Anisotropic superconductivity and elongated vortices with unusual bound states in quasi-one-dimensional nickel-bismuth compounds

Abstract

We report low temperature scanning tunneling microscopy and spectroscopy studies of Ni-Bi films grown by molecular beam epitaxy. Highly anisotropic and twofold symmetric superconducting gaps are revealed in two distinct composites, Bi-rich NiBi3 and near-equimolar NixBi, both sharing quasi-one-dimensional crystal structure. We further reveal axially elongated vortices in both phases, but Caroli-de Gennes-Matricon states solely within the vortex cores of NiBi3. Intriguingly, although the localized bound state splits energetically off at a finite distance ~10 nm away from a vortex center along the minor axis of elliptic vortex, no splitting is found along the major axis. We attribute the elongated vortices and unusual vortex behaviors to the combined effects of twofold superconducting gap and Fermi velocity. The findings provide a comprehensive understanding of the electron pairing and vortex matter in quasi-one-dimensional superconductors

arXiv comment7 pages, 7 figures

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• Surface symmetry breaking and disorder effects on superconductivity in perovskite BaBi3 epitaxial films
• Moving vortices in anisotropic superconductors
• Enhancement of vortex liquid phase and reentrant behavior in NiBi3 single crystals
• Correlated electronic structure of high-temperature superconductor Ba${}_2$CuO${}_{3+\delta }$
• Quantized bound states around a vortex in anisotropic superconductors
• Anomalous superconducting proximity effect of planar Pb-RhPb2 heterojunctions in the clean limit
• Pearl vortices in anisotropic superconducting films