A photoelectron spectroscopy and x-ray absorption study of single crystal with adsorbed Cs: on the origin of the states affected by electron doping and evidence for spatially resolved electron doping

Abstract

The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of Bi 2 Sr 2 CaCu 2 O 8 has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O 1s, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O 1s, Cu 2p and Ca 2p edges.The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu-O layer. It is evident from bulk-and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of Bi 2 Sr 2 CaCu 2 O 8 locally through spatially resolved electron doping.When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi-O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.

Evidence of Pseudogap Related Core Level Shifts inBi2Sr2Ca1Tjernberg1, Nylén2, Chiaia3 et al. 1997Phys. Rev. Lett.233140View full textAdd to dashboardCite

“…This can also be seen as a decrease in full width at half maximum (FWHM). The correlation between the XAS prepeak and the low BE shoulder in the O 1s spectrum has been noted previously [4,16,17]. There is not only a change in the O 1s spectra shape but also a shift in energy as Y is introduced.…”

“…The correlation between the suppression of the prepeak in the O K edge XAS and the decrease of the low BE shoulder in the O 1s spectra is a strong indication that the O 2p holes connected to the XAS prepeak [16,17,19] are related to the shoulder on the O 1s core level [16,17]. It has been suggested that the O 1s core level consists of three lines and that they can be referred to as Bi-O, Sr-O, and Cu-O in order of decreasing BE [16].…”

Core-level photoemission and x-ray absorption study of Na-covered and oxygen-deficientBa0.6K0.4BiONylén1, Beutler2, Zakharov3 et al. 1998Phys. Rev. B3110View full textAdd to dashboardCite

“…It was found that core levels were affected by the sodium overlayer by means of binding energy shifts and changes in peak widths, consistent with a local increase of the band filling. The intensity of the photoemission from the Fermi level was not affected by the sodium overlayer, in contrast to measurements on Bi 2 Sr 2 CaCu 2 O 8 with various Cs coverages, 21 which confirms the n-type nature of the charge carriers in Ba 0.6 K 0.4 BiO 3 . The asymmetry of the Bi 4 f core level, often seen as a resolved highbinding-energy component, is shown to be strongly dependent on the surface quality and oxygen deficiency, and is explained as reflecting the varying concentration of Bi atoms with reduced valency.…”

Photoemission spectromicroscopy study of aBi2Sr2CaCu2

“…It is assigned to metallic Bi arising from the partial disruption of the BiO surface. 11 The length scale of the observed inhomogeneities was determined by acquiring a patchwork of images which is displayed in Fig. 3 ͑size 300 ϫ300 m 2 ͒.…”