Electronic Landscape of Ce-based Intermetallics: CeCu$_2$Si$_2$ at an Extreme

TL;DR

This study investigates how chemical substitution and pressure influence the electronic and magnetic phases of CeCu$_2$Si$_2$, revealing complex interactions between unit cell volume, electronic shell filling, and superconductivity.

Contribution

It demonstrates that chemical substitution can mimic high-pressure effects, providing new pathways to explore quantum phase transitions in Ce-based intermetallics.

Findings

Pressure suppresses magnetic order in CeCu$_2$Si$_2$ with chemical substitution.

Superconductivity reemerges at low disorder levels under pressure.

Electronic behavior is governed by a combination of unit cell volume and shell filling effects.

Abstract

CeCu$_2$Si$_2$ is an exemplary correlated electron metal that features two domes of unconventional superconductivity in its temperature-pressure phase diagram. The first dome surrounds an antiferromagnetic quantum critical point, whereas the more exotic second dome may span the termination point of a line of $f$-electron valence transitions. This behavior has received intense interest, but what has been missing are ways to access the high pressure behavior under milder conditions. Here we study Si $\rightarrow$ P chemical substitution, which compresses the unit cell volume but simultaneously weakens the hybridization between the $f$- and conduction electron states and encourages complex magnetism. At concentrations that show magnetism, applied pressure suppresses the magnetic ordering temperature and superconductivity is recovered for samples with low disorder. These results reveal that the electronic behavior in this system is controlled by a nontrivial combination of effects from unit cell volume and electronic shell filling. Guided by this topography we discuss prospects for uncovering a valence fluctuation quantum phase transition in the broader family of Ce-based ThCr$_2$Si$_2$-type materials through chemical substitution.