Double Nanowires for Hybrid Quantum Devices

Abstract

Parallel 1D semiconductor channels connected by a superconducting strip constitute the core platform in several recent quantum device proposals that rely, for example, on Andreev processes or topological effects. In order to realize these proposals, the actual material systems must have high crystalline purity, and the coupling between the different elements should be controllable in terms of their interfaces and geometry. A strategy for synthesizing double InAs nanowires by the vapor‐liquid‐solid mechanism using III‐V molecular beam epitaxy is presented. A superconducting layer is deposited onto nanowires without breaking the vacuum, ensuring pristine interfaces between the superconductor and the two semiconductor nanowires. The method allows for a high yield of merged as well as separate parallel nanowires with full or half‐shell superconductor coatings. Their utility in complex quantum devices by electron transport measurements is demonstrated.

Asymmetric Little–Parks oscillations in full shell double nanowires

“…Here, we report the Little-Parks effect in closely-spaced InAs double nanowires fully covered by a thin epitaxial superconducting Al shell 13 . The nanowires are used as a template to shape the shell.…”

“…The InAs double nanowires are grown by the vapor-liquid-solid method, with Au droplets as growth catalysts. The growth is followed by in-situ Al epitaxy 13,16 . A typical example of the as-grown Al-coated double nanowires is shown in the scanning electron micrograph Fig.…”

“…1b, and 2) corner-to-corner (C-C). The relative orientations are chosen by properly designing the positions of the gold droplets through electron beam lithography; however, the exact relative positions are subject to variability 13 . The primary sources of misalignment may relate to the Au particle formation mechanism and to Au particle diffusion.…”

“…The clamping of the upper segments of these nanowires, which appears to be responsible for the observed single shell behavior, may be avoided by the growth of thicker, less flexible double nanowires 13 . Independent Little-Parks oscillations in the two nanowires may aid in attaining independent pairs of flux-induced Majorana zero modes in each nanowire, while the shared phase winding demonstrated in this work may be of utility to further characterize Majorana zero modes.…”

“…As the single-cylinder model predicts the presence of the asymmetry for any misalignment, the degree of asymmetry can be used as an accurate measurement of the degree of misalignment of the field with the long axis of the sample. For completeness, we note that similar double nanowires, however, with only half-shell superconductor coverage are addressed in several parallel works [13][14][15] . arXiv:2106.01181v1 [cond-mat.supr-con] 2 Jun 2021…”