Dirac semimetals,the materials featuring fourfold degenerate Dirac points,are critical states of topologically distinct phases.Such gapless topological states have been accomplished by a band-inversion mechanism,in wh...Dirac semimetals,the materials featuring fourfold degenerate Dirac points,are critical states of topologically distinct phases.Such gapless topological states have been accomplished by a band-inversion mechanism,in which the Dirac points can be annihilated pairwise by perturbations without changing the symmetry of the system.Here,we report an experimental observation of Dirac points that are enforced completely by the crystal symmetry using a nonsymmorphic three-dimensional phononic crystal.Intriguingly,our Dirac phononic crystal hosts four spiral topological surface states,in which the surface states of opposite helicities intersect gaplessly along certain momentum lines,as confirmed by additional surface measurements.The novel Dirac system may release new opportunities for studying elusive(pseudo)and offer a unique prototype platform for acoustic applications.展开更多
基金supported by the National Key R&D Program of China(Grant 2018YFA0305800)the National Natural Science Foundation of China(Grant Nos.,11774275,11890701,11674250,and 11534013)+1 种基金the Natural Science Foundation of Hubei Province(Grant No.2017CFA042)the Young Top-notch Talent for Ten Thousand Talent Program(2019-2022).
文摘Dirac semimetals,the materials featuring fourfold degenerate Dirac points,are critical states of topologically distinct phases.Such gapless topological states have been accomplished by a band-inversion mechanism,in which the Dirac points can be annihilated pairwise by perturbations without changing the symmetry of the system.Here,we report an experimental observation of Dirac points that are enforced completely by the crystal symmetry using a nonsymmorphic three-dimensional phononic crystal.Intriguingly,our Dirac phononic crystal hosts four spiral topological surface states,in which the surface states of opposite helicities intersect gaplessly along certain momentum lines,as confirmed by additional surface measurements.The novel Dirac system may release new opportunities for studying elusive(pseudo)and offer a unique prototype platform for acoustic applications.
