Merboldt Marco, Schüler Michael, Schmitt David, Bange Jan Philipp, Bennecke Wiebke, Gadge Karun, Pierz Klaus, Schumacher Hans Werner, Momeni Davood, Steil Daniel, Manmana Salvatore R, Sentef Michael A, Reutzel Marcel, Mathias Stefan
I. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany.
PSI Center for Scientific Computing, Theory and Data, Paul Scherrer Institute, Villigen PSI, Switzerland.
Nat Phys. 2025;21(7):1093-1099. doi: 10.1038/s41567-025-02889-7. Epub 2025 May 6.
Floquet engineering-the coherent dressing of matter via time-periodic perturbations-is a mechanism to realize and control emergent phases in materials out of equilibrium. However, its applicability to metallic quantum materials and semimetals such as graphene is an open question. The report of light-induced anomalous Hall effect in graphene remains debated, and a time-resolved photoemission experiment has suggested that Floquet effects might not be realizable in graphene and other semimetals with relatively short decoherence times. Here we provide direct spectroscopic evidence of Floquet effects in graphene through electronic structure measurements. We observe light-matter-dressed Dirac bands by measuring the contribution of Floquet sidebands, Volkov sidebands and their quantum path interference to graphene's photoemission spectrum. Our results demonstrate that Floquet engineering in graphene is possible, even though ultrafast decoherence processes occur on the timescale of a few tens of femtoseconds. Our approach offers a way to experimentally realize Floquet engineering strategies in metallic and semimetallic systems and for the coherent stabilization of light-induced states with potentially non-trivial topological properties.
弗洛凯工程——通过时间周期微扰对物质进行相干修饰——是一种在非平衡态材料中实现和控制涌现相的机制。然而，其在金属量子材料和诸如石墨烯等半金属中的适用性仍是一个悬而未决的问题。关于石墨烯中光诱导反常霍尔效应的报道仍存在争议，并且一项时间分辨光电子能谱实验表明，在石墨烯和其他退相干时间相对较短的半金属中可能无法实现弗洛凯效应。在此，我们通过电子结构测量提供了石墨烯中弗洛凯效应的直接光谱证据。我们通过测量弗洛凯边带、沃尔科夫边带及其量子路径干涉对石墨烯光电子能谱的贡献，观测到了光与物质修饰的狄拉克能带。我们的结果表明，即使在几十飞秒的时间尺度上会发生超快退相干过程，石墨烯中的弗洛凯工程也是可行的。我们的方法为在金属和半金属系统中通过实验实现弗洛凯工程策略以及相干稳定具有潜在非平凡拓扑性质的光诱导态提供了一条途径。
