Unconventional pairing in single FeSe layers

Abstract

Superconductivity in single FeSe layers on SrTiO${}_{3}$ shows a much higher critical temperature ${T}_{c}$ than in bulk FeSe, illustrating the potential of interface engineering. Yet the underlying mechanism of boosting ${T}_{c}$ is not understood. Both conventional and unconventional pairing mechanisms have been suggested to be responsible for this effect. Here, the authors show experimentally that phonons do not contribute significantly to the high ${T}_{c}$ but instead the intrinsic spin fluctuations of the electrons themselves lead to Cooper pairing.