Coexistence of multiple silicene phases in silicon grown on Ag(111)

Silicene, the silicon equivalent of graphene, is attracting increasing scientific and technological attention in view of the exploitation of its exotic electronic properties. This novel material has been theoretically predicted to exist as a free-standing layer in a low-buckled, stable form, and can be synthesized by the deposition of Si on appropriate crystalline substrates. By employing low-energy electron diffraction and microscopy, we have studied the growth of Si on Ag(111) and observed a rich variety of rotationally non-equivalent silicene structures. Our results highlight a very complex formation diagram, reflecting the coexistence of different and nearly degenerate silicene phases, whose relative abundance can be controlled by varying the Si coverage and growth temperature. At variance with other studies, we find that the formation of single-phase silicene monolayers cannot be achieved on Ag(111)

Anomalous spectral evolution with bulk sensitivity in BiPd

We investigate the electronic structure of a noncentrosymmetric superconductor, BiPd using photoemission spectroscopy with multiple photon energies ranging from ultraviolet to hard x-ray. Experimental data exhibit interesting difference in the surface and bulk electronic structures of this system. While the surface Bi core level peaks appear at lower binding energies, the surface valence band features are found at the higher binding energy side of the bulk valence band; valence band is primarily constituted by the Pd 4d states. These changes in the electronic structure cannot be explained by the change in ionicity of the constituent elements via charge transfer. Analysis of the experimental data indicates that the Bi-Pd hybridization physics plays the key role in deriving the anomalous spectral evolution and the electronic properties of this system.Comment: Proceedings of DAE SSPS 201

Spin Selective Evolution of Zhang-Rice State in Binary Transition Metal Oxide

The Zhang-Rice (ZR) state is a strongly hybridized bound state formed by the transition metal and oxygen atoms. The spin-fluctuations within the ZR state are known to play an important role in high-$T_\mathrm{c}$ superconductivity in cuprates. Here, we employ a combination of angle-resolved photoemission spectroscopy (ARPES), X-ray photoemission spectroscopy (XPS), and {\it ab initio} embedded dynamical mean-field theory (eDMFT) to investigate the influence of magnetic ordering on the spectral characteristics of the valence band and Mn 2$p$ core-level in MnO (001) ultrathin films. Our results demonstrate that a complex spin-selective evolution of Mn 3$d$$-$O 2$p$ hybridization develops due to the long-range antiferromagnetic (AFM) ordering. This hybridization significantly alters the spectral shape and weight of the ZR state. Specifically, in the AFM phase, we observed the sharpening of the ZR state and band folding with the periodicity of the AFM unit cell of MnO(001). We also demonstrated a strong connection between the spectral evolution of the ZR state and the non-local screening channels of the photoexcited core holes. Further, our detailed temperature-dependent study reveals the presence of short-range antiferromagnetic correlations that exist at much higher temperatures than $T_\mathrm{N}$. Such comprehensive studies showing the evolution of the ZR state across the magnetic transitions and its implication to the core-hole screening have never been reported in any 3$d$ binary transition metal oxides.Comment: 8 pages, 4 figure

Is graphene on copper doped?

Angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy have been used to characterise epitaxially ordered graphene grown on copper foil by low-pressure chemical vapour deposition. A short vacuum anneal to 200 °C allows observation of ordered low energy electron diffraction patterns. High quality Dirac cones are measured in ARPES with the Dirac point at the Fermi level (undoped graphene). Annealing above 300 °C produces n-type doping in the graphene with up to 350 meV shift in Fermi level, and opens a band gap of around 100 meV. Dirac cone dispersion for graphene on Cu foil after vacuum anneals (left: 200 °C, undoped; right: 500 °C, n-doped). Centre: low energy electron diffraction from graphene on Cu foil after 200 °C anneal. Data from Antares (SOLEIL)

Unveiling the stacking-dependent electronic properties of 2D ultrathin rare-earth metalloxenes family LnX2_2 (Ln = Eu, Gd, Dy; X = Ge, Si)

The studies of electronic effects in reduced dimensionality have become a frontier in nanoscience due to exotic and highly tunable character of quantum phenomena. Recently, a new class of 2D ultrathin Ln$X_2$ metalloxenes composed of a triangular lattice of lanthanide ions (Ln) coupled with 2D-Xenes of silicene or germanene ($X_2$) was introduced and studied with a particular focus on magnetic and transport properties. However, the electronic properties of metalloxenes and their effective functionalization remain mainly unexplored. Here, using a number of experimental and theoretical techniques, we trace the evolution of electronic properties and magnetic ground state of metalloxenes triggered by external perturbations. We demonstrate that the band structure of Ln$X_2$ films can be uniquely modified by controlling the Xenes stacking, thickness, varying the rare-earth and host elements, and applying an external electric field. Our findings suggest new pathways to manipulate the electronic properties of 2D rare-earth magnets that can be adjusted for spintronics applications.Comment: 7 pages, 3 figure

Giant Rashba-splitting of one-dimensional metallic states in Bi dimer lines on InAs(100)

Bismuth produces different types of ordered superstructures on the InAs(100) surface, depending on the growth procedure and coverage. The (2 × 1) phase forms at completion of one Bi monolayer and consists of a uniformly oriented array of parallel lines of Bi dimers. Scanning tunneling and core level spectroscopies demonstrate its metallic character, in contrast with the semiconducting properties expected on the basis of the electron counting principle. The weak electronic coupling among neighboring lines gives rise to quasi one-dimensional Bi-derived bands with open contours at the Fermi level. Spin- and angle-resolved photoelectron spectroscopy reveals a giant Rashba splitting of these bands, in good agreement with ab initio electronic structure calculations. The very high density of the dimer lines, the metallic and quasi one-dimensional band dispersion and the Rashba-like spin texture make the Bi/InAs(100)-(2 × 1) phase an intriguing system, where novel transport regimes can be studied

Growth, Morphology and Stability of Au in Contact with the Bi2Se3(0001) Surface

We report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3(0001) single crystal surface. At room temperature Au forms islands, according to the Volmer-Weber growth mode. Upon annealing to 100{\deg} C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, such as Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10-8 mbar) regime

Two Distinct Phases of Bilayer Graphene Films on Ru(0001)

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows to synthesize two distinct phases of bilayer graphene with different properties. The first phase has Bernal AB stacking with respect to the first graphene layer, displays weak vertical interaction and electron doping. The long-range ordered moir\'e pattern modulates the crystal potential and induces replicas of the Dirac cone and minigaps. The second phase has AA stacking sequence with respect to the first layer, displays weak structural and electronic modulation and p-doping. The linearly dispersing Dirac state reveals the nearly-freestanding character of this novel second layer phase