(en anglais) The human brain disconnectomeCentre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau
Patients with brain lesions provide a unique opportunity to understand the functioning of the human mind. However, even when focal, brain lesions have local and remote effects that impact functionally and structurally connected circuits. Similarly, function emerges from the interaction between brain areas rather than their sole activity. We will discuss a set of complementary solutions to measure the impact of a given lesion upon the neuronal circuits as well as ideas and theories explaining the functioning of the human brain.
Taken together, these neuroimaging measures will help discern the natural history of events occurring in the brain after a lesion, as well as assist in the localization of functions.
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(en anglais) Neuroinspired Artificial Intelligence with Memory NanodevicesCentre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau
When performing artificial intelligence tasks, computers and graphics cards consume considerably more energy for moving data between logic and memory units than for doing actual arithmetic. Brains, by contrast, achieve vastly superior energy efficiency by fusing logic and memory entirely, performing a form of "in-memory" computing. Currently emerging memory nanodevices such as (mem)resistive, phase change and magnetic memories give us an opportunity to achieve similar tight integration between logic and memory.
In this talk, we will look at neuroscience inspiration to extract lessons on the design of such systems. We will first study the reliance of brains on approximate memory strategies, which can be reproduced for artificial intelligence. We will give the example of a hardware neural network relying on resistive memory. Based on measurements on a hybrid CMOS and resistive Hafnium oxide memory chip, we will see that such systems can exploit the properties of emerging memories without the need of error correcting codes, and achieve extremely high energy efficiency. Second, we will see that brains use the physics of their memory devices in a way that is much richer than only storage. This can inspire radical electronic designs, where memory devices become a core part of computing. We will illustrate this concept by our works using magnetic memories as artificial neurons. We have fabricated neural networks where magnetic memories used as nonlinear oscillators implement neurons, and their electrical couplings implement synapses. We will see that such designs can harness the rich physics and dynamics inherent to magnetic memories, without suffering from their drawbacks. This physics-rich approach nevertheless raises important challenges that we will highlight.
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(en anglais) Broadband Ferromagnetic Resonance Spectroscopy: The “Swiss Army Knife” for Understanding Spin-Orbit PhenomenaCentre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau
Modern spin-based technologies rely on multiple, simultaneous phenomena that originate from the spin-orbit interaction in magnetic systems. These include damping, magnetic anisotropy, orbital moments, and spin-orbit torques that are manifested in the spin-Hall and Rashba-Edelstein effects. While cavity based ferromagnetic resonance (FMR) spectroscopy has been used to characterize magnetic materials for many decades, recent advances in broadband and phase-sensitive FMR techniques have allowed further refinement, improved accuracy, and new measurement capability. In fact, broadband FMR techniques can now precisely measure spin-orbit torques at the thin-film level without the requirement of device fabrication.
Broadband FMR measurements have also improved our fundamental understanding of magnetic damping. Numerous extrinsic relaxation mechanisms can obscure the measurement of the intrinsic damping of a material. This created a challenge to our understanding of damping because experimental data were not always directly comparable to theory. As a result of the improved ability to quantify all of these relaxation mechanisms, many theoretical models have been refined. In fact, this has recently led to both the prediction and discovery of new materials with ultra-low magnetic damping that will be essential for future technologies based on spintronics, magnonics, spin-logic and high-frequency devices.
I will begin this lecture with a basic introduction to spin-orbit phenomena, followed by an overview of modern broadband FMR techniques and analysis methods. I will then discuss some recent successes in applying broadband FMR to improve our ability to control damping in metals and half-metals, quantify spin-orbit torques and spin-diffusion lengths in multilayers, and determine the interrelationships among damping, orbital moments, and magnetic anisotropy , . The impact of these result on specific technologies will also be discussed.
Read more in the attached announcement.
(en anglais) Quantum thermal transport in circuitsCentre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau
Heating drives a crossover from quantum to classical behaviors. However, heat itself is ruled by the laws of quantum mechanics. In small electrical circuits, the fundamental implications span from a different quantum thermodynamics to the quantum phase influence on heat. In addition, the flow of heat provides a revealing and complementary probe for the investigation of intriguing phases of matter, by unveiling neutral states invisible to electrical transport. In the long term, quantum thermal phenomena will ineluctably constitute an essential parameter for the quantum engineering of nanocircuits. Other envisioned possibilities include novel calorimetry devices and thermal machines.
Whereas the quantum transport of electricity is being actively investigated since more than three decades, the thermal facet is more challenging to access. In particular, there is no equivalent of the ammeter for the flow of heat. Only recently experimental observations are emerging, such as the universal thermal conductance quantum, heat interferometry, or the heat conductance across a superconducting quantum bit. After a general introduction of the field, I will present the experimental determination of the universal limit imposed to heat flow by quantum mechanics, and the observation of heat Coulomb blockade, a many-body quantum effect that can selectively apply to heat but not to electricity in violation of the standard Wiedemann-Franz law.
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(en anglais) New Developments in the Application of Focused Ion Beam Technology – Sources + Computation + Ions = Better FIB SCIence.Centre de Nanosciences et de Nanotechnologies, Amphithéatre, Palaiseau
Focused Ion Beam (FIB) technology has much of its roots in the semiconductor industry, for circuit edit, mask repair and, later for TEM lamella sample preparation. Powered by its long-standing front-running ion source technology, the gallium-based liquid metal ion source, FIB has been developed for a number of applications beyond sample preparation, including serial sectioning, in situ techniques, and direct-write patterning. Furthermore, in recent years, the two major developments have opened new avenues of research in FIB technology: the first is the rapid development of new source technologies, including plasma sources, liquid metal alloy sources, and gas field ion sources, which brings much of the periodic table to bear for novel applications. The second is the advent of computational microscopy, in which scanning systems are evolving to allow high-speed characterization and on-the-fly adjustment during FIB and electron source use.
In this talk, I will show how these two new developments have expanded the boundaries of our thinking about FIB technology through several examples. The first is in the development of new electronic and optical materials based on ion implantation using novel sources and direct-write lithography. Following, this, I will demonstrate serial sectioning methods using plasma FIB for large-volume mesoscale applications. We will show that data processing and the use of on-the-fly sparse scanning with offline reconstructions can make dealing with large datasets more feasible and faster.
Associate Professor, Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario,08/2016–present
Materials Research Engineer, Materials Science and Technology Division, U.S. Naval Research Laboratory, Washington, DC, USA
Postdoc: National Institute of Standards and Technology,2006-2007
Postdoc: Electronic Division: U.S. Naval Research Laboratory,2003-2006
Ph.D.: University of Florida,2002
(en anglais) Coupling organic molecules to nanophotonic structuresCentre de Nanosciences et de Nanotechnologies, Salle A003, Palaiseau
Photons lie at the heart of many quantum technologies. They are the only logical choice for sending quantum information over long distances, they have been used for many demonstrations of quantum simulations, they are often employed in microscopy to perform high‐resolution imaging and they are promising candidates for quantum computing and networking. Still, they are difficult to generate and collect with high efficiency. In this talk I will discuss the use of organic molecules for generating, processing and storing single photons. When dibenzoterrylene (DBT) is embedded in anthracene it is photostable and forms a two‐level system which when excited will emit a photon at a wavelength of ~780 nm. This is desirable as a number of atomic quantum technologies based on rubidium interact efficiently with light at this wavelength. When cooled to 4K, DBT can be used to generate coherent, lifetime‐limited photons. I will show our work in characterising a single molecule at temperatures down to 4 K and show that coherent Rabi oscillations are then seen in the excited state population. I will then discuss our recent work to couple the emission from single molecules into nanophotonic waveguides including hybrid plasmonic systems and dielectric nanowire waveguides crossed with organic filled micro‐capillaries. Finally I will discuss the use of nanophotonic and optical fibre cavities to further enhance the collection of photons from single molecules.
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(en anglais) Quantum effects at superconducting phase transitionsCentre de Nanosciences et de Nanotechnologies, Amphithéatre, Palaiseau
While superconductivity is the archetype of quantum matter, with an entangled ground state of time-reversed states, the superconducting order parameter is essentially a classical field as a consequence of the Bose condensation of a macroscopic number of Cooper pairs. Yet, in some situations, the quantum dynamic of this superconducting order parameter can be observed experimentally. In a first example, I will show that the transport properties of superconducting thin films near the superconductor-insulator transition follow scaling laws that reflect the increased quantum fluctuations across the phase transition. In a second example, I will describe a Scanning Tunneling Spectroscopy (STS) study of the superconducting properties of ultra high vacuum (UHV) grown Pb nanocrystals where we identified a lower size limit for the existence of superconductivity. This size limit, called the Anderson limit, is the consequence of quantum fluctuations in pairing amplitude and is reached when the electronic level spacing becomes larger than the superconducting pairing energy. Finally, I will describe the project of Electron-Spin-Resonant- STM spectroscopy developed in the STM group of C2N, an experimental method that has potential applications for the study of quantum dynamics in atomically precise spin systems.
Legend: UHV grown superconducting Pb nanocrystals on InAs
(en anglais) Some current trends in the physics of superconducting flux vorticesCentre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau
Owing to the prospect of spectacular dissipation-less applications such as powerful magnets and exquisitely sensitive detectors with an ever-smaller need for refrigeration of the material, the discovery of new classes of high temperature superconducting materials is usually
accompanied by much excitement. However, fashioning actual superconducting applications meets with different limitations of fundamental, material, and technological nature. At the same time, type II superconductors, in which the magnetic field partially permeates the material in the form of quantized flux lines (or vortices), provide an exciting playground for the study of different flux-line aggregation states.
In this presentation, I shall briefly dwell on the state of the art in the field of superconductivity, before describing some examples of recent research on vortex physics: the interaction of vortex lines with disorder and the occurrence of different vortex states in the iron-based high temperature superconductors, and the physics and application of cuprate high temperature superconducting films for RF and HF current limiting devices. I shall finish with a number of perspectives.
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(en anglais) “Spin-Orbit Technologies: From Magnetic Memory to Terahertz Generation”Centre de Nanosciences et de Nanotechnologies, Amphithéatre, Palaiseau
Spintronic devices utilize an electric current to alter the state of a magnetic material and thus find great applications in magnetic memory. Over the last decade, spintronic research has focused largely on techniques based on spin-orbit coupling, such as spin-orbit torques (SOTs), to alter the magnetic state. The phenomenon of spin-orbit coupling in magnetic heterostructures was also recently used to generate terahertz emission and thus bridge the gap between spintronics and optoelectronics research.
I will introduce the basic concepts of SOTs, such as their physical origin, the effect of SOTs on a magnetic material, and how to quantitatively measure this effect [1,2]. Next, I will discuss the latest trends in SOT research, such as the exploration of novel material systems like topological insulators and two-dimensional materials to improve the operation efficiency [2,3]. Following this, some of the technical challenges in SOT-based magnetic memory will be highlighted . Moving forward, I will introduce the process of terahertz generation in magnetic heterostructures , where the spin-orbit coupling phenomenon plays a dominant role. I will discuss the details of how this terahertz emission process can be extended to novel material systems such as ferrimagnets  and topological materials . The final section will focus on how the terahertz generation process can be used to measure SOTs in magnetic heterostructures, thus highlighting the interrelation between terahertz generation and the SOTs, which are linked by the underlying spin-orbit coupling.
 X. Qiu et al., “Characterization and manipulation of spin orbit torque in magnetic heterostructures,” Adv. Mater., 30, 1705699 (2018).
 Y. Wang et al., “FMR-related phenomena in spintronic devices” J. Phys. D: Appl. Phys., 51, 273002 (2018).
 R. Ramaswamy et al., “Recent advances in spin-orbit torques: Moving towards device applications” Appl. Phys. Rev., 5, 031107 (2018).
 Y. Wu et al., “High-performance THz emitters based on ferromagnetic/nonmagnetic heterostructures” Adv. Mater., 29, 1603031 (2017).
 M. Chen, et al., “Terahertz emission from compensated magnetic heterostructures,” Adv. Opt. Mater., 6, 1800430 (2018).
 X. Wang, et al., “Ultrafast spin-to-charge conversion at the surface of topological insulator thin films” Adv. Mater. 30, 1802356 (2018).
Hyunsoo Yang obtained the bachelor’s degree from Seoul National University and the PhD degree from Stanford University. He worked at C&S Technology, Seoul; LG Electronics, San Jose, CA; and Intelligent Fiber Optic Systems, Sunnyvale, CA, USA. From 2004 to 2007, he was at the IBM-Stanford Spintronic Science and Applications Center, IBM Almaden Research Center. He is currently a GlobalFoundries chaired associate professor in the Department of Electrical and Computer Engineering, National University of Singapore, working on various magnetic materials and devices for spintronics applications. He has authored 170 journal articles, given 100 invited presentations, and holds 15 patents. Prof. Yang was a recipient of the Outstanding Dissertation Award for 2006 from the American Physical Society’s Topical Group on Magnetism and Its Applications and the IEEE Magnetic Society Distinguished Lecturer for 2019.
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(en anglais) Twistable electronics with dynamically rotatable heterostructuresCentre de Nanosciences et de Nanotechnologies, Amphithéatre, Palaiseau
A simple, yet effective, way to modify the properties of 2D materials is by stacking them in a
van der Waals heterostructures and controlling the relative angular orientation between its
layers. This in situ band structure manipulation offers unique opportunities toward
understanding of multiple physical phenomena and the design of novel opto-electronic
devices. A striking example of this is the recent observation of strongly correlated states and
intrinsic superconductivity in twisted bilayer graphene. The clearest example of the effects of
angular alignment in a heterostructure is graphene on hexagonal boron nitride (BN), in which
the layer orientation determines the wavelength of a superimposed moiré superlattice. The superpotential modifies the native band structure of graphene opening an energy gap and generating minigaps at higher energies. However, current techniques are limited to
fabrication of samples with fixed interlayer angles. Studies of angular dependence are therefore limited to static properties, and require multiple samples, which imposes experimental challenges and introduces uncertainty due to sample-to-sample variations.
In this talk I will present a new technique which allows to modify in situ optical, mechanical and electronic properties of a BN/graphene/BN heterostructures, in this the angle between layers is changed continuously with a control better than 0.2 degrees. Combining these three
measurements in the same device demonstrates the new capability to precisely tune in situ the properties of a van der Waals heterostructure. Our new experimental technique opens the possibility to study the angle-dependent properties of van der Waals heterostructures and in situ band structure engineering of 2D materials.