Optical absorption in two-dimensional materials with tilted Dirac cones

Abstract

Two-dimensional semimetals with tilted Dirac cones in the electronic band structure are shown to exhibit spatial separation of carriers belonging to different valleys under illumination. In stark contrast to gapped Dirac materials this optovalleytronic phenomenon occurs in systems with intact inversion and time-reversal symmetry that host massless Dirac cones in the band structure, thereby retaining the exceptional graphene-like transport properties. As a result we demonstrate that optical valley separation is possible at arbitrarily low photon frequencies including the deep infrared and terahertz regimes with full gate tunability via Pauli blocking. As a specific example of our theory, we demonstrate tunable valley separation in the proposed two-dimensional tilted Dirac cone semimetal 8-P mmn borophene for incident infrared photons at room temperature.

Unraveling Correlated Electronic States in Layered Manganese-Based Perovskites

“…We consider that the electronic properties are governed by the electron population density, which is determined by atomic positions within the material. This is further supported by other studies, which have theoretically as well as experimentally proved that polarization angle could affect the electronic response in two-dimensional materials. − …”

Extreme Optical Anisotropy in the Type-II Dirac Semimetal NiTe2 for Applications to Nanophotonics

“…From Figure 2b, it is also apparent that both permittivity components exhibit large imaginary parts that can strongly affect the overall electromagnetic response. However, broadband loss-anisotropic metamaterials can be exploited in several applications such as diffraction-free propagation, 35 perfect absorption, 36 and thermoplasmonic effects. 37 To confirm the extreme optical anisotropy of NiTe 2 , we carry out electron energy loss spectroscopy (EELS) experiments in the reflection geometry; 32,38,39 details on the experimental methods are provided in the Supporting Information.…”

“…From Figure b, it is also apparent that both permittivity components exhibit large imaginary parts that can strongly affect the overall electromagnetic response. However, broadband loss-anisotropic metamaterials can be exploited in several applications such as diffraction-free propagation, perfect absorption, and thermoplasmonic effects …”

“…These results provide the groundwork for an efficient harnessing of topological semimetals in nanophotonic applications. Of particular interest for future studies will be NiTe 2 -based refractive index sensors, 2 perfect absorbers 36 for bio/chemical sensing, photodetection, solar energy harvesting, and even photothermal membrane distillation. 41 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Bipolar electron waveguides in two-dimensional materials with tilted Dirac cones

“…For the other two types, the equienergy contours are open: in a type-II cone the equienergy contours are hyperbolic, while in type-III they are parabolic [8,9]. These various cone geometries lead to remarkably different physical properties [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. In certain materials, the Dirac cones can be naturally tilted due to the material's inherent crystal structure and properties, and there is a plethora of theoretical materials that have been predicted to possess tilted Dirac cones [7,[30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”