Photoemission from single crystals of EuBa2Cu3O7−x cleaved below 20 k: temperature-dependent oxygen loss

Abstract

The first low-temperature photoemission spectra from well-oxygenated and characterized, cleaved single crystals of the 1:2:3-type superconductors, specifically $\mathrm{Eu}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$, are presented. In contrast with polycrystalline or higher-temperature single-crystalline studies, a distinct and very stable density of states is found at the Fermi edge below 20 K. As the crystal is warmed even to 80 K the emission is rapidly lost from both the upper and lower portions of the Cu-O hybrids. At room temperature there is a loss of intensity at the Fermi edge with an accompanying change in the Ba $4d$ core-level line shape and the presence of a charging effect indicative of an insulating surface. These results imply that upon warming from 20 K there is very rapid oxygen loss from the cleaved surface with a resulting loss of superconducting behavior. This suggests that future photoemission experiments, especially those investigating detailed band structure, should be performed at low temperatures.