Cha Soonyoung, Kim Minjeong, Kim Youngjae, Choi Shinyoung, Kang Sejong, Kim Hoon, Yoon Sangho, Moon Gunho, Kim Taeho, Lee Ye Won, Cho Gil Young, Park Moon Jeong, Kim Cheol-Joo, Kim B J, Lee JaeDong, Jo Moon-Ho, Kim Jonghwan
Center for Van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, Republic of Korea.
Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Republic of Korea.
Nat Commun. 2022 Nov 4;13(1):6630. doi: 10.1038/s41467-022-34337-y.
Under strong laser fields, electrons in solids radiate high-harmonic fields by travelling through quantum pathways in Bloch bands in the sub-laser-cycle timescales. Understanding these pathways in the momentum space through the high-harmonic radiation can enable an all-optical ultrafast probe to observe coherent lightwave-driven processes and measure electronic structures as recently demonstrated for semiconductors. However, such demonstration has been largely limited for semimetals because the absence of the bandgap hinders an experimental characterization of the exact pathways. In this study, by combining electrostatic control of chemical potentials with HHG measurement, we resolve quantum pathways of massless Dirac fermions in graphene under strong laser fields. Electrical modulation of HHG reveals quantum interference between the multi-photon interband excitation channels. As the light-matter interaction deviates beyond the perturbative regime, elliptically polarized laser fields efficiently drive massless Dirac fermions via an intricate coupling between the interband and intraband transitions, which is corroborated by our theoretical calculations. Our findings pave the way for strong-laser-field tomography of Dirac electrons in various quantum semimetals and their ultrafast electronics with a gate control.
在强激光场作用下，固体中的电子通过在亚激光周期时间尺度内穿过布洛赫能带中的量子路径来辐射高谐波场。通过高谐波辐射理解动量空间中的这些路径，可实现全光超快探测，以观察相干光波驱动过程并测量电子结构，正如最近在半导体中所展示的那样。然而，对于半金属而言，这种展示在很大程度上受到限制，因为带隙的缺失阻碍了对精确路径的实验表征。在本研究中，通过将化学势的静电控制与高谐波产生（HHG）测量相结合，我们解析了强激光场作用下石墨烯中无质量狄拉克费米子的量子路径。高谐波产生的电调制揭示了多光子带间激发通道之间的量子干涉。随着光与物质的相互作用偏离微扰区域，椭圆偏振激光场通过带间和带内跃迁之间的复杂耦合有效地驱动无质量狄拉克费米子，这得到了我们理论计算的证实。我们的研究结果为各种量子半金属中狄拉克电子的强激光场断层成像及其具有栅极控制的超快电子学铺平了道路。
