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 • C. We show that the onset of superconductivity in our samples is coincident with the formation of ordered NiBi3 intermetallic alloy, a known s-wave superconductor. We calculate that the annealing process has an activation energy of (0.86±0.06) eV. As a consequence, gentle heating of the bilayers will cause formation of the superconducting NiBi3 at the Ni/Bi interface, which poses a challenge to studying any distinct properties of Bi/Ni bilayers without degrading that interface.

A Highly Reversible Lithium Metal Anode by Constructing Lithiophilic Bi‐Nanosheets

“…As shown in Figure S7a (Supporting Information), Bi 2 O 3 species (164.5, 159.3 eV) existed on the NBF surface before sputtering implying the slight oxidation of Bi. [53,54] Because of the existence of both Bi (162.6, 157.2 eV) and Ni (869.7, 852.5 eV) elements during sputtering, we infer the formation of NiBi or NiBi 3 alloy, [55,56] which strengthens the combination between Ni and Bi. The disappearance of Bi signal after 50 min argon ion sputtering means the thickness of modification layer is about 250 nm.…”

Topical Review of Quantum Materials and Heterostructures Studied by Polarized Neutron Reflectometry

“…[51] The most recent development in the study of superconductors has been the discovery of interfacial and 2D superconductors. Recently, a PNR study elucidated the origin of the unusual superconductivity of Ni/Bi interfaces, [52] showing that interfacial alloying can lead to a new superconducting phase of Ni 3 Bi. Currently, there is also growing interest in achieving superconductor/ ferromagnet bilayers for spin-triplet superconductivity.…”

Reaction-Diffusion-Driven Stoichiometric Gradient in Coevaporated Superconducting NiBi3 Thin Films

“…In contrast, NiBi 3 shows an interesting phenomenon called the coexistence of superconductivity and ferromagnetism (CSF), where the same electron is responsible for both magnetic and superconducting behavior. − So, synthesizing the pure phase of an NiBi 3 intermetallic compound in the form of thin films and filtering the Ni and Bi impurities still remain a challenge. There have been many reports on the synthesis of NiBi 3 by different methods, and the magnetic and superconducting behaviors depend on the methods of preparation. ,,− Further, different growth procedures result in mixed phases such as NiBi 3 with NiBi and trace Bi or trace Ni. The superconducting and magnetoresistance measurements of single crystals of NiBi 3 , grown by a self-flux method, is observed to be free of the NiBi phase and any other magnetic impurity, whereas ferromagnetic fluctuations exist on the surface of the crystal below 150 K .…”

“…Interestingly, NiBi and NiBi 3 are also observed to be superconductors with superconducting transition temperatures of 4.25 and 4.1 K, respectively. ,− It is well-known that magnetic impurities in a superconducting material suppresses the superconducting transition temperature as the copper pair is destroyed by the local magnetic field of the magnetic impurity. In contrast, NiBi 3 shows an interesting phenomenon called the coexistence of superconductivity and ferromagnetism (CSF), where the same electron is responsible for both magnetic and superconducting behavior. − So, synthesizing the pure phase of an NiBi 3 intermetallic compound in the form of thin films and filtering the Ni and Bi impurities still remain a challenge. There have been many reports on the synthesis of NiBi 3 by different methods, and the magnetic and superconducting behaviors depend on the methods of preparation. ,,− Further, different growth procedures result in mixed phases such as NiBi 3 with NiBi and trace Bi or trace Ni.…”