Highly tunable hybrid metamaterials employing split-ring resonators strongly coupled to graphene surface plasmons

Metamaterials and plasmonics are powerful tools for unconventional manipulation and harnessing of light. Metamaterials can be engineered to possess intriguing properties lacking in natural materials, such as negative refractive index. Plasmonics offers capabilities to confine light in subwavelength dimensions and to enhance light-matter interactions. Recently,graphene-based plasmonics has revealed emerging technological potential as it features large tunability, higher field-confinement and lower loss compared to metal-based plasmonics. Here,we introduce hybrid structures comprising graphene plasmonic resonators efficiently coupled to conventional split-ring resonators, thus demonstrating a type of highly tunable metamaterial, where the interaction between the two resonances reaches the strong-coupling regime. Such hybrid metamaterials are employed as high-speed THz modulators, exhibiting over 60% transmission modulation and operating speed in excess of 40 MHz. This device concept also provides a platform for exploring cavity-enhanced light-matter interactions and optical processes in graphene plasmonic structures for applications including sensing, photo-detection and nonlinear frequency generation

Quantum-dot lithium in the strong-interaction regime: Depolarization of electron spins by a magnetic field

Magnetic field usually leads to a polarization of electron spins. It is shown that in a system of {\em strongly interacting} particles applying magnetic field may lead to an opposite effect -- depolarization of electron spins. Results of the work are based on an exact-diagonalization study of quantum-dot lithium -- a system of three Coulomb interacting two-dimensional electrons in a parabolic confinement potential.Comment: 4 pages, incl 3 figure

Giant enhancement of the third harmonic in graphene integrated in a layered structure

Graphene was shown to have strongly nonlinear electrodynamic properties. In particular, being irradiated by an electromagnetic wave with the frequency $\omega$, it can efficiently generate higher frequency harmonics. Here we predict that in a specially designed structure "graphene -- dielectric -- metal" the third-harmonic ($3\omega$) intensity can be increased by more than two orders of magnitude as compared to an isolated graphene layer.Comment: 4 pages, 3 figure

Gate-tunable nonlinear refraction and absorption in graphene-covered silicon nitride waveguides

The nonlinear optical properties of graphene have received significant interest in the past years. Especially third-order nonlinear effects have been demonstrated to be large. Recently several groups have shown, through four-wave mixing (FWM) and third harmonic generation (THG) experiments, that the optical nonlinearity of graphene can be tuned through electrostatic gating. These effects are quantified by a strongly tunable vertical bar sigma((3))(s)vertical bar, with sigma((3))(s) the complex third-order conductivity. Here, by simultaneously observing cross-phase and cross-amplitude modulation on a silicon nitride waveguide covered with gated graphene, we are able to confirm such strong tunability for these nonlinear effects as well. Moreover, we can separately quantify the real and imaginary parts of sigma((3))(s), which respectively represent nonlinear absorption and refraction. This unveils a tunability that is far more drastic than what could be observed through FWM or THG, including sign changes in both the nonlinear absorption and refraction. Our results are confirmed by a theoretical model for the optical nonlinearity of graphene. The ability to tailor the nonlinearity of graphene to this extent can lead to new opportunities, such as nanophotonic devices with electrically tunable nonlinear properties