Giant Rashba splitting of quasi-1D surface states on Bi/InAs(110)-(2×\times1)

Electronic states on the Bi/InAs(110)-(2$\times$1) surface and its spin-polarized structure are revealed by angle-resolved photoelectron spectroscopy (ARPES), spin-resolved ARPES, and density-functional-theory calculation. The surface state showed quasi-one-dimensional (Q1D) dispersion and a nearly metallic character; the top of the hole-like surface band is just below the Fermi level. The size of the Rashba parameter ($\alpha_{\rm R}$) reached quite a large value ($\sim$5.5 eV\AA). The present result would provide a fertile playground for further studies of the exotic electronic phenomena in 1D or Q1D systems with the spin-split electronic states as well as for advanced spintronic devices.Comment: 8 pages (double column), 7 figures and 1 tabl

Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface

We investigate the bismuth (111) surface by means of time and angle resolved photoelectron spectroscopy. The parallel detection of the surface states below and above the Fermi level reveals a giant anisotropy of the Spin-Orbit (SO) spitting. These strong deviations from the Rashba-like coupling cannot be treated in $\textbf{k}\cdot \textbf{p}$ perturbation theory. Instead, first principle calculations could accurately reproduce the experimental dispersion of the electronic states. Our analysis shows that the giant anisotropy of the SO splitting is due to a large out-of plane buckling of the spin and orbital texture.Comment: 5 pages, 4 figure

Z7Z_7 Orbifold Models in M-Theory

Among $T^7/\Gamma$ orbifold compactifications of $M$-theory, we examine models containing the particle physics Standard Model in four-dimensional spacetimes, which appear as fixed subspaces of the ten-dimensional spacetimes at each end of the interval, $I^1\simeq S^1/Z_2$, spanning the $11^\text{th}$ dimension. Using the $Z_7$ projection to break the $E_8$ gauge symmetry in each of the four-planes and a limiting relation to corresponding heterotic string compactifications, we discuss the restrictions on the possible resulting gauge field and matter spectra. In particular, some of the states are non-local: they connect two four-dimensional Worlds across the $11^\text{th}$ dimension. We illustrate our programmable calculations of the matter field spectrum, including the anomalous U(1) factor which satisfies a universal Green-Schwarz relation, discuss a Dynkin diagram technique to showcase a model with $SU(3)\times SU(2)\times U(1)^5$ gauge symmetry, and discuss generalizations to higher order orbifolds.Comment: 23 pages, 2 figures, 4 tables; LaTeX 3 time

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

We report the evolution of the surface electronic structure and surface material properties of a topological crystalline insulator (TCI) Pb1-xSnxSe as a function of various material parameters including composition x, temperature T and crystal structure. Our spectroscopic data demonstrate the electronic groundstate condition for the saddle point singularity, the tunability of surface chemical potential, and the surface states' response to circularly polarized light. Our results show that each material parameter can tune the system between trivial and topological phase in a distinct way unlike as seen in Bi2Se3 and related compounds, leading to a rich and unique topological phase diagram. Our systematic studies of the TCI Pb1-xSnxSe are valuable materials guide to realize new topological phenomena.Comment: 10 pages, 7 figures. Expanded version of arXiv:1403.156