Strong-coupling superconductivity of SrIr2 and SrRh2: Phonon engineering of metallic Ir and Rh

TL;DR

This study investigates the superconducting properties of SrIr₂ and SrRh₂ Laves phases, revealing strong electron-phonon coupling influenced by phonon modifications in their metallic structures, with experimental and theoretical insights.

Contribution

It provides new experimental and theoretical analysis of superconductivity in SrIr₂ and SrRh₂, highlighting the role of phonon engineering and spin-orbit coupling in these materials.

Findings

Superconducting transition temperatures of 6.07 K and 5.41 K confirmed.

Strong electron-phonon coupling mainly from low-frequency Ir and Rh vibrations.

Phonon modifications in Ir and Rh tetrahedrons enhance EPC compared to elemental metals.

Abstract

Experimental and theoretical studies on superconductivity in SrIr$_2$ and SrRh$_2$ Laves phases are presented. The measured resistivity, heat capacity, and magnetic susceptibility confirm the superconductivity of these compounds with $T_c$ = 6.07 K and 5.41 K, respectively. Electronic structure calculations show that the Fermi surface is mostly contributed by 5$d$ (4$d$) electrons of Ir (Rh), with Sr atoms playing the role of electron donors. The effect of the spin-orbit coupling is analyzed and found to be important in both materials. Lattice dynamics and electron-phonon coupling (EPC) are studied and the strong electron-phonon interaction is found, contributed mostly by the low-frequency Ir and Rh vibrations. The enhancement of EPC when compared to weakly-coupled metallic Ir and Rh is explained by the strong modifications in the propagation of phonons in the network of Ir (Rh) tetrahedrons, which are the building blocks of the Laves phase, and originate from the metallic fcc structures of elemental iridium and rhodium.