Neutron Spectroscopy in RBa2Cu3Ox (R=Rare Earth, 6≤x≤7) Compounds: Charge Transfer, Phase Separation, Spin Fluctuations
Inelastic neutron scattering has been employed to study the perovskitetype high-T c superconducting compounds RBa2Cu3O x (R = rare earth;6 = x = 7). The variation of the energies and intensities of the observed crystalline-electric-field (CEF) transitions versus the oxygen content x is shown to be predominantly related to a charge transfer process between the chains and the planes. The observed energy spectra are the result of a superposition of two different metallic components and a semiconducting one, i.e., there is clear experimental evidence for phase separation. A two-dimensional bond percolation model explains the appearance of superconductivity as well as the critical oxygen concentrations associated with the two-plateau structure of T c . The line shape of some low-energy R3+ excitations turns out to be highly asymmetric which we interpret in terms of an exchange interaction between the R3+ spins and fluctuating Cu2+ spins. The latter are most likely associated with low-energy spin excitations of spin-polarized polynuclear clusters of Cu2+ ions. From a line-width analysis of the CEF transitions we derive the evolution of the fractal sizes of the clusters versus the oxygen concentration x. Magnetic field-dependent neutron spectroscopic experiments give further evidence for the existence of spin-polarized clusters which are suggested to be the elementary building blocks giving rise to high-temperature superconductivity above the percolation threshold.
KeywordsAnisotropy Eter Perovskite Doyle
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- 6.A. Furrer, P. Allenspach, J. Mesot, U. Staub, H. Blank, H. Mutka, C. Vettier, E. Kaldis, J. Karpinski, S. Rusiecki, and A. Mirmelstein, Eur. J. Solid State Inorg. Chem. 28, 627 (1991).Google Scholar
- 9.A. Furrer, J. Mesot, U. Staub, F. Fauth, and M. Guillaume, to be published in J. Alloys and Compounds.Google Scholar
- 13.M.T. Hutchings, in F. Seitz and D. Turnbull (eds.), Solid State Physics, Vol 16, Academic, New York, 1964, p. 227.Google Scholar
- 18.P. Allenspach, A. Furrer, and B. Rupp, in V.L. Aksenov, N.N. Bogolubov, and N.M. Plakida (eds.), Progress in High-Temperature Superconductivity, Vol. 21, World Scientific, Singapore, 1990, p. 318.Google Scholar
- 24.I.N. Kurkin, I.Kh. Salikhov, L.L. Sedov, M.A. Teplov, and R.Sh. Zdanov, Zh. Eksp. Teor. Fiz. 103, 1342 (1992) & JETP 76, 657 (1993).Google Scholar
- 25.P. Wachter and R. Pittini, Proc. ICMAS-93, Superconducting Materials (Paris, December 13–15, 1993), to be published.Google Scholar
- 31.S.W. Lovesey, Theory of neutron scattering from condensed matter, Vol. 2 (Clarendon, Oxford, 1984), p. 6.Google Scholar
- 36.E. Sigmund and G.U. Seibold, private communication.Google Scholar