期刊
ELIGHT
卷 3, 期 1, 页码 -出版社
SPRINGERNATURE
DOI: 10.1186/s43593-022-00039-7
关键词
Higher-band topology; Orbital degrees of freedom; Generalized chiral symmetry; Bulk polarization; Winding number; Breathing Kagome lattice
类别
The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter. High orbitals in higher-order topological insulators (HOTIs) have not been realized, but p-orbital corner states have been demonstrated in a photonic HOTI, unveiling their underlying topological invariant and symmetry protection.
The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter including orbital superfluidity and topological semimetals. Despite tremendous efforts in engineering synthetic cold-atom, as well as electronic and photonic lattices to explore orbital physics, thus far high orbitals in an important class of materials, namely, higher-order topological insulators (HOTIs), have not been realized. Here, we demonstrate p-orbital corner states in a photonic HOTI, unveiling their underlying topological invariant, symmetry protection, and nonlinearity-induced dynamical rotation. In a Kagome-type HOTI, we find that the topological protection of p-orbital corner states demands an orbital-hopping symmetry in addition to generalized chiral symmetry. Due to orbital hybridization, nontrivial topology of the p-orbital HOTI is hidden if bulk polarization is used as the topological invariant, but well manifested by the generalized winding number. Our work opens a pathway for the exploration of intriguing orbital phenomena mediated by higher-band topology applicable to a broad spectrum of systems.
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