Journal
PHYSICAL REVIEW LETTERS
Volume 121, Issue 3, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.121.033904
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Funding
- Army Research Office [W911NF-15-1-0413]
- National Science Foundation [PHY-1404510]
- National Key R&D Program of China [2017YFA0303800, 2016YFA0301101]
- Chinese National Science Foundation [11674247, 91750204, 11674180]
- Natural Science Foundation of Shanghai [18ZR1442900]
- Singapore MOE Academic Research Fund (Tier 2 Grant) [MOE2015-T2-2-008]
- Singapore MOE Academic Research Fund (Tier 3 Grant) [MOE2016-T3-1-006]
- Institute for Basic Science in Korea [YSF-R024-Y1]
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We demonstrate intervalley 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 nonadiabatic 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 graphenelike systems.
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