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

Abstract

In search of the origin of superconductivity (SC) in diluted rhenium superconductors and their significantly enhanced T c compared to pure Be (0.026 K), we investigated the intermetallic ReBe 22 compound, mostly by means of muon-spin rotation/relaxation (μSR). At a macroscopic level, its bulk SC (with T c =9.4 K) was studied via electrical resistivity, magnetization, and heat-capacity measurements. The superfluid density, as determined from transverse-field μSR and electronic specific-heat measurements, suggest that ReBe 22 is a fully-gapped superconductor with some multigap features. The larger gap value, D = 1.78 l 0 T k B 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 bandstructure calculations. The absence of spontaneous magnetic fields below T c , as determined from zero-field μSR measurements, indicates a preserved time-reversal symmetry in the superconducting state of ReBe 22 . 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 T c value of ReBe 22 .

Probing nodeless superconductivity in LaMSi ( M=Ni , Pt) using muon-spin rotation and relaxation

“…A decrease in fluctuation frequency of electronic moments as temperature decreases may cause to increase. Similar behavior is observed in a number of superconductors [51][52][53]. However, the exact nature and source of this behavior is still unknown and therefore requires further investigation.…”

Multigap superconductivity in centrosymmetric and noncentrosymmetric rhenium-boron superconductors

“…Conversely, many conventional superconductors, as e.g., Al, Sn, and Zn, are located at T c /T F 10 −4 . Between these two categories lie several multigap superconductors, e.g., LaNiC 2 , Nb 5 Ir 3 O, ReBe 22 , NbSe 2 , and MgB 2 [60][61][62][63][64]. Although there is no conclusive evidence for them to be classified as unconventional superconductors, the rhenium-boron superconductors lie clearly far off the conventional band.…”

Quantifying the Charge Carrier Interaction in Metallic Twisted Bilayer Graphene Superlattices

“…It should be noted that Equation (3) in its full form has been never applied to the analysis of experimental R ( T ) data, because the sum of strongly non-linear integrals has over-parametrization problem. Moreover, the majority of all published works utilizes Equation (3) where only electron–phonon integrand, i.e., p = 5, is included [ 34 , 35 , 36 ].…”

“…Here, we implemented Equation (7) to fit the R ( T ) data in TBG superlattices. First of all, we tested the validity of Equation (7) to be a proper fitting tool for classical electron–phonon materials, including electron–phonon mediated superconductors, from which we chose ReBe 22 [ 34 ], as well as normal metal copper, and ferromagnetic iron and cobalt (for pure metals raw R ( T ) data were taken from the classical papers by White and Woods [ 40 ] and by Matula [ 41 ]), as well as for highly-compressed ε-phase of iron, which exhibits the superconducting state (for which raw R ( T ) data were reported by Shimizu et al [ 42 ] and by Jaccard et al [ 37 ]. In Figure 1 , we show R ( T ) data and data fits for these materials.…”

“… ρ ( T ) data and fits to generalized Bloch–Grüneisen (BG) equation (Equations (7) and (9)) for ( a ) pure Cu; ( b ) ReBe 22 ; ( c ) pure ferromagnetic γ-Fe; ( d ) pure ferromagnetic Co; and ( e , f ) pure non-ferromagnetic highly-compressed ε-Fe. The raw data are reported in [ 34 , 37 , 40 , 42 , 44 ]. The red is the fitting curve, and 95% confidence bands are shown by a pink shaded area.…”