arXiv subjects

M. Sicot

Publications and source records attributed to M. Sicot.

8 recordsLinked to original sources

arXiv2021

Dispersing and semi-flat bands in the wide band gap two-dimensional semiconductor bilayer silicon oxide

Epitaxial bilayer silicon oxide is a transferable two-dimensional material predicted to be a wide band gap semiconductor, with potential applications for deep UV optoelectronics, or as a building block of van der Waals heterostructures. The prerequisite to any sort of such applications is the knowledge of the electronic band structure, which we unveil using angle-resolved photoemission spectroscopy and rationalise with the help of density functional theory calculations. We discover dispersing bands related to electronic delocalisation within the top and bottom planes of the material, with two linear crossings reminiscent of those predicted in bilayer AA-stacked graphene, and semi-flat bands stemming from the chemical bridges between the two planes. This band structure is robust against exposure to air, and can be controled by exposure to oxygen. We provide an experimental lower-estimate of the band gap size of 5 eV and predict a full gap of 7.36 eV using density functional theory calculations.

cond-mat.mtrl-sci↗

arXiv2019

Electronic band structure of ultimately thin silicon oxide on Ru(0001)

Silicon oxide can be formed in a crystalline form, when prepared on a metallic substrate. It is a candidate support catalyst and possibly the ultimately-thin version of a dielectric host material for two-dimensional materials (2D) and heterostructures. We determine the atomic structure and chemical bonding of the ultimately thin version of the oxide, epitaxially grown on Ru(0001). In particular, we establish the existence of two sub-lattices defined by metal-oxygen-silicon bridges involving inequivalent substrate sites. We further discover four electronic bands below Fermi level, at high binding energies, two of them forming a Dirac cone at K point, and two others forming semi-flat bands. While the latter two correspond to hybridized states between the oxide and the metal, the former relate to the topmost silicon-oxygen plane, which is not directly coupled to the substrate. Our analysis is based on high resolution X-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations.

cond-mat.mtrl-sci↗

arXiv2018

Band structure and Fermi surfaces of the reentrant ferromagnetic superconductor Eu(Fe0.86Ir0.14)2As2

The electronic structure of the reentrant superconductor Eu(Fe$_{0.86}$Ir$_{0.14}$)$_{2}$As$_{2}$ (T$_c$ = 22 K) with coexisting ferromagnetic order (T$_M$ = 18 K) is investigated using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS). We study the in-plane and out-of-plane band dispersions and Fermi surface (FS) of Eu(Fe$_{0.86}$Ir$_{0.14}$)$_{2}$As$_{2}$. The near E$_F$ Fe 3d-derived band dispersions near the $Γ$ and X high-symmetry points show changes due to Ir substitution, but the FS topology is preserved. From momentum dependent measurements of the superconducting gap measured at T = 5 K, we estimate an essentially isotropic s-wave gap ($Δ\sim5.25\pm 0.25$ meV), indicative of strong-coupling superconductivity with 2$Δ$/k$_{B}$T$_{c}\simeq$ 5.8. The gap gets closed at temperatures T $\geq$ 10 K, and this is attributed to the resistive phase which sets in at T$_M$ = 18 K due to the Eu$^{2+}$-derived magnetic order. The modifications of the FS with Ir substitution clearly indicates an effective hole doping with respect to the parent compound.

cond-mat.mtrl-sci↗

arXiv2017

Evidence for weakly correlated oxygen holes in the highest-T$_{c}$ cuprate superconductor HgBa$_2$Ca$_2$Cu$_3$O$_{8+δ}$

We study the electronic structure of HgBa$_2$Ca$_2$Cu$_3$O$_{8+δ}$ (Hg1223 ; T$_{c}$ = 134 K) using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Resonant valence band PES across the O K-edge and Cu L-edge identify correlation satellites originating in O 2p and Cu 3d two-hole final states, respectively. Analyses using the experimental O 2p and Cu 3d partial density of states show quantitatively different on-site Coulomb energy for the Cu-site (U$_{dd}$ = 6.5$\pm$0.5 eV) and O-site (U$_{pp}$ = 1.0$\pm$0.5 eV). Cu$_{2}$O$_{7}$-cluster calculations with non-local screening explain the Cu 2p core level PES and Cu L-edge XAS spectra, confirm the U$_{dd}$ and U$_{pp}$ values, and provide evidence for the Zhang-Rice singlet state in Hg1223. In contrast to other hole-doped cuprates and 3d-transition metal oxides, the present results indicate weakly correlated oxygen holes in Hg1223.

cond-mat.str-el↗

arXiv2015

Quasi one-Dimensional Band Dispersion and Metallization In long Range Ordered Polymeric wires

We study the electronic structure of an ordered array of poly(para-phenylene) chains produced by surface-catalyzed dehalogenative polymerization of 1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular states is measured as a function of oligomer length by scanning tunneling spectroscopy, with Fermi level crossings observed for chains longer than ten phenyl rings. Angle-resolved photoelectron spectroscopy reveals a graphene-like quasi one-dimensional valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the organic band-structure, including the k dispersion, the gap size and electron charge transfer mechanisms which drive the system into metallic behaviour. Therefore the entire band structure of a carbon-based conducting wire has been fully determined. This may be taken as a fingerprint of π-conjugation of surface organic frameworks.

cond-mat.mes-hall↗

arXiv2010

Spatial corrugation and bonding of single layer graphene on Rh(111)

Topographic scanning tunneling microscopy (STM) images of epitaxial single layer graphene on the Rh(111) surface reveal that extended single crystalline graphene domains are produced without any defects on a large scale. High resolution imaging shows that the moiré structure resulting from the lattice mismatch between the Rh(111) substrate and graphene is highly corrugated, containing regions of an additional spatial modulation in the moiré supercell compared with those previously reported for graphene on Ir(111) or graphene on Ru(0001). These areas, which correspond to the "bridge" regions of the moiré structure appear as depressions in STM images indicating a strong orbital hybridization between the graphene layer and the metallic substrate. Valence-band photoemission confirms the strong hybridization between graphene and Rh(111) which leads to the pronounced corrugation of the graphene layer. Our findings underline the importance of considering substrate effects in epitaxially grown graphene layers for the design of graphene-based nanoscale systems.

cond-mat.mtrl-sci↗

arXiv2010

Induced magnetism of carbon atoms at the graphene/Ni(111) interface

We report an element-specific investigation of electronic and magnetic properties of the graphene/Ni(111) system. Using magnetic circular dichroism, the occurrence of an induced magnetic moment of the carbon atoms in the graphene layer aligned parallel to the Ni 3d magnetization is observed. We attribute this magnetic moment to the strong hybridization between C $π$ and Ni 3d valence band states. The net magnetic moment of carbon in the graphene layer is estimated to be in the range of $0.05-0.1 μ_B$ per atom.

cond-mat.mtrl-sci↗

arXiv2008

Correlation between magnetism and spin-dependent transport in CoFeB alloys

We report a correlation between the spin polarization of the tunneling electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a correlation is surprising since the TSP involves s-like electrons close to the Fermi level (EF), while the magnetic moment mainly arises due to all d-electrons below EF. We show that probing the s and d-bands individually provides clear and crucial evidence for such a correlation to exist through s-d hybridization, and demonstrate the tuneability of the electronic and magnetic properties of CoFeB alloys.

cond-mat.mtrl-sci↗