"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

Monday, June 17, 2021 (14h) :
Spin and valley properties in transition metal dichalcogenide: from monolayers to hybrid structures
See détails here

Starting May 2021, the GDR HOWDI offers its members a monthly virtual meeting with a guest speaker followed by a debate.

To break the scientific isolation in this period of pandemic, the GDR HOWDI offers its members a monthly virtual meeting with a guest speaker followed by a debate. The themes of the 4 axes of the GDR will be covered in turn and special attention will be given to the participation of young researchers (doctoral student at the end of their thesis or postdoc).

The first edition will take place on Friday May 21 with the participation of Piran Kidambi (Vanderbilt Univ., USA)

The zoom link will be sent via the GDR newsletter and on this web page.

Do not hesitate to send us your suggestions of speakers for the next editions

Wednesday afternoon, March 24th, 2021
Due to the ongoing sanitary crisis, it is still impossible to gather the community of our new GDR "HOWDI" physically. However, we will celebrate this new start with a short virtual kick-off meeting, on Wed. March 24, 2021 afternoon. The program of the meeting will be announced shortly; it will consist of a general presentation of the thematic lines of the new GDR, a series of selected focused scientific talks and an open discussion about your needs and wishes for the future of the GDR.

Please check the preliminary program here.

To join the meeting please use this zoom link
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