Two-band superconductivity in a Mo–Re alloy with an equal concentration of the components

Abstract

An observed correlation between the critical temperature of a superconducting transition in high-temperature superconductors and a proximity of their electronic structure to the topological Lifshitz transition needs to be verified on simple model materials. Here we show that such an object could be a Mo–Re alloy with an equal concentration of constituent elements. We present new evidence of the presence of two energy gaps in this material, obtained using point-contact spectroscopy, and argue that the studied Mo–Re alloy can be used for implementing new quantum effects associated with the phase difference of electron wave functions from the different bands.

Proximity Effect between a Two-Band Superconductor and a Ferromagnet

“…[6] were in good agreement with 2.3 meV and 0.7 meV as well as with 1.9 meV and 0.5 meV for a Mo0.6Re0.4 alloy obtained by other authors [19]. 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.…”

“…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].…”

Control of the effective value of the critical current of the RF SQUID by the high-frequency electromagnetic field

“…However, the experiments made in this work demonstrate that variations of the HF field amplitude effectively transform the characteristics of RF SQUIDs from a classical hysteretic regime to a regime formally similar to nonhysteretic. 8,9 Such control of the main parameter of the RF SQUID is particularly interesting for two-zone superconductors [10][11][12] and HTSs. 13,14 Somewhat unexpectedly, the regions with conversion coefficients exceeding the classical value for the hysteretic regime were observed at the AFCs of RF SQUIDs during this transformation.…”