Fig. 1: Device structure and designs.
From: Topological quantum cascade laser with Dirac-scaled valley edge modes
a An illustration of electrically pumped VH THz QCL cavity. The zoom-in diagram indicates the dimension and structure of unit lattice used in various regions of the device. The yellow box highlights the Dirac lattices used in scaling the topological interface. b FESEM image of the fabricated device of DDirac = 6. The magnified sub-diagrams in i-iii present the lattice pattern in different regions of fabricated devices, while iv labels the convention of device used in this work. Here, the constructed waveguide is around 6-unit lattices wide, hence DDirac = 6. c Simulated dispersion of the Dirac scaled waveguide. The dispersion of the VH mode is colored in blue while the higher order trivial modes are greyed out for clarity. d Illustration of VH mode normalized E-field across the Dirac scaled waveguide. Its mode distribution follows a plateau like envelope in Dirac lattice regions and quickly decays into the gapped region.
