Iridium 5$\textit{d}$-electron driven superconductivity in ThIr$_3$

TL;DR

This study reports the discovery and characterization of ThIr$_{3}$ as a 5d-electron driven superconductor with a critical temperature of 4.41 K, highlighting the role of iridium's 5d states in its superconductivity.

Contribution

The paper provides the first detailed synthesis, experimental characterization, and band structure analysis of ThIr$_{3}$, revealing its moderate-strength superconductivity driven mainly by iridium 5d electrons.

Findings

ThIr$_{3}$ is a type II superconductor with T$_{c}$ = 4.41 K.

Superconductivity is mainly governed by iridium 5d states.

Electronic interactions may compete with superconductivity in ThIr$_{3}$.

Abstract

Polycrystalline sample of superconducting ThIr$_{3}$ was obtained by arc-melting Th and Ir metals. Powder x-ray diffraction revealed that the compound crystalizes in a rhombohedral crystal structure (R-3m, s.g. no. 166) with the lattice parameters: a = 5.3394(1) $\r{A}$ and c = 26.4228(8) $\r{A}$. Normal and superconducting states were studied by magnetic susceptibility, electrical resistivity and heat capacity measurements. The results showed that ThIr$_{3}$ is a type II superconductor (Ginzburg-Landau parameter $\kappa$ = 38) with the critical temperature T$_{c}$ = 4.41 K. The heat capacity data yielded the Sommerfeld coefficient $\gamma$ = 17.6 mJ mol$^{-1}$ K$^{-2}$ and the Debye temperature $\Theta_{D}$ = 169 K. The ratio $\Delta$C / ($\gamma$ T$_{c}$) = 1.6, where $\Delta$C stands for the specific heat jump at T$_{c}$, and the electron-phonon coupling constant $\lambda_{e-p}$ = 0.74 suggest that ThIr$_{3}$ is a moderate-strength superconductor. The experimental studies were supplemented by band structure calculations, which indicated that the superconductivity in ThIr$_{3}$ is governed mainly by 5d states of iridium. The significantly smaller band-structure value of Sommerfeld coefficient as well as the experimentally observed quadratic temperature dependence of resistivity and enhanced magnetic susceptibility suggest presence of electronic interactions in the system, which compete with superconductivity.