Séminaire DMONS-DSI, axes 4 et 5 présenté par Jorge Iñiguez

Jorge Iñiguez (Materials Research and Technology Department, LIST, Department of Physics and Materials Science, University of Luxembourg)

Résumé :
Ferroelectric materials have been around for many decades, and yet they continue to challenge our imagination with unexpected behaviors. The most recent and important ferroelectric revival features nanostructures displaying exotic properties that seemed all but impossible not long ago but are now revealed by modern characterization techniques. For example, transmission electron microscopy has allowed us to visualize mesmerizing dipole vortexes and skyrmions in superlattices combining ferroelectric (PbTiO3) and dielectric (SrTiO3) layers [1], confirming the kind of electrostatic/frustration effects predicted earlier by some theory groups [2] and doubted by most.

In this talk I will review the theoretical models [3] that were used to anticipate the rich behaviors that currently generate so much excitement and describe how they allowed us to predict the occurrence of ferroelectric skyrmions [4] that were experimentally confirmed shortly after [5]. I will also discuss some of the most surprising properties of these frustrated ferroelectric states, in particular their negative capacitance behavior, which leads to a miraculous-sounding voltage amplification [6,7]. I will conclude by commenting on the most exciting opportunities in the field.

My main collaborators in these works were M.A.P. Gonçalves and Mónica Graf (formerly at LIST, now at the Czech Academy of Sciences), and Hugo Aramberri (LIST). Collaborators at the University of Cantabria (Junquera), UC Berkeley (Ramesh) and elsewhere were involved in some of the projects. Work in Luxembourg funded by the Luxembourg National Research Fund through projects FNR/C15/MS/10458889/NEWALLS, C18/MS/12705883/REFOX and INTER/RCUK/18/12601980.

[1] Observation of polar vortices in oxide superlattices, A.K. Yadav et al., Nature 530, 198 (2016).
[2] Unusual phase transitions in ferroelectric nanodisks and nanorods, I.I. Naumov, L. Bellaiche and H. Fu,
Nature 432, 737 (2004).
[3] First-principles model potentials for lattice-dynamical studies: general methodology and example of
application to ferroic perovskite oxides, J.C. Wojdel et al., J. Phys. Condens. Matt. 25, 305401 (2013).
[4] Theoretical guidelines to create and tune electric skyrmion bubbles, M.A.P. Gonçalves et al., Science
Advances 5, eaau7023 (2019).
[5] Observation of room-temperature polar skyrmions, S. Das et al., Nature 568, 368 (2019).
[6] Negative capacitance in multidomain ferroelectric superlattices, P. Zubko et al., Nature 534, 524 (2016).
[7] Giant voltage amplification from electrostatically-induced incipient ferroelectric states, M. Graf, H.
Aramberri, P. Zubko and J. Íñiguez, Nature Materials (2022) https://doi.org/10.1038/s41563-022-01332-z

contact : Riccardo HERTEL : riccardo.hertel@ipcms.unistra.fr

Séminaire DMO présenté par : Pr. Naoya NISHI

Pr. Naoya NISHI from Kyoto Univ. Japan

Résumé : Ionic liquids can be immiscible with water and oil and can form the two (and even three) phase system. The soft liquid/liquid interfaces of ionic liquids can be utilized as a platform for (electro)chemical reactions. In this talk, I will introduce the structure of the electrochemical liquid/liquid interfaces of ionic liquids by using x-ray reflectometry and molecular dynamics simulation and also introduce our recent efforts to electrochemically utilize the soft interface for reductive deposition of metal nanostructures. 

Contact: laurent.douce@ipcms.unistra.fr

Séminaire Axe 3 & DMO présenté par Dr. Chantal Daniel

Dr. Chantal Daniel (Laboratoire de Chimie Quantique, UMR7177 CNRS – Université de Strasbourg)

Coordination compounds, characterized by fascinating and tunable electronic properties, easily bind proteins, polymers, wires or DNA. Upon irradiation these molecular systems develop functions finding applications in solar cells, photocatalysis, luminescent and conformational probes, electron transfer triggers and diagnostic or therapeutic tools. The control of these functions is activated by the light wavelength, the metal/ligands cooperation and the environment within the first picoseconds (ps). After a brief summary of the theoretical background, this contribution reviews case studies, from 1strow to 3rd row transition metal complexes, that illustrate how spin-orbit, vibronic couplings and quantum effects drive the photophysics of this class of molecules at the early stage of the photoinduced elementary processes within the fs-ps time scale range. Besides the “routine” modeling of spectra, computational chemistry may contribute at their interpretation providing valuable information about the various chemical and optical contributions to the (chiro-)optical properties and about their correlation, not only with nuclear arrangement, but also with spin-vibronic effects which are especially relevant in transition metal complexes.

Séminaire Axe 4 « Magnétisme » présenté par Paul NOËL

Paul NOËL (ETH Zürich)

Résumé : Spinorbitronics has traditionally relied on heavy metal systems to provide efficient spin-charge interconversion. Among these materials, 5d transition metals such as Pt, Ta or W offer large spin-charge conversion efficiency for spin current detections and large spin orbit torques for efficient current induced magnetization switching in SOT-MRAM devices [1].
Recently spin-orbit effects in oxides became the focus of intense interest and were exploited to realize various exotic phenomena connected with spintronics applications [2]. Among the multiple systems of interest for oxide spinorbitronics, the two-dimensional electron gas (2DEG) obtained at the surface/interface of strontium titanate (SrTiO3) attracted great attention due to its efficient and tunable spin-charge conversion [3] and large unidirectional magnetoresistance [4] associated with the Rashba Edelstein effect. While SrTiO3 is insulating in the bulk it is possible to obtain a conductive 2DEG at its surface by depositing a thin layer of insulating LaAlO3 [5]. A similar 2DEG can be obtained by depositing a thin layer of a reducing metal such as Al, Ta or Y on top of SrTiO3 alleviating the need for the high-temperature growth of crystalline LaAlO3 [6,7] and allowing the modulation of the carrier density through the adjustment of the metallic layer thickness. In the Al/SrTiO3 system, the gate tunability of the spin to charge conversion was demonstrated and a connection between the band structure of SrTiO3 and the conversion was evidenced. In particular the conversion is enhanced at certain Fermi level position corresponding to avoided band crossings and topological features [8].
Another interest of SrTiO3 is the possibility to induce ferroelectricity at low temperature. While SrTiO3 is paraelectric, it is possible to induce ferroelectricity at cryogenic temperature in STO based structure either by doping with Calcium [9] or by applying high electric field [10]. When combining the ferroelectricity of SrTiO3 with a conductive 2DEG at its surface it is possible to obtain the persistent control of the 2DEG properties such as the conductivity and carrier density as well as the non-volatile control of the spin to charge current conversion [11,12]. In particular it is possible to control the sign of the spin to charge conversion in a persistent way in a ferroelectric-like STO based structures. This non-volatile effect opens the way to the electric-field control of spin currents and to ultralow-power spintronics in which non volatility would be provided by ferroelectricity rather than by ferromagnetism [13].

1 A. Manchon, J. Železný, I. M. Miron, T. Jungwirth, J. Sinova, A. Thiaville, K. Garello, and P. Gambardella, Current-Induced Spin-Orbit Torques in Ferromagnetic and Antiferromagnetic
Systems, Rev. Mod. Phys. 91, 035004 (2019).
2 F. Trier, P. Noël, J.-V. Kim, J.-P. Attané, L. Vila, and M. Bibes, Oxide Spin-Orbitronics: Spin–Charge Interconversion and Topological Spin Textures, Nat Rev Mater 7, 4 (2022).
3 E. Lesne et al., Highly Efficient and Tunable Spin-to-Charge Conversion through Rashba Coupling at Oxide Interfaces, Nature Mater 15, 12 (2016).
4 D. C. Vaz, F. Trier, A. Dyrdał, A. Johansson, K. Garcia, A. Barthélémy, I. Mertig, J. Barnaś, A. Fert, and M. Bibes, Determining the Rashba Parameter from the Bilinear Magnetoresistance
Response in a Two-Dimensional Electron Gas, Phys. Rev. Materials 4, 071001 (2020).
5 A. Ohtomo and H. Y. Hwang, A High-Mobility Electron Gas at the LaAlO3/SrTiO3 Heterointerface, Nature 427, 6973 (2004).
6T. C. Rödel et al., Universal Fabrication of 2D Electron Systems in Functional Oxides, Advanced Materials 28, 1976 (2016).
7 L. M. Vicente-Arche, S. Mallik, M. Cosset-Cheneau, P. Noël et al., Metal/SrTiO3 Two-Dimensional Electron Gases for Spin-to-Charge Conversion, Phys. Rev. Materials 5, 064005 (2021).
8 D. C. Vaz, P. Noël et al., Mapping Spin–Charge Conversion to the Band Structure in a Topological Oxide Two-Dimensional Electron Gas, Nat. Mater. 18, 11 (2019).
9 J. G. Bednorz and K. A. Müller, Sr1-xCaxTiO3: An xy Quantum Ferroelectric with Transition to Randomness, Phys. Rev. Lett. 52, 2289 (1984).
10 J. Hemberger, P. Lunkenheimer, R. Viana, R. Böhmer, and A. Loidl, Electric-Field-Dependent Dielectric Constant and Nonlinear Susceptibility in SrTiO3Phys. Rev. B 52, 13159 (1995).
11 J. Bréhin, F. Trier, L. M. Vicente-Arche, P. Hemme, P. Noël et al., Switchable Two-Dimensional Electron Gas Based on Ferroelectric Ca-SrTiO3, Phys. Rev. Materials 4, 041002 (2020).
12 P. Noël et al., Non-Volatile Electric Control of Spin–Charge Conversion in a SrTiO3 Rashba System, Nature 580, 7804 (2020).
13 M. Bibes, L. Vila, J.-P. Attané, P. Noël, and D. C. Vaz, Electronic Device, Digital Port, Analog Component, and Method for Generating a Voltage, US20220076868A1 (10 March 2022).

Pour tout contact : Matthieu BAILLEUL : matthieu.bailleul@ipcms.unistra.fr

Pour les personnes souhaitant suivre le séminaire en visio voici ci-dessous les liens de connexion Zoom :

https://cnrs.zoom.us/j/92405602824?pwd=NEpsWU1PbG4vMUFQT0dsQjJuRmc3UT09 ID de réunion : 924 0560 2824
Code secret : ZjB91d

Séminaire AXE 1 – Sciences et Matériaux Quantiques présenté par Francesco FOGLIANO

Francesco FOGLIANO (University of Basel, Switzerland)

In recent years nano-optomechanical systems have proven to be a powerful resource to detect ultra-weak forces, thus providing new insights on fundamental interactions. I will present recent advancements that extend the experimental range of ultrasensitive force measurements based on optically readout vibrations of suspended silicon carbide nanowires. Novel experimental regime will be discussed: first the operation at ultralow optical power at dilution temperatures; second in the ultrastrong coupling regime of cavity optomechanics.

Operating force sensors at dilution temperatures permits to reduce their thermal noise and further benefit from an increased mechanical coherence. However this requires eliminating the sources of unwanted vibrations, such as electrical or mechanical noises, and operating at ultralow optical powers to avoid unwanted laser heating. I will expose the experimental developments that lead to observe a nanowire featuring a noise temperature measured at the 32 mK level, while exploiting novel optical readout schemes operating in the photon counting regime. I will briefly discuss their mechanical and thermal properties at low temperatures and report on enhanced force sensitivities of a few tens of zN/√Hz. In the second part I will describe a novel cavity nano-optomechanical experiment at room temperature that consists in inserting the vibrating extremity of a suspended nanowire with sub-wavelength sized diameter, in a high finesse fiber micro-cavity. The combination of its small mode volume, of the extreme force sensitivity of the nanowires and of the large optomechanical interaction strength demonstrated makes the system very interesting for further explorations of the field of cavity nano-optomechanics. In particular this implementation should allow to enter the so-called ultrastrong coupling regime, where one single intracavity photon can displace the oscillator by more than its zero point fluctuations. By scanning the nanowire within the cavity mode volume and measuring its impact on the cavity mode, it is possible to obtain a map of the 2D optomechanical interaction. Vice versa, by using the toolbox of nanowire-based force-sensing protocols, it is possible to explore the backaction of the optomechanical interaction and map the optical force field experienced by the nanowire. I will conclude with a brief discussion on a more recent work, aimed to implement a hybrid optomechanical system at 4K. The platform is based on a tunable fiber-cavity and on a resonator-in-the-middle configuration. It is suitable for studying a broad range of nanomechanical resonators (including nanowires, nanowires with embedded emitters, carbon nanotube, magnetic 2D material and functionalized membranes), as well as to approach the regime of single-photon cavity optomechanics.

Contact : Arnaud GLOPPE (arnaud.gloppe@ipcms.unistra.fr)

Séminaire DSI présenté par Benedikt LASSALLE

Benedikt LASSALLE, synchrotron-soleil

Résumé :

Controlling the composition, morphology and size of nanomaterials is key to tune their properties and function. This control requires fundamental insights into the processes that govern the synthesis of nanomaterials, but also their behaviour under functioning conditions. X-ray absorption spectroscopy is an ideal tool to observe such phenomena, since it can be used to probe reactions under in situ conditions, allowing experimental setups that are close to synthetic or operating conditions.
In this presentation, we will report our work on the structure and function of electrocatalytic materials, such as oxides and sulfides, that are active for the oxygen (OER) and hydrogen evolution reactions (HER). Using in situ X-ray absorption spectroscopy as our major tool, we will show how the local and electronic structure of the materials evolve during these catalytic reactions and influence their efficiency.
In a second part, we will present our recent work concerning the combination of microfluidic systems with X-ray techniques and their potential application to understand the synthesis of nanomaterials. This will be exemplified with an upcoming project to be carried out in collaboration with the team of Ovidiu Ersen at the IPCMS, which deals with the study of hybrid perovskites synthesis by a combination of XAS and electronic microscopy.

Pour tout contact : Ovidiu Ersen (0388107028 – ovidiu.ersen@ipcms.unistra.fr)

Séminaire DCMI présenté par Francisco J. Terán

iMdea Nanociencia, Campus Universitario de Cantoblanco, 28049 Madrid, Spain
Nanobiotecnología (iMdea Nanociencia), Unidad Asociada al Centro Nacional de Biotecnología-CSIC , Campus Universitario de Cantoblanco, 28049 Madrid, Spain
Nanotech Solutions SL, Ctra Madrid 23, 40150 Villacastín, Spain

par Zoom :

ID de réunion : 835 1668 0265
Code secret : v1fGRa

Résumé : Nowadays, the progress of nanoparticle engineering enables the synthesis of magnetic nanocrystals with customized physical, chemical, and/or biological properties. Recent works underline the influence of biological entities on determining the magnetic response of magnetic nanoparticles under alternating magnetic fields. Here, I will present some examples showing the potential of AC magnetometry for probing the interactions between magnetic nanoparticles and biological molecules and cells. First, the elucidation of the colloidal stability of iron oxide nanoparticles under physiological conditions1,3. Second, the influence of cell internalization on the dynamical magnetic response of iron oxide nanoparticles.2 Finally, the potential of using AC magnetometry as a powerful and useful tool for quick characterization of the distinct bioconjugation steps of magnetic nanoparticles with recognition ligands and drugs will be shown.

  • 1.- A. Aires et al. Chem.Nano.Mat 2016 DOI: 10.1002/cnma.201600333
  • 2.- D. Cabrera et al. ACS Nano 12(3), 2741 (2018)
  • 3.- A. Aires et al. METHOD FOR DETECTION OF AN ANALYTE; Patent application: WO2019/092131

Séminaire DON : présenté par Emilien PROST

Emilien Prost est candidat au poste CDD IR dans l’équipe Femtomag suite au départ de Y.Brelet.

Numerous applications have emerged thanks to the development of terahertz (THz) sources and detection making such pulses an interesting tool for ultrafast science [1]. We introduce a new THz platform relying on THz generation by air-plasma induced by a two-color short laser pulse and on Air Biased Coherent Detection [2]. Using this technique, we measure the THz electric field in the time-domain and can retrieve the spectrum by taking its Fourier transform. Using air as the generation and detection medium allows for the production of high electric field strength in the MV/cm range and smooth broadband spectra, making those pulses interesting to explore ultrafast phenomena. Numerous materials exhibit ro-vibrational bands and phonons in the THz range. We used this THz platform to perform THz time-domain spectroscopy (THz-TDS) [3] of condensed phase materials. The propagation through a sample modifies the temporal profile of the THz pulse. It is thus possible to retrieve the spectral feature of a sample by comparing the Fourier transform of the temporal trace with and without sample.