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arXiv · 1807.04531

Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene

Yong Sun·Daniel Leykam·Stephen Nenni·Daohong Song·Hong Chen·Y. D. Chong·Zhigang Chen
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Abstract

We demonstrate inter-valley Bloch oscillation (BO) and Landau-Zener tunneling (LZT) in an optically-induced honeycomb lattice with a refractive index gradient. Unlike previously observed BO in a gapped square lattice, we show non-adiabatic beam dynamics that are highly sensitive to the direction of the index gradient and the choice of the Dirac cones. In particular, a symmetry-preserving potential leads to nearly perfect LZT and coherent BO between the inequivalent valleys, whereas a symmetry-breaking potential generates asymmetric scattering, imperfect LZT, and valley-sensitive generation of vortices mediated by a pseudospin imbalance. This clearly indicates that, near the Dirac points, the transverse gradient does not always act as a simple scalar force as commonly assumed, and the LZT probability is strongly affected by the sublattice symmetry as analyzed from an effective Landau-Zener Hamiltonian. Our results illustrate the anisotropic response of an otherwise isotropic Dirac platform to real-space potentials acting as strong driving fields, which may be useful for manipulation of pseudospin and valley degrees of freedom in graphene-like systems.

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Yong Sun, Daniel Leykam, Stephen Nenni, Daohong Song, Hong Chen, Y. D. Chong, Zhigang Chen. 2018-07-12. Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene. https://doi.org/10.1103/physrevlett.121.033904

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