370 research outputs found
Universal Rashba Spin Precession of Two-Dimensional Electrons and Holes
We study spin precession due to Rashba spin splitting of electrons and holes
in semiconductor quantum wells. Based on a simple analytical expression that we
derive for the current modulation in a broad class of experimental situations
of ferromagnet/nonmagnetic semiconductor/ferromagnet hybrid structures, we
conclude that the Datta-Das spin transistor (i) is feasible with holes and (ii)
its functionality is not affected by integration over injection angles. The
current modulation shows a universal oscillation period, irrespective of the
different forms of the Rashba Hamiltonian for electrons and holes. The analytic
formulas approximate extremely well exact numerical calculations of a more
elaborate Kohn--Luttinger model.Comment: 7 pages, 2 eps figures included, minor change
High performance Tunnel Field Effect Transistors based on in-plane transition metal dichalcogenide heterojunctions
In-plane heterojunction tunnel field effect transistors based on monolayer
transition metal dichalcogenides are studied by means of self-consistent
non-equilibrium Green's functions simulations and an atomistic tight-binding
Hamiltonian. We start by comparing several heterojunctions before focusing on
the most promising ones, i.e WTe2-MoS2 and MoTe2-MoS2. The scalability of those
devices as a function of channel length is studied, and the influence of
backgate voltages on device performance is analysed. Our results indicate that,
by fine-tuning the design parameters, those devices can yield extremely low
sub-threshold swings (below 5mV/decade) and Ion/Ioff ratios higher than 1e8 at
a supply voltage of 0.3V, making them ideal for ultra-low power consumption.Comment: 10 page
Anti-IL5 Drugs in COVID-19 Patients: Role of Eosinophils in SARS-CoV-2-Induced Immunopathology
SARS-CoV-2 infection stimulates a complex activation of the immune system. Eosinophils belong to the host’s defense equipment against respiratory viruses. In the first phase of the infection, eosinophils contribution is probably appropriate and beneficial, as they facilitate the suppression of the viral replication. However, in severe COVID-19 patients, during the second and third phases of the disease, eosinophils may participate in a maladaptive immune response and directly contribute to immunopathology. In fact, in severe patients, the immune response is prevalently T helper 1 type, but T helper 2 is also present. Eosinophils’ expansion and activation are stimulated by Type 2 cytokines, especially IL-5. Moreover, bronchial asthma, in which eosinophils play a central role, seems not to be a major risk factor for severe COVID-19. Among possible explanations, asthmatic patients are often treated with corticosteroids, which have been demonstrated to reduce the progression to critical COVID-19 in hospitalized patients. In addition to steroids, severe asthmatic patients are currently treated with biological drugs that target Type 2 immune response. Because IL-5 is necessary for the growth, survival, and activation of eosinophils, IL-5 inhibitors, such as mepolizumab, decrease the peripheral blood count of eosinophils, but do not influence eosinophils activation in the airway. In severe COVID-19 patients, the blockade of eosinophils’ activation might contrast harmful immunity
Effect of dephasing on the current statistics of mesoscopic devices
We investigate the effects of dephasing on the current statistics of
mesoscopic conductors with a recently developed statistical model, focusing in
particular on mesoscopic cavities and Aharonov-Bohm rings. For such devices, we
analyze the influence of an arbitrary degree of decoherence on the cumulants of
the current. We recover known results for the limiting cases of fully coherent
and totally incoherent transport and are able to obtain detailed information on
the intermediate regime of partial coherence for a varying number of open
channels. We show that dephasing affects the average current, shot noise, and
higher order cumulants in a quantitatively and qualitatively similar way, and
that consequently shot noise or higher order cumulants of the current do not
provide information on decoherence additional or complementary to what can be
already obtained from the average current.Comment: 4 pages, 4 figure
Superconducting proximity effect in interacting double-dot systems
We study subgap transport from a superconductor through a double quantum dot
with large on-site Coulomb repulsion to two normal leads. Non-local
superconducting correlations in the double dot are induced by the proximity to
the superconducting lead, detectable in non-local Andreev transport that splits
Cooper pairs in locally separated, spin-entangled electrons. We find that the
-- characteristics are strongly asymmetric: for a large bias voltage of
certain polarity, transport is blocked by populating the double dot with states
whose spin symmetry is incompatible with the superconductor. Furthermore, by
tuning gate voltages one has access to splitting of the Andreev excitation
energies, which is visible in the differential conductance.Comment: 5 pages, 4 figure
Reinterpreting Low Resistance in Sb–MoS Ohmic Contacts by Means of Ab Initio Transport Simulations
By using an in-house nonequilibrium Green’s function (NEGF)-based ab initio simulator, we investigate the physical mechanisms driving the Sb(0112)–MoS2 system to exhibit the lowest reported contact resistance, RC =42 Ω·μm, to the 2-D semiconductor MoS2. We can find that the transport from the hybridized bands in the Sb–MoS2 heterojunction is quite ineffective and that the back-gateinduced doping of MoS2 in the contact region is crucial to explain the experiments. In fact, by accounting in our ab initio simulations for the presence of a back gate according to the experiments, it is possible to match the band structure of the MoS2 in the Sb–MoS2 heterojunction with that of the external MoS2 layer, which drastically increases the electronic transmission throughout the contact, and ultimately pushes RC close to the quantum limit. Furthermore, we extend the applicability of our previously demonstrated simulation methodology and thus investigate a field-effect transistors (FETs)-like device including an ab initio description of the carrier injection at the Sb–MoS2 contac
Non-local Andreev transport through an interacting quantum dot
We investigate sub-gap transport through a single-level quantum dot tunnel
coupled to one superconducting and two normal-conducting leads. Despite the
tendency of a large charging energy to suppress the equilibrium proximity
effect, a finite Andreev current through the dot can be achieved in
non-equilibrium situations. We propose two schemes to identify non-local
Andreev transport. In one of them, the presence of strong Coulomb interaction
leads to negative values of the non-local conductance as a clear signal of
non-local Andreev transport.Comment: 5 pages, 4 figure
On the imaging of electron transport in semiconductor quantum structures by scanning-gate microscopy: successes and limitations
This paper presents a brief review of scanning-gate microscopy applied to the
imaging of electron transport in buried semiconductor quantum structures. After
an introduction to the technique and to some of its practical issues, we
summarise a selection of its successful achievements found in the literature,
including our own research. The latter focuses on the imaging of GaInAs-based
quantum rings both in the low magnetic field Aharonov-Bohm regime and in the
high-field quantum Hall regime. Based on our own experience, we then discuss in
detail some of the limitations of scanning-gate microscopy. These include
possible tip induced artefacts, effects of a large bias applied to the scanning
tip, as well as consequences of unwanted charge traps on the conductance maps.
We emphasize how special care must be paid in interpreting these scanning-gate
images.Comment: Special issue on (nano)characterization of semiconductor materials
and structure
Arianna, Medea e le altre. Astuzia al femminile e arte greca
Nel mondo del mito greco la definizione funzionale di un personaggio appare sempre intimamente connessa alla sua per-cezione etica e alla sua collocazione nel quadro sociale e culturale. È il caso di personaggi come Arianna, Medea o Circe, le cui azionisi proiettano sempre nel mondo femminile dell’oikos. Nella prima parte del contributo Marco Giuman analizza i modi attraverso iquali il concetto di mētis femminile sia adattato dai repertori dell’arte greca alle figure di eroine e come questo sia tradotto in sensoiconografico. La seconda parte dell’articolo, curata da Elisabetta Pala, consiste in un approfondimento della figura di Arianna, e piùprecisamente sui suoi strumenti di mētis per eccellenza: corona e gomitolo. Da un raffronto dei resoconti delle fonti letterarie e delletestimonianze iconografiche tra VII e V secolo a.C. si cerca di stabilire un’anteriorità cronologica tra i due oggetti, nonché le rispettivefunzioni e valenze simboliche.In the Greek mythical world the functional definition of a protagonist seems strictly connected with his ethical and culturalperception in the society. That is the case of Ariadne, Medea or Circe, whose actions are always linked to the feminine concept of oikos.In the first part of this work Marco Giuman analyses the ways through which the feminine idea of mētis is iconographically adapted byGreek artists to the mythical heroines. The second part of the paper, by Elisabetta Pala, deepens on Ariadne’s character, more preciselyon her own metis-tools: the crown and the thread. Comparing literary sources and iconography from VII to V century B.C. the authortries to establish which object comes earlier, as well as their respective functions and symbolic values
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