Towards coherent light-matter interaction in quantum Hall regime using orbital angular momentum of light*

When the spatial extent of the electronic wavefunction becomes larger or comparable to the excitation wavelength, intriguing perspectives become accessible beyond the dipole approximation including a direct optical probe of the wavefunction’s spatial coherence and manipulation of the electronic states [1,2,3]. For elemental or artificial atoms such as quantum dots,  such a large-scale wavefunction is rarely possible. However, the quantum Hall regime offers an exciting domain for the exploration of such ideas since Landau levels allow the wave functions to be extended to a length scale comparable to optical wavelengths.

When light containing orbital angular momentum (OAM) interacts with electronic Landau levels, it acts as a flux pump that radially moves the electrons through the sample, manifested as a radial photocurrent (PC) [3]. Motivated by this, we study the light-matter interaction in graphene in the quantum Hall regime. We investigate this effect for a graphene system with Corbino geometry and measure the radial current. In this geometry, we perform differential photocurrent measurements, revealing the photocurrent difference between opposite OAMs with opposite magnetic fields. This current flip hints at the coherent interaction of light with the carriers in our sample.

Our results open new avenues for direct measurement of the spatial and spectral coherence of an electron's wavefunction, with fundamental and practical implications in coherent light-matter interaction.

[1] M. Gullans et al., Phys. Rev. B 95, 235439 (2017)

[2] T. Grass et al. Phys. Rev. B 101, 155127 (2020)

[3] Bin Cao et al, Phys. Rev. B 103, L241301 (2021)