High-harmonic generation at particle–hole multiphoton excitation in gapped bilayer graphene

Second and third harmonics generation by coherent sub-THz radiation at induced Lifshitz transitions in gapped bilayer graphene

“…The investigations of the temperature dependence of the excitation of the Fermi-Dirac sea are cleared that for considering cases it exhibits a tenuous dependence on the optimal temperatures: the excited isolines are slightly smeared out with temperature increase. This effect is small since U ≫ T and one can expect that harmonic spectra will be robust against temperature change in contrast to the gap U = 0 case where harmonics radiation is suppressed with the increase of temperature in [22], [27]. So, the temperature dependence was missed.…”

“…Since the interband transitions can be neglected when γ ≫ 1, then the wavefield cannot provide enough energy for the creation of an electron-hole pair, and the generation of harmonics is suppressed. So that, in the nonadiabatic regime due to the large ionization probabilities the intensity of harmonics can be significantly enhanced compared with tunneling one [22], [27]. If γ ∼ 1 or γ ≪ 1, interband transitions take place.…”

“…In the following we use the microscopic nonlinear quantum theory of interaction of coherent electromagnetic radiation with gapped bilayer graphene which was developed in [22], [27]. To get the sub-THz frequencies, let propose two linearly polarized plane electromagnetic waves with carrier frequency ω and slowly varying amplitude of the electric field E a f (t):…”

High harmonic generation in triangular graphene quantum dots

“…In the last decade, there has been a growing interest to extend high harmonic generation (HHG) to twodimensional (2D) crystals and nanostructures, such as semimetallic graphene [1], and semiconductor transition metal dichalcogenidescite [2]. The role of graphene as an effective nonlinear optical material has been discussed in many theoretical [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], and experimental [23], [24] studies that consider various extreme nonlinear optical effects, in particular, HHG, which takes place in strong coherent radiation fields in the multiphoton regime at excitation of such nanostructures [25], [26]. On the other hand, apart from the remarkable and unique electronic and optical properties of graphene, the lack of an energy gap as a semimetal greatly limits their applicability, in contrast, for example, to bilayer graphene [27][28][29][30][31][32].…”

High laser harmonics induced by the Berry curvature in time-reversal invariant materials

“…22 The mentioned novel materials with broken inversion symmetry are intensively considered as an effective medium for the high-order wave mixing and high harmonic generation (HHG). In particular, HHG has been considered in gapped graphene 23 and bilayer graphene systems, 24 in monolayers of black phosphorus, 25 transition metal dichalcogenides, [27][28][29] hexagonal boron nitride, 26 and in buckled two-dimensional hexagonal nanostructures. 30,31 The HHG in 2D nanostructures originates either from the intraband electronic current or from the interband transitions.…”