Resistive and magnetic 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 a band insulator. By doping electrons into the system, it is surprising to find that superconductivity appears together with a semiconducting normal state. This evolution is clearly different from the cuprate and the iron pnictide systems, and is interpreted as approaching the Pomeranchuk transition with a von Hove singularity and the possible charge-density-wave instability. Furthermore, ferromagnetism, which may arise from the Ce magnetic moments, has been observed in the low-temperature region in all samples, suggesting the coexistence of superconductivity and ferromagnetism in the superconducting samples.

• Received 24 August 2012

DOI:https://doi.org/10.1103/PhysRevB.86.214518