Mo-Re alloy: A new benchmark two-band superconductor

Abstract

Multigap superconductivity, emerging in metals with several bands crossing the Fermi level, favors exotic superconducting orders that have no equivalent in a single-band counterpart. In this context, it is important to search for new materials with well-established two (or more) gaps having distinctly different sizes. In this work, we confirm previous statements and present new evidence to support the claim that Mo-Re alloy with a comparable concentration of the components is a two-band/two-gap superconductor. The differential conductance spectra obtained in point-contact experiments demonstrate the presence of a bosonic, undamped collective mode and its harmonics associated with the superconducting state. Following previous works on MgB2, we have identified these features as manifestations of the so-called Leggett mode arising due to relative phase fluctuations between two superconducting order parameters.

Proximity Effect between a Two-Band Superconductor and a Ferromagnet

“…In the next publication [7], we presented point-contact evidences of the presence of two significantly distinct energy gaps ∆l = 1.65 meV and ∆s = 0.55 meV with the dominant contribution of the band with a smaller gap in a Mo-Re alloy with approximately equal component concentrations. In the paper [8], the presence of the two gaps was confirmed by revealing bosonic, undamped collective modes and their harmonics, which were identified as manifestation of a Leggett mode arising due to relative phase fluctuations between two superconducting order parameters. In all previous point-contact experiments, we were dealing with contacts formed by a silver tip and a Mo-Re alloy film.…”

“…The presence of two gaps has been experimentally confirmed in several other superconducting materials, such as Nb-doped SrTiO3 [3], pnictide superconductors [4,5], and Mo-Re alloy [6][7][8]. Despite the relatively large number of publications devoted to the unusual properties of systems based on two-gap superconductors, a number of experimental issues, including the proximity effect between dirty two-band superconductors (S) and ferromagnets (F), remain unclear.…”

“…The analysis of the measured curves is based on the oversimplified Blonder-Tinkham-Klapwijk (BTK) approach [7,8] employed to fit experimental data of S/F point-contact spectra with the interface being described by a single parameter 0 / ( )…”

“… related to its transparency, where U0δ(x) is the effective potential localized at the interface, and vF is the Fermi velocity. The second important fitting quantity is the so-called Dynes parameter Γ determined by the conditions of sample preparation and the temperature of the experiment [7,8]. When the normal counter-electrode is ferromagnetic, it should be noticed that its spin polarization is not a bulk property, as was often assumed, but at least partially an interface characteristic [16].…”