A band structure scenario for the giant spin-orbit splitting observed at the Bi/Si(111) interface

The Bi/Si(111) (sqrt{3} x sqrt{3})R30 trimer phase offers a prime example of a giant spin-orbit splitting of the electronic states at the interface with a semiconducting substrate. We have performed a detailed angle-resolved photoemission (ARPES) study to clarify the complex topology of the hybrid interface bands. The analysis of the ARPES data, guided by a model tight-binding calculation, reveals a previously unexplored mechanism at the origin of the giant spin-orbit splitting, which relies primarily on the underlying band structure. We anticipate that other similar interfaces characterized by trimer structures could also exhibit a large effect.Comment: 11 pages, 13 figure

Tunable spin-gaps in a quantum-confined geometry

We have studied the interplay of a giant spin-orbit splitting and of quantum confinement in artificial Bi-Ag-Si trilayer structures. Angle-resolved photoelectron spectroscopy (ARPES) reveals the formation of a complex spin-dependent gap structure, which can be tuned by varying the thickness of the Ag buffer layer. This provides a means to tailor the electronic structure at the Fermi energy, with potential applications for silicon-compatible spintronic devices

New Mechanism for Spin-Orbit Splitting of Conduction States in Surface Alloys

We present Angle-Resolved Photoelectron Spectroscopy (ARPES) data on spin-orbit split states in two XAg2 surface alloys grown on an Ag(111) substrate, and of the Si(111)-AgBiAg2 trilayer system. We briefly discuss the origin of the unusually large energy and momentum splitting, and the possibility of tuning by surface engineering the spin polarization at the Fermi level. [DOI: 10.1380/ejssnt.2009.264

Validation of Finite Element Structural Simulation for Ohmic Microcontact

AbstractIn the current literature, there is no model able to accurately predict the electrical resistance value of rough micro- contacts. Such model requires a coupled thermo-electro-structural analysis that is very difficult to validate in a straightforward manner. In the present approach, atomic force microscopy (AFM) scanned data of contact surface with roughness are used to build finite element (FE) model. As a first step towards multiphysics analysis, the aim of this study is to validate results of structural simulation of a rough gold micro-contact.A setup with a nanoindenter and a real microswitch is used to extract force-displacement curves. These results are compared to FE simulations which allow evaluating the effects of the main parameters. It is shown that the accuracy of these structural simulations is acceptable for an accurate evaluation of the electrical contact resistance

Anisotropic spin gaps in BiAg2_2-Ag/Si(111)

We present a detailed analysis of the band structure of the BiAg$_2$/Ag/Si(111) trilayer system by means of high resolution Angle Resolved Photoemission Spectroscopy (ARPES). BiAg2/Ag/Si(111) exhibits a complex spin polarized electronic structure due to giant spin-orbit interactions. We show that a complete set of constant energy ARPES maps, supplemented by a modified nearly free electron calculation, provides a unique insight into the structure of the spin polarized bands and spin gaps. We also show that the complex gap structure can be continuously tuned in energy by a controlled deposition of an alkali metal.Comment: 6 pages, 5 figure

Quantum confinement effects in Pb Nanocrystals grown on InAs

In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by quantum confinement effects in the Pb nanocrystals. We identified three distinct regimes of quantum confinement. For the largest nanocrystals, quantum confinement effects appear through the formation of quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.Comment: Main 12 pages, Supp: 6 page

Long range coherent magnetic bound states in superconductors

The quantum coherent coupling of completely different degrees of freedom is a challenging path towards creating new functionalities for quantum electronics. Usually the antagonistic coupling between spins of magnetic impurities and superconductivity leads to the destruction of the superconducting order. Here we show that a localized classical spin of an iron atom immersed in a superconducting condensate can give rise to new kind of long range coherent magnetic quantum state. In addition to the well-known Shiba bound state present on top of an impurity we reveal the existence of a star shaped pattern which extends as far as 12 nm from the impurity location. This large spatial dispersion turns out to be related, in a non-trivial way, to the superconducting coherence length. Inside star branches we observed short scale interference fringes with a particle-hole asymmetry. Our theoretical approach captures these features and relates them to the electronic band structure and the Fermi wave length of the superconductor. The discovery of a directional long range effect implies that distant magnetic atoms could coherently interact leading to new topological superconducting phases with fascinating properties

A novel mutation in the GFAP gene expands the phenotype of Alexander disease

Background: Alexander disease, an autosomal dominant leukodystrophy, is caused by missense mutations in GFAP. Although mostly diagnosed in children, associated with severe leukoencephalopathy, milder adult forms also exist. Methods: A family affected by adult-onset spastic paraplegia underwent neurological examination and cerebral MRI. Two patients were sequenced by WES. A candidate variant was functionally tested in an astrocytoma cell line. Results: The novel variant in GFAP N-terminal head domain (p.Gly18Val) cosegregated in multiple relatives (LOD score: 2.7). All patients, even those with the mildest forms, showed characteristic signal changes or atrophy in the brainstem and spinal cord MRIs, and abnormal MRS. In vitro, this variant did not cause significant protein aggregation, in contrast to most Alexander disease mutations characterized so far. However, cell area analysis showed larger size, a feature previously described in patients and mouse models. Conclusion: We suggest that this variant causes variable expressivity and an attenuated phenotype of Alexander Disease type II, probably associated with alternative pathogenic mechanisms, i.e. astrocyte enlargement. GFAP analysis should be considered in adult-onset neurologic presentations with pyramidal and bulbar symptoms, in particular when characteristic findings, such as the tadpole sign, are present in MRI. WES is a powerful tool to diagnose atypical cases

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