In this paper, we report a successful realization and integration of a gold two-dimensional hole array (2DHA) structure with semiconductor InAs quantum dot (QD). We show experimentally that a properly designed 2DHA-QD photodetector can facilitate a strong plasmonic-QD interaction, leading to a 130% absolute enhancement of infrared photoresponse at the plasmonic resonance. Our study indicates two key mechanisms for the performance improvement. One is an optimized 2DHA design that permits an efficient coupling of light from the far-field to a localized plasmonic mode. The other is the close spatial matching of the QD layers to the wave function extent of the plasmonic mode. Furthermore, the processing of our 2DHA is amenable to large scale fabrication and, more importantly, does not degrade the noise current characteristics of the photodetector. We believe that this demonstration would bring the performance of QD-based infrared detectors to a level suitable for emerging surveillance and medical diagnostic applications.

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We have laid out the results of a rigorous theoretical investigation into the response of electron dressed states, i.e., interacting Floquet states arising from the off-resonant coupling of Dirac spin-1 electrons in the α-T3 model, to external radiation with various polarizations. Specifically, we have examined the role played by the parameter α that is a measure of the coupling strength with the additional atom at the center of the honeycomb graphene lattice and which, when varied, continuously gives a different Berry phase. We have found that the electronic properties of the α -T3 model (consisting of a flat band and two cones) could be modified depending on the polarization of the imposed irradiation. We have demonstrated that under elliptically-polarized light the lowenergy band structure of such lattice directly depends on the valley index τ . We have obtained and analyzed the corresponding wave functions, their symmetries and the corresponding Berry phases, and revealed that such phases could be finite even for a dice lattice, which has not been observed in the absence of the dressing field. This results lead to possible radiation-generated band structure engineering, as well as experimental and technological realization of such optoelectronic devices and photonic crystals.

We investigated the Dirac electrons transmission through a potential barrier in the presence of circularly polarized light. An anomalous photon-assisted enhanced transmission is predicted and explained in a comparison with the well-known Klein paradox. It is demonstrated that the perfect transmission for nearly-head-on collision in an infinite graphene is suppressed in gapped dressed states of electrons, which is further accompanied by shift of peaks as a function of the incident angle away from the head-on collision. In addition, the perfect transmission in the absence of potential barrier is partially suppressed by a photon-induced gap in illuminated graphene. After the effect of rough edges of the potential barrier or impurity scattering is included, the perfect transmission with no potential barrier becomes completely suppressed and the energy range for the photon-assisted perfect transmission is reduced at the same time.

In the presence of external off-resonance and circularly-polarized irradiation, we have derived a many-body formalism and performed a detailed numerical analysis for both the conduction and optical currents in α − T3 lattices. The calculated complex many-body dielectric function, as well as conductivities of displacement and transport currents, display strong dependence on the latticestructure parameter α, especially approaching the graphene limit with α → 0. Unique features in dispersion and damping of plasmon modes are observed with different α values, which are further accompanied by a reduced transport conductivity under irradiation. The discovery in this paper can be used for designing novel multi-functional nanoelectronic and nanoplasmonic devices. I. INTRODUCTIONSo far, the α − T 3 model seems to present prospective opportunities for revolutionizing low-dimensional physics through novel two-dimensional (2D) materials. 1 Its atomic configuration consists of a graphene-type honeycomb lattice along with an additional site, i.e., a hub atom at the center of each hexagon. 2 An essential structure parameter α = tan φ, which enters into the low-energy Dirac-Weyl pseudospin-1 Hamiltonian for α − T 3 model, is found to be the ratio between the rim-to-hub and rim-to-rim hopping coefficients. This parameter affects all fundamental electronic properties of the α − T 3 lattice through topological characteristics embedded in its pseudospin-1 wave functions. Parameter α can vary from 0 to 1, corresponding to different types of α − T 3 materials, and the control of it could lead to some important technological applications for electronic and optoelectronic devices. Here, the case with α = 0 relates to graphene with a completely separated flat band, whereas α = 1 results in a pseudospin-1 dice lattice which has been fabricated and studied considerably. 3,4 Consequently, the α − T 3 model may be viewed as an interpolation between graphene and the dice lattice (or pseudospin-1 T 3 model). Its low-energy dispersion consists of a Dirac cone, similar to that for graphene, 5 as well as a flat band with zero-energy separating the valence from the conduction band for these pseudospin-1 materials. 6,7 In recent years, there have been numerous attempts for experimental realization of the α − T 3 model. Its topological characteristics, i.e., a Dirac cone with three bands touching at a single point, was observed in the triplon band structure of SrCu 2 (BO 3 ) 2 , as an example of general Mott-Hubbard insulators. 8 Moreover, dielectric photonic crystals with zero refractive index also display Dirac cone dispersion at the center of the Brillouin zone under an accidental degeneracy. 9,10 Most importantly, there exist various types of photonic Lieb lattices, 11,12 consisting of a 2D array of optical waveguides. Such waveguide-lattice structure is shown to have a three-band structure, including a perfectly flat middle band.Further to a relatively recent proposal on α − T 3 model, there have been a lot of crucial publications devoted to inv...

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The surface bound electronic states of three-dimensional topological insulators, as well as the edge states in two-dimensional topological insulators, are investigated in the presence of a circularly polarized light. The strong coupling between electrons and photons is found t o give rise to an energy gap as well as a unique energy dispersion of the dressed states, different from both graphene and conventional two-dimensional electron gas (2DEG). The effects of electron-photon interaction, barrier height and width on the electron tunneling through a p − n junction and on the ballistic conductance in topological insulators are demonstrated by numerical calculations. A critical energy for an incident electron to tunnel perfectly through a barrier is predicted, where electrons behave as either massless Dirac-like or massive Schrödinger-like particles above or below this threshold value. Additionally, these effects are compared with those in zigzag graphene nanoribbons and a 2DEG. Both the similarities and the differences are demonstrated and explained.

Numerical and closed-form analytic expressions for plasmon dispersion relations and rates of dissipation are first obtained at finite-temperatures for free-standing gapped graphene. These closedsystem results are generalized to an open system with Coulomb coupling of graphene electrons to an external electron reservoir. New plasmon modes, as well as new plasmon dissipation channels, are found in this open system, including significant modifications arising from the combined effect of thermal excitation of electrons and an energy bandgap in gapped graphene. Moreover, the characteristics of the new plasmon mode and the additional plasmon dissipation may be fully controlled by adjusting the separation between the graphene layer from the surface of a thick conductor. Numerical results for the thermal shift of plasmon frequency in a doped gapped graphene layer, along with its sensitivity to the local environment, are demonstrated and analyzed. Such phenomenon associated with the frequency shift of plasmons may be applied to direct optical measurement of local electron temperature in transistors and nanoplasmonic structures.