[en] Highly pure single crystals of YIG were obtained by an FZ method, and a remarkable photoinduced change in permeability was observed. The permeability of samples held at a temperature of 77 K was decreased by more than 90% by illumination. The photoinduced change remained, to some extent, at temperatures up to about 260 K. By annealing at 1100 degrees C (in an oxygen atmosphere for six hours) in the sample preparation stage, the magnitude of the effect was reduced to 40%. After samples at 77 K were strongly illuminated, the loss factor below 5 kHz showed a pair of peaks, in contrast with the flat curve for unilluminated samples on warming to 300 K. The activation energies corresponding to the peaks were found to be 0.3 and 0.1 eV. The mechanism of the effect is discussed in relation to relaxation processes related to these peaks, and F⁰ centers, or oxygen vacancies with two trapped electrons, are though to play an essential role

[en] The photomagnetic phenomenon is found to be reproducible also with irradiation of γ-rays in yttrium iron garnets (YIG). The change of initial permeability (μ_i) of YIG crystals under ⁶⁰Co γ-irradiation at 77 K has been measured by the usual transformer method. A remarkable decrease of μ_i is observed and R = Δμ_i/μ_i is plotted against exposure time (t) or an amount of doses (D) of γ-rays in a logarithmic form. R is proportional to D^1.5 at low doses while it is proportional to D^0.17 at high doses (t > 5 min)

[en] A highly purified YIG single crystal is obtained by a floating zone method and found to show a remarkable photoinduced effect on an initial permeability μ'. Besides, the temperature vanishing the effect is found to be 250 to 260 K, which is higher by about 50 K than previously reported. A pair of Fe²⁺-oxygen vacancy is supposed to be a photomagnetic center in this crystal. Furthermore, photoinduced double peaks on tan δ-temperature curve for this sample are, for the first time, observed in the temperature range 77 to 300 K. This observation is suggestive of two limited migration modes of electrons. Several alternative models are introduced to explain the phenomenon, including a possible mechanisms of the photomagnetic center. For comparison, the behavior of the sample grown by flux method is also reported. (author)

[en] In this paper, the authors describe a new technique for the deposition of a-Si:H, in which the growing film surface is periodically irradiated with high-intensity xenon light pulses. The films show high stability of the photoconductivity under illumination, but also exhibit a high dark conductivity, so that the photosensitivity is reduced. Infrared and Raman scattering measurements indicate little difference in the Si-H and Si-Si bonding structures compared to reference films; however, there is a large increase in the sub-bandgap absorption in addition to a shift of the Fermi level, implying some subtle modification of the film growth process caused by the irradiation. Results on the preparation and stability testing of solar cells fabricated using this technique are also described

[en] During warming a ⁶⁰Co γ-ray irradiated sample of yttrium iron garnet (YIG), the disaccommodation (DA) was found to occur in the temperature interval 100-200 K. The result is correlated with a highly mobile oxygen vacancy

[en] A radius of a dense star on the colour superconducting phase is investigated in an extended NJL type model with two flavours of quarks. Since the model is non-renormalizable, the results depend on the regularization procedure. Here, we apply the dimensional regularization and evaluate the radius of a dense star. Evaluating the TOV equation, we show the relationship between the mass and radius of the dense star in the dimensional regularization

[en] We investigate color superconducting phase at high density in the extended Nambu-Jona-Lasinio model for two-flavor quarks. Because of the nonrenormalizability of the model, physical observables may depend on the regularization procedure; that is why we apply two types of regularization, the cutoff and the dimensional one to evaluate the phase structure, the equation of state, and the relationship between the mass and the radius of a dense star. To obtain the phase structure we evaluate the minimum of the effective potential at finite temperature and chemical potential. The stress tensor is calculated to derive the equation of state. Solving the Tolman-Oppenheimer-Volkoff equation, we show the relationship between the mass and the radius of a dense star. The dependence on the regularization is found not to be small, interestingly. The dimensional regularization predicts color superconductivity phase at rather large values of μ (in agreement with perturbative QCD in contrast to the cutoff regularization), in the larger temperature interval, the existence of heavier and larger quark stars.

[en] We discuss how the cosmological baryon asymmetry can be achieved by the lepton family asymmetries of heavy Majorana neutrino decays and how the lepton family asymmetries are related to CP violation in neutrino oscillation, in the minimal seesaw model with two heavy Majorana neutrinos. We derive the most general formula for CP violation in neutrino oscillation in terms of the heavy Majorana masses and Yukawa mass term. It is shown that the formula is very useful to classify several models in which e, μ, and τ leptogenesis can be separately realized and to see how they are connected with low energy CP violation. To make the models predictive, we take texture with two zeros in the Dirac matrix. In particular, we find some interesting cases in which CP violation in neutrino oscillation can happen while lepton family asymmetries do not exist at all. On the contrary, we can find e-, μ-, and τ-leptogenesis scenarios in which the cosmological CP violation and low energy CP violation measurable via neutrino oscillations are very closely related to each other. By determining the allowed ranges of the parameters in the models, we predict the sizes of CP violation in neutrino oscillation and vertical bar V_e3^MNS vertical bar. Finally, the leptonic unitarity triangles are reconstructed

[en] We study lepton flavor number violating rare B decays, b→sl_h^±l_l^±, in a seesaw model with low scale singlet Majorana neutrinos motivated by the resonant leptogenesis scenario. The branching ratios of inclusive decays b→sl_h^±l_l^± with two almost degenerate singlet neutrinos at TeV scale are investigated in detail. We find that there exists a class of seesaw model in which the branching fractions of b→sτμ and τ→μγ can be as large as 10^-10 and 10^-9 within the reach of Super B factories, respectively, without being in conflict with neutrino mixings and mass-squared difference of neutrinos from neutrino data, invisible decay width of Z, and the present limit of Br(μ→eγ). In the model, the lepton number asymmetries are vanishing

[en] Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps