On two Be-based superconductors

MoBe₂₂ and WBe₂₂ compounds belong to the binary XBe₂₂ (X = 4d or 5d metal) family of superconductors, whose critical temperature depends strongly on X. Despite the multiphase nature of these samples, it is possible to investigate the superconducting properties of MoBe₂₂ and WBe₂₂ at the macro- and microscopic level. A concurrent analysis by means of magnetization and heat-capacity measurements, as well as muon-spin spectroscopy (μSR) was implemented. At ambient pressure, both compounds enter the superconducting state below 2.6 ± 0.1 K (MoBe₂₂) and 4.1 ± 0.10 K (WBe₂₂) and show modest upper critical fields [(μ₀H_c2(0) = 48 ± 1 mT and μ₀H_c2(0) = 58 ± 1 mT, respectively]. In WBe₂₂, the temperature-dependent superfluid density suggests a fully gapped superconducting state, well-described by an s-wave model with a single energy gap. Heat-capacity data confirm that such a model applies to both compounds. Finally, ac magnetic susceptibility measurements under applied pressures up to 2.1 GPa reveal a linear suppression of the superconducting temperature, typical of conventional superconducting compounds.