Аннотация: An exact diagonalization of the Hamiltonian in the p-d model of a CuO6 cluster was used to obtain dependences on the model parameters of the lowest-energy two-hole terms: the energy difference between the 2p orbitals of planar and apical oxygen Delta(apex) = epsilon(2p) - epsilon[2p(apex)], the crystal field parameter Delta(d) = epsilon(3z2-r2)-epsilon(x2-y2), and the ratio of the distances between the copper atom and the apical and planar oxygen atoms d(apex)/d(pl). In the limit of large d(apex)/d(pl) and Delta(d), OUT model is equivalent to the three-band p-d model and, in this case, large singlet-triplet splitting Delta epsilon greater than or equal to 1 eV is also observed. As the parameters decrease, a singlet-triplet crossover is observed. Two mechanisms are identified for stabilization of the tripler term B-3(1g)(0) as the ground state. It is shown that for realistic values of the parameters, reduction of the p-d model to the three-band model is limited by the low energies of the current excitations because of the presence of the lower excited B-3(1g), and (1)A(1g) cluster states. Intercluster hopping causes strong mixing of singlet and triplet states far from the Gamma point. The results of the calculations are compared with data obtained by angle-resolved photoelectron emission in Sr2CuO2Cl2. (C) 1998 American Institute of Physics.
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Держатели документа:
LV Kirensky Phys Inst, Krasnoyarsk 660036, Russia
ИФ СО РАН
Доп.точки доступа:
Ovchinnikov, S. G.; Овчинников, Сергей Геннадьевич; Гавричков, Владимир Александрович