T_C-x Phase Diagrams and Infrared Spectra Due to Axial Charge-Transfer Modes in La_<2-x>Sr_xCuO_4 : a Composite-Boson Model

概要

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T_C-x phase diagrams for La_<2-x>Sr_xCuO_4 are derived from a model where in-plane holes dimerize to form bosons via the polarization-induced pairing aided by nearby apical oxygens O(A). O(A) are off-centered 'a la Toyozawa' by coupling to the E_u bending mode of dual O(A)-Cu(P)-O(A) bonds which enhances their polarizability. Apex oxygens are also gates through which change leaks from CuO_2 planes across Sr-containing La-O layers to effect the interlayer coupling. The latter is mainly controlled by coupling to the A_<2u> stretching mode of the dual bond. The Cu(P)-O(A) covalent bonding is doping-dependent. It modulates the electronic energies and thereby the axial charge leak. Dome-shaped T_C-x diagrams result from the interplay between the increasing hole concentration and decreasing gate opening as x grows. They compare well with experimental T_C-x data reported for La_<2-x>Sr_xCuO_4.
社団法人日本物理学会の論文
1993-07-15