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

TL;DR

This study compares magnetic excitations in Bi-based multilayer cuprates with different numbers of CuO2 planes, revealing stronger magnetic interactions in multilayer structures which may explain higher superconducting transition temperatures.

Contribution

It provides the first direct comparison of magnetic excitation spectra in Bi-2201 and Bi-2223 using RIXS, linking multilayer structure to magnetic exchange strength and superconductivity.

Findings

Paramagnon energy is higher in Bi-2223 than in Bi-2201 near the anti-nodal zone boundary.

Magnetic excitations in the nodal direction are strongly damped and nearly non-dispersive.

Magnetism in doped cuprates appears to be partially itinerant in nature.

Abstract

The cuprate high temperature superconductors exhibit a pronounced trend in which the superconducting transition temperature, $T_{\rm c}$, increases with the number of CuO$_2$ planes, $n$, in the crystal structure. We compare the magnetic excitation spectrum of Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+\delta}$ (Bi-2201) and Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10 + \delta}$ (Bi-2223), with $n=1$ and $n=3$ respectively, using Cu $L_3$-edge resonant inelastic x-ray scattering (RIXS). Near the anti-nodal 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 $T_{\rm c}$ vs.\ $n$ scaling. In contrast, the nodal direction exhibits very strongly damped, almost non-dispersive excitations. We argue that this implies that the magnetism in the doped cuprates is partially itinerant in nature.