Angle-resolved photoemission spectroscopy ofSr2CuO2Cl2

Abstract

We have investigated the lowest binding-energy electronic structure of the model cuprate Sr 2 CuO 2 Cl 2 using angle-resolved photoemission spectroscopy. Our data from about 80 cleavages of Sr 2 CuO 2 Cl 2 single crystals give a comprehensive, self-consistent picture of the nature of the first electron-removal state in this model undoped CuO 2-plane cuprate. First, we show a strong dependence on the polarization of the excitation light which is understandable in the context of the matrix element governing the photoemission process, which gives a state with the symmetry of a Zhang-Rice singlet. Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice singlet on the exciting photon energy is shown to be consistent with interference effects connected with the periodicity of the crystal structure in the crystallographic c direction. Thirdly, we measured the dispersion of the first electron-removal states along ⌫→(,) and ⌫→(,0), the latter being controversial in the literature, and have shown that the data are best fitted using an extended tJ model, and extract the relevant model parameters. An analysis of the spectral weight of the first ionization states for different excitation energies within the approach used by Leung et al. ͓Phys. Rev. B 56, 6320 ͑1997͔͒ results in a strongly photon-energy dependent ratio between the coherent and incoherent spectral weight. The possible reasons for this observation and its physical implications are discussed.

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

“…The energy of ∼1.5 eV is within reason for transitions from lower-lying states to the ZRB near the Fermi level (e.g. the "1 eV peaks" observed in ARPES of various other cuprates, [45][46][47][48] and the bands calculated by Markiewicz and Bansil 35 or Wagner et. al.…”

The electronic structure of cuprates from high energy spectroscopy

“…7, the Zhang-Rice singlet intensity in ARPES is also strongly dependent on the photon energy. This is important, bearing in mind the low intensity of the first electron removal states (for example near to the high symmetry point ( ,0) in Sr 2 CuO 2 Cl 2 ), and severely complicates the comparison of data from earlier studies , which corresponds to a real space distance of some 7.9 Å [30]. This distance in turn corresponds to the c-axis separation of the CuO 2 planes, and therefore this oscillatory dependence on the photon energy can be attributed to interference effects of the photoelectron wave diffracted from the c-axis periodicity of the layered crystal structure, similar to the explanation of the strong photon energy dependence of the photoemission intensity from the molecular orbitals of C 60 [32].…”

“…For the good fit to the data presented in Fig. 8, the following parameters were taken: J=t 1 =0.22 eV, t 2 /t 1 =-0.1 and t 3 /t 1 =0.2 [30]. A further area in which the comparison of experiment and theory can be enlightening is that of the k-dependence of the spectral weight of the ARPES features.…”

Possible propagation of the Zhang–Rice singlet as a probable Cooper channel in the CuO2 planes

“…As stated above, the formulation in [2] assumes that the ZRS is formed from the hybridization of a hole on each square of O atoms to the central Cu to form the local singlet. It follows that this FER approach to investigate the propagation of a single hole in the CuO 2 plane is a natural starting point to investigate the superconducting cuprates and the ZRS states are believed to be the theoretical construction of the FER states in photoemission experiments [15].…”

“…Interestingly the ZRS is obviously a two-hole state [4,15,16] and this makes it straightforward for us to apply to the CuO 2 planes our recently developed formulation of the statistical equivalent of the Hubbard (t-U and t − t ′ − U) model using a highly simplified correlated variational approach (HSCVA) [17]. The simplicity of this approach makes it easy to give 2 useful insight on how the competition between itineracy and localization in strongly correlated systems could lead to the exciting properties in these systems in d = 1, 2, 3.…”