Caging-Pnictogen-Induced Superconductivity in Skutterudites IrX3 (X = As, P)

TL;DR

This study reports the discovery of hole-doped skutterudite superconductors XδIr4X12-δ (X = P, As), highlighting their unique electronic states, pressure effects on Tc, and a novel doping strategy without extra elements.

Contribution

It introduces the first hole-doped skutterudite superconductors and demonstrates a new doping method using caged structures without adding additional elements.

Findings

Superconductivity with Tc up to 4.8 K in IrAs3 and IrP3.

Electronic states dominated by caged X atoms, differing from electron-doped skutterudites.

Pressure influences local phonon modes and enhances Tc.

Abstract

Here we report on a new kind of compound, X{\delta}Ir4X12-{\delta} (X = P, As), the first hole-doped skutterudites superconductor. We provide atomic resolution images of the caging As atoms using scanning transmission electron microscopy (STEM). By inserting As atoms into the caged structure under a high pressure, superconductivity emerges with a maximum transition temperature (Tc) of 4.4 K (4.8 K) in IrAs3 (IrP3). In contrast to all of the electron-doped skutterudites, the electronic states around the Fermi level in X{\delta}Ir4X12-{\delta} are dominated by the caged X atom, which can be described by a simple body-centered tight-binding model, implying a distinct paring mechanism. Our density functional theory (DFT) calculations reveal an intimate relationship between the pressure-dependent local-phonon mode and the enhancement of Tc. The discovery of X{\delta}Ir4X12-{\delta} provides an arena to investigate the uncharted territory of hole-doped skutterudites, and the method proposed here represents a new strategy of carrier doping in caged structures, without introducing extra elements.