The dispersion laws of two-dimensional plasmons in narrow-gap HgTe/CdHgTe quantum wells are calculated taking into account the spatial dispersion of the electron susceptibility. At the energy scale of the band gap the dependence of plasmon frequencies on the wave vector is shown to be close to linear that changes significantly the critical concentration of noneqilibrium electron-hole gas corresponding to 'switching-on' the carrier recombination with plasmon emission. The recombination rates with the plasmon emission have been calculated. The 'plasmon' recombination is shown to dominate at the carrier concentration over (1.2-2) 10 11 cm −2 in a 5-nm-wide HgTe quantum well (band gap of 35 meV) that makes plasmon generation (spasing) in THz frequency range feasible.

Magneto-absorption in HgTe/CdHgTe quantum wells with an inverted band structure in magnetic fields up to 30 T has been studied. It has been shown that the positions of magneto-absorption lines for transitions from the zero-mode Landau levels in a wide range of magnetic field cannot in principle be described in the “single-electron” approximation using the eight-band Kane model even taking into account effects associated with the absence of spatial inversion symmetry. The revealed dependence of the energies of optical transitions on the magnetic field can be qualitatively explained within a “many-body” picture, where transitions between Landau levels are considered as collective modes hybridized by the electron-electron interaction.

Nonlinear nanophotonics leverages engineered nanostructures to funnel light into small volumes and intensify nonlinear optical processes with spectral and spatial control. Owing to its intrinsically large and electrically tunable nonlinear optical response, graphene is an especially promising nanomaterial for nonlinear optoelectronic applications. Here we report on exceptionally strong optical nonlinearities in graphene–insulator–metal heterostructures, which demonstrate an enhancement by three orders of magnitude in the third-harmonic signal compared with that of bare graphene. Furthermore, by increasing the graphene Fermi energy through an external gate voltage, we find that graphene plasmons mediate the optical nonlinearity and modify the third-harmonic signal. Our findings show that graphene–insulator–metal is a promising heterostructure for optically controlled and electrically tunable nano-optoelectronic components.

The so-called buffer layer (BL) is a carbon rich reconstructed layer formed during SiC (0001) sublimation.The covalent bonds between some carbon atoms in this layer and underlying silicon atoms makes itdifferent from epitaxial graphene. We report a systematical and statistical investigation of the BLsignature and its coupling with epitaxial graphene by Raman spectroscopy. Three different BLs arestudied: bare buffer layer obtained by direct growth (BL0), interfacial buffer layer between graphene andSiC (c-BL1) and the interfacial buffer layer without graphene above (u-BL1). To obtain the latter, wedevelop a mechanical exfoliation of graphene by removing an epoxy-based resin or nickel layer. The BLsare ordered-like on the whole BL growth temperature range. BL0 Raman signature may vary from sampleto sample but forms patches on the same terrace. u-BL1 share similar properties with BL0, albeit withmore variability. These BLs have a strikingly larger overall intensity than BL with graphene on top. Thesignal high frequency side onset upshifts upon graphene coverage, unexplainable by a simple straineffect. Two fine peaks (1235, 1360 cm1), present for epitaxial monolayer and absent for BL and transferred graphene. These findings point to a coupling between graphene and BL.