778 research outputs found
Intrinsic instability of electronic interfaces with strong Rashba coupling
We consider a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures, which includes a Rashba spin-orbit
coupling proportional to the electric field perpendicular to the interface.
Based on the standard mechanism of polarity catastrophe, we assume that the
electric field is proportional to the electron density. Under these simple and
general assumptions, we show that a phase separation instability occurs for
realistic values of the spin-orbit coupling and of the band parameters. This
could provide an intrinsic mechanism for the recently observed inhomogeneous
phases at the LaAlO_3/SrTiO_3 or LaTiO_3/SrTiO_3 interfaces.Comment: 5 pages, 4 figure
Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling
We propose a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures that includes a Rashba spin-orbit coupling
proportional to an electric field oriented perpendicularly to the interface.
Taking into account the electron density dependence of this electric field
confining the electron gas at the interface, we report the occurrence of a
phase separation instability (signaled by a negative compressibility) for
realistic values of the spin-orbit coupling and of the electronic
band-structure parameters at zero temperature. We extend the analysis to finite
temperatures and in the presence of an in-plane magnetic field, thereby
obtaining two phase diagrams which exhibit a phase separation dome. By varying
the gating potential the phase separation dome may shrink and vanish at zero
temperature into a quantum critical point where the charge fluctuates
dynamically. Similarly the phase separation may be spoiled by a planar magnetic
field even at zero temperature leading to a line of quantum critical points.Comment: 17 pages, 17 figure
Possible mechanisms of electronic phase separation in oxide interfaces
LaAlO3/SrTiO3 ad LaTiO3/SrTiO3 interfaces are known to host a strongly
inhomogeneous (nearly) two-dimensional electron gas (2DEG). In this work we
present three unconventional electronic mechanisms of electronic phase
separation (EPS) in a 2DEG as a possible source of inhomogeneity in oxide
interfaces. Common to all three mechanisms is the dependence of some
(interaction) potential on the 2DEG's density. We first consider a mechanism
resulting from a sizable density-dependent Rashba spin-orbit coupling. Next, we
point out that an EPS may also occur in the case of a density-dependent
superconducting pairing interaction. Finally, we show that the confinement of
the 2DEG to the interface by a density-dependent, self-consistent electrostatic
potential can by itself cause an EPS.Comment: 4 pages and 4 figures, Proceedings of the International Conference
"Superstripes 2014", 25-31 July 2015, Erice, Ital
Transmission of Impacts during Mechanical Grape Harvesting and Transportation
The aim of the research was to study vibrational stress on grapes during mechanical harvesting, transfer and delivery to the winery, in order to identify the most critical stages and the consequent effects on the winemaking.
An instrumented sphere was used to evaluate and memorise the impacts in the grape harvester and means of transport.
Three treatments, obtained by differing harvesting method (manual and mechanical) and transport type (short and long distance), were compared. A correlation was sought between the transmitted stresses and characteristics of the harvested product.
The effects on product quality were evaluated by chemical analyses of the musts and sensorial analysis of the end-product, vinified using the same procedure
The positivity scale: Concurrent and factorial validity across late childhood and early adolescence
Despite the well-established protective functions of positivity (i.e., a dispositional selfevaluative tendency to view oneself, life, and future under a positive outlook) from middle adolescence to old age, its reliable assessment and contribution to a proper psychological functioning have received little attention during previous developmental phases. In this article, we aimed to evaluate the psychometric properties and construct validity of the eight-item Positivity Scale (P Scale; Caprara et al., 2012) during late childhood and early adolescence in a sample of British students (N = 742; 48% boys) from both primary (M age = 10.75, SD = 0.52) and secondary schools (M age = 13.38 years, SD = 0.94). First, results from confirmatory factor analysis (CFA) attested to the plausibility of the hypothesized 1-factor structure of the P Scale in a revised CFA model including the correlation between the residuals of two items similar in their wording. Next, we found evidence for strong (scalar) measurement invariance of the P Scale across late childhood and early adolescence as well as for its concurrent validity as indicated by expected relations of positivity to indicators of adjustment (i.e., prosocial behavior) and maladjustment (i.e., externalizing and internalizing problems). Overall, these findings support the concurrent and factorial validity of the P Scale as a short self-report instrument to measure children's tendency to view their experience from a positive stance. We discuss the implications of our results for improving the wording of the items composing P Scale as well as for understanding the dispositional mechanisms conducive to psychological health and wellbeing across late childhood and early adolescence
Exploiting SERS sensitivity to monitor DNA aggregation properties
In the last decades, DNA has been considered far more than the system carrying the essential genetic instructions. Indeed, because of the remarkable properties of the base-pairing specificity and thermoreversibility of the interactions, DNA plays a central role in the design of innovative architectures at the nanoscale. Here, combining complementary DNA strands with a custom-made solution of silver nanoparticles, we realize plasmonic aggregates to exploit the sensitivity of Surface Enhanced Raman Spectroscopy (SERS) for the identification/detection of the distinctive features of DNA hybridization, both in solution and on dried samples. Moreover, SERS allows monitoring the DNA aggregation process by following the temperature variation of a specific spectroscopic marker associated with the Watson-Crick hydrogen bond formation. This temperature-dependent behavior enables us to precisely reconstruct the melting profile of the selected DNA sequences by spectroscopic measurements only
Confinement of superconducting fluctuations due to emergent electronic inhomogeneities
The microscopic nature of an insulating state in the vicinity of a
superconducting state, in the presence of disorder, is a hotly debated
question. While the simplest scenario proposes that Coulomb interactions
destroy the Cooper pairs at the transition, leading to localization of single
electrons, an alternate possibility supported by experimental observations
suggests that Cooper pairs instead directly localize. The question of the
homogeneity, granularity, or possibly glassiness of the material on the verge
of this transition is intimately related to this fundamental issue. Here, by
combining macroscopic and nano-scale studies of superconducting ultrathin NbN
films, we reveal nanoscopic electronic inhomogeneities that emerge when the
film thickness is reduced. In addition, while thicker films display a purely
two-dimensional behaviour in the superconducting fluctuations, we demonstrate a
zero-dimensional regime for the thinner samples precisely on the scale of the
inhomogeneities. Such behavior is somehow intermediate between the Fermi and
Bose insulator paradigms and calls for further investigation to understand the
way Cooper pairs continuously evolve from a bound state of fermionic objects
into localized bosonic entities.Comment: 29 pages 9 figure
DNA-functionalized gold nanoparticle assemblies for Surface Enhanced Raman Scattering
The programmable assembly of DNA strands is a promising tool for building tailored bottom-up nanostructures. Here, we present a plasmonic nanosystem obtained by the base-pairing mediated aggregation of gold nanoparticles (NPs) which are separately functionalized with two different single-stranded DNA chains. Their controlled assembly is mediated by a complementary DNA “bridge” sequence. We monitor the formation of DNA assembled NP aggregates in solution, and we study their Surface Enhanced Raman Scattering (SERS) response by comparison with the single NP constituents. We interpret the revealed SERS signatures in terms of the molecular and NP organization at the nanoscale, demonstrating that the action of the DNA bridge molecule yields regular NP aggregates with controlled interparticle distance and reproducible SERS response. In perspective, this demonstrates the potential of the present system as a stable, biocompatible, and recyclable SERS sensor
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