Topological insulators are most frequently constructed using lattices with specific degeneracies in their linear spectra,such as Dirac points.For a broad class of lattices,such as honeycomb ones,these points and assoc...Topological insulators are most frequently constructed using lattices with specific degeneracies in their linear spectra,such as Dirac points.For a broad class of lattices,such as honeycomb ones,these points and associated Dirac cones generally appear in non-equivalent pairs.Simultaneous breakup of the time-reversal and inversion symmetry in systems based on such lattices may result in the formation of the unpaired Dirac cones in bulk spectrum,but the existence of topologically protected edge states in such structures remains an open problem.Here a photonic Floquet insulator on a honeycomb lattice with unpaired Dirac cones in its spectrum is introduced that can support unidirectional edge states appearing at the edge between two regions with opposite sublattice detuning.Topological properties of this system are characterized by the nonzero valley Chern number.Remarkably,edge states in this system can circumvent sharp corners without inter-valley scattering even though there is no total forbidden gap in the spectrum.Our results reveal unusual interplay between two different physical mechanisms of creation of topological edge states based on simultaneous breakup of different symmetries of the system.展开更多
基金Natural Science Basic Research Program of Shaanxi Province(2024JC-JCQN-06)National Natural Science Foundation of China(12074308,12304370)+1 种基金Fundamental Research Funds for the Central Universities(sxzy012024146)Research Project of the Institute of Spectroscopy of the Russian Academy of Sciences(FFUU-2024-0003)。
文摘Topological insulators are most frequently constructed using lattices with specific degeneracies in their linear spectra,such as Dirac points.For a broad class of lattices,such as honeycomb ones,these points and associated Dirac cones generally appear in non-equivalent pairs.Simultaneous breakup of the time-reversal and inversion symmetry in systems based on such lattices may result in the formation of the unpaired Dirac cones in bulk spectrum,but the existence of topologically protected edge states in such structures remains an open problem.Here a photonic Floquet insulator on a honeycomb lattice with unpaired Dirac cones in its spectrum is introduced that can support unidirectional edge states appearing at the edge between two regions with opposite sublattice detuning.Topological properties of this system are characterized by the nonzero valley Chern number.Remarkably,edge states in this system can circumvent sharp corners without inter-valley scattering even though there is no total forbidden gap in the spectrum.Our results reveal unusual interplay between two different physical mechanisms of creation of topological edge states based on simultaneous breakup of different symmetries of the system.
