光子石墨烯中谷 Landau–Zener–Bloch 振荡与赝自旋不平衡的观测
Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene
AI总结：
该研究在光诱导蜂窝晶格中观测谷间 Bloch 振荡与 Landau–Zener 隧穿，揭示对称性和梯度方向如何调控赝自旋不平衡、涡旋及谷间动力学。
摘要：
我们在一个具有折射率梯度的光诱导蜂窝晶格中演示了谷间 Bloch 振荡（BO）和 Landau–Zener 隧穿（LZT）。不同于此前在有带隙方晶格中观测到的 BO，我们展示了对折射率梯度方向及 Dirac 锥选择高度敏感的非绝热泵浦动力学。具体而言，保持对称性的势会在不等价谷之间产生近乎完美的 LZT 和相干 BO，而破缺对称性的势则产生非对称散射、不完美的 LZT，以及由赝自旋不平衡介导的、对谷敏感的涡旋生成。这清楚表明，在 Dirac 点附近，横向梯度并不总像通常假设的那样充当简单的标量力；正如从有效 Landau–Zener Hamiltonian 所分析的，LZT 概率会受到子晶格对称性的强烈影响。我们的结果阐明了原本各向同性的 Dirac 平台对作为强驱动场的实空间势所表现出的各向异性响应，这或可用于操控类石墨烯系统中的赝自旋和谷自由度。
英文摘要：
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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