Experimental realization of chiral Landau levels in two-dimensional Dirac cone systems with inhomogeneous effective mass

Chiral zeroth Landau levels are topologically protected bulk states.In particle physics and condensed matter physics,the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise to the chiral anomaly.Previous experimental works on such chiral Landau levels are mainly based on three-dimensional Weyl degeneracies coupled with axial magnetic fields.Their realizations using two-dimensional Dirac point systems,being more promising for future applications,were never experimentally realized before.Here we propose an experimental scheme for realizing chiral Landau levels in a two-dimensional photonic system.By introducing an inhomogeneous effective mass through breaking local parity-inversion symmetries,a synthetic in-plane magnetic field is generated and coupled with the Dirac quasi-particles.Consequently,the zeroth-order chiral Landau levels can be induced,and the one-way propagation characteristics are experimentally observed.In addition,the robust transport of the chiral zeroth mode against defects in the system is also experimentally tested.Our system provides a new pathway for the realization of chiral Landau levels in two-dimensional Dirac cone systems,and may potentially be applied in device designs utilizing the chiral response and transport robustness.

Hidden-symmetry-enforced nexus points of nodal lines in layer-stacked dielectric photonic crystals

It was recently demonstrated that the connectivities of bands emerging from zero frequency in dielectric photonic crystals are distinct from their electronic counterparts with the same space groups.We discover that in an AB-layerstacked photonic crystal composed of anisotropic dielectrics,the unique photonic band connectivity leads to a new kind of symmetry-enforced triply degenerate points at the nexuses of two nodal rings and a Kramers-like nodal line.The emergence and intersection of the line nodes are guaranteed by a generalized 1/4-period screw rotation symmetry of Maxwell’s equations.The bands with a constant kz and iso-frequency surfaces near a nexus point both disperse as a spin-1 Dirac-like cone,giving rise to exotic transport features of light at the nexus point.We show that spin-1 conical diffraction occurs at the nexus point,which can be used to manipulate the charges of optical vortices.Our work reveals that Maxwell’s equations can have hidden symmetries induced by the fractional periodicity of the material tensor components and hence paves the way to finding novel topological nodal structures unique to photonic systems.

Severe Lymphopenia and Related T-cell Immunity in an Avian Influenza A (H7N9)-Infected Patient

To the Editor:Following H7N9infection,the host lymphocyte immunity plays an antiviral role.[l] Furthermore,low frequencies of T-cells correlate with disease severity.[2]Herein,we present a H7N9-infected patient with life-threatening lymphopenia (only 0.06× 10^9/L in the peripheral blood),which we have barely ever seen before.We also measured the proportidns of T-cell subpopulations in the blood and bronchoalveolar lavage fluid (BALF).

Intrinsic in-plane nodal chain and generalized quaternion charge protected nodal link in photonics

Nodal lines are degeneracies formed by crossing bands in three-dimensional momentum space.Interestingly,these degenerate lines can chain together via touching points and manifest as nodal chains.These nodal chains are usually embedded in two orthogonal planes and protected by the corresponding mirror symmetries.Here,we propose and demonstrate an in-plane nodal chain in photonics,where all chained nodal lines coexist in a single mirror plane instead of two orthogonal ones.Nodal lines are degeneracies formed by crossing bands in three-dimensional momentum space.Interestingly,these degenerate lines can chain together via touching points and manifest as nodal chains.These nodal chains are usually embedded in two orthogonal planes and protected by the corresponding mirror symmetries.Here,we propose and demonstrate an in-plane nodal chain in photonics,where all chained nodal lines coexist in a single mirror plane instead of two orthogonal ones.The chain point is stabilized by the intrinsic symmetry that is specific to electromagnetic waves at theГpoint of zero frequency.By adding another mirror plane,we find a nodal ring that is constructed by two higher bands and links with the in-plane nodal chain.The nodal link in momentum space exhibits non-Abelian characteristics on a C_(2)T-invariant plane,where admissible transitions of the nodal link structure are determined by generalized quaternion charges.Through near-field scanning measurements of bi-anisotropic metamaterials,we experimentally mapped out the in-plane nodal chain and nodal link in such systems.The chain point is stabilized by the intrinsic symmetry that is specific to electromagnetic waves at the r point of zero frequency.By adding another mirror plane,we find a nodal ring that is constructed by two higher bands and links with the in-plane nodal chain.The nodal link in momentum space exhibits non-Abelian characteristics on a C2T-invariant plane,where admissible transitions of the nodal link structure are determined by generalized quaternion charges.Through near-field scanning measurements of bi-anisotropic metamaterials,we experimentally mapped out the in-plane nodal chain and nodal link in such systems.