RESUMO
We report the observation of superconductivity in (Pt0.2Ir0.8)3Zr5 with a chiral space group (P6122) at low temperatures. The bulk nature of the superconductivity at a transition temperature of 2.2 K was confirmed using specific heat measurements. We revealed that (Pt0.2Ir0.8)3Zr5 obeys the weak-coupling Bardeen-Cooper-Schrieffer model, and the dominant mechanism in the upper critical field is the orbital pair-breaking limit rather than the Pauli-Clogston limit. This indicates that the antisymmetric spin-orbit coupling caused by the chiral crystal structure does not significantly affect the superconductivity of (Pt0.2Ir0.8)3Zr5.
RESUMO
Recently, c-axis negative thermal expansion (NTE) was observed in a CoZr2 superconductor and related transition-metal zirconides. Here, we investigated the structural, electronic, and superconducting properties of Co1-xNixZr2 to achieve systematic control of c-axis NTE and switching from NTE to positive thermal expansion (PTE) by Ni substitution. At x ≤ 0.3, c-axis NTE was observed, and the thermal expansion constant αc approached zero with increasing x. At x = 0.4-0.6, c-axis thermal expansion close to zero thermal expansion (ZTE) was observed, and PTE appeared for x ≥ 0.7. On the superconducting properties, we observed bulk superconductivity for x ≤ 0.6, and bulk nature of superconductivity is suppressed by Ni heavy doping (x ≥ 0.7). For x ≤ 0.6, the evolution of the electronic density of states well explains the change in the superconducting transition temperature (Tc), which suggests conventional phonon-mediated superconductivity in the system. By analyzing the c/a ratio, we observed a possible collapsed transition in the tetragonal lattice at around x = 0.6-0.8. The lattice collapse would be the cause of the suppression of superconductivity in Ni-rich Co1-xNixZr2 and the switching from NTE to PTE.
