We report the observation of highly anisotropic Dirac fermions in a Bi square net of SrMnBi(2), based on a first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. We found that the Dirac dispersion is generally induced in the (SrBi)(+) layer containing a double-sized Bi square net. In contrast to the commonly observed isotropic Dirac cone, the Dirac cone in SrMnBi(2) is highly anisotropic with a large momentum-dependent disparity of Fermi velocities of ~8. These findings demonstrate that a Bi square net, a common building block of various layered pnictides, provides a new platform that hosts highly anisotropic Dirac fermions.

We performed angle resolved photoemission (ARPES) studies on Cu(111) and Au(111) surface states with circularly polarized light. Existence of local orbital angular momentum (OAM) is confirmed as has been predicted to be broadly present in a system with an inversion symmetry breaking (ISB). The single band of Cu(111) surface states is found to have chiral OAM in spite of very small spin-orbit coupling (SOC) in Cu, which is consistent with theoretical prediction. As for Au(111), we observe split bands for which OAM for the inner and outer bands are parallel, unlike the Bi2Se3 case. We also performed first principles calculation and the results are found to be consistent with the experimental results. Moreover, majority of OAM is found to be from d-orbitals and a small contribution has p-orbital origin which is anti-aligned to the spins. We derive an effective Hamiltonian that incorporates the role of OAM and used it to extract the OAM and spin structures of surface states with various SOC strength. We discuss the evolution of angular momentum structures from pure OAM case to a strongly spin-orbit entangled state. We predict that the transition occurs through reversal of OAM direction at a k-point in the inner band if the system has a proper SOC strength.PACS numbers: 71.15.Mb

Increased airway responsiveness (AR) is frequently associated with bronchiectasis. Roxithromycin is a new semisynthetic macrolide antibiotic that also has anti-inflammatory activities. This study was designed to see whether roxithromycin could favourably alter the degree of AR in patients with bronchiectasis and increased AR. Twenty five children with bronchiectasis, who had an increased AR (defined as a provocative concentration of methacholine causing a 20% fall in forced expiratory volume in one second (FEV1) (PC20) <25 mg x mL(-1) evaluated by the dosimeter method), were randomized, double-blind into two parallel groups. Thirteen of the children were treated with roxithromycin (4 mg x kg(-1) b.i.d.) for 12 weeks and 12 received placebo. FEV1, sputum purulence and leucocyte scores were assessed every 3 weeks. To estimate AR, high-dose methacholine challenge tests were performed before and after treatment. On the dose-response curve to methacholine, PD20 and maximal response (two indices of AR) were measured. Changes in FEV1 were not observed during the course of the study in both groups. A significant improvement in sputum features was noted after 6 weeks of treatment in the roxithromycin group. After 12 weeks of roxithromycin therapy, the geometric mean (range of 1 SD) of provocative cumulative dose producing a 20% fall in FEV1 (PD20) increased significantly (p<0.01) to 169.2 (83.2-344.2) breath units (BU) (1 BU denotes one inhalation of 1 mg x mL(-1) methacholine) and the mean+/-SD of maximal response decreased significantly (p<0.01) to 32.5+/-6.8%, as compared with the initial values (PD20 87.1 (47.3-160.4) BU; maximal response 40.9+/-7.4%). No significant changes in either parameter were observed in the placebo group. Our results indicate that roxithromycin may decrease the degree of airway responsiveness in patients with bronchiectasis and increased airway responsiveness. Further study is necessary to determine the mechanism by which roxithromycin reduces airway responsiveness in bronchiectasis and its clinical impact.

We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.

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