Extra Seminar - Würzburg ToCoTronics Colloquium

The 1-band and 3-band Hubbard models of cuprate superconductors indicate very different values of effective electronic parameters, such as the on-site Coulomb energy and Cu-O hybridization strength. In contrast, 3-band electronic parameters of several cuprates are very similar to corresponding values obtained from cluster model calculations which describe experimental electron spectroscopy and scattering results. 
In the first part, we discuss the electronic structure of electron-doped Pr_1.3−xLa_0.7 Ce_xCuO₄ (PLCCO; Tc = 27 K, x = 0.1) and hole-doped Bi₂Sr₂CaCu₂O_8+δ (Bi2212; Tc = 90 K) cuprates using x-ray absorption spectroscopy and resonant photoemission spectroscopy (Res-PES). From Res-PES across the O K-edge and Cu L-edge, we identify the O 2p and Cu 3d partial density of states and their two-hole Auger final state correlation satellites, respectively. Applying the Cini-Sawatzky method to experimental data provides the oxygen on-site Coulomb energy U_p = 3.3 ± 0.5 eV for PLCCO, and U_p = 5.6 ± 0.5 eV for Bi2212. On the other hand, copper on-site Coulomb energy U_d = 6.5 ± 0.5 eV for Bi2212, consistent with earlier studies on La_2−x Sr_xCuO₄ (Tc = 33 K), YBa₂Cu₃O₇ (Tc = 90 K) and HgBa₂Ca₂Cu₃O_8+d (Tc = 133 K) cuprates.
In the second part, based on a simple Cu₂O cluster model and using estimated values of U_d  and U_p, we optimize the charge-transfer energy D and Cu-O hopping t_pd  to obtain the Heisenberg exchange interaction J  known from neutron scattering, for several cuprates. The 1-band parameters U ̃ and t ̃ are described using the 3-band parameters, thus revealing the equivalence of the 1-band and 3-band models. The ground-state singlet weights obtained from an exact diagonalization shows the role of Zhang-Rice singlets. The results provide a reliable method to connect electronic parameters from spectroscopy and the 3-band model with values of J from scattering and band dispersion experiments, and the 1-band Hubbard model.

References:

[1] A. Chainani, M. Horio, C.-M. Cheng, D. Malterre, K. Sheshadri, M. Kobayashi, K. Horiba, H. Kumigashira, T. Mizokawa, M. Oura, M. Taguchi, Y. Mori, A. Takahashi, T. Konno, T. Ohgi, H. Sato, T. Adachi,  Y. Koike,  T. Mochiku, K. Hirata, S. Shin,  M. K. Wu,  and A. Fujimori, Oxygen on-site Coulomb energy in Pr_1.3−xLa_0.7 Ce_xCuO₄ and Bi₂Sr₂CaCu₂O_8+δ and its relation with Heisenberg exchange, Phys. Rev. B 107, 195152 (2023).

[2] K. Sheshadri, D. Malterre, A. Fujimori, and A. Chainani, Connecting the one-band and three-band Hubbard models of cuprates via spectroscopy and scattering experiments, Phys. Rev. B 107, 085125 (2023).