Multifaceted effects of spin fluctuations mediating pairing in the cuprate superconductors

In unconventional cuprate superconductors, pairing is hypothesized as being mediated by spin fluctuations arising from electron-electron interactions. A long-standing issue is the apparent dual roles, enabling pairing and being paired, played by the same electrons in a single low energy band. Here we study this problem in Nd_2-xCe_xCuO₄ using angle-resolved photoemission spectroscopy and specific heat. Near optimal doping, improved experimental conditions enable unambiguous detection of Bogoliubov quasiparticles that show the strongest coherence peak and the maximum superconducting gap at the antiferromagnetic “hot spot” momenta. In contrast, the same momenta also host strong antiferromagnetic suppression of states, manifesting in a small specific heat anomaly. Our findings indicate spin fluctuations provide two intertwined ingredients, pairing potential strength and density of states within the antiferromagnetic gap, whose competition bounds superconductivity.