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

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.

"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

Lundi, 17 Juin 2021 (14h) :
Spin and valley properties in transition metal dichalcogenide : from monolayers to hybrid structures
Plus d’infos ici

Séminaire virtuel mensuel sur les thématiques du GDR

Pour rompre l’isolement scientifique en cette période de pandémie, le GDR HOWDI propose à ses membres, une rencontre virtuelle mensuelle autour d’un orateur invité suivi d’un débat. Les thématiques des 4 axes du GDR seront couvertes à tour de rôle et une attention particulière sera donnée à la participation de jeunes chercheurs (doctorant en fin de thèse ou postdoc).

La première édition aura lieu le vendredi 21 mai avec la participation de Piran Kidambi (Vanderbilt Univ., USA)

Le lien zoom pour participer à la réunion sera communiqué via la newsletter du GDR ainsi que sur [ce site web- article 338].

N’hésitez pas à nous soumettre vos suggestions d’orateurs pour les prochaines éditions

Mercredi après-midi 24 mars 2021 (13h30)
les conditions sanitaires ne nous permettent pas encore de réunir physiquement la communauté du nouveau GDR HOWDI, néanmoins, nous souhaitons marquer ce nouveau départ par un événement virtuel sur une demi-journée le mercredi 24 mars 2021 après midi. Le programme sera annoncé prochainement ; il comprendra une présentation générale des grandes thématiques et du nouveau contour du GDR, quelques exposés scientifiques sur des avancées récentes et une discussion libre sur vos attentes et vos souhaits pour les futures actions du GDR.

Le programme préliminaire est disponible ici.

Voici le lien zoom pour rejoindre la réunion
ID de réunion : 831 4177 7570 ; Code secret : 956936

HOWDI : HeterOstructures of van der Waals materials with low DImensionality
For the coming five years, our network (GDR after "groupement de recherche") will cover the study of van der Waals heterostructures, following four main directions :
 synthesis, nanofabrication, caracterisations
 electronic transport and its relationship with other fields
 optics, excitonics, photonics
 magnetism, spintronics, electronic correlations