ORBi Collection: Physics
http://hdl.handle.net/2268/154
The Collection's search engineSearch this channelsearch
http://orbi.ulg.ac.be/simple-search
Velocimetry of superconducting vortices based on stroboscopic resonances
http://hdl.handle.net/2268/202860
Title: Velocimetry of superconducting vortices based on stroboscopic resonances
<br/>
<br/>Author, co-author: Jelic, Zeljko; Milosevic, Milorad; Silhanek, Alejandro
<br/>
<br/>Abstract: An experimental determination of the mean vortex velocity in superconductors mostly
relies on the measurement of flux-flow resistance with magnetic field, temperature, or driving
current. In the present work we introduce a method combining conventional transport
measurements and a frequency-tuned flashing pinning potential to obtain reliable estimates
of the vortex velocity. The proposed device is characterized using the time-dependent
Ginzburg-Landau formalism, where the velocimetry method exploits the resonances in mean
vortex dissipation when temporal commensuration occurs between the vortex crossings and
the flashing potential. We discuss the sensitivity of the proposed technique on applied current,
temperature and heat diffusion, as well as the vortex core deformations during fast
motion.Tue, 25 Oct 2016 08:59:46 GMTQuasi-One-Dimensional Metal-Insulator Transitions in Compound Semiconductor Surfaces
http://hdl.handle.net/2268/202595
Title: Quasi-One-Dimensional Metal-Insulator Transitions in Compound Semiconductor Surfaces
<br/>
<br/>Author, co-author: Zhao, J. Z.; Fan, W.; Verstraete, Matthieu; Zanolli, Zeila; Fan, J.; Yang, X. B.; Xu, H.; Tong, S. Y.Sat, 15 Oct 2016 04:31:13 GMTMagnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling
http://hdl.handle.net/2268/202536
Title: Magnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling
<br/>
<br/>Author, co-author: Fagnard, Jean-François; Morita, Mitsuru; Nariki, Shinya; Teshima, Hidekazu; Caps, Hervé; Vanderheyden, Benoît; Vanderbemden, Philippe
<br/>
<br/>Abstract: Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been pointed out that ferromagnets can help in reducing the crossed field effect, namely the magnetization decay that is observed under the application of AC transverse magnetic fields. In this work, we pursue a detailed study of the influence of the geometry of the ferromagnetic part on both trapped fields and crossed field effects. The magnetic properties of the hybrid superconducting/soft ferromagnetic structures are characterized by measuring the magnetic moment with a bespoke magnetometer and the local magnetic field density with Hall probes. The results are interpreted by means of 2D and 3D numerical models yielding the distribution of the superconducting currents as a function of the ferromagnet geometry. We examine in details the distortion of the shielding superconducting currents distribution in hybrid structures subjected to crossed magnetic fields. These results confirm the existence of an optimum thickness of the ferromagnet, which depends on the saturation magnetization of the ferromagnetic material and the current density of the superconductor. A hybrid structure providing an efficient protection against the crossed magnetic field while maintaining the magnetic induction along the axis of the structure is suggested. The limitations of the 2D modelling in this configuration are discussed.Thu, 13 Oct 2016 06:55:43 GMTDroplet formation by squeezing in a microfluidic cross-junction
http://hdl.handle.net/2268/202526
Title: Droplet formation by squeezing in a microfluidic cross-junction
<br/>
<br/>Author, co-author: Van Loo, Stéphanie; Stoukatch, Serguei; Kraft, Michael; Gilet, Tristan
<br/>
<br/>Abstract: In microfluidics, flow focusing is widely used to produce water-in-oil droplets in microchannels at high frequency. We here report an experimental study of droplet formation in a microfluidic cross-junction with a minimum number of geometrical parameters. We mostly focus on the squeezing regime, which is composed of two distinct steps : filling and pinching. The duration of each step (and corresponding volumes of each liquid phase) are analyzed. They vary according to both water and oil flow rates. These variations provide several insights about the fluid flows in both phases. We propose several scaling laws to relate the droplet volume and frequency to the flow rate of both phases. We also discuss the influence of surfactant and channel compliance on droplet formation.Wed, 12 Oct 2016 12:57:24 GMTRefractive and diffractive contribution of linear chromatic aberration (LCA) on depth-of-focus with trifocal intraocular lenses (IOLs)
http://hdl.handle.net/2268/202163
Title: Refractive and diffractive contribution of linear chromatic aberration (LCA) on depth-of-focus with trifocal intraocular lenses (IOLs)
<br/>
<br/>Author, co-author: Loicq, Jerôme; Gatinel, Damien
<br/>
<br/>Abstract: Purpose:
To investigate the refractive and diffractive contribution of LCA on depth of focus extension of trifocal IOLs in polychromatic light conditions
Setting:
University of Liège, Belgium; Fondation Ophtalmologique A. de Rothschild, Paris
Methods:
The LCAs associated with the three focal points of hydrophobic and hydrophilic diffractive FineVision trifocal IOLs (PhysIOL SA, Liège, Belgium), were simulated in an Arizona eye model and experimentally measured on an optical bench at 480, 546 and 650 nm. The effect of Abbe number and aperture on different IOL materials was also evaluated. Based on wavelength–dependent MTF through-focus curves and PSF properties, polychromatic behavior of the trifocal IOLs was assessed under mesopic and photopic conditions.
Results:
LCA amplitude and sign were different for each of the trifocal IOL focal points. The diffractive LCA for near and intermediate was independent of IOL material (GFree versus hydrophilic acrylic, 26%), while far vision LCA appeared to be controlled by the material Abbe number. Under polychromatic conditions, the LCA contributed to depth of focus extension with different types of lens material, providing maximal visual acuity under white light conditions at all distances.
Conclusions:
Diffractive trifocal IOLs show chromatic aberrations with an increase in depth of focus under polychromatic light. This effect likely contributes to the extended range of vision.Fri, 30 Sep 2016 11:28:59 GMTLeidenfrost drops on a heated liquid pool
http://hdl.handle.net/2268/202136
Title: Leidenfrost drops on a heated liquid pool
<br/>
<br/>Author, co-author: Maquet, Laurent; sobac, benjamin; darbois-texier, baptiste; Duchesne, Alexis; rednikov, alexey; colinet, pierre; Dorbolo, StéphaneThu, 29 Sep 2016 15:12:46 GMTChaotic Bohmian trajectories for stationary states
http://hdl.handle.net/2268/202130
Title: Chaotic Bohmian trajectories for stationary states
<br/>
<br/>Author, co-author: Cesa, Alexandre; Martin, John; Struyve, Ward
<br/>
<br/>Abstract: In Bohmian mechanics, the nodes of the wave function play an important role in the generation of chaos. However, so far, most of the attention has been on moving nodes; little is known about the possibility of chaos in the case of stationary nodes. We address this question by considering stationary states, which provide the simplest examples of wave functions with stationary nodes. We provide examples of stationary wave functions for which there is chaos, as demonstrated by numerical computations, for one particle moving in 3 spatial dimensions and for two and three entangled particles in two dimensions. Our conclusion is that the motion of the nodes is not necessary for the generation of chaos. What is important is the overall complexity of the wave function. That is, if the wave function, or rather its phase, has complex spatial variations, it will lead to complex Bohmian trajectories and hence to chaos. Another aspect of our work concerns the average Lyapunov exponent, which quantifies the overall amount of chaos. Since it is very hard to evaluate the average Lyapunov exponent analytically, which is often computed numerically, it is useful to have simple quantities that agree well with the average Lyapunov exponent. We investigate possible correlations with quantities such as the participation ratio and different measures of entanglement, for different systems and different families of stationary wave functions. We find that these quantities often tend to correlate to the amount of chaos. However, the correlation is not perfect, because, in particular, these measures do not depend on the form of the basis states used to expand the wave function, while the amount of chaos does.Thu, 29 Sep 2016 11:51:19 GMTCompetition of phonon and magnon effects in the temperature dependence of spinwave stiffness
http://hdl.handle.net/2268/202099
Title: Competition of phonon and magnon effects in the temperature dependence of spinwave stiffness
<br/>
<br/>Author, co-author: Ostler, Thomas; Verstraete, Matthieu; Di Gennaro, Marco; Miranda, Alonso; Romero, Aldo
<br/>
<br/>Abstract: Magnons are the elementary magnetic excitations in ordered solids. Understanding such collective excitations is important for a number of technologically relevant fields, such as, magnonics [1] or spin caloritronics [2]. The central interactions in spin caloritronics are the couplings of phonons with electrons and spin degrees of freedom. Furthermore, understanding the effects of temperature on the phonon and spin degrees of freedom adds a further complexity. In the present work we have developed a multiscale model of ferromagnetic materials and demonstrate the effect of temperature dependent phonon displacements on the magnons spectra. Our results show that the for Fe and Ni the effect of phonon displacements acts to reduce the Curie temperature, whereas for Permalloy the opposite is true due to an increased long-ranged exchange interaction. This increased exchange interaction results in an increasing spin-wave stiffness with increasing temperature, overcoming the usual decrease due to magnon softening. To determine the effects of increasing the phonon temperature we have developed a multiscale model whereby we begin by calculating the thermal displacement of phonons, $\sqrt{\langle u^2(T) \rangle}$, calculated using the phonopy software package [3] using electronic ground state and phonon properties determined using the ABINIT software package [4]. Then the exchange constants are determined using the SPRKKR package [5]. Finally, we use linear spin wave theory to determine the effect of the phonon temperature on the exchange alone, demonstrating an increasing frequency of the acoustic magnon branch. We take into account the thermal effects of the magnetic system through the use of the atomistic spin dynamics approach. Magnon softening due to thermal effects demonstrates a more modest increase in the exchange stiffness (over the purely phononic effect), however, an overall increase is still observed. \newline \newline [1] A. V. Chumak, V. I. Vasyuchka, A. A. Serga, and B. Hillebrands, Nature Physics, {\bf 11}, 453–461 (2015). \newline [2] G. E. W. Bauer, E. Saitoh, and B. J. van Wees, Nature Materials {\bf 11}, 391 (2012). \newline [3] Atsushi Togo and Isao Tanaka, Scr. Mater., {\bf 108}, 1-5 (2015) \newline [4] X. Gonze \textit{et al.} Computer Physics Communications {\bf 180}, 2582-2615 (2009). \newline [5] T. Huhne \textit{at al.} Physical Review B, {\bf 58}, 10236 (1998).Wed, 28 Sep 2016 15:30:27 GMTDroplet manipulation on fiber networks
http://hdl.handle.net/2268/202077
Title: Droplet manipulation on fiber networks
<br/>
<br/>Author, co-author: Weyer, Floriane; Pan, Zhao; Truscott, Tadd; Vandewalle, NicolasWed, 28 Sep 2016 09:25:13 GMTAnomalous diffusion and non-monotonic relaxation processes in Ge-Se liquids
http://hdl.handle.net/2268/202062
Title: Anomalous diffusion and non-monotonic relaxation processes in Ge-Se liquids
<br/>
<br/>Author, co-author: Yildirim, Can; Raty, Jean-Yves; Micoulaut, Matthieu
<br/>
<br/>Abstract: We investigate the dynamical properties of liquid GexSe100−x as a function of Ge content by
first-principles molecular dynamic simulations for a certain number of temperatures in the liquid
state. The focus is set on ten compositions (where x ≤ 33%) encompassing the reported flexible to
rigid and rigid to stressed-rigid transitions. We examine diffusion coefficients, diffusion activation
energies, glassy relaxation behavior, and viscosity of these liquids from Van Hove correlation and
intermediate scattering functions. At fixed temperature, all properties/functions exhibit an anomalous
behavior with Ge content in the region 18%-22%, and provide a direct and quantitative link to the
network rigidity.Tue, 27 Sep 2016 10:17:58 GMTPerformances comparison of a laser ultrasonic system using 10.6 µm infrared or 532 nm visible generation beam for the investigation of CFRP
http://hdl.handle.net/2268/202055
Title: Performances comparison of a laser ultrasonic system using 10.6 µm infrared or 532 nm visible generation beam for the investigation of CFRP
<br/>
<br/>Author, co-author: Vandenrijt, Jean-François; Walter, Julien; Brouillette, Tomy; Georges, Marc
<br/>
<br/>Abstract: The investigation of complex shaped carbon fiber parts is a common need of the industry. Classical ultrasonic systems are commonly used, wide-spread and very efficient. However, these techniques are often limited to simple shape objects. Major problems arise when the shape of the element to be investigated is complex (peak, valley, small radius of curvature…). To overcome these problems laser ultrasonic systems can be used and the recent developments show promising results.
Laser ultrasonic systems can use different wavelengths for ultrasound generation. Usually CO2 lasers emitting at 10.6 µm wavelength are used. When a laser ultrasonic system is mounted on a robotic arm, very complex shaped objects can be considered. However, the optical fibers for 10.6 µm wavelength are not capable to cope with laser ultrasonic system requirements. Therefore, infrared systems use jointed articulated beam delivery systems which reduce the flexibility of the robot arm and significantly limit the feasible scan paths.
To circumvent this limitation, an all-fibered laser ultrasonic system can be used. In our case the ultrasound is generated with a pulsed laser operating at 532 nm. This system is placed on a robotic
arm, the beam delivery is performed through an optical fiber only. Therefore, this system is capable of analyzing very complex shaped objects due to the use of optical fiber only for laser beam transport.
But visible generation is known to be less efficient and produces lower quality signals. In order to balance the advantages and limitations of both of these systems a CFRP plate including artificial defects has been investigated with different ultrasonic systems. First we used classical phased-array ultrasounds as a reference to compare the performances of visible and infrared generation systems. The plate has then been investigated with a 10.6 µm laser ultrasonic system. The results are compared with an all-fibered laser ultrasonic system working at 532 mn wavelength.
Data acquired by each system allow comparing the visibility of the ultrasonic echoes and the amplitude of background noise. We observe the impact of frequency filtering. We show the main differences on the A-scans and C-scan generated by each system. From these elements, we show the advantages and limitations of each system for the investigation of CFRP with a focus on complex shaped object.Mon, 26 Sep 2016 20:56:10 GMTCoupled Boltzmann Equation Solver: Effects of the Electron-Phonon Interaction on the Transport Coefficients
http://hdl.handle.net/2268/202014
Title: Coupled Boltzmann Equation Solver: Effects of the Electron-Phonon Interaction on the Transport Coefficients
<br/>
<br/>Author, co-author: Pike, Nicholas; Dewandre, Antoine; Verstraete, Matthieu
<br/>
<br/>Abstract: Recent experimental and theoretical calculations point to a complex interplay between the electron and phonon baths in a wide variety of materials [1,2]. We propose a method of coupling the Boltzmann equations for the electron and phonon baths within the relaxation time approximation which we use to calculate the thermoelectric transport coefficients. Our model for the coupled Boltzmann Equation solver includes analytic models, including ${\bf k \cdot p}$ Hamiltonians and tight-binding Hamiltonians, for both the electron and phonon energies and analytic models for the electron and phonon relaxation mechanisms. From these calculations we hope to better understand the role and interplay of electron-phonon and phonon-phonon interactions on the thermoelectric transport coefficients.
[1] - Phys. Rev. Lett. ${\bf 114}$, 115901 (2015). [2] - PNAS ${\bf 112}$, 14777-14782 (2015).Sat, 24 Sep 2016 06:24:39 GMTCooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
http://hdl.handle.net/2268/201976
Title: Cooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
<br/>
<br/>Author, co-author: Damanet, François; Braun, Daniel; Martin, John
<br/>
<br/>Abstract: We investigate superradiance and subradiance of indistinguishable atoms with quantized motional states, starting with an initial total state that factorizes over the internal and external degrees of freedom of the atoms. Due to the permutational symmetry of the motional state, the cooperative spontaneous emission, governed by a recently derived master equation [F. Damanet et al., Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates γ and γ0 and a single parameter dd describing the dipole-dipole shifts. We solve the dynamics exactly for N = 2 atoms, numerically for up to 30 atoms, and obtain the large-N limit by a mean-field approach. We find that there is a critical difference γ0 − γ that depends on N beyond which superradiance is lost. We show that exact nontrivial dark states (i.e., states other than the ground state with vanishing spontaneous emission) only exist for γ = γ0 and that those states (dark when γ = γ0) are subradiant when γ < γ0.Fri, 23 Sep 2016 07:05:46 GMTExcitation functions of the natCr(p,x)44Ti, 44Fe(p,x)44Ti, natNi(p,x)44Ti and 93Nb(p,x)44Ti reactions at energies up to 2.6 GeV
http://hdl.handle.net/2268/201958
Title: Excitation functions of the natCr(p,x)44Ti, 44Fe(p,x)44Ti, natNi(p,x)44Ti and 93Nb(p,x)44Ti reactions at energies up to 2.6 GeV
<br/>
<br/>Author, co-author: Titarenko, Yu. E.; Batyaev, V. F.; Pavlov, K. V.; Titarenko, A. Yu.; Zhivun, V. M.; Chauzova, M. V.; Balyuk, S. A.; Bebenin, P. V.; Ignatyuk, A. V.; Mashnik, S. G.; Leray, Sylvie; Boudard, Alain; David, Jean-Christophe; Mancusi, Davide; Cugnon, Joseph; Yariv, Yair; Nishihara, K.; Matsuda, N.; Kumawat, H.; Stankovskiy, A. Yu.Thu, 22 Sep 2016 09:37:15 GMTProcesses involving few degrees of freedom in the frame of the Intranuclear Cascade approaches
http://hdl.handle.net/2268/201956
Title: Processes involving few degrees of freedom in the frame of the Intranuclear Cascade approaches
<br/>
<br/>Author, co-author: Cugnon, Joseph; Boudard, Alain; David, Jean-Christophe; Leray, Sylvie; Mancusi, DavideThu, 22 Sep 2016 09:16:45 GMTUltra-narrow superconducting junctions: electromigration to shed light on quantum point contacts
http://hdl.handle.net/2268/201933
Title: Ultra-narrow superconducting junctions: electromigration to shed light on quantum point contacts
<br/>
<br/>Author, co-author: Baumans, Xavier; Cerbu, Dorin; Adami, Obaïd-Allah; Zharinov, Vyacheslav; Verellen, Niels; Papari, Gianpaolo; Scheerder, Jeroen; Zhang, Gufei; Moshchalkov, Victor; Silhanek, Alejandro; Van de Vondel, Joris
<br/>
<br/>Abstract: Superconducting nanowires have been, for years now, a topic of great interest due to
their potential application in single photon detectors and in quantum computing
circuits. In this context, it is of fundamental importance to better understand the
undesired and harmful appearance of thermal and quantum fluctuations of the
superconducting order parameter [1]-[3] as a function of the wire width.
Although superconductors in the mesoscopic regime (i.e. size comparable to ξ and/or
λ) have been explored both experimentally and theoretically in depth, the
superconducting nanoworld (i.e. at scales of the fermi wavelength) has received much
less attention. The lack of experimental results is in part due to the difficulty of sample
fabrication, at dimensions beyond the limit reached by conventional lithographic
techniques. A promising direction consists of controlling the local displacement of
atom by an electron wind, a process known as electromigration (EM) [4] . This effect
relies on the combination of local temperature rise and substantial current crowding at
nanoconstrictions. While uncontrolled, EM is responsible for the breakdown of small
electronic devices, it can be used in a controllable way to further decrease locally the
cross section of the nanowire towards single atomic contacts.
In this work, we explore in-situ controlled EM to fabricate nano-constrictions immersed
in cryogenic environment. We demonstrate that a transition from thermally assisted
phase slips (TAPS) to quantum phase slips (QPS) takes place when the effective cross
section becomes smaller than ~ 150 nm 2 . In the regime dominated by QPS the
nanowire loses completely its capacity to carry current without dissipation, even at the
lowest possible temperature [5] . We also demonstrate that the bow-tie shaped
constrictions exhibit a negative magnetoresistance at low magnetic fields [5] which can
be attributed to the suppression of superconductivity in the contact leads [6] . Strikingly,
the detrimental effect caused by the repeated EM can be healed by simply inverting
the current direction. These findings reveal the strong potential of the proposed
fabrication method to explore various fascinating superconducting phenomena in
atomic-size constrictions.Wed, 21 Sep 2016 14:27:11 GMTInternal structures of clusters in driven granular gas
http://hdl.handle.net/2268/201911
Title: Internal structures of clusters in driven granular gas
<br/>
<br/>Author, co-author: Noirhomme, MartialWed, 21 Sep 2016 07:36:41 GMTShell structure and few-nucleon removal in intranuclear cascade
http://hdl.handle.net/2268/201896
Title: Shell structure and few-nucleon removal in intranuclear cascade
<br/>
<br/>Author, co-author: Mancusi, Davide; Boudard, Alain; Carbonell, Jaume; Cugnon, Joseph; David, Jean-Christophe; Leray, SylvieTue, 20 Sep 2016 14:25:36 GMTSelf-assembly of capillary multipoles
http://hdl.handle.net/2268/201838
Title: Self-assembly of capillary multipoles
<br/>
<br/>Author, co-author: Poty, Martin; Lagubeau, Guillaume; Lumay, Geoffroy; Vandewalle, Nicolas
<br/>
<br/>Abstract: Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced. Their 3d shape is chosen in order to create capillary multipoles. The capillary interactions between these components can be either attractive or repulsive depending on the interface local deformations along the liquid-air interface. In order to understand how the shape of an object deforms the interface, we developed an original profilometry method. The measurements show that specific structures can be programmed by selecting the 3d branched shapes.Mon, 19 Sep 2016 12:32:29 GMTImprinting superconducting vortex trajectories in a magnetic layer
http://hdl.handle.net/2268/201749
Title: Imprinting superconducting vortex trajectories in a magnetic layer
<br/>
<br/>Author, co-author: Shaw, Gorky
<br/>
<br/>Abstract: We experimentally show that the principle of local polarization of a magnetic layer can be applied for imprinting, into a soft magnetic layer of permalloy (Py), the trajectory of vortices moving in a superconducting film (Nb). In full analogy with a magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py layer. We have used the magneto-optical imaging technique to investigate the mutual interaction between superconducting vortices and ferromagnetic domains. In general, we observe that the flux propagation is delayed at the border of the magnetic layer. For thick Py layers, the stripe magnetic domain pattern guides the smooth flux penetration as well as the abrupt vortex avalanches in the Nb film. More interestingly, in thin Py layers without stripe domains, vortices leave clear imprints of locally polarized magnetic moments along their trajectories. Furthermore, the printings were found to be stable and could still be observed at room temperature, allowing for ex situ observation of the flux penetration in superconductors. We expect our findings to pave the way for further studies for optimizing magnetic recording of superconducting vortex trajectories.Tue, 13 Sep 2016 15:51:54 GMT