Hiroki Hayamizu

Highly Anisotropic Gap Function in a Nonmagnetic Superconductor Y5Rh6Sn18

The low temperature specific heat of R 5 Rh 6 Sn 18 (R = Y, Lu) was measured under various magnetic fields ( H ) up to 8 T. In a zero field, electronic specific heat of Y 5 Rh 6 Sn 18 shows a T 3 dependence, indicating an anisotropic superconducting gap, although that of Lu 5 Rh 6 Sn 18 shows an exponential dependence. In addition, the coefficient of the T -linear term γ( H ) of Y 5 Rh 6 Sn 18 in specific heat in the mixed state is found to obey a square root dependence. This is another evidence that Y 5 Rh 6 Sn 18 has the anisotropic superconducting gap. On the other hand, the γ( H ) of Lu 5 Rh 6 Sn 18 shows linear dependence, which means the isotropic superconducting gap.

Superconducting Properties of Ca3T4Sn13 (T = Co, Rh, and Ir)

We present the results of the superconducting properties of R 3 T 4 Sn 13 (R = La, Sr, and Ca; T = Co, Rh, and Ir) with quasi skutterudite structure by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. It is shown that the superconductivity is of conventional s-wave type and lies in the extremely strong-coupling regime. Electron–phonon coupling constants λ ep were estimated to be almost 1 for R 3 T 4 Sn 13 , respectively. The result can be categorized as a strong-coupling superconductor; this categorization is in good agreement with the results of specific heat measurements. The λ ep and the electronic density of states at the Fermi level ( N ( E F )) increases with the superconducting transition temperature. However, superconducting transition temperature of Co-compound cannot be explained by the difference of N ( E F ). From these results, we concluded that T c of R 3 T 4 Sn 13 can be described by the strength of the λ ep .

Superconducting State in the Ternary Germanide Y2AlGe3 with Related ThCr2Si2-Type Structure

Superconductivity in a ternary germanide, Y 2 AlGe 3 , was revealed at the transition temperature of 4.5 K by electrical resistivity and magnetic susceptibility measurements. The magnetization versus magnetic field ( M – H ) curve indicated that Y 2 AlGe 3 was a type-II superconductor. The lower critical field H c1 (0) and the upper critical field H c2 (0) were estimated to be 1.66(8) mT and 1.26(15) T. The coherence length ξ(0) GL , penetration depth λ(0) GL , and Ginzburg–Landau (GL) parameter κ(0) obtained from the critical fields were 16.2(5) nm, 631(16) nm, and 38(3), respectively. Specific heat measurements revealed that Y 2 AlGe 3 was a weak-coupling BCS superconductor with an isotropic superconducting gap. The electron–phonon mass enhancement parameter λ γ was calculated to be 0.13, which was in good agreement with the weak-coupling limit inferred from the specific heat Δ C e /γ T c and 2Δ(0)/ k B T c .