Eur. Phys. J. Special Topics 188, 131-152 (2010)
https://doi.org/10.1140/epjst/e2010-01302-4

Regular Article

Electron interactions and charge ordering in CuO₂ compounds

¹ Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
² Central Research Institute of the Electric Power Industry, Komae, Tokyo 201-8511, Japan
³ Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
⁴ Department of Physics and Astronomy, University of British Columbia, Vancouver V6T 1Z4, Canada
⁵ Canadian Institute for Advanced Research, Toronto M5G 1Z8, Canada

^a e-mail: bernhard.muschler@wmi.badw.de
^b Present address: Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

Received: 14 July 2010
Revised: 12 August 2010
Published online: 11 October 2010

Abstract

We present results of inelastic light scattering experiments on single-crystalline La_2-xSr_xCuO₄ in the doping range 0.00 ≤ x = p ≤ 0.30 and Tl₂Ba₂CuO_6+δ at p = 0.20 and p = 0.24. The main emphasis is placed on the response of electronic excitations in the antiferromagnetic phase, in the pseudogap range, in the superconducting state, and in the essentially normal metallic state at x ≥ 0.26, where no superconductivity could be observed. In most of the cases we compare B_1g and B_2g spectra which project out electronic properties close to (π, 0) and (π/2,π/2), respectively. In the channel of electron-hole excitations we find universal behavior in B_2g symmetry as long as the material exhibits superconductivity at low temperature. In contrast, there is a strong doping dependence in B_1g symmetry: (i) In the doping range 0.20 ≤ p ≤ 0.25 we observe rapid changes of shape and temperature dependence of the spectra. (ii) In La_2-xSr_xCuO₄ new structures appear for x < 0.13 which are superposed on the electron-hole continuum. The temperature dependence as well as model calculations support an interpretation in terms of charge-ordering fluctuations. For x ≤ 0.05 the response from fluctuations disappears in B_1g and appears in B_2g symmetry in full agreement with the orientation change of stripes found by neutron scattering. While, with a grain of salt, the particle-hole continuum is universal for all cuprates the response from fluctuating charge order in the range 0.05 ≤ p < 0.16 is so far found only in La_2-xSr_xCuO₄. We conclude that La_2-xSr_xCuO₄ is close to static charge order and, for this reason, may have a suppressed T_c.