9 research outputs found

### Normal metal to ferromagnetic superconductor tunneling

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

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 $T_c$ 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

A long-wavelength, low-frequency effective theory is obtained from
$t_1-t_2-J$ 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
$t_1-t_2-J$ model, with the help of gauge invariant fields. It is argued that
the resulting Fermi quasiparticles of the $t_1-t_2-J$ 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

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