Probing the Goldstone spin wave excitations of an easy-plane canted-antiferromagnet

Spin wave, also known as magnon, is one kind of low energy collective excitations in quantum magnets, which has the potential of transferring information in applications. Spin wave dispersions carry information about both magnon properties and the nature of the magnetic ground states. In experiments, specialized techniques, such as Inelastic neutron scattering and Brillouin light scattering, are usually needed in probing spin wave dispersions in different magnetic systems [1]. Here I will talk about a new all-electrical technique for quantum Hall magnets based on bilayer graphene van der Waals heterostructures.  With a Fabry-Pérot cavity structure, we electrically probe magnons with selective momenta and energies, which allow us to extract the dispersion. We obtained the gapless linear dispersion of spin waves in the predicted easy-plane canted antiferromagnetic order in the E=0 Landau level of bilayer graphene [2-4]. I will discuss the temperature and magnetic field dependence of the high-speed spin wave propagation based on the hydrodynamic theory. I will also discuss the potential of this technique in the exploration of collective excitations of spin and isospin-ordered ground states in van der Waals heterostructures.

[1] V. V. Kruglyak et al., J. Phys. D: Appl. Phys. 43, 264001 (2010)

[2] Kharitonov, PRL 109, 046803 (2012)

[3] Takei et al., PRL 116, 216801 (2016)

[4] Pientka et al., PRL 119, 027601 (2017)