327 research outputs found
Control of the Coupling Strength and the Linewidth of a Cavity-Magnon Polariton
The full coherent control of hybridized systems such as strongly coupled
cavity photon-magnon states is a crucial step to enable future information
processing technologies. Thus, it is particularly interesting to engineer
deliberate control mechanisms such as the full control of the coupling strength
as a measure for coherent information exchange. In this work, we employ cavity
resonator spectroscopy to demonstrate the complete control of the coupling
strength of hybridized cavity photon-magnon states. For this, we use two
driving microwave inputs which can be tuned at will. Here, only the first input
couples directly to the cavity resonator photons, whilst the second tone
exclusively acts as a direct input for the magnons. For these inputs, both the
relative phase and amplitude can be independently controlled.
We demonstrate that for specific quadratures between both tones, we can
increase the coupling strength, close the anticrossing gap, and enter a regime
of level merging. At the transition, the total amplitude is enhanced by a
factor of 1000 and we observe an additional linewidth decrease of at
resonance due to level merging. Such control of the coupling, and hence
linewidth, open up an avenue to enable or suppress an exchange of information
and bridging the gap between quantum information and spintronics applications.Comment: 9 pages, 6 figure
Improved spectral stability in spin transfer nano-oscillators: single vortex versus coupled vortices dynamics
We perform a comparative study of spin transfer induced excitation of the
gyrotropic motion of a vortex core with either uniform or vortex spin
polarizers. The microwave output voltage associated with the vortex dynamics,
detected in both cases, displays a strong reduction of phase fluctuations in
the case of the vortex polarizer, with a decrease of the peak linewidth by one
order of magnitude down to 200kHz at zero field. A thorough study of rf
emission features for the different accessible vortex configurations shows that
this improvement is related to the excitation of coupled vortex dynamics by
spin transfer torques
Nonlinear behavior and mode coupling in spin transfer nano-oscillators
By investigating thoroughly the tunable behavior of coupled modes, we
highlight how it provides new means to handle the properties of spin transfer
nano-oscillators. We first demonstrate that the main features of the microwave
signal associated with coupled vortex dynamics i.e. frequency, spectral
coherence, critical current, mode localization, depends drastically on the
relative vortex core polarities. Secondly we report a large reduction of the
nonlinear linewidth broadening obtained by changing the effective damping
through the control of the core configuration. Such a level of control on the
nonlinear behavior reinforces our choice to exploit the microwave properties of
collective modes for applications of spintronic devices in novel generation of
integrated telecommunication devices
Early changes in diaphragmatic function evaluated using ultrasound in cardiac surgery patients: a cohort study.
Little is known about the evolution of diaphragmatic function in the early post-cardiac surgery period. The main purpose of this work is to describe its evolution using ultrasound measurements of muscular excursion and thickening fraction (TF). Single-center prospective study of 79 consecutive uncomplicated elective cardiac surgery patients, using motion-mode during quiet unassisted breathing. Excursion and TF were measured sequentially for each patient [pre-operative (D1), 1 day (D2) and 5 days (D3) after surgery]. Pre-operative median for right and left hemidiaphragmatic excursions were 1.8 (IQR 1.6 to 2.1) cm and 1.7 (1.4 to 2.0) cm, respectively. Pre-operative median right and left thickening fractions were 28 (19 to 36) % and 33 (22 to 51) %, respectively. At D2, there was a reduction in both excursion (right: 1.5 (1.1 to 1.8) cm, p < 0.001, left: 1.5 (1.1 to 1.8), p = 0.003) and thickening fractions (right: 20 (15 to 34) %, p = 0.021, left: 24 (17 to 39) %, p = 0.002), followed by a return to pre-operative values at D3. A positive moderate correlation was found between excursion and thickening fraction (Spearman's rho 0.518 for right and 0.548 for left hemidiaphragm, p < 0.001). Interobserver reliability yielded a bias below 0.1 cm with limits of agreement (LOA) of ± 0.3 cm for excursion and - 2% with LOA of ± 21% for thickening fractions. After cardiac surgery, the evolution of diaphragmatic function is characterized by a transient impairment followed by a quick recovery. Although ultrasound diaphragmatic excursion and thickening fraction are correlated, excursion seems to be a more feasible and reproducible method in this population
Immobilization of heavy metal in contaminated mine technosols using biochar: A phytomanagement strategy
Soil contamination by metal(loid)s is one of the most important environmental problem. It leads to loss
of environment biodiversity and soil functions and can have harmful effects on human health. Therefore,
contaminated soils could be remediated, using phytomanagement. Indeed, plant growth will improve soil
conditions while accumulating metal(loid)s and modifying their mobility. However, due to the poor
fertility and high metal(loid)s levels of these soils, amendments, like biochar, has to be applied.
Phytomanagement is a technique for rehabilitating these soils and reducing the spread of pollutants. To this end, it is advisable to stabilize the mobility of pollutants in the soil before planting plants. Biochar, produced by the pyrolysis of biomass under low oxygen conditions, has gathered attention in the last few years due to its capability to reduce metal(loid)s bioavailability and mobility in soils, as well as its beneficial effects on soil fertility. Indeed, biochar amendment to polluted soil induced usually an increase of pH, water holding capacity, and nutrient contents, associated with a decrease of metal(loid)s concentrations in soil pore water, through sorption on biochar. We tested different biochar concentrations from different wood feedstock in mesocosm and then on a field experimental plot presenting a significant arsenic (500 to 1000 mg/kg) and lead (15000 to 20000 mg/kg) pollution. Biochar from hardwood feedstock and more particularly the one obtained from bark and presenting the finest grain size (Lebrun et al. 2018) has shown good efficiency by reducing the availability of lead in soil pore water by more than 90% and keeping arsenic levels in the soil pore water below critical environmental concentrations. For the all plant species tested (Phaseolus, Populus, Salix, Ailanthus altissima, Alnus, Agrostis, and Trifolium) in biochar amended soils we show that biochar has allowed the establishment of a dense vegetation whereas until then the soils were bare and unsuitable for any plant development (Lebrun et al 2019, Nandillon et al 2019).
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Origin of spectral purity and tuning sensitivity in a vortex-based spin transfer nano-oscillator
We investigate the microwave characteristics of a spin transfer nano-oscillator (STNO) based on coupled vortices as a function of the perpendicular magnetic field . While the generation linewidth displays strong variations on (from 40 kHz to 1 MHz), the frequency tunability in current remains almost constant (~7 MHz/mA). We demonstrate that our vortex-based oscillator is quasi-isochronous independently of , so that the severe nonlinear broadening usually observed in STNOs does not exist. Interestingly, this does not imply a loss of frequency tunability, which is here governed by the current induced Oersted field. Nevertheless this is not sufficient to achieve the highest spectral purity in the full range of either: we show that the observed linewidth broadenings are due to the excited mode interacting with a lower energy overdamped mode, which occurs at the successive crossings between harmonics of these two modes. These findings open new possibilities for the design of STNOs and the optimization of their performance
Non-hermiticity in spintronics: oscillation death in coupled spintronic nano-oscillators through emerging exceptional points
The emergence of exceptional points (EPs) in the parameter space of a
non-hermitian (2D) eigenvalue problem is studied in a general sense in
mathematical physics, and has in the last decade successively reached the scope
of experiments. In coupled systems, it gives rise to unique physical phenomena,
which enable novel approaches for the development of seminal types of highly
sensitive sensors. Here, we demonstrate at room temperature the emergence of
EPs in coupled spintronic nanoscale oscillators and hence exploit the system's
non-hermiticity. We describe the observation of amplitude death of
self-oscillations and other complex dynamics, and develop a linearized
non-hermitian model of the coupled spintronic system, which properly describes
the main experimental features. Interestingly, these spintronic nanoscale
oscillators are deployment-ready in different applicational technologies, such
as field, current or rotation sensors, radiofrequeny and wireless devices and,
more recently, novel neuromorphic hardware solutions. Their unique and
versatile properties, notably their large nonlinear behavior, open up
unprecedented perspectives in experiments as well as in theory on the physics
of exceptional points. Furthermore, the exploitation of EPs in spintronics
devises a new paradigm for ultrasensitive nanoscale sensors and the
implementation of complex dynamics in the framework of non-conventional
computing
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