Anderson Transition in Disordered Graphene

We use the regularized kernel polynomial method (RKPM) to numerically study the effect disorder on a single layer of graphene. This accurate numerical method enables us to study very large lattices with millions of sites, and hence is almost free of finite size errors. Within this approach, both weak and strong disorder regimes are handled on the same footing. We study the tight-binding model with on-site disorder, on the honeycomb lattice. We find that in the weak disorder regime, the Dirac fermions remain extended and their velocities decrease as the disorder strength is increased. However, if the disorder is strong enough, there will be a {\em mobility edge} separating {\em localized states around the Fermi point}, from the remaining extended states. This is in contrast to the scaling theory of localization which predicts that all states are localized in two-dimensions (2D).Comment: 4 page

The interaction of Xe and Xe + K with graphene

We have investigated the electronic properties of monolayer graphene with adsorbed layers of xenon or potassium, or a combination of the two. The formation of the first Xe layer is characterized by a dipole polarization which is quenched by a second Xe layer. By comparing K on Xe on graphene to K on bare graphene, we determine the K contribution to trigonal warping and mass renormalization due to electron–phonon coupling. The former is found to be small but significant, while the latter is shown to be negligible. Thus, previously determined values of electron–phonon coupling for K on graphene are shown to be intrinsic to doped graphene and not determined by the proximity of K ions to the graphene

Band structure and many body effects in graphene

We have determined the electronic bandstructure of clean and potassium-doped single layer graphene, and fitted the graphene π bands to a one- and three-near-neighbor tight binding model. We characterized the quasiparticle dynamics using angle resolved photoemission spectroscopy. The dynamics reflect the interaction between holes and collective excitations, namely plasmons, phonons, and electron-hole pairs. Taking the topology of the bands around the Dirac energy for n-doped graphene into account, we compute the contribution to the scattering lifetimes due to electron-plasmon and electron phonon coupling

Topological surface states above the Fermi energy in Hf2Te2P\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}

We report a detailed experimental study of the band structure of the recently discovered topological material $\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}$. Using the combination of scanning tunneling spectroscopy and angle-resolved photo-emission spectroscopy with surface K-doping, we probe the band structure of $\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}$ with energy and momentum resolution above the Fermi level. Our experiments show the presence of multiple surface states with a linear Dirac-like dispersion, consistent with the predictions from previously reported band structure calculations. In particular, scanning tunneling spectroscopy measurements provide the first experimental evidence for the strong topological surface state predicted at 460 meV, which stems from the band inversion between Hf-d and Te-p orbitals. This band inversion comprised of more localized d-states could result in a better surface-to-bulk conductance ratio relative to more traditional topological insulators.Comment: Supplementary materials available upon reques

The electronic structure of the high-symmetry perovskite iridate Ba2IrO4

We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba$_2$IrO$_4$ (Ba-214), an antiferromagnetic ($T_N=230$ K) insulator. Ba-214 does not exhibit the rotational distortion of the IrO$_6$ octahedra that is present in its sister compound Sr$_2$IrO$_4$ (Sr-214), and is therefore an attractive reference material to study the electronic structure of layered iridates. We find that the band structures of Ba-214 and Sr-214 are qualitatively similar, hinting at the predominant role of the spin-orbit interaction in these materials. Temperature-dependent ARPES data show that the energy gap persists well above $T_N$, and favour a Mott over a Slater scenario for this compound.Comment: 13 pages, 9 figure