Influence of 30 MeV 32S irradiation on the electronic states of Ln 2− xCe xCuO 4−δ cuprates

Abstract

Polycrystalline samples of Ln 2− x Ce x CuO 4−δ (Ln=Nd, Sm) (the T' type high- T c superconductors) with x=0 and 0.15 as a “simple” model compound for other HTSC's have been irradiated with 30 MeV 32S ions at room temperature in order to study the differences in electronic structure between ideal and disordered materials. Irradiation has been performed in an ultra-high vacuum chamber with subsequent in-situ photoelectron spectroscopy (PES). 32S fluences have been varied between 2×10 12 cm -2 and 1×10 15 cm -2. After irradiation the valence band and several core-level spectra of Cu, O and Ln=Nd, Sm have been recorded. For each compound and fluence we observe preferential depletion of oxygen and deposition of these fragments on the surface, indicated by characteristic changes in the valence band and O 1s core-level spectra. For low fluences ( Φt<10 -13 cm -2) oxygen removement takes place preferentially in the Ln-O planes (i.e. in the dopant layers). At a certain threshold fluence (Φ t) Cu + , which depends essentially on the Ln-O hybridization, we observe strong formation of monovalent copper in the valence band and Cu 2p spectra indicating considerable oxygen depletion also of the Cu-O layers.