The concept, analysis, and design of series switches for graphene-strip plasmonic waveguides at near infrared frequencies are presented. Switching is achieved by using graphene's field effect to selectively enable or forbid propagation on a section of the graphene strip waveguide, thereby allowing good transmission or high isolation, respectively. The electromagnetic modeling of the proposed structure is performed using full-wave simulations and a transmission line model combined with a matrix-transfer approach, which takes into account the characteristics of the plasmons supported by the different graphene-strip waveguide sections of the device. The performance of the switch is evaluated versus different parameters of the structure, including surrounding dielectric media, electrostatic gating and waveguide dimensions. 2018 OCIS codes: (240.6680) Surface plasmons; (130.2790) Guided waves; (250.6715) Switching

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The ordering of the classical Ising model on the Archimedean lattice that is topologically equivalent to the Shastry-Sutherland one is studied in order to understand the fascinating magnetic properties experimentally observed in rare-earth tetraborides such as TmB4. The long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction which is expected to be predominant in these systems is taken into account, and the magnetization plateaus and rich ordering behaviors depending on the Fermi wave vector are investigated in details by Monte Carlo simulation. The experimental 1/2 magnetization step can be qualitatively reproduced and its stability against the change of is confirmed, suggesting that the coupling between conduction electrons and localized moments may play an important role in modulating the magnetization behaviors in these systems.

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The undoped three-orbital spin-fermion model with the additional biquadratic interaction which arises from various factors, such as quantum or thermal fluctuation, is studied using the Monte Carlo method in order to investigate the spin orders in pnictide superconductors. The simulations show that the experimentally observed nematic state can be stabilized by the positive biquadratic interaction, suggesting that such interaction may be another origin for nematicity in pnictides in addition to the couplings to the lattice degrees of freedom. Furthermore, the so-called flux state at low temperatures is identified when a rather weak negative biquadratic interaction is introduced, which is the same as the phase predicted in earlier theoretical work.