Pressure Induced 18 K Superconductivity and Two Superconducting Phases in CuIr2S4

TL;DR

This study discovers pressure-induced superconductivity in CuIr₂S₄ reaching 18.2 K, with two distinct phases emerging under high pressure linked to structural changes, surpassing previous temperature limits for this material class.

Contribution

It reports the first observation of two separate superconducting phases in CuIr₂S₄ under pressure, with the highest T_c of 18.2 K, and connects these phases to structural lattice distortions.

Findings

Superconductivity appears at pressures above 18 GPa.

Two distinct superconducting phases coexist over a broad pressure range.

A maximum T_c of 18.2 K is achieved, exceeding previous records.

Abstract

We report pressure-induced superconductivity in the spinel CuIr$_{2}$S$_{4}$ with a transition temperature ($T_{\text{c}}$) reaching \textbf{18.2 K}, establishing a new record for this class of materials and surpassing the decades-old limit of 13.7 K. Our electrical transport and synchrotron X-ray diffraction studies up to 224 GPa reveal the emergence of \textbf{two distinct superconducting phases} from a charge-ordered insulating state. The first phase (SC-I) appears around 18 GPa, and forms a dome-shaped superconducting region in which the resistivity exhibits a pronounced, field- and current-sensitive drop without reaching strict zero above our base temperature. Above 111.8 GPa, a second, lower-$T_{\text{c}}$ phase (SC-II) emerges and coexists with SC-I over a broad pressure range, and SC-II ultimately develops a true zero-resistance state above 122.2 GPa. These superconducting phases are intimately linked to a cascade of structural transitions that systematically distort the frustrated pyrochlore lattice of Ir atoms. Our results expand the potential for superconductivity in spinels and demonstrate a pathway to high-$T_{\text{c}}$ pairing directly from a correlated insulating state driven by lattice tuning.