Dispersing bimagnons and doping induced bimagnon-charge modes in superconducting cuprates

TL;DR

This study uses resonant inelastic x-ray scattering to investigate magnetic excitations in cuprates, revealing dispersing bimagnons in undoped compounds and a new coupled bimagnon-charge mode in doped high-Tc superconductors.

Contribution

It provides the first high-resolution measurements of bimagnon excitations and identifies a novel collective mode in doped cuprates, advancing understanding of magnetic dynamics in superconductivity.

Findings

Dispersing bimagnon excitations observed in undoped compounds.

A new coupled bimagnon-charge mode detected in optimally doped LSCO.

Theoretical fits match data without free parameters for undoped samples.

Abstract

In the early days of high temperature superconductivity it was already recognized that magnetic properties of these materials are intimately related to the superconducting ones . When doped, the long-range ordered antiferromagnetic background of pristine copper-oxide insulators melts away and makes room for a spin liquid and superconductivity. By resonant inelastic x-ray scattering (RIXS) in the soft regime we probe the hitherto inaccessible dynamical multiple-spin correlations of the magnetic background in a series of parent compounds and in high Tc materials [NCCO (Nd2-xCexCuO4) and LSCO (La2-xSrxCuO4)]. High resolution measurements allows the clear observation of dispersing bimagnon excitations. In the undoped compounds the theory, fits the data on these coherent spin excitations without free parameters. In nearly optimally doped LSCO we observe the appearance of a new collective excitation at an energy of 250 +/- 60 meV having the signature of a coupled bimagnon-charge mode. It has a strongly reduced dispersion and lies in a so far unexplored region of momentum and energy space in the mid-infrared.