Special seminar - Yue Cao, University of Colorado: "Deciphering the Spin-Orbital Coupled Wavefunction"

Thu, Mar 20, 2014, 12:00 pm to 1:30 pm
Jadwin 111
Understanding the structure of the wavefunction is essential for depicting the surface states of a topological insulator. Owing to the inherent strong spin–orbit coupling, the conventional hand-waving picture of the Dirac surface state with a single chiral spin texture is incomplete, as this ignores the orbital components of the Dirac wavefunction and their coupling to the spin textures. Using orbital-selective spin-resolved ARPES and first-principles calculations, we show the Dirac wavefunction has a spin–orbital texture — a superposition of orbital wavefunctions coupled with the corresponding spin textures. Specifically, we observe (a) above the Dirac point, the in-plane p orbital tangential to the constant energy surface couples to the right-handed spin texture, while the pz orbital has the standard left-handed spin texture; and (b) the in-plane orbital wavefunction is asymmetric relative to the Dirac point, being predominantly tangential (radial) to the k-space constant energy surfaces above (below) the Dirac point. Our observation of the spin-orbital texture not only provides direct proof that total angular momentum is conserved in the Dirac states, but also has profound physical implications concerning future measurement and control of the electron spin in topological insulators and more generally in other material systems with spin-orbit coupling. References: 1. Y. Cao, J. A. Waugh, X.-W. Zhang, et al. Nature Physics 9, 499-504 (2013). 2. Y. Cao, J. A. Waugh, N. C. Plumb, et al. arXiv: 1211.5998 (2012). Host: Ali Yazdani, Princeton University