The emergence of superconductivity in BaNi2(Ge1-xPx)2 at a structural instability

TL;DR

This study investigates how substituting phosphorus for germanium in BaNi2(Ge1-xPx)2 suppresses a structural dimer transition and induces superconductivity, revealing phonon softening and electron-phonon coupling enhancements near the critical composition.

Contribution

It demonstrates that dimer breaking via chemical substitution can induce superconductivity at a structural instability in BaNi2(Ge1-xPx)2, a novel tuning mechanism.

Findings

Superconductivity emerges near x=0.7 with Tc up to 2.9 K.

Structural transition to orthorhombic symmetry is suppressed at the critical composition.

Phonon softening and enhanced electron-phonon coupling are observed at the instability.

Abstract

The physical properties and structural evolution of the 122-type solid solution BaNi2(Ge1-xPx)2 are reported. The in-plane X-X (X = Ge1-xPx) dimer formation present in the end member BaNi2Ge2, which results in a structural transition to orthorhombic symmetry, is completely suppressed to zero temperature on P substitution near x = 0.7, and a dome-shape superconducting phase with a maximum Tc = 2.9 K emerges. Clear indications of phonon softening and enhanced electron-phonon coupling are observed at the composition of the structural instability. Our findings show that dimer breaking offers new possibilities as a tuning parameter of superconductivity.