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

Isolation of a transcriptionally active element of high copy number retrotransposons in sweetpotato genome

Many plant retrotransposons have been characterized, but only three families (Tnt1, Tto1 and Tos17) have been demonstrated to be transpositionally competent. We followed a novel approach that enabled us to identify an active element of the Ty1-copia retrotransposon family with estimated 400 copies in the sweetpotato genome. DNA sequences of Ty1 -copia reverse transcriptase (RTase) from the sweetpotato genome were analyzed, and a group of retrotransposon copies probably formed by recent transposition events was further analyzed. 3’RACE on callus cDNA amplified transcripts containing long terminal repeats (LTR) of this group. The sequence -specific amplification polymorphism (S-SAP) patterns of the LTR sequence in the genomic DNA were compared between a normal plant and callus lines derived from it. A callus -specific S-SAP product was found into which the retrotransposon detected by the 3’RACE had been transposed apparently during cell culture. We conclude that our approach provides an effective way to identify active elements of retrotransposons with high copy numbers.</p