Spin-Wave Excitations in Effectively Half-Filled Mott Insulators(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We study spin-wave excitations in an effectively half-filled Hubbard model, where the effectively half-filled situation is realized when all holes doped in the exactly half-filled parent compound become self-trapped lattice polarons, and their hopping rate is much slower than the neutron scattering time of magnetic excitation measurements. It is further assumed that the doped holes become stabilizing centers of spin vortices; thus, the spin texture is not necessarily that of an antiferromagnet. We derive a new spin Hamiltonian that is suitable for this situation by extending the usual antiferromagnetic Heisenberg model. It is shown that two modes of spin-wave excitations exist in this new spin Hamiltonian: the first is the one exhibits antiferromagetic dispersion in high energy excitations; the other shows a sharp commensurate peak at the excitation energy maximum, and a broadened dispersion at energies below. It is shown that the sum of these two modes form an hourglass-shaped magnetic excitation spectrum observed in the underdoped cuprate.
社団法人日本物理学会の論文
2008-10-15