Abstract-Ultrafast terahertz nonlinear optics of Landau level transitions in a monolayer graphene

Go Yumoto, Ryusuke Matsunaga, Hiroki Hibino, and Ryo Shimano

https://journals.aps.org/prl/accepted/85071Yb3X8a14b5b084a77887f1fd7112a6574506


We investigated the ultrafast terahertz (THz) nonlinearity in a monolayer graphene under the strong magnetic field using THz pump-THz probe spectroscopy. An ultrafast suppression of the Faraday rotation associated with inter-Landau level (LL) transitions is observed, reflecting the Dirac electron character of non-equidistant LLs with large transition dipole moments. A drastic modulation of electron distribution in LLs is induced by far off-resonant THz pulse excitation in the transparent region. Numerical simulation based on the density matrix formalism without rotating wave approximation reproduces the experimental results, indicating that the strong light-matter coupling regime where the Rabi frequency exceeds the carrier wave frequency and even the relevant energy scale of the inter-LLs transition is realized.

Abstract-Large optical anisotropy for terahertz light of stacked graphene ribbons with slight asymmetry

Satoru Suzuki¹ and Hiroki Hibino¹

1 NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporation, 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
http://scitation.aip.org/content/aip/journal/jap/117/17/10.1063/1.4919703
J. Appl. Phys. 117, 174302 (2015); http://dx.doi.org/10.1063/1.4919703

The optical properties of stacked graphene microribbons in the terahertz region were simulated by the finite element method. The microribbons, which couple with terahertz light through the excitation of plasmons, were stacked with micrometer-scale vertical spacing (∼0.1λ or larger). Reflection and absorption spectra were found to strongly depend on the direction of incident light (forward or backward incidence), when the stacking structure was made slightly asymmetric by changing the ribbon width or the chemical potentials in each layer. At a certain frequency, light reflection is almost completely suppressed only for one incidence direction. The high directivity is considered to be due to the phasing effects of electromagnetic waves emitted from each layer like in a Yagi-Uda antenna.