well makes the former have larger gap-to-disorder ratio [1]. We use gates to define a nanowire on a shallow Ge quantum well, which enables superconductor to be compatible in this platform, and observe up to 5 quantized conductance plateaus, which indicates low disorder level in the nanowire. We also notice a strong anisotropy of the effective g factor, which shows heavy hole character dominates. The observed large out-of-plane effective g factor is important for the future MZM device.



[1] Laubscher, K., Sau, J. D., & Das Sarma, S. (2024). Germanium-based hybrid semiconductor-superconductor topological quantum computing platforms: Disorder effects. Physical Review. B, 110(15), Article 155431. https://doi.org/10.1103/PhysRevB.110.155431