Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity...

In an attempt to provide a clearer understanding of the impressive increase in Tc under pressure in elemental Li, linear response calculation of the phonon dispersion curves, electron-phonon matrix elements, phonon linewidths and mode λ’s have been carried out on a finer mesh (24 in the Brillouin zone) than done previously, for the volume corresponding to 20 GPa pressure. The result illustrates...

We report a comprehensive angle-resolved photoemission spectroscopy study of the tridimensional electronic bands in the recently discovered Fe selenide superconductor ((Tl,Rb)(y)Fe(2-x)Se2 (T(c)=32  K). We determined the orbital characters and the k(z) dependence of the low energy electronic structure by tuning the polarization and the energy of the incident photons. We observed a small 3D elec...

The distribution of valence electrons in metals usually follows the symmetry of the underlying ionic lattice. Modulations of this distribution often occur when those electrons are not stable with respect to a new electronic order, such as spin or charge density waves. Electron density waves have been observed in many families of superconductors, and are often considered to be essential for supe...

Based on the generalized tight-binding model we study the electronic structure of all the semiconductor nanotubes with their diameters between 7.5 Å and 15.5 Å. We find that the van Hove peak separations versus nanotube diameters shows a qualitative difference from the well known plot based on zone-folding models. It has been clarified that the top of the valence band of the (n, m) nanotube in ...

Based on an inverted bulk band order, antimony thin films presumably could become topological insulators if quantum confinement effect opens up a gap in the bulk bands. Coupling between topological surface states (TSS) from opposite surfaces, however, tends to degrade or even destroy their novel characters. Here the evolution and coupling of TSS on Sb(111) thin films from 30 bilayers down to 4 ...

The spin-orbit interaction-a fundamental electroweak force-is equivalent to an effective magnetic field intrinsic to crystals, leading to band spin splitting for certain k points in sufficiently low-symmetry structures. This (Dresselhaus) splitting has usually been calculated at restricted regions in the Brillouin zone via small wave vector approximations (e.g., k.p), potentially missing the "b...

Two wideband left-handed (LH) transmission lines are presented. A pure LH transmission line (PLH TL) materialized by a defected ground structure with an inter-digital capacitor on a microstrip line has a wide LH propagation region without a right-handed (RH) branch in the reduced Brillouin zone. Another is a broadband LH rectangular waveguide utilized by a shorted stub and twisted Eplane posts....

The compressed, incommensurate approximately (9.5 x 9.5) moire superstructure of the Ag monolayer on Cu(111) displays a filled surface state band with a Fermi energy gap at the Brillouin zone boundary. By contrast, the surface band is gapless for the less compressed, commensurate (9 x 9) moire of two Ag layers. A simple estimate of the energy gain rendered by opening this gap gives a value simi...

A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inv...