Superconductivity Appears in the Vicinity of an Insulating-Like Behavior in CeO$_{1-x}$F$_{x}$BiS$_{2}$

TL;DR

This study reveals that in CeO$_{1-x}$F$_{x}$BiS$_{2}$, superconductivity emerges near an insulating-like state, with evidence of coexisting ferromagnetism, challenging conventional understanding of superconducting phase diagrams.

Contribution

It demonstrates the appearance of superconductivity alongside insulating behavior in CeO$_{1-x}$F$_{x}$BiS$_{2}$, and suggests coexistence with ferromagnetism, differing from typical high-temperature superconductor systems.

Findings

Superconductivity appears with insulating normal state.

Parent CeOBiS$_2$ is a bad metal, not an insulator.

Ferromagnetism coexists with superconductivity in samples.

Abstract

Resistive and magnetization properties have been measured in BiS$_2$-based samples CeO$_{1-x}$F$_{x}$BiS$_{2}$ with a systematic substitution of O with F (0 $<$ x $<$ 0.6). In contrast to the band structure calculations, it is found that the parent phase of CeOBiS$_2$ is a bad metal, instead of an band insulator. By doping electrons into the system, it is surprising to find that superconductivity appears together with an insulating normal state. This evolution is clearly different from the cuprate and the iron pnictide systems, and is interpreted as approaching the von Hove singularity. Furthermore, ferromagnetism which may arise from the Ce moments, has been observed in the low temperature region in all samples, suggesting the co-existence of superconductivity and ferromagnetism in the superconducting samples.