9 research outputs found

    Normal metal to ferromagnetic superconductor tunneling

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    We study the point-contact tunneling between normal metal and ferromagnetic superconductor. In the case of magnon-induced pairing the tunneling conductance is continuous and smooth function of the applied voltage. For small values of the applied voltage the Ohm law holds. We show that one can obtain the magnetization and the superconducting order parameter from the tunneling conduc- tance. In the case of paramagnon-induced superconductivity the tunneling does not depend on the magnetization. We argue that tunneling experiment can unambiguously determine the correct pairing mechanism in the ferromagnetic superconductors.Comment: 6 pages, 4 figur

    Magnon-Paramagnon Effective Theory of Itinerant Ferromagnets

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    The present work is devoted to the derivation of an effective magnon-paramagnon theory starting from a microscopic lattice model of ferromagnetic metals. For some values of the microscopic parameters it reproduces the Heisenberg theory of localized spins. For small magnetization the effective model describes the physics of weak ferromagnets in accordance with the experimental results. It is written in a way which keeps O(3) symmetry manifest,and describes both the order and disordered phases of the system. Analytical expression for the Curie temperature,which takes the magnon fluctuations into account exactly, is obtained. For weak ferromagnets TcT_c is well below the Stoner's critical temperature and the critical temperature obtained within Moriya's theory.Comment: 14 pages, changed content,new result

    Generalized CP^1 model from t_1-t_2-J model

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    A long-wavelength, low-frequency effective theory is obtained from t1t2Jt_1-t_2-J model. The action is written in terms of two-component bose spinor fields (CP^1 fields) and two spinless Fermi fields. The generalized CP^1 model is invariant under U(1) gauge transformations. The bose fields and one of the Fermi fields have charge +1 while the other Fermi field has charge -1 with respect to these transformations. A simple mean-feild theory of a gauge-symmerty breaking, based on a four-fermion interaction, is discussed. An effective theory of frustrated antiferromagnetism is obtained integrating out the Fermi fields around the mean-fields. Another option is used to parametrize the long distance fluctuations in t1t2Jt_1-t_2-J model, with the help of gauge invariant fields. It is argued that the resulting Fermi quasiparticles of the t1t2Jt_1-t_2-J model have both charge and spin. The effective action is rewritten in terms of spin 1/2 Fermi spinor, which has the charge of the holes, and unit vector.Comment: 22 pages, RevTex, no figure

    Quantum simulation of superexchange magnetism in linear ion crystals

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    Summarization: We present a system for the simulation of Heisenberg models with spins s=12 and s=1 with a linear crystal of trapped ions. We show that the laser-ion interaction induces a Jaynes-Cummings-Hubbard interaction between the atomic V-type level structure and the two phonon species. In the strong-coupling regime the collective atom and phonon excitations become localized at each lattice site and form an effective spin system with varying length. We show that the quantum-mechanical superexchange interaction caused by the second-order phonon hopping processes creates a Heisenberg-type coupling between the individual spins. Trapped ions allow to control the superexchange interactions by adjusting the trapping frequencies, the laser intensity, and the detuning.Presented on: Physical Review