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

Here, we report on a new kind of compound, X delta Ir4X12-delta(X = P, As), thefirst hole-doped skutterudites superconductor. We provide atomic-resolution images ofthe caging As atoms using scanning transmission electron microscopy (STEM). Byinserting As atoms into the caged structure under a high pressure, superconductivityemerges 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 theFermi level in X delta Ir4X12-delta are dominated by the caged X atom, which can be described bya simple body-centered tight-binding model, implying a distinct pairing mechanism. Ourdensity functional theory (DFT) calculations reveal an intimate relationship betweenthe pressure-dependent local-phonon mode and the enhancement ofTc. The discoveryof X delta Ir4X12-delta provides an arena to investigate the uncharted territory of hole-doped skutterudites, and the method proposed hererepresents a new strategy of carrier doping in caged structures, without introducing extra elements

Automated summary

A new kind of compound, X delta Ir4X12-delta, the first hole-doped skutterudites superconductor, is reported. Atomic-resolution images of caging As atoms are provided using scanning transmission electron microscopy (STEM). By inserting As atoms into the caged structure under high pressure, superconductivity emerges with a maximum transition temperature (Tc) of 4.4 K (4.8 K) in IrAs3 (IrP3). The electronic states in X delta Ir4X12-delta are dominated by the caged X atom, suggesting a distinct pairing mechanism. Density functional theory (DFT) calculations reveal a close relationship between the pressure-dependent local-phonon mode and the enhancement of Tc. The discovery of X delta Ir4X12-delta provides a new arena to investigate hole-doped skutterudites, and the proposed method represents a new strategy of carrier doping in caged structures without introducing extra elements.