Direct observation of photonic Landau levels and helical edge states in strained honeycomb lattices

Omar Jamadi,Aristide Lemaître,Marijana Milićević,Isabelle Sagnes,Jacqueline Bloch,Abdelmounaim Harouri,Elena Rozas,Alberto Amo,Tomoki Ozawa,Luc Le Gratiet,Iacopo Carusotto,Grazia Salerno

doi:10.1038/s41377-020-00377-6

Abstract

We report the realization of a synthetic magnetic field for photons and polaritons in a honeycomb lattice of coupled semiconductor micropillars. A strong synthetic field is induced in both the s and p orbital bands by engineering a uniaxial hopping gradient in the lattice, giving rise to the formation of Landau levels at the Dirac points. We provide direct evidence of the sublattice symmetry breaking of the lowest-order Landau level wavefunction, a distinctive feature of synthetic magnetic fields. Our realization implements helical edge states in the gap between n = 0 and n = ±1 Landau levels, experimentally demonstrating a novel way of engineering propagating edge states in photonic lattices. In light of recent advances in the enhancement of polariton–polariton nonlinearities, the Landau levels reported here are promising for the study of the interplay between pseudomagnetism and interactions in a photonic system.

Highlights

One of the most remarkable consequences of the application of an external magnetic field to a twodimensional electron gas is the quantum Hall effect
We report propagating helical edge states associated with the n = 0 Landau level, the synthetic field analogue of the chiral edge states responsible for transport in the quantum Hall effect
Due to the additional lateral confinement provided by the refractive index contrast between the semiconductor and air, the micropillars act as artificial photonic atoms

Summary

Introduction

One of the most remarkable consequences of the application of an external magnetic field to a twodimensional electron gas is the quantum Hall effect. In this phenomenon, the parabolic band dispersion of the electron gas rearranges into discretized Landau levels[1]. When the Fermi energy is located between two Landau levels, the system is insulating in the bulk and possesses conducting channels on the edge. These channels are so robust to disorder that they can be used for metrology applications[2].

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Conclusion