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3eme séminaire virtuel : Preden Rouleau (CEA)

"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