The crystalline electric field as a direct probe for charge transfer processes in high-temperature superconductors

Abstract We describe the inelastic neutron scattering technique to observe the crystal field as a direct probe of the local symmetry and the charge distribution at the rare earth site. For RBa 2 Cu 3 O x ( R = Ho , Er ; 6 x 2 planes. An empirical relation between T c and the observed charge transfer δρ was derived which is highly nonlinear close to T c = 90 K . Crystal-field studies performed for ErBa 2 Cu 3 O 7 and ErBa 2 Cu 4 O 8 under pressure can be consistently described within this picture.