150 research outputs found
New perspectives in the ultrafast spectroscopy of many-body excitations in correlated materials
Ultrafast spectroscopies constitute a fundamental tool to investigate the
dynamics of non-equilibrium many-body states in correlated materials.
Two-pulses (pump-probe) experiments have shed new light on the interplay
between high-energy electronic excitations and the emerging low-energy
properties, such as superconductivity and charge-order, in many interesting
materials. Here we will review some recent results on copper oxides and we will
propose the use of high-resolution multi-dimensional techniques to investigate
the decoherence processes of optical excitations in these systems. This novel
piece of information is expected to open a new route toward the understanding
of the fundamental interactions that lead to the exotic electronic and magnetic
properties of correlated materials.Comment: Invited by S.I.F. To appear in Nuovo Cimento C. 7 pages, 4 figure
Thermal boundary resistance from transient nanocalorimetry: a multiscale modeling approach
The Thermal Boundary Resistance at the interface between a nanosized Al film
and an Al_{2}O_{3} substrate is investigated at an atomistic level. A room
temperature value of 1.4 m^{2}K/GW is found. The thermal dynamics occurring in
time-resolved thermo-reflectance experiments is then modelled via macro-physics
equations upon insertion of the materials parameters obtained from atomistic
simulations. Electrons and phonons non-equilibrium and spatio-temporal
temperatures inhomo- geneities are found to persist up to the nanosecond time
scale. These results question the validity of the commonly adopted lumped
thermal capacitance model in interpreting transient nanocalorimetry
experiments. The strategy adopted in the literature to extract the Thermal
Boundary Resistance from transient reflectivity traces is revised at the light
of the present findings. The results are of relevance beyond the specific
system, the physical picture being general and readily extendable to other
heterojunctions.Comment: 12 pages, 8 figure
Temperonic Crystal: a superlattice for temperature waves in graphene
The temperonic crystal, a periodic structure with a unit cell made of two
slabs sustaining temperature wave-like oscillations on short time-scales, is
introduced. The complex-valued dispersion relation for the temperature scalar
field is investigated for the case of a localised temperature pulse. The
dispersion discloses frequency gaps, tunable upon varying the slabs thermal
properties. Results are shown for the paradigmatic case of a graphene-based
temperonic crystal. The temperonic crystal extends the concept of superlattices
to the realm of temperature waves, allowing for coherent control of ultrafast
temperature pulses in the hydrodynamic regime at above liquid nitrogen
temperatures.Comment: 5 pages, 3 figure
Analytical model of the acoustic response of nanogranular films adhering on a substrate
A 1D mechanical model for nanogranular films, based on a structural
interface, is here presented. The analytical dispersion relation for the
frequency and lifetimes of the acoustics breathing modes is obtained in terms
of the interface layer thickness and porosity. The model is successfully
benchmarked both against 3D Finite Element Method simulations and experimental
photoacoustic data on a paradigmatic system available from the literature. A
simpler 1D model, based on an homogenized interface, is also presented and its
limitations and pitfalls discussed at the light of the more sophisticated
pillar model. The pillar model captures the relevant physics responsible for
acoustic dissipation at a disordered interface. Furthermore, the present
findings furnish to the experimentalist an easy-to-adopt, benchmarked
analytical tool to extract the interface layer physical parameters upon fitting
of the acoustic data. The model is scale invariant and may be deployed, other
than the case of granular materials, where a patched interface is involved
Temperature dependence of the thermal boundary resistivity of glass-embedded metal nanoparticles
The temperature dependence of the thermal boundary resistivity is
investigated in glass-embedded Ag particles of radius 4.5 nm, in the
temperature range from 300 to 70 K, using all-optical time-resolved
nanocalorimetry. The present results provide a benchmark for theories aiming at
explaining the thermal boundary resistivity at the interface between metal
nanoparticles and their environment, a topic of great relevance when tailoring
thermal energy delivery from nanoparticles as for applications in nanomedicine
and thermal management at the nanoscaleComment: 4 pages, 3 figure
Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator
We use time- and energy-resolved optical spectroscopy to investigate the
coupling of electron-hole excitations to the magnetic environment in the
relativistic Mott insulator NaIrO. We show that, on the picosecond
timescale, the photoinjected electron-hole pairs delocalize on the hexagons of
the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations
and the exchange of energy with the short-range-ordered zig-zag magnetic
background. The possibility of mapping the magnetic dynamics, which is
characterized by typical frequencies in the THz range, onto high-energy (1-2
eV) charge excitations provides a new platform to investigate, and possibly
control, the dynamics of magnetic interactions in correlated materials with
strong spin-orbit coupling, even in the presence of complex magnetic phases.Comment: 5 pages, 4 figures, supplementary informatio
Towards an Integrated System as Point-of-Care Device for the Optical Detection of Sepsis Biomarkers
Severe infection and sepsis are a common, expensive, and frequently fatal conditions in critically ill patients. The sepsis diagnosis is not trivial, since it is an extremely complex chain of events involving inflammatory and anti-inflammatory processes, cellular reactions, and circulatory disorders. For these reasons, delay in diagnosis and initiation of drug treatments have shown to be crucial for this pathology. Moreover, a multitude of biomarkers has been proposed, many more than for other pathologies. In order to select optimal treatments for the highly heterogeneous group of sepsis patients and to reduce costs, novel multiplexed tools that better characterize the patient and his or her specific immune response are highly desired. In order to achieve the fundament of drastically improved multi-analyte detection and to attain low limits of detection in diagnostics, the area of point-of-care testing (POCT) technology is developing quickly, leading to the production of instruments, the reliability of which is continuously increasing. For this purpose, a selection of two biomarkers—C-reactive protein (CRP) and neopterin (NP)—was studied in this paper and a fluorescence-based integrated optical system, suitable for future POCT applications, was implemented that is capable of performing the simultaneous measurement of the two different biomarkers in replicate. A limit of detection of 10 and 2.1 µg L−1 was achieved for CRP and NP spiked in commercially available human serum, respectively. Moreover, measurements on both biomarkers were also performed on serum samples collected from septic patients
Strong enhancement of d-wave superconducting state in the three-band Hubbard model coupled to an apical oxygen phonon
We study the hole binding energy and pairing correlations in the three-band
Hubbard model coupled to an apical oxygen phonon, by exact diagonalization and
constrained-path Monte Carlo simulations. In the physically relevant
charge-transfer regime, we find that the hole binding energy is strongly
enhanced by the electron-phonon interaction, which is due to a novel
potential-energy-driven pairing mechanism involving reduction of both
electronic potential energy and phonon related energy. The enhancement of hole
binding energy, in combination with a phonon-induced increase of quasiparticle
weight, leads to a dramatic enhancement of the long-range part of d-wave
pairing correlations. Our results indicate that the apical oxygen phonon plays
a significant role in the superconductivity of high- cuprates.Comment: 5 pages, 5 figure
Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme
Accessing fluid infiltration in nanogranular coatings is an outstanding
challenge, of relevance for applications ranging from nanomedicine to
catalysis. A sensing platform, allowing to quantify the amount of fluid
infiltrated in a nanogranular ultrathin coating, with thickness in the 10 to 40
nm range, is here proposed and theoretically investigated by multiscale
modelling. The scheme relies on impulsive photoacoustic excitation of
hypersonic mechanical breathing modes in engineered gas-phase synthesised
nanogranular metallic ultathin films and time-resolved acousto-optical read-out
of the breathing modes frequency shift upon liquid infiltration. A superior
sensitivity, exceeding 26x103 cm^2/g, is predicted upon equivalent areal mass
loading of a few ng/mm^2. The capability of the present scheme to discriminate
among different infiltration patterns is discussed. The platform is an ideal
tool to investigate nano fluidics in granular materials and naturally serves as
a distributed nanogetter coating, integrating fluid sensing capabilities. The
proposed scheme is readily extendable to other nanoscale and mesoscale porous
materials.Comment: 14 pages, 4 figure
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