Multigap superconductivity and Shubnikov–de Haas oscillations in single crystals of the layered boride OsB2

Abstract

Single crystals of superconducting OsB2 [Tc=2.10(5) K] have been grown using a Cu-B eutectic flux. We confirm that OsB2 crystallizes in the reported orthorhombic structure (space group Pmmn) at room temperature. Both the normal and superconducting state properties of the crystals are studied using various techniques. Heat capacity versus temperature C(T) measurements yield the normal state electronic specific heat coefficient γ=1.95(1) mJ/mol K2 and the Debye temperature ΘD=539(2) K. The measured frequencies of Shubnikov–de Haas oscillations are in good agreement with those predicted by band structure calculations. Magnetic susceptibility χ(T,H), electrical resistivity ρ(T), and C(T,H) measurements (H is the magnetic field) demonstrate that OsB2 is a bulk low-κ [κ(Tc)=2(1)] type-II superconductor that is intermediate between the clean and dirty limits [(ξ(T=0)/ℓ=0.97)] with a small upper critical magnetic field Hc2(T=0)=186(4) Oe. The penetration depth is λ(T=0)=0.300 μm. An anomalous (not single-gap BCS) T dependence of λ was fitted by a two-gap model with Δ1(T=0)/kBTc=1.9 and Δ2(T=0)/kBTc=1.25, respectively. The discontinuity in the heat capacity at Tc, ΔC/γTc=1.32, is smaller than the weak-coupling BCS value of 1.43, consistent with the two-gap nature of the superconductivity in OsB2. An anomalous increase in ΔC at Tc of unknown origin is found in finite H; e.g., ΔC/γTc≈2.5 for H≈25 Oe.

Source-reported materials — not catalogue approval

Similar papers