Superconducting Compounds

We report a detailed characterization of the noncentrosymmetric superconductor Re 24 Ti 5 using powder x-ray diffraction (XRD), magnetic susceptibility, electrical resistivity, thermal conductivity, Seebeck coefficient, and specific heat measurements. Rietveld refinement of powder XRD data confirms that Re 24 Ti 5 crystallizes in the α-Mn structure. All measured quantities demonstrate a bulk superconducting transition at T c = 5.8 K. Our low-temperature specific heat data measured down to 0.5 K yield a Sommerfeld coefficient γ = 111.8 mJ mol −1 K −2 , which implies a high density of states at the Fermi level. Moreover, the electronic specific heat in the superconducting state was found to obey a typical s-wave expression, revealing a single gap /k B = 10.6 K. This value gives a ratio of 2 /k B T c = 3.68, higher than the value of 3.5 predicted from BCS theory. On this basis, we conclude that the noncentrosymmetric Re 24 Ti 5 compound can be characterized as a moderately coupled BCS-type superconductor. Furthermore, the obtained parameters from the present study of Re 24 Ti 5 were compared to those of the isostructural compound Re 23.8 Nb 5.2 , indicating the similarity between both systems.

Section: Introductionmentioning

confidence: 99%

Investigation of normal and superconducting states in noncentrosymmetric Re₂₄Ti₅

Lue¹,

Liu²,

Kuo³

et al. 2013

“…Although these materials have been extensively studied, we can find only a few results on superconductivity in this system. Superconductivity has been reported for TaB and Ta 2 B with critical temperatures of 4.0 and 3.12 K, respectively [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Ta_1−xHf_xB: a new FeB-prototype superconductor

Machado¹,

Corrêa²,

Luz

et al. 2015

In this work, we report superconductivity in the new ternary Ta 1−x Hf x B system. We also show clearly evidence that appropriate amounts of Hf substitution at the Ta site induce the stabilization of the orthorhombic FeB prototype structure in this system. Bulk superconductivity is confirmed by magnetization, electronic transport and specific heat measurements. The Hall signal has temperature dependence and the specific heat data at low temperature deviate from the conventional exponential temperature dependence in Ta 0.7 Hf 0.3 B. These results suggest multiband superconductivity in this compound.

“…Superconducting systems containing rhenium have also been synthesized, for example ReB (T c = 2.8 K) [10], Re 3 B (T c = 4.7 K), ReB 2 (T c = 4.5-6.3 K) [11] and Re 7 B 3 (T c = 3.3 K) [12]. With regard to Mo-Re alloys, superconductivity was confirmed by Collver et al [13], who studied superconducting transition temperatures in 4d-5d (Mo-Re) and in 5d-5d (W-Re) amorphous and crystalline alloys.…”

Section: Introductionmentioning

confidence: 99%

The effect of structure on flux instability and on the superconducting properties of the Mo₂Re₃B_x–Mo₃Re₂B_xeutectic

Andrzejewski¹,

Guilmeau²,

Kowałczyk³

2008

We report on the structure and basic properties of a new eutectic system composed of Mo2Re3Bx and Mo3Re2Bx (x≈1) ternary borides. The alloy exhibits a complex globular structure and areas of locally ordered lamellar patterns. The superconducting areas are separated by a thin normal layer of excess boron and behave like an S–N–S′ Josephson junction network. Strong microwave absorption observed below 5 K implies a phase-locked transition having occurred in the network. The phase-locked state is accompanied by flux instability, most likely due to the rapid decoupling of the superconducting areas. A distinct, two-step superconducting transition was observed, which points to a lack of a proximity effect and demonstrates that the eutectic is an inhomogeneous system. The measured parameters of the dominating Mo3Re2Bx phase were Tc = 6.4 K, μ0Hc1 = 13 mT and μ0Hc2 = 6.5 T. These were found to correspond to the penetration depth λ = 2040 Å, coherence length ξ = 70 Å and Ginzburg–Landau parameter κ = 29. The linear temperature dependence of Hc2(T) in the Mo3Re2Bx phase implies a possible unconventional mechanism of pairing. The content of the minor Mo2Re3Bx phase was too low to warrant measurement of any parameters except the critical temperature Tc = 8.7 K.