Quantum critical fluctuations in an Fe-based superconductor

We show that the characteristic scaling of a marginal Fermi liquid is present in inelastic light scattering data of an Fe-based superconductor tuned through a QCP by chemical doping. From the doping dependence of the imaginary time dynamics we were able to distinguish regions dominated by quantum critical behavior from those of classical critical responses. This dichotomy reveals a connection between the marginal Fermi liquid behavior and quantum criticality. In particular, the overlap between regions of high superconducting transition temperatures and quantum critical scaling suggests a contribution from quantum fluctuations to the formation of superconductivity.