Unconventional superconductivity in many materials is believed to be mediated by magnetic fluctuations. It is an open question how magnetic order can emerge from a superconducting condensate and how it competes with the magnetic spin resonance in unconventional superconductors. Here we study a model $d$-wave superconductor that develops spin-density wave order, and find that the spin resonance is unaffected by the onset of static magnetic order. This result suggests a scenario, in which the resonance in ${\mathrm{Nd}}_{0.05}{\mathrm{Ce}}_{0.95}{\text{CoIn}}_5$ is a longitudinal mode with fluctuating moments along the ordered magnetic moments.

• Received 2 May 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.187002