Polarized x-ray-absorption study ofTl2Ba2

Eric Pellegrin

¹

,

N. Nücker

²

,

J. Fink

³

et al.

Role of out-of-plane copper orbitals in thallium cuprate

“…These results are in agreement with the study of Pellegrin et al, 13 which has concluded no direct correlation between Cu 3d z 2 Ϫr 2 and T c in Tl bilayer and three layer superconductors though their study was restricted to only one doping hole concentration.…”

“…The existence of an energy splitting using a bulk sensitive FY mode is in contradiction with the previous studies reporting no splitting in various high-T c superconductors using FY and EELS techniques. 11,13,14,19,21 This probably can TABLE I. Comparison between density of covalent and doping holes in the two Tl͑2212͒ thin films synthesized in low ͑1 bar͒ and medium ͑10 bar͒ oxygen pressures.…”

“…Several polarized Cu L 3 -XAS measurements have led to the conclusion that the unoccupied Cu 3d states mainly have 3d x 2 Ϫy 2 character with 10-20 % weight of Cu 3d z 2 Ϫr 2 character. [11][12][13][14][15][16][17][18][19] Most of these reports also detect an energy shift of about 200-500 meV between the E ʈ (a,b) and E ʈ c polarized spectra. 12,15,18,20 Except for a few, 17 the majority of studies reporting relatively high weight of Cu 3d z 2 Ϫr 2 and an energy shift between white lines of different polarizations used a surface sensitive total yield ͑TY͒ as the mode of detection.…”

“…12,15,16,18,20 On the other hand, studies using bulk sensitive fluorescence yield ͑FY͒ mode of detection and electron energy loss spectroscopy ͑EELS͒ showed less weight for the out-of-plane Cu 3d z 2 Ϫr 2 states and no or negligible energy shift between the E ʈ (a,b) and E ʈ c polarized spectra. 11,13,14,19,[21][22][23] In the XAS studies on nearly optimally doped Tl͑2212͒ and Tl͑2223͒ thin films and single crystals, [11][12][13][14] the fraction of holes with 3d z 2 Ϫr 2 character has been reported to be 10-12 % to the total number of Cu 3d holes. It is suggested that this amount is an admixture of 3d z 2 Ϫr 2 states in the in-plane Cu 3d -O 2p x,y band.…”

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

“…More recently, however, Pellegrin et al [28] have shown a very substantial intensity for the Cu 3d z 2 signal by FY measurements on the Tl 2 Ba 2 Ca 2 Cu 3 O 11 (Tl-2223) system. This result compels one to think that there may, after all, be no uniformity in the behaviour of the various superconducting cuprates in respect of the relative intensity of the out-of-plane Cu 3d z 2 orbitals and that, as suggested by them, the weightage of these orbitals may be of no consequence to their superconducting behaviour.…”