Spin waves in curved magnetic shellsC2N - Centre de Nanosciences et de Nanotechnologies, , Palaiseau
The exploration of three-dimensional architectures has recently become a focus in several research fields, including the study of ferromagnets and superconductors. Depending on the underlying order parameter and interactions, twisting and bending flat samples into curved shells can lead to many emerging effects when the bending radius is comparable to the system's characteristic length scales. Curvature-induced emergent anisotropies and magnetochiral interactions have been widely studied in ferromagnetic systems, resulting in the discovery of various fascinating phenomena such as stabilizing skyrmions and merons on Gaussian and paraboloid bumps, pinning of domain walls or suppression of the Walker breakdown.
The impact of curvature and three-dimensional shape on magnetization dynamics, namely on the propagation of spin waves, manifests in several aspects: For example, the curvature of magnetic shells can modify the dynamic magnetic pseudo charges. As a result, magneto-chiral symmetry breaking of magnetostatic origin can lead to asymmetric spin-wave dispersion , nonreciprocal spatial mode profiles, and strongly modify nonlinear magnetization dynamics . Moreover, a nontrivial topology of three-dimensional magnetic specimens can induce a topological Berry phase of spin waves or impose selection rules on the dynamics of magnetic textures. Furthermore, achiral symmetry breaking, induced, for example, by lowering rotational symmetries, can lead to symmetry-governed splitting of degenerate modes [3,4]. This talk will focus on the aforementioned geometrical effects on magnetization dynamics and introduce numerical techniques for studying spin waves in curved magnetic shells. To this end, the finite-element micromagnetic modeling package TetraX is presented , which can efficiently calculate spin-wave dispersions and spatial mode profiles in various curvilinear geometries.
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Astronomy meets photonics: a unique potential for the next decadeC2N, Amphitheater, Palaiseau
New discoveries in astronomy rely primarily on the astronomers' ability to develop and exploit new technologies to process and analyze the very few distant stellar photons collected by telescopes. On the other side photonics has demonstrated, through numerous applications, a strong potential to route and manipulate light, which can be seen as an appealing alternative to classical free space optics. For the last ten years, "astrophotonics" has brought together these two fields and tried to improve on the versatility, robustness and simplification of, otherwise, increasingly complex and bulky instruments onboard the 10m or future 40m telescopes.
In this talk, I will focus on the recent achievements of "photonics for astronomy" mainly in the infrared part of the spectrum. I will review some of the major constrains in observational astrophysics that we are facing when developing new astronomical instrumentation and attempt to give a perspective, based on examples applicable to techniques such as interferometry and coronography, for future synergies that may profoundly impact optical and infrared instrumentation for ground- and space-based astronomy in the upcoming decade.
Keywords: high-angular resolution astronomy, infrared instrumentation, astrophotonics
Advanced numerical methodology for designing passive and active nanophotonic devicesC2N, Amphitheater, Palaiseau
In this presentation, I am excited to share with you our cutting-edge optimization approach
for multiobjective metasurface setups. Our method is based on statistical learning, which
utilizes surrogate modeling to predict the behavior of new designs during the optimization
process [1-2]. This approach allows us to rapidly converge to the global set of optimal
solutions while reducing the number of solver calls and iterations compared to traditional
global evolutionary strategies.
We put our optimization approach to the test by optimizing a 3D achromatic metalens with a
numerical aperture greater than 0.5. Our results were remarkable, achieving focusing
efficiencies of almost 50% for three colors (red, green, blue). This achievement sets a new
record for RGB metalens of this kind, and it was accomplished using simple cylindrical
nanopillar geometries that are easier to fabricate than complex freeform geometries .
Additionally, we developed a adopted our novel optimization method to consider the
fabrication imperfections relying on the metamodel context .
In the second part of my presentation, I will discuss our innovative design strategy to achieve
full phase modulation of light reflected from an arbitrary active metasurface with near-unity
efficiency . We adopted our advanced optimization method and considered the near-field
coupling between strongly resonant pixels and the nonlocal response to maximize the active
beam steering performance. This breakthrough technology has exciting applications in
imaging microscopy, high-resolution image projection, optical communication, and 3D light
detection and ranging (LiDAR).
Overall, our cutting-edge optimization approach together with our innovative design
strategies represent significant breakthroughs in the field of metasurface setups, with the
potential to transform a wide range of applications.
 M. Elsawy, et al, «Global optimization of metasurface designs using statistical learning methods», Scientific
Reports, Vol. 9, No. 17918, (2019).
 M. Elsawy, et. al, Multiobjective statistical learning optimization of RGB metalens, ACS Photonics, Vol. 8,No. 8,
pp. 2498–2508 (2021).
 M. Elsawy, et. al, Optimization of metasurfaces under geometrical uncertainty using statistical learning,
Optics Express 29(19), 29887–29898 (2021).
 M. Elsawy, et. al, Universal Active Metasurfaces for Ultimate Wavefront Molding by Manipulating the
Reflection Singularities. Laser Photonics Rev, 2200880, (2023)
keywords: Nanophotonics designs, Multiobjective optimization, Active metasurface, RGB Metalens, Geometrical imperfections
Mahmoud Elsawy is an experienced researcher with a demonstrated history of working in the field of electromagnetic modeling for linear and nonlinear Photonic devices. He received his PhD from the University of Aix-Marseille, France, in 2017, specializing in optics, photonics, and image processing. The topic of his PhD thesis was dedicated to the development of computational models for the design of realistic integrated nonlinear plasmonic waveguides. He spent a year as a postdoctoral researcher at the Institut Fresnel in Marseille, France. After a postdoc at Inria Sophia Antipolis, France, in the field of numerical optimization of nanophotonics, he became a permanent member of the Atlantis project team in December 2020 as an Inria Starting Faculty Position (ISFP) His research activities focus on the modeling and design of innovative passive and programmable metasurface devices.
High performance silicon and silicon metamaterials for integrated photonicsC2N, Amphitheater, Palaiseau
Silicon based photonics has been under great scrutiny in recent years due to their potential for making highly compact monolithic integration of multifunctional electronic and photonic devices on the same substrate. The most popular platform is the high index contrast silicon-on-insulator (SOI) system. The high refractive index contrast between the silica cladding and the silicon waveguide core facilitates the confinement and guiding of light in structures within submicron or nanometer dimensions. In addition, the mature silicon microfabrication technology establishes a firm foundation for making low-cost and compact integrated photonic devices. A wide range of active and passive optical devices has been realized on the SOI platform. The applications of these devices can be found in high-speed communications, health industry, chemical and biological analysis, environmental monitoring, optical interconnects, and renewable energy. This talk will focus on the research work by Dr. Ye’s group at Carleton University, ranging from fundamental metamaterial design using subwavelength gratings, polarization rotators and splitters, polarization-insensitive and broadband grating couplers, mode-division multiplexers, multimode couplers, spectral filters, nano-grating antennas, to optical phased arrays.
keywords : Silicon photonics, subwavelength gratings, polarization control, optical antennas, micro-rings/disks
Dr. Winnie Ye is a Fellow of the Engineering Institute of Canada (EIC) and a Full Professor in the Department of Electronics at Carleton University. She was also a Canada Research Chair (Tier II) in Nano-scale IC Design for Reliable Opto-Electronics and Sensors from 2009 to 2021. Her expertise is in silicon photonics and its applications in telecommunications, data communication, biophotonics, and renewable energy. Dr. Ye received her B.Eng., M.A.Sc. and Ph.D degree in Electrical and Computer Engineering from Carleton University and the University of Toronto, respectively. Dr. Ye returned to Carleton as a faculty member in 2009.
femto-second to pico-second laser pulse to switch magnetizationC2N - Centre de Nanosciences et de Nanotechnologies, , Palaiseau
During the last decade all-optical ultrafast magnetization switching in magnetic material thin film without the assistance of an applied external magnetic field has been explored [1,2]. It has been shown that femto-second light pulses can induce magnetization reversal in a large variety of magnetic materials [3,4]. However, so far, only certain particular ferrimagnetic thin films exhibit magnetization switching via a single femto-second optical pulse. All optical helicity dependent switching of a ferromagnetic layer could be demonstrated for a low number of pulses . Recently the single-pulse switching of various magnetic material (ferrimagnetic, ferromagnetic) within a magnetic spin-valve structure have been demonstrated. Our experimental study reveals that the magnetization states are determined by spin-polarized currents generated by the light pulse interactions with the GdFeCo layer . A detail study showing how spin-polarized currents are generated and how they interact with a Ferromagnetic (FM) layer can lead to magnetization switching will be presented [7,8]. Magnetization dynamics measurement show that the reversal of the FM layer happens in less than one picosecond which can be modelled [9,10]. Finally single pulse, ultra fast switching could also be observed in Gd free spin valve structure.
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 P. Scheid, et al JMMM 2022 https://doi.org/10.1016/j.jmmm.2022.169596
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 J. Igarashi, et al Nano. Lett. 20, 12, 8654–8660 2020
 S. Iihama et al J. Phys. Soc. Jpn 90, 081009 2021
 Q. Remy, et al Nature Com 14 (1), 445 2023
 J. Igarashi et al Nature Mat, 114 36 2023
Figure 1 : Sketch of a spin-valve structure used to demonstrate femto-second single pulse switching of each magnetic layer independently. The generation of femto-second spin current is shown to play a major role.
Dynamically Reconfigurable Nanophotonic Devices Enabled by Phase-change MaterialsC2N, Amphitheater, Palaiseau
A new platform for miniaturized reconfigurable nanophotonics through integration of dielectric, semiconductor, and plasmonic materials with nonvolatile phase-change materials will be discussed. This platform enables reconfigurable photonic building blocks with subwavelength features. Two groups of reconfigurable devices based on integrated photonic structures and metasurfaces along with their unique features for state-of-the-art applications will be discussed. Design, fabrication, and application of this platform for state-of-the-art devices and systems will be covered.
Keywords: Nanophotonics, Phase-change materials, Reconfigurable devices, Metaphotonics
Ali Adibi is the director of Bio and Environmental Sensing Technologies (BEST) and a professor and Joseph M. Pettit chair in the School of Electrical and Computer Engineering, Georgia Institute of Technology. His research group has pioneered several structures in the field of integrated nanophotonics for both information processing and sensing. He is the author of more than 200 journal papers and 450 conference papers. He is the editor-in-chief of the Journal of Nanophotonics, and the nanophotonic program track chair of the Photonics West meeting. He is the recipient of several awards including Presidential Early Career Award for Scientists and Engineers, Packard Fellowship, NSF CAREER Award, and the SPIE Technology Achievement Award. He is also a fellow of Optica, SPIE, and AAAS.
Bright Fluorescent Polymeric Nanomaterials for Biosensing and BioimagingC2N, Amphitheater, Palaiseau
Dye-loaded fluorescent polymeric nanoparticles (NPs) appear as an attractive alternative to inorganic NPs, such as quantum dots (QDots). Confining large number of dyes with bulky counterions within small polymeric nanoparticles makes the latter particularly bright and enable phenomenon of giant light-harvesting. Functionalization of these NPs with DNA yields FRET-based color switching nanoprobes for nucleic acids with single-molecule sensitivity and compatibility with RGB camera of a smartphone, important for cancer diagnostics. We also found that the energy transfer between two NPs connected by DNA duplexes does not follow canonical Förster law, allowing efficient long-range FRET at distances up to 20 nm, important for construction of ultrasensitive biosensors. When applied to cells, the small size of NPs was found essential for their free diffusion in cytosol and detection of intracellular RNA. At the animal level, the high brightness of NPs enabled single-particle tracking in the mice brain and visualization of crossing the blood-brain barrier. The developed small dye-loaded polymeric NPs open the route to ultrabright tools for sensing and tracking of biomolecules in biology and medicine.
Andrey Klymchenko obtained his PhD degree in 2003 from Kyiv National University. Then, he worked as post-doctoral fellow in the University of Strasbourg and Catholic University of Leuven. Then, he joined CNRS in 2006, received CNRS Bronze Medal in 2010 and was promoted to Director of Research in 2014. In 2015, he obtained ERC consolidator grant BrightSens. In 2021, he received Prix du Dr et de Mme Henri LABBE from French Academy of Sciences and he was elected a member of Academia Europaea. He is a leader of “Nanochemistry and Bioimaging” group and a co-founder of a start-up BrightSens Diagnostics. He is a co-author of over 250 peer-reviewed articles and 12 patents.
Magnetic and Information Dynamics in the Skyrmion SystemC2N, Amphitheater, Palaiseau
Abstract: i) Magnetic Skyrmions are chiral particles and the diffusion is accompanied by a rotational motion which can be expressed by taking the diffusion coefficient as a tensor . A skyrmion in a two-dimensional harmonic potential will rotate infinitely in the thermal equibirum. This rotation has zero angular momentum and does not violate the Bohr-Van Leeuwen’s theorem .
ii) From the LLG equation by taking the excitation of spin waves inside the skyrmion as the collective coordinates in addition to the center coordinate, it was shown that the center of magnetization has mass, but the center of charge has no mass .
iii) The information flow between two dipole-interacting skyrmions were obtained experimentaly. Analysis revealed that the system is not Markovian but hidden Markov system with a non-zero calculation power without consuming any energy in thermal equilibrium.
Acknowledgments We acknowledge to H. Mori, K. Emoto, S. Miki, M. Goto, H. Nomura and E. Tamura of Osaka University and R. Ishikawa of ULVAC Inc.. The project was supported by JSPS KAKENHI (S) JP20H05666 and JST CREST JPMJCR20C1.
 Y. Suzuki, S. Miki and E. Tamura, Physics Letters A, 413, (2021) 127603.
 S. Miki, Y. Jibiki, E. Tamura, M. Goto, M. Oogane, J. Cho, et al., J. Phys. Soc. Jpn., 90, 083601 (2021).
 Y. Suzuki, S. Miki, H. Nomura, E. Tamura, cond-mat, arXiv:2208.01835.
 R. Ishikawa, M. Goto, H. Nomura, and Y. Suzuki, Appl. Phys. Lett., 119, 072402 (2021).
Keywords: Skyrmion, Gyro-diffusion, Skyrmion mass, Hidden Markov system
In 1984, Suzuki graduated Tsukuba Univ. and started his carier at AIST. The thesis work was on the “MBE growth of the magnetic multilayers”. In 2003, he moved to Osaka Univ.. His research topics were “Magnetic Quantum well states”, “Magnetic tunnel junctions”, “spin-torque diode effect”, and “Voltage Control of Magnetic Anisotropy”.
He published about 400 papers and is getting about 20,000 citations.
From 1993 to 1994, he stayed at IEF-Universite Paris-sud as a “boursier”.
Europeanisation of my PhD Project with the EUGLOH European Alliance : A reallistic Picture ?C2N - Centre de Nanosciences et de Nanotechnologies, , Palaiseau
C2N PhD student seminarC2N, Amphitheatre, Palaiseau
- Xin Zheng (C2N Photonics Department) - GRadien INdex (GRIN) optics in silicon photonics
- Junbum Park (C2N Nanoelectronics Department) - Full Band Monte Carlo simulation of 2D h-BN nanostructure for phonon transport based on ab initio calculation
- Kamel-Eddine Harabi (C2N Nanoelectronics Department) - Memristor Based Artificial Intelligence Accelerators using
In/Near Memory Computing Paradigm
- Cléophanie Brochard (C2N Materials Department) - Heat transport in Van der Waals heterostructures