Spin-fluctuation-mediated unconventional superconductivity can emerge at the border of magnetism, featuring a superconducting order parameter that changes sign in momentum space. Detection of such a sign-change is experimentally challenging, since most probes are not phase-sensitive. The observation of a spin resonance mode (SRM) from inelastic neutron scattering is often seen as strong phase-sensitive evidence for a sign-changing superconducting order parameter, by assuming the SRM is a spin-excitonic bound state. Here, we show that for the heavy fermion superconductor CeCoIn5, its SRM defies expectations for a spin-excitonic bound state, and is not a manifestation of sign-changing superconductivity. Instead, the SRM in CeCoIn5 likely arises from a reduction of damping to a magnon-like mode in the superconducting state, due to its proximity to magnetic quantum criticality. Our findings emphasize the need for more stringent tests of whether SRMs are spin-excitonic, when using their presence to evidence sign-changing superconductivity.
@article{arxiv.2005.08441,
title = {Nature of the spin resonance mode in CeCoIn$_5$},
author = {Yu Song and Weiyi Wang and John S. Van Dyke and Naveen Pouse and Sheng Ran and Duygu Yazici and A. Schneidewind and Petr Cermak and Y. Qiu and M. B. Maple and Dirk K. Morr and Pengcheng Dai},
journal= {arXiv preprint arXiv:2005.08441},
year = {2020}
}
Comments
accepted for publication in Communications Physics