Engineering intrinsic π-electron magnetism in atomically-precise carbon nanostructures
April 8, 2022, 11h00.

Roman FASEL - Engineering intrinsic π-electron magnetism in atomically-precise carbon nanostructures
Please check the attached abstract.

Détails de connexion pour la session zoom :

Sujet : GDR HOWDI SEMINAR -
Heure : 8 avril 2022 11:00 AM Paris
https://zoom.us/j/99872391294?pwd=ZlhtdXBNVzRRaFlMWEs4ZW9VbFE2QT09

ID de réunion : 998 7239 1294

Code secret : b0tbYx

A Summer School on Raman and Photoluminescence spectroscopies on Low Dimensional Systems will be organized in Montpellier from the 04 to 08 of July 2022.
Registration is now open !

A Summer School on Low Dimensional Systems will be organized in Montpellier from the 04 to 08 of July 2022. This school aims to provide the theoretical and methodological basis of Raman and Photoluminescence spectroscopies on carbon nanotubes, graphene, TMD... Oral presentations will address fundamental lectures on the physical processes, more applied lessons will display examples illustrated by practicals.

The specificity of this training is to combine theoretical courses and practicals. It will benefit from the knowledge of several experts in the field. This session will be able to welcome a maximum of 25 people (researchers, engineers and doctoral students...). This school is for beginners in this field as well as those who want to update their knowledge. It will be held in english.

https://coulomb.umontpellier.fr/Summer-School-on-Low-Dimensional-Systems-du-4-au-8-juillet-2022

Information : laurent.alvarez@umontpellier.fr

« 2D materials for optoelectronics and spin/valley-tronics » : mini-colloque atux « Journées de la Matière Condensée » (JMC2022), Lyon du 22 au 26 Août 2022.

A mini-colloquium on « 2D materials for optoelectronics and spin/valley-tronics » will be held at the « Journées de la Matière Condensée » (JMC2022) that will take place in Lyon on Aug. 22-26, 2022 (http://jmc2022.univ-lyon1.fr).

Please check the details in the attached file :

Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on superconducting 2H-NbSe 2
Mardi 8 Fevrier 2022, 11h

Prochain séminaire virtuel du GDR HOWDI : Mardi 8 Février 2022 à 11h.
Katharina FRANKE (Freie Universitaet, Berlin)
"Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on superconducting 2H-NbSe_2”

Résumé :

Magnetic adatom chains on superconducting substrates are promising platforms for topological superconductivity and Majorana zero modes. Signatures of these have been found in densely packed chains with direct exchange interaction among the adatoms. In contrast, the dilute limit of chains, where the atoms are sufficiently far spaced that direct hybridization of their d orbitals is negligible, but close enough for substrate-mediated interactions, has not been investigated previously. Engineering dilute adatom chains with substantial substrate-mediated interactions requires samples sustaining long-range Yu-Shiba-Rusinov (YSR) states. While these decay
quickly with 1/ 𝑘 𝑟 (with 𝑘 being the Fermi wave vector and 𝑟 the distance to the impurity) on three-dimensional superconductors, the decay of YSR states on two-dimensional superconductors is much slower, scaling with 1/√ 𝑘 𝑟 [1].
Here, we explore the well known quasi-two-dimensional superconductor 2H-NbSe 2 as a substrate for magnetic adatom structures. Individual Fe atoms induce Yu-Shiba-Rusinov states, which spatially extend over several nanometers with their energy and symmetry influenced by the crystal field and by the co-existing charge-density wave (CDW) [2]. When two Fe atoms are placed on equivalent adsorption sites at a distance of 1 nm, the YSR states are shifted in energy and split. While the splitting indicates hybridization of the YSR states, the strong shift can only be explained by RKKY coupling of quantum spins [3]. We deliberately increase the chain length by adding individual Fe atoms with the STM tip, up to a length of 51 atoms. In each step we track the evolution of the YSR states. We find signatures of YSR band formation consistent with ferromagnetic coupling of quantum spins [4].

[1] G. C. Ménard, et al., Nat. Phys. 11, 1013 (2015).
[2] E. Liebhaber et al., Nano Lett. 20, 339 (2020).
[3] E. Liebhaber, et al., arxiv2107.06361 (2021).
[4] J. F. Steiner, et al., arxiv2107.00031 (2021).

Informations de connection :

Sujet : GDR HOWDI SEMINAR - Katharina FRANKE - Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on superconducting 2H-NbSe2

8 févr. 2022 11:00 AM Paris

https://zoom.us/j/95506784928?pwd=aXV3MUdCUWJtdkZtRFJrS1IzaDFNZz09

meeting ID : 955 0678 4928

Code secret : uJ8QWP

Le colloque annuel du GDR et GDR-I Howdi (ex-Graphene and co) aura lieu du 9 au 13 mai 2022 à Dourdan (91).

Après plusieurs reports en raison de la crise sanitaire COVID19, nous sommes en mesure d’annoncer enfin la tenue de la réunion annuelle du GDR du 9 au 13 mai au VVF de Dourdan (91).
Toutes les informations utiles seront publiées très prochainement ici.

Le GDR rend hommage à l’un de ses membres récemment disparu.

François Ducastelle nous a quittés brutalement le 2 juillet dernier.
Nous adressons nos condoléances à sa famille et à ses proches.

Membre éminent de notre GDR depuis des années, nous souhaitons lui rendre hommage et rendre hommage à ses nombreuses contributions scientifiques lors de plusieurs évènements cette année.
La conférence Graphene 2021, qui s’est tenue à Grenoble en octobre 2021, lui a été dédiée. Une adresse en son hommage a été prononcée lors de l’ouverture de la conférence.
Une session spéciale lui sera dédiée lors de notre prochaine réunion annuelle en mai 2022 à Dourdan.
Une page en sa mémoire est consultable sur le site web de son laboratoire.
Vos témoignages peuvent être déposés dans un livre électronique.

École pratique et théorique sur les spectroscopies de systèmes de basse dimension, organisée par des membres du GDR à Montpellier du 4 au 8 juillet 2022.

La prochaine édition de l’école d’été sur les spectroscopies (luminescence et Raman) de systèmes de basse dimension aura lieu à Montpellier du 4 au 8 juillet 2022.

Toutes les informations pratiques et inscriptions sont ici.

Proximity effects in van der Waals heterostructures
Friday, 3 dec 2021, 14h

Le prochain séminaire virtuel du GDR HOWDI aura lieu le vendredi 3 décembre 2021 à 14h.
Nous recevrons Sergio Valenzuela (Catalan Institute of Nanoscience and Nanotechnology (ICN2), Spain)
"Proximity effects in van der Waals heterostructures”

Résumé :

The isolation of a large variety of two-dimensional materials (2DM) and their co-integration in van der Waals heterostructures has opened new avenues for innovative material design and engineering. In particular, the structural interface quality in the atomically smooth 2DMs allows us to imprint properties of interest in a chosen 2DM by proximity-induced effects. Such an approach is particularly compelling for spintronic devices, which harness their functionality from thin layers of magnetic and non-magnetic materials and their interfaces [1]. In this talk, I will present recent experiments in which we investigate the spin dynamics in graphene-transition metal dichalcogenides heterostructures. I will show that the spin-orbit coupling in graphene can be strongly enhanced by proximity effects. As a consequence, the spin relaxation becomes highly anisotropic, with spin lifetimes that are markedly different depending on the spin orientation [2,3]. I will further demonstrate that the proximity-induced spin-orbit coupling leads to strongly enhanced spin-to-charge interconversion [4]. By performing spin precession experiments in appropriately designed Hall bars, we are able to separate the contributions of the spin Hall and the spin galvanic effects. Remarkably, their corresponding conversion efficiencies can be tailored by electrostatic gating in magnitude and sign, peaking near the graphene charge neutrality point and having a large magnitude even at room temperature.

[1] J. F. Sierra et al, Nature Nanotechnol. 16, 856 (2021).
[2] L. A. Benítez et al., Nature Phys. 14 (2018)
[3] L. A. Benítez, et al., APL Materials 7, 120701 (2019)
[4] L. A. Benítez et al., Nature Mater. 19, 170 (2020)

Pour se connecter :

Sujet : GDR HOWDI SEMINAR - Sergio O. Valenzuela - Proximity effects in van der Waals heterostructures

Heure : 3 déc. 2021 01:50 PM Paris

https://zoom.us/j/94348027597?pwd=RmJXK1A5VklVVDhqeGpJanpQRGVTUT09

ID de réunion : 943 4802 7597

Code secret : 4bZgs8

"Heterostrain determines the flatbands in twisted gaphene layers.”

Le prochain séminaire virtuel du GDR HOWDI aura lieu le mardi 9 novembre 2021 à 14h.
Nous recevrons Vincent Renard (Grenoble, France)
"Heterostrain determines the flatbands in twisted gaphene layers.”

Résumé :

The strongly correlated electron physics recently observed in twisted graphene layers develops in flat bands , which are very sensitive to the relative arrangement between the layers. The twist angle as attracted most of the attention as it is the leading structural parameter. Heterostrain, the in-plane deformation of one layer with respect to the other, is an ubiquitous source of modification of the relative arrangement between the layers which effect has been much less investigated. Performing a detailed meta-analysis of published scanning tunneling microscope data, I will show that heterostrain allows to understand quantitatively the large sample variability observed in experiments in the non interacting limit and raises the question of its influence on strongly correlated electron phases.

Pour se connecter :

https://zoom.us/j/97179781921?pwd=VGVXR0ZvL1h1UDlYZGVmazA1eDNvZz09

ID de réunion : 971 7978 1921
Code secret : Cn3vKz

"Unveiling excitonic properties of magnons in a quantum Hall ferromagnet."

The next virtual meeting of the GDR HOWDI will be given by Preden Rouleau (CEA) next Tuesday (July 20) at 11h.

"Unveiling excitonic properties of magnons in a quantum Hall ferromagnet."

Zoom connection informations are attached below.

Abstract of the talk :

Magnons enable transferring a magnetic moment or spin over macroscopic distance. In quantum Hall ferromagnets, it has been predicted in the early 90s [1] that spin and charge are entangled, meaning that any change of the spin texture modifies the charge distribution. As a direct consequence of this entanglement, magnons carry an electric dipole moment. Here we report the first evidence of the existence of this electric dipole moment in a graphene quantum Hall ferromagnet [2,3] using a Mach-Zehnder interferometer as a quantum sensor. As magnons propagate towards the interferometer across the insulating bulk, their electric dipole moment modifies the Aharonov-Bohm flux through the interferometer, affecting both the phase and visibility of the interferences. In particular, we relate the phase shift to the sign of this electric dipole moment, the exponential loss of visibility to the flux of emitted magnons, and we show that the magnon emission is a Poissonian process. Finally, we probe the emission energy threshold of the magnons close to filling factor ν=1. For transient states, between ν=0 and ν=1, we observe that the emission energy threshold diminishes towards zero, which might be linked to the emergence of gapless mode predicted in the canted-antiferromagnetic (CAF) phase at ν=0 [4-5]. Being able to couple the spin degree of freedom to an electrostatic potential is a remarkable property of quantum Hall ferromagnets that could be very promising for spintronics.

[1] Sondhi, S. L., Karlhede, A., Kivelson, S. A. & Rezayi, E. H. Skyrmions and the crossover from the integer to fractional quantum Hall effect at small Zeeman energies. Phys. Rev. B 47, 16419–16426 (1993).

[2] Yang, K., Das Sarma, S. & MacDonald, A. H. Collective modes and skyrmion excitations in graphene SU (4) quantum Hall ferromagnets. Phys. Rev. B 74, (2006).

[3] Wei, N., Huang, C. & MacDonald, A. H. Scattering of magnons at graphene quantum-Hall-magnet junctions. Phys. Rev. Lett. 126, 117203 (2021)

[4] Brey, L., Fertig, H. A., Côté, R. & MacDonald, A. H. Skyrme Crystal in a Two-Dimensional Electron Gas. Phys. Rev. Lett. 75, 2562–2565 (1995).

[5] Jolicoeur, T. & Pandey, B. Quantum Hall skyrmions at ν=0,±1 in monolayer graphene. Phys. Rev. B 100, (2019).

Sujet : Séminaire GDR HOWDI - Preden ROULLEAU 20/07 11am

Heure : 20 juil. 2021 11:00 AM Paris

https://zoom.us/j/96918566063?pwd=bmRFNmpkWUl1bVdiUTRUejNQTzg1dz09