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We investigate the kinetic inductance of hybrid nanowires consisting of epitaxial Al grown epitaxially on an InAs quantum well. The nanowires form the inductive element in lumped-element microwave resonators in the GHz regime. Both the kinetic inductance and the quality factor become strongly anisotropic as a function of the angle between wire and in-plane field. With increasing transverse field, the kinetic inductance first rapidly drops by about 1% and then slightly recovers before dropping more gradually. The quality factor drops in a similar non-monotonic fashion, but much more drastically, namely by 99.5%, indicating the emergence of an effective dissipation mechanism. The behavior varies only slightly on the direction of the wire with respect to the crystal lattice. Reference wires consisting of Al, that was grown epitaxially on GaAs wafers without quantum well, did show only regular orbital pair breaking.
Our observations can be quantitatively analyzed in terms of Bogoliubov Fermi surfaces [1], i.e., an anisotropic closing of the superconducting gap that is most pronounced in the direction transverse to the in-plane field [2]. Studying similar heterostructures, Phan et al. [3] did observe the biggest effect for magnetic field parallel to the wire and interpreted this as an anisotropy of the g-factor. The latter orientation of the anisotropy can also be explained as a consequence of residual pinned vortices [4].
[1] D. F. Agterberg, P. M. R. Brydon, C. Timm, Phys. Rev. Lett. 118, 127001 (2017)
[2] N. F. Q. Yuan, L. Fu, Phys. Rev. B 97, 115139 (2018)
[3] D. Phan et al., Phys. Rev. Lett. 128, 107701 (2022)
[4] L. Fuchs et al., Phys. Rev. X 12, 041020 (2022)