• Acta Physica Sinica
  • Vol. 69, Issue 9, 094206-1 (2020)
Yan-Lan Wang and Yan Li*
Author Affiliations
  • School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
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    DOI: 10.7498/aps.69.20191962 Cite this Article
    Yan-Lan Wang, Yan Li. Pseudospin states and topological phase transitions in two-dimensional photonic crystals made of dielectric materials[J]. Acta Physica Sinica, 2020, 69(9): 094206-1 Copy Citation Text show less

    Abstract

    Based on the transmission properties of against backscattering and robustness against defects, photonic topological insulators have opened up a novel way to steer the propagation of electromagnetic wave. In order to construct the photonic analogs of the quantum spin Hall effect in an electronic system, we propose a simple two-dimensional photonic crystal made of dielectric materials to realize topologically protected edge states associated with the photonic pseudospin. The photonic crystal comprises a honeycomb array of equilateral-triangle-ring-shaped silicon rods embedded in an air host. By simply rotating the silicon rods around their respective centers by 60°, the band inversion between a twofold degenerated dipolar mode and a twofold degenerated quadrupolar mode is clearly observed in the Brillouin zone center. For the double twofold degenerated states, the chirality of the time-averaged Poynting vector surrounding the unit cell center (i.e., right-hand or left-hand circular polarizations) plays the role of the pseudospin degree of freedom in the present photonic system, and their point group symmetry can be utilized to construct a pseudo-time-reversal symmetry. By utilizing ${{k}} \cdot {{p}}$ perturbation theory, we develop an effective Hamiltonian for the associated dispersion relation around the Brillouin zone center and calculate the spin Chen number, which indicates that the band inversion leads to a topological phase transition from a trivial to a nontrivial state. With numerical simulations, we unambiguously demonstrate that the unidirectional propagation of pseudospin-dependent edge state along the interface between a topologically nontrivial photonic crystal and a trivial one, and robustness of the edge states against different defects including sharp bend and cavity, regardless of the type of interface. The photonic system proposed by us consists of dielectric materials and the corresponding lattice structure is simple. And without changing the fill ratio or changing the positions of the silicon rods, a simple rotation of the silicon rods can generate the topological phase transition. So the potential applications of the pseudospin-dependent edge states based on our design are expected in more efficient way.
    Yan-Lan Wang, Yan Li. Pseudospin states and topological phase transitions in two-dimensional photonic crystals made of dielectric materials[J]. Acta Physica Sinica, 2020, 69(9): 094206-1
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