Itinerant effects and enhanced magnetic interactions in Bi-based multilayer cuprates

The cuprate high temperature superconductors exhibit a pronounced trend in which the superconducting transition temperature T-c increases with the number of CuO2 planes n in the crystal structure. We compare the magnetic excitation spectrum of Bi2+xSr2-xCuO6+delta (Bi-2201) and Bi(2)Sr(2)Ca(2)Cu3O(10+delta) (Bi-2223), with n = 1 and 3, respectively, using Cu L-3-edge resonant inelastic x-ray scattering. Near the antinodal zone boundary we find the paramagnon energy in Bi-2223 is substantially higher than that in Bi-2201, indicating that multilayer cuprates host stronger effective magnetic exchange interactions, providing a possible explanation for the T-c vs n scaling. In contrast, the nodal direction exhibits very strongly damped, almost nondispersive excitations. We argue that this implies that the magnetism in the doped cuprates is partially itinerant in nature.