Crossover between Local-Moment Magnetism and Itinerant-Electron Magnetism in the t-J Model(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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A Kondo-lattice theory is applied to the t-J model on a quasi-two dimensional lattice. The Kondo temperature T_K or k_BT_K is defined as an energy scale of local quantum spin fluctuations, with k_B the Boltzmann constant. The bandwidth W^* of quasiparticles, which is approximately given by W^*≃4k_BT_K, is renormalized by the Fock-type term of the superexchange interaction. When the lifetime width γ of quasiparticles is so small and temperature T is so low that γ/W^*≲1 and k_BT/W^*≲1, the renormalization is large. Even in the limit of the half filling, for example, the bandwidth W^* is nonzero and of the order of |J|, with J the superexchange interaction constant between nearest neighbors. The Kondo temperature k_BT_K, which also gives a measure of the strength of the quenching of magnetic moments by local quantum spin fluctuations, increases away from the half filling; it is smaller for larger γ. Therefore, local-moment magnetism, which is characterized by T_N≫T_K, with T_N the Neel temperature, appears for almost half fillings, and itinerant-electron magnetism, which is characterized by T_N≲T_K, appears for fillings away from the half filling; T_N is higher for larger γ. The antiferromagnetic region as a function of electron fillings is wider for larger γ; this result implies that it is wider in more disordered systems than it is in less disordered ones. The difference or asymmetry of disorder between electron-doped and hole-doped cuprate oxide superconductors must be, at least partly, responsible for that of antiferromagnetic phases between them.
社団法人日本物理学会の論文
2005-12-15

Crossover between Local-Moment Magnetism and Itinerant-Electron Magnetism in the t-J Model(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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