Role of Local Ru Hexamers in Superconductivity of Ruthenium Phosphide

TL;DR

This study reveals high-temperature local Ru hexamer distortions in RuP, suggesting local electronic precursors play a key role in its superconductivity, distinct from magnetic fluctuation mechanisms.

Contribution

It uncovers local Ru hexamer distortions in RuP associated with electronic transitions, highlighting a non-magnetic pathway to superconductivity in ruthenium pnictides.

Findings

Large Ru6 hexamer distortions form above electronic transition

Local symmetry breaking occurs at high temperatures

Pseudogap fluctuations may influence superconductivity

Abstract

Superconductivity in binary ruthenium pnictides occurs proximal to and upon suppression of a mysterious non-magnetic ground state, preceded by a pseudogap phase associated with Fermi surface instability, and its critical temperature, T$_{c}$, is maximized around the pseudogap quantum critical point. By analogy with isoelectronic iron based counterparts, antiferromagnetic fluctuations became "usual suspects" as putative mediators of superconducting pairing. Here we report on a high temperature local symmetry breaking in RuP, the parent of the maximum-Tc branch of these novel superconductors, revealed by combined nanostructure-sensitive powder and single crystal X-ray total scattering experiments. Large local Ru$_{6}$ hexamer distortions associated with orbital-charge trimerization form above the two-stage electronic transition in RuP. While hexamer ordering enables the nonmagnetic ground state and presumed complex oligomerization, the relevance of pseudogap fluctuations for superconductivity emerges as a distinct prospect. As a transition metal system in which partial d-manifold filling combined with high crystal symmetry promotes electronic instabilities, this represents a further example of local electronic precursors underpinning the macroscopic collective behavior of quantum materials.