# Superconductivity and quantum criticality in heavy fermions CeIrSi$_3$ and CeRhSi$_3$

## TL;DR

This study investigates the relationship between superconductivity and quantum criticality in heavy fermion compounds CeIrSi$_3$ and CeRhSi$_3$, revealing pressure-dependent changes in their superconducting gap structures and suggesting a link with antiferromagnetic order.

## Contribution

It introduces a novel high-resolution measurement system for studying superconducting gap structures under pressure and provides new insights into the connection between unconventional superconductivity and magnetic quantum critical points.

## Key findings

- CeIrSi$_3$ exhibits a transition from nodal to fully gapped superconductivity near the QCP.
- CeRhSi$_3$ maintains a nodal gap across all pressures studied.
- Unconventional behaviors may be linked to coexisting antiferromagnetic order.

## Abstract

Superconductivity and magnetism are mutually exclusive in most alloys and elements, so it is striking that superconductivity emerges around a magnetic quantum critical point (QCP) in many strongly correlated electron systems (SCES). In the latter case superconductivity is believed to be unconventional and directly influenced by the QCP. However, experimentally unconventional superconductivity has neither been established nor directly been linked to any mechanism of the QCP. Here we report measurements in the heavy-fermion superconductors CeIrSi$_3$ and CeRhSi$_3$. The measurements were performed with a newly developed system, first of its kind, that allows high-resolution studies of the superconducting gap structure under pressure. Superconductivity in CeIrSi$_3$ shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi$_3$ does not possess an obvious pressure-tuned QCP and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that unconventional behaviours may be connected with the coexisting antiferromagnetic order. This study provides a new viewpoint on the interplay of superconductivity and magnetism in SCES.