High-pressure synthesis and superconductivity of the novel Laves phase BaIr2

TL;DR

This study reports the successful synthesis of BaIr2, a new Laves phase superconductor with a Tc of 2.7 K, highlighting its weak-coupling nature and the influence of spin-orbit interaction on its electronic structure.

Contribution

First synthesis of BaIr2, a previously unsynthesized Laves phase, and characterization of its superconducting and electronic properties.

Findings

BaIr2 exhibits bulk superconductivity at 2.7 K.

BaIr2 is a type-II superconductor with an upper critical field of 67.7 kOe.

Electronic structure calculations show strong spin-orbit interaction effects.

Abstract

Superconductors comprising 5d transition metals of Ir and Pt have been widely explored because they have the potential of unique superconductivity caused by the strong spin-orbit interaction (SOI). We successfully synthesized BaIr2, the last Laves phase remaining unsynthesized in the MgCu2-type AM2 (A = Ca, Sr, Ba; M = Rh, Pd, Ir, Pt). BaIr2 was crystallized at 925 C under a pressure of 3.3 GPa via a solid-state reaction between Ba and Ir powders; it was found to have the longest a-lattice constant of 8.038(1) A among AM2. BaIr2 exhibited bulk superconductivity at a transition temperature (Tc) of 2.7 K. BaIr2 was found to have a type-II superconductor with an upper critical field of 67.7 kOe, which was above the Pauli paramagnetic limit (50 kOe). The electron-phonon coupling constant and normalized specific heat jump were measured to be 0.63 and 1.2, respectively, indicating that BaIr2 is a weak-coupling superconductor. The electronic-structure calculations for BaIr2 revealed that the Ir-5d states are dominant at the Fermi energy (EF) and the density of states at the EF is strongly affected by SOI as in the case of CaIr2 and SrIr2.