Universal Dispersive Excitations in the High-Temperature Superconductors

Abstract

High-resolution neutron scattering experiments on optimally doped La${}_{2-x}$Sr${}_x$CuO${}_4$ have been performed which reveal that the magnetic excitations are dispersive. The dispersion is found to be the same as in the YBa${}_2$Cu${}_3$O${}_{6+x}$ family, and is quantitatively related to that observed with charge sensitive probes. The excitations are also found to broaden rapidly with increasing energy, forming a continuum at higher energy, and bear a remarkable resemblance to multi-particle excitations observed in low-dimensional antiferromagnets and some magnetic metals. The magnetic correlations are two dimensional, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting one-dimensional magnets.

4 pages, 4 figures