Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2018
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| _version_ | 1866929214777720832 |
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| author | Sun, Yong Leykam, Daniel Nenni, Stephen Song, Daohong Chen, Hong Chong, Y. D. Chen, Zhigang |
| author_facet | Sun, Yong Leykam, Daniel Nenni, Stephen Song, Daohong Chen, Hong Chong, Y. D. Chen, Zhigang |
| contents | 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_1807_04531 |
| institution | arXiv |
| publishDate | 2018 |
| record_format | arxiv |
| spellingShingle | Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene Sun, Yong Leykam, Daniel Nenni, Stephen Song, Daohong Chen, Hong Chong, Y. D. Chen, Zhigang Optics Mesoscale and Nanoscale Physics 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. |
| title | Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene |
| topic | Optics Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/1807.04531 |