Cyclotron radiation and emission in graphene

Peculiarity in the cyclotron radiation and emission in graphene is theoretically examined in terms of the optical conductivity and relaxation rates to propose that graphene in magnetic fields can be a candidate to realize the Landau level laser, proposed decades ago [H. Aoki, Appl. Phys. Lett. {\bf 48}, 559 (1986)].Comment: 4 pages, 3 figure

Dynamical scaling analysis of the optical Hall conductivity in the quantum Hall regime

Dynamical scaling analysis is theoretically performed for the ac (optical) Hall conductivity $\sigma_{xy}(\varepsilon_F,\omega)$ as a function of Fermi energy $\varepsilon_F$ and frequency $\omega$ for the two-dimensional electron gas and for graphene. In both systems, results based on exact diagonalization show that $\sigma_{xy}(\varepsilon_F,\omega)$ displays a well-defined dynamical scaling, for which the dynamical critical exponent as well as the localization exponent are fitted and plugged in. A crossover from the dc-like bahavior to the ac regime is identified. The dynamical scaling analysis has enabled us to quantify the plateau in the ac Hall conductivity previously obtained, and to predict that the plateaux structure in ac is robust enough to be observed in the THz regime.Comment: 5 pages, 3 figure

Faraday rotation in bilayer and trilayer graphene in the quantum Hall regime

Optical Hall conductivity, as directly related to Faraday rotation, is theoretically studied for bilayer and trilayer graphene. In bilayer graphene, the trigonal warping of the band dispersion greatly affects the resonance structures in Faraday rotation not only in the low-energy region where small Dirac cones emerge, but also in the higher-energy parabolic bands as a sequence of satellite resonances. In ABA-stacked trilayer, the resonance spectrum is a superposition of effective monolayer and bilayer contributions with band gaps, while ABC trilayer exhibits a distinct spectrum peculiar to the cubic-dispersed bands with a strong trigonal warping, where the signals associated with low-energy Dirac cones should be directly observable owing to a large Lifshitz transition energy ($\sim 10 meV$).Comment: 10 pages, 7 figure

Optical Hall conductivity in 2DEG and graphene QHE systems

We have revealed from a numerical study that the Hall plateaus are retained in the optical Hall conductivity $\sigma_{xy}(\omega)$ in the ac ($\sim$ THz) regime in both of the ordinary two-dimensional electron gas and graphene in the quantum Hall regime, although the plateau height in ac deviates from integer multiples of $e^2/h$. The effect remains unexpectedly robust against a significant strength of disorder, which we attribute to an effect of localization. We predict the ac Hall plateaus are observable through the Faraday rotation with the rotation angle characterized by the fine-structure constant $\alpha$. In this paper we clarify the relationship between plateau structures and the disorder strength by performing numerical calculation.Comment: 4 pages, 2 figures, EP2DS-18 in Kobe (2009

Two parameter flow of \sigma_{xx}(\omega) - \sigma_{xy}(\omega) for the graphene quantum Hall system in ac regime

Flow diagram of $(\sigma_{xx}, \sigma_{xy})$ in finite-frequency ($\omega$) regime is numerically studied for graphene quantum Hall effect (QHE) system. The ac flow diagrams turn out to show qualitatively similar behavior as the dc flow diagrams, which can be understood that the dynamical length scale determined by the frequency poses a relevant cutoff for the renormalization flow. Then the two parameter flow is discussed in terms of the dynamical scaling theory. We also discuss the larger-$\omega$ regime which exhibits classical flows driven by the raw frequency $\omega$.Comment: 6 pages, 4 figure

A new crystal plasticity constitutive equation based on crystallographic misorientation theory

Since plastic deformation of polycrystal sheet metal is greatly affected by its initial and plastic deformed textures, multi-scale finite element (FE) analysis based on homogenization with considering micro-polycrystal morphology is required [1]. We formulated a new crystal plasticity constitutive equation to introduce not only the effect of crystal orientation distribution, but also the size of crystal grain and/or the effect of crystal grain boundary for the micro-FE analysis. The hardening evolution equation based on strain gradient theory [2], [3] was modified to introduce curvature of crystal orientation based on crystallographic misorientation theory. We employed two-scale structure, such as a microscopic polycrystal structure and a macroscopic elastic/plastic continuum. Our analysis code predicts the plastic deformation of polycrystal metal in the macro-scale, and simultaneously the crystal texture and misorientation evolutions in the micro-scale. In this study, we try to reveal the relationship between the plastic deformation and the microscopic crystal misorientation evolution by using the homogenized FE procedure with the proposed crystal plasticity constitutive equation. The crystallographic misorientation evolution, which affects on the plastic deformation of FCC polycrystal metal, was investigated by using the multi-scale FE analysis. We confirmed the availability of our analysis code employing the new constitutive equation through the comparison of a uniaxial tensile problem with the numerical result and the experimental one

Synthesis of ferromagnetic Bi-substituted yttrium iron garnet films by laser ablation

Bismuth‐substituted yttrium iron garnet (Bi:YIG) films were deposited on gadolinium gallium garnet substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Bi‐substituted YIG films by laser ablation. Films have a garnet single phase above the substrate temperature of 490 °C, and the film composition does not deviate largely from the target composition and it is almost constant in the temperature range between 490 and 580 °C. The saturation magnetization of the film is 1500 G at room temperature. Faraday rotation angle θF at a wavelength of 830 nm at room temperature is -0.3×104 °/cm

ジッセンテキ ナ ギジュツシャ イクセイ ノ タメ ノ ソウセイガタ キャリア キョウイク プロジェクト

The purposes of the this project using long-term internship programs is that students of master or doctoral course learn skills to communicate to the engineers of a client on equal terms as well as their expertise, in order to create pai-type practical engineers. By this program, we expect students to acquire skills for time management, communication and enterprising ability. From 2011 to 2012, 62 graduate students (58 master’s students and 4 doctoral students) joined this program. The students joined internship program at companies or governments for a period of 180~270 hours with their training goals for the collaborative research, as well as lectures on MOT. We tried joint internship with under-graduate students for MC or DC students, and introduction of intellectual property education during this project. We summarized the outcome of this project on this paper and future issues to be considered in order to develop the program