Pressure-induced reemergence of superconductivity in BaIr2Ge7 and Ba3Ir4Ge16 with cage structures

TL;DR

This study reports the discovery of pressure-induced reemergence of superconductivity in two cage-structured compounds, BaIr2Ge7 and Ba3Ir4Ge16, with increased critical temperatures linked to pressure-induced phonon softening.

Contribution

It reveals a novel pressure-induced reemergence of superconductivity in caged compounds, highlighting the role of cage shrinkage and phonon softening.

Findings

Superconductivity reemerges at higher Tc under pressure.

Reentrant superconductivity linked to cage structure changes.

High-pressure measurements support phonon softening mechanism.

Abstract

The clathrate-like or caged compounds have attracted continuing interest due to their structural flexibility as well as fertile physical properties. Here we report a pressure-induced reemergence of superconductivity in BaIr2Ge7 and Ba3Ir4Ge16, two new caged superconductors with two-dimensional building blocks of cage structures. After suppressing the ambient-pressure superconducting (SC-I) state, a new superconducting (SC-II) state emerges unexpectedly, with Tc increased to a maximum of 4.4 K and 4.0 K for BaIr2Ge7 and Ba3Ir4Ge16, respectively. Combined with high-pressure synchrotron x-ray diffraction and Raman measurements, we propose that the reemergence of superconductivity in the caged superconductors can be ascribed to a pressure-induced phonon softening linked to the cage shrink.