STM imaging of electronic waves on the surface of Bi2_2Te3_3: topologically protected surface states and hexagonal warping effects

Scanning tunneling spectroscopy studies on high-quality Bi$_2$Te$_3$ crystals exhibit perfect correspondence to ARPES data, hence enabling identification of different regimes measured in the local density of states (LDOS). Oscillations of LDOS near a step are analyzed. Within the main part of the surface band oscillations are strongly damped, supporting the hypothesis of topological protection. At higher energies, as the surface band becomes concave, oscillations appear which disperse with a particular wave-vector that may result from an unconventional hexagonal warping term.Comment: 4 pages, 4 figures. Revised manuscript with improved analysis and figure

Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2_2Se3_3

We characterize the occupied and unoccupied electronic structure of the topological insulator Bi$_2$Se$_3$ by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:Sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.Comment: Accepted to Physical Review Letter

The Impact of the Christian Faith on Library Service

The library profession is in flux and uncertainty due to its lack of a well-founded philosophy of service. The Christian faith provides the necessary philosophical framework. Three implications follow from the application of a Christian worldview to library practice. First, Christian librarians should provide access to collections that will allow students to integrate faith and learning. Second, they should demonstrate love and concern for library users by offering diligent, humble service.Third, they should teach students the ethical use of information resources. Christianity has an impact on “library service” in three areas. First, the word library presumes a collection of library materials: books, periodicals, microfilms, motion pictures, cassettes, records, and other forms of media. Second, the word service signifies the way the librarian goes about helping people find answers to their information needs.Third, correct use of library resources connotes proper library ethics. Before this paper discusses these three areas, it will be useful to survey the current state of library philosophy