University of Minnesota
School of Physics & Astronomy
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Martin Greven

Universal relation between magnetic resonance and superconducting gap in unconventional superconductors
G. Yu, Y. Li, E. M. Motoyama, M. Greven , Nature Physics 5, 873 (2009)

Download from http://www.nature.com/nphys/journal/v5/n12/full/nphys1426.html

Abstract

Unconventional superconductors such as the high-transition temperature cuprates, heavy-fermion systems and iron arsenide-based compounds exhibit antiferromagnetic fluctuations that are dominated by a resonance, a collective spin-one excitation mode in the superconducting state. Here we demonstrate the existence of a universal linear relation, $Er \propto 2\Delta$, between the magnetic resonance energy (Er) and the superconducting pairing gap ($\Delta$), spanning two orders of magnitude in energy. This relation is valid for materials that range from being close to the Mott-insulating limit to being on the border of itinerant magnetism. Since the common excitonic picture of the resonance has not led to such universality, our observation suggests a much deeper connection between antiferromagnetic fluctuations and unconventional superconductivity.