Enhanced Tc and multiband superconductivity in the fully-gapped ReBe22 superconductor

• Published in: New journal of physics Vol. 21; no. 7; pp. 073034 - 73049
• Main Authors: Shang, T, Amon, A, Kasinathan, D, Xie, W, Bobnar, M, Chen, Y, Wang, A, Shi, M, Medarde, M, Yuan, H Q, Shiroka, T
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 23.07.2019
• Subjects: BCS theory; Coupling; Critical field (superconductivity); Fluids; intermetallics; multigap; Muon spin relaxation; Muon spin rotation; Physics; Rhenium; Superconductivity; Superfluidity; Temperature dependence; time-reversal symmetry; μSR
• ISSN: 1367-2630
• DOI: 10.1088/1367-2630/ab307b

In search of the origin of superconductivity (SC) in diluted rhenium superconductors and their significantly enhanced Tc compared to pure Be (0.026 K), we investigated the intermetallic ReBe22 compound, mostly by means of muon-spin rotation/relaxation ( SR). At a macroscopic level, its bulk SC (with Tc = 9.4 K) was studied via electrical resistivity, magnetization, and heat-capacity measurements. The superfluid density, as determined from transverse-field SR and electronic specific-heat measurements, suggest that ReBe22 is a fully-gapped superconductor with some multigap features. The larger gap value, Δ 0 l = 1.78 k B T c , with a weight of almost 90%, is slightly higher than that expected from the BCS theory in the weak-coupling case. The multigap feature, rather unusual for an almost elemental superconductor, is further supported by the field-dependent specific-heat coefficient, the temperature dependence of the upper critical field, as well as by electronic band-structure calculations. The absence of spontaneous magnetic fields below Tc, as determined from zero-field SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of ReBe22. In general, we find that a dramatic increase in the density of states at the Fermi level and an increase in the electron-phonon coupling strength, both contribute to the highly enhanced Tc value of ReBe22.