Anisotropic Mixing Research Articles

Self-oscillation in a photorefractive phase-conjugate mirror with linear absorption II Anisotropic four-wave mixing

The effects of linear absorption on the degenerate and nondegenerate self-oscillation of a photorefractive phase-conjugate mirror under condition of anisotropic four-wave mixing are considered. The phase conjugation results from nonlinear mixing of two strong undepleted orthogonally polarized counterpropagating pump waves with a probe wave. We consider two types of situation for orthogonally polarized pump beams corresponding to two crystal families: one such as the Bi12SiO20 crystal family (sillenite family) and the other such as the BaTiO3 and strontium barium niobate crystal family. In both of these crystal families the degenerate and nondegenerate self-oscillations are shown to occur in the presence of linear absorption, which tends to increase the value of the coupling coefficient required for self-oscillation. Numerical results are presented that exhibit various features of degenerate and nondegenerate self-oscillation in both crystal families for different values of the phase ϕb of the backward grating.

Phase-conjugate waves generated by anisotropic four-wave mixing in LiNbO3and LiTaO3optical waveguides

We report on anisotropic four-wave mixing in planar optical LiNbO 3 and LiTaO 3 waveguides fabricated by indiffusion of titanium and iron layers. The generation of phase-conjugate waves in the waveguides is demonstrated, and the experimental results are compared to numerical solutions of the corresponding system of coupled wave equations. We observe a different behaviour of the phase-conjugate wave power on pump power in LiNbO 3 and LiTaO 3 waveguides, respectively. While the reflectivity of the signal beam saturates in LiTaO 3 for strong pump beams, there is a distinct increase in LiNbO 3 .

Superconductivity with two critical temperatures.

The weak-coupling thermodynamics in zero magnetic field is extended to the case displaying two second-order transitions. First, a free-energy functional is obtained from a generalized Bardeen-Cooper-Schrieffer (BCS) Hamiltonian by assuming a symmetry on the pairing interaction. This functional is applicable for the cases of an anisotropic Fermi surface, nonunitary states, and mixing of two irreducible representations. Second, the Landau theory of second-order transitions is extended to describe the lower transition. Here, the transition cannot occur independently without affecting the component of the upper transition. Third, a numerical calculation is performed for a model system of an elliptic Fermi surface, and theoretical curves for the specific heat with two and three discontinuities are presented. It is found from this calculation that a lower transition can occur to form a more uniform gap at T=0, provided that (1) two channels \ensuremath{\Gamma}=1,2 have fairly close ${\mathit{T}}_{\mathit{c}0}^{(\mathrm{\ensuremath{\Gamma}})}$\ensuremath{\equiv}1.13${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$ exp[-1/N(0)${\mathit{V}}^{(\mathrm{\ensuremath{\Gamma}})}$]; (2) an isotropic gap cannot be formed within the basis functions of the upper transition. Finally, two theoretical curves of ${\mathit{A}}_{1\mathit{g}}$-${\mathit{E}}_{1\mathit{g}}$ mixing are compared with a specific-heat experiment of ${\mathrm{UPt}}_{3}$. They give a good fit over the entire temperature range, and a second-order transition is suggested.

Anisotropic mixing in Kondo systems

We take account of the anisotropy of the mixing interaction in the Anderson Hamiltonian to lift the degeneracy of the local state. Without introducing new parameters we are able to calculate the crystal field splittings and linewidths of the local f states in Kondo-type cerium compounds.

Amplified reflection through anisotropic four-wave mixing in BaTiO_3

We have demonstrated cw non-phase-conjugate amplified reflection in single-crystal BaTiO(3) using anisotropic four-wave mixing. We show that the reflected beam is polarized orthogonally to the readout beam and that it is a true reflection of the image beam, not a phase conjugate. The maximum reflectivity measured was approximately 200%.

Anisotropic p-f mixing mechanism explaining anomalous magnetic properties in Ce monopnictides. IV. Ferromagnetic state

For pt.III see ibid., vol.19, p.2721 (1985). Extremely strong magnetic anisotropy in the ordered phases in CeSb and CeBi is explained by the anisotropic mixing mechanism between the 4f states and the valence bands. The character of the ferromagnetic ground state is investigated in detail. The anisotropy energy calculated by using realistic valence bands is consistent with the strong anisotropy observed experimentally.

Electroweak effects in p-wave superconductors

The unification of electromagnetism and weak interactions leads to anisotropic mixing of the electroweak gauge bosons in p-wave superconductors. It also leads to parity violating components in the gap matrix.

Anisotropic p−ƒ mixing mechanism explaining anomalous magnetic properties in Ce monopnictides

Anomalously small crystalline field splitting in the paramagnetic region and extremely strong magnetic anisotropy in the ordered phases in CeSb and CeBi are explained based on the anisotropic mixing mechanism between the 4ƒ states and the valence bands. In the paramagnetic region, the mixing gives the effective crystalline field splitting which is estimated to cancel the splitting of the point charge model in good agreement with experiment. The anisotropy energy of CeSb calculated by using the realistic valence bands is consistent with the strong anisotropy observed experimentally.

A model for unusual magnetic anisotropy of Ce pnictides

Unusually strong magnetic anisotropies in CeSb and CeBi are accounted for by the anisotropic mixing mechanism between the 4f states and the valence bands. The anisotropy energy of CeSb is calculated using the valence bands obtained by the APW band calculations and good agreement with the observed large anisotropy is obtained. This mechanism is consistent with the fact that no such strong anisotropy is found in light Ce pnictides.

UNUSUAL ANISOTROPY MECHANISM IN CE-PNICTIDES DUE TO VIRTUAL VALENCE FLUCTUATION

Unusual strong magnetic anisotropies in CeBi and CeSb are explained based on the anisotropic mixing mechanism between the 4f states and the valence electrons, This is consistent with the fact that no such strong anisotropy is found in other Ce-pnictides.