Microscopic analysis of proximity-induced superconductivity and metallization effects in superconductor-germanium hole nanowires

Abstract

Low-dimensional germanium hole devices are promising systems with many potential applications such as hole spin qubits, Andreev spin qubits, and Josephson junctions, and can serve as a basis for the realization of topological superconductivity. This vast array of potential uses for Ge largely stems from the exceptionally strong and controllable spin-orbit interaction (SOI), ultralong mean free paths, long coherence times, and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. However, when brought into proximity with a superconductor (SC), metallization normally diminishes many useful properties of a semiconductor, for instance, typically reducing the g factor and SOI energy, as well as renormalizing the effective mass. In this paper, we consider metallization of a Ge nanowire (NW) in proximity to a SC, explicitly taking into account the three-dimensional (3D) geometry of the NW. We find that proximitized Ge exhibits a unique phenomenology of metallization effects, where the 3D cross section plays a crucial role. For instance, in contrast to expectations, we find that SOI can be enhanced by strong coupling to the superconductor. We also show that the thickness of the NW plays a critical role in determining both the size of the proximity-induced pairing potential and metallization effects, since the coupling between the NW and SC strongly depends on the distance of the NW wave function from the interface with the SC. In the absence of electrostatic effects, we find that a sizable gap opens only in thin NWs ($d\lesssim 3$ nm). In thicker NWs, the wave function must be pushed closer to the SC by electrostatic effects in order to achieve a sizable proximity gap such that the required electrostatic field strength can simultaneously induce a strong SOI.

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Cited by in corpus (8)

• Majorana zero modes in gate-defined germanium hole nanowires
• Majorana bound states in germanium Josephson junctions via phase control
• Germanium-based hybrid semiconductor-superconductor topological quantum computing platforms: Disorder effects
• InP/GaSb core-shell nanowires: a novel hole-based platform with strong spin-orbit coupling for full-shell hybrid devices
• Superconducting Proximity Effect in Two-Dimensional Hole Gases
• Theory of superconducting proximity effect in hole-based hybrid semiconductor-superconductor devices
• Hole subband dispersions and strong `spin'-orbit coupling in a cylindrical Ge nanowire
• Supercurrent and multiple Andreev reflections in Ge hut nanowire Josephson Junctions