title: Unveiling pseudospin and angular momentum in photonic graphene.
abstract: Pseudospin, an additional degree of freedom inherent in graphene, plays a key role in understanding many fundamental phenomena such as the anomalous quantum Hall effect, electron chirality and Klein paradox. Unlike the electron spin, the pseudospin was traditionally considered as an unmeasurable quantity, immune to Stern-Gerlach-type experiments. Recently, however, it has been suggested that graphene pseudospin is a real angular momentum that might manifest itself as an observable quantity, but so far direct tests of such a momentum remained unfruitful. Here, by selective excitation of two sublattices of an artificial photonic graphene, we demonstrate pseudospin-mediated vortex generation and topological charge flipping in otherwise uniform optical beams with Bloch momentum traversing through the Dirac points. Corroborated by numerical solutions of the linear massless Dirac-Weyl equation, we show that pseudospin can turn into orbital angular momentum completely, thus upholding the belief that pseudospin is not merely for theoretical elegance but rather physically measurable.
authors: MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China.
authors: Daohong
authors: D
authors: Song
authors: Department of Mathematics and Applied Mathematics, University of Crete, Heraklion, 70013 Crete, Greece.
authors: Vassilis
authors: V
authors: Paltoglou
authors: 1] MOE Key Laboratory of Space Applied Physics and Chemistry, Shaanxi Key Laboratory of Optical Information Technology, School of Science, Northwestern Polytechnical University, Xi'an 710129, China [2] Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA.
authors: Sheng
authors: S
authors: Liu
authors: Zhou Pei-Yuan Center for Applied Mathematics, Tsinghua University, Beijing 100084, China.
authors: Yi
authors: Y
authors: Zhu
authors: Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA.
authors: Daniel
authors: D
authors: Gallardo
authors: MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China.
authors: Liqin
authors: L
authors: Tang
authors: MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China.
authors: Jingjun
authors: J
authors: Xu
authors: Department of Applied Mathematics, University of Colorado, 526 UCB, Boulder, Colorado 80309, USA.
authors: Mark
authors: M
authors: Ablowitz
authors: Department of Mathematics and Applied Mathematics, University of Crete, Heraklion, 70013 Crete, Greece.
authors: Nikolaos K
authors: NK
authors: Efremidis
authors: 1] MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China [2] Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA.
authors: Zhigang
authors: Z
authors: Chen