On the Origin of Superconductivity at Nickel-Bismuth Interfaces

Abstract

Unconventional superconductivity has been suggested to be present at the interface between bismuth and nickel in thin-film bilayers. In this work, we study the structural, magnetic and superconducting properties of sputter deposited Bi/Ni bilayers. As-grown, our films do not display a superconducting transition, however, when stored at room temperature, after about 14 days our bilayers develop a superconducting transition up to 3.8 K. To systematically study the effect of low temperature annealing on our bilayers, we perform structural characterization with X-ray diffraction and polarized neutron reflectometry, along with magnetometry and low temperature electrical transport measurements on samples annealed at $70{}^{\circ }$C. We show that the onset of superconductivity in our samples is coincident with the formation of ordered NiBi${}_3$ intermetallic alloy, a known $s$-wave superconductor. We calculate that the annealing process has an activation energy of $(0.86\pm 0.06)$eV. As a consequence, gentle heating of the bilayers will cause formation of the superconducting NiBi${}_3$ at the Ni/Bi interface, which poses a challenge to studying any distinct properties of Bi/Ni bilayers without degrading that interface.

arXiv comment13 pages, 7 figures

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Cited by in corpus (5)

• Fully-gapped superconductivity with preserved time-reversal symmetry in NiBi${}_3$ single crystals
• Ni/Bi bilayers: The effect of thickness on the superconducting properties
• Absence of spontaneous time-reversal symmetry breaking and ferromagnetism in superconducting NiBi3 single crystal
• Observation of the crossover from quantum fluxoid to half-quantum fluxoid in a chiral superconducting device
• Charge-to-spin conversion in epitaxial and polycrystalline Bi and Bi/Ag layers