174 research outputs found
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
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
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
Anisotropic spin gaps in BiAg-Ag/Si(111)
We present a detailed analysis of the band structure of the
BiAg/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
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