Magnetic Kagome Superconductor CeRu$_2$

TL;DR

This study explores the coexistence and interplay of superconductivity and magnetism in the kagome lattice superconductor CeRu$_2$, revealing pressure-tuned phase transitions and a complex phase diagram with potential for novel quantum states.

Contribution

It provides the first detailed investigation of pressure effects on superconductivity and magnetism in CeRu$_2$, highlighting the intertwined nature of these orders in a kagome lattice.

Findings

Superconductivity in CeRu$_2$ persists up to 6 K at ambient pressure.

High pressure induces a resurgence of superconductivity above 28 GPa.

Pressure causes complex phase transitions and the emergence of secondary superconducting states.

Abstract

Materials with a kagome lattice provide a platform for searching for new electronic phases and investigating the interplay between correlation and topology. Various probes have recently shown that the kagome lattice can host diverse quantum phases with intertwined orders, including charge density wave states, bond density wave states, chiral charge order, and, rarely, superconductivity. However, reports of the coexistence of superconductivity and magnetic order in kagome materials remain elusive. Here we revisit a magnetic superconductor CeRu$_2$ with a kagome network formed by Ru atoms. Our first-principles calculations revealed a kagome flat band near the Fermi surface, indicative of flat-band magnetism. At ambient pressure, CeRu$_2$ exhibits a superconducting transition temperature ($T_{\text{c}}$) up to ~ 6 K and a magnetic order at ~ 40 K. Notably, superconductivity and related behavior can be tuned by adjusting the amount of Ru. We conducted a systematic investigation of the superconductivity and magnetic order in CeRu$_2$ via magnetic, resistivity, and structural measurements under pressure up to ~ 168 GPa. An unusual phase diagram that suggests an intriguing interplay between the compound's superconducting order parameters has been constructed. A $T_{\text{c}}$ resurgence was observed above pressure of ~ 28 GPa, accompanied by the sudden appearance of a secondary superconducting transition. Our experiments have identified tantalizing phase transitions driven by high pressure and suggest that the superconductivity and magnetism in CeRu$_2$ are strongly intertwined.