XAS study of hole density and symmetry in a Bi2Sr2CaCu2O8+δ single crystal

Polarized x-ray absorption spectroscopy study of the symmetry of unoccupied electronic states near the Fermi level in the system

“…It has been ascribed to transitions from 2p to a hybridized 4s, 4p and 3d z 2 state [14]. Bianconi et al [10,11] have ascribed it to a multiple-scattering resonance from the Bi-O band hybridized with the CuO 2 band with d-like symmetry.…”

“…Figure 6 shows the three spectra with their fitted components A, B, C and D. Peak A is the same as discussed above. Peak B at about 530.5 eV is associated with the 'upper Hubbard band' and ascribed to the transition 3d 9 → 1s3d 10 of the undoped material [12][13][14][15]18], which is allowed due to the admixture of 3d 10 L with 3d 9 in the ground state. The intensity of peak B is thus a measure of covalency of the Cu-O bond in the CuO 2 layers.…”

“…High-energy spectroscopy techniques, especially polarized x-ray absorption measurements, have been widely used in probing the electronic states near the Fermi level in these rather complex materials [1,2]. In particular, a number of polarized x-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) studies have been made to obtain valuable information on the symmetry of unoccupied states in the normal state [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], and to understand the behaviour of holes in the superconducting state [19,20]. The Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) compound has attracted more attention because interpretation in the 1-2-3 system is more complicated due to presence of the two non-equivalent Cu sites and because the surfaces of 1-2-3 compounds are unstable at room temperature under UHV conditions.…”

“…More investigations of the Cu L 3 edge [6,7,10,11,14,15] have reported a positive energy shift of about 300-500 meV between the E a, b and E c polarized spectra, but other studies [9,12,16] detect either no shift or a very small relative weight of d z 2 holes with no shift at all. The surface-sensitive total electron yield (TY) mode of detection was used in all the above cases.…”

Electronic structure studies of the Bi2212 system by polarised X-ray absorption measurement

“…In addition, its stability in UHV conditions has put the Bi2212 compound into the category of the most suitable systems for such studies, the results of which may probably represent the whole class of high-T~ oxides. To date there are a number of inconsistent reports [3][4][5][6][7][8][9][10][11][12][13][14][15] about the symmetry of the Cu 3d and O 2p holes in the Bi2212 system. Some concluded to the presence of a significant (10-20%) weight of 3dz2_ r2 (3dz2) symmetry states [4][5][6][7][8] while others [9] reported there was only ~ 5% weight of the 3dz2 states.…”