Dragging of light by moving media was predicted by Fresnel1 and verified by Fizeau’s celebrated experiments2 with flowing water. This momentous discovery is among the experimental cornerstones of Einstein’s special relativity theory and is well understood3,4 in the context of relativistic kinematics. By contrast, experiments on dragging photons by an electron flow in solids are riddled with inconsistencies and have so far eluded agreement with the theory5–7. Here we report on the electron flow dragging surface plasmon polaritons8,9 (SPPs): hybrid quasiparticles of infrared photons and electrons in graphene. The drag is visualized directly through infrared nano-imaging of propagating plasmonic waves in the presence of a high-density current. The polaritons in graphene shorten their wavelength when propagating against the drifting carriers. Unlike the Fizeau effect for light, the SPP drag by electrical currents defies explanation by simple kinematics and is linked to the nonlinear electrodynamics of Dirac electrons in graphene. The observed plasmonic Fizeau drag enables breaking of time-reversal symmetry and reciprocity10 at infrared frequencies without resorting to magnetic fields11,12 or chiral optical pumping13,14. The Fizeau drag also provides a tool with which to study interactions and nonequilibrium effects in electron liquids.
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Acknowledgements Research on the physics and imaging of the plasmonic Fizeau effect at Columbia was supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0018426. D.A.B. acknowledges the support from MIT Pappalardo Fellowship. M.M.F. is supported by the Office of Naval Research under grant ONR-N000014-18-1-2722. Work in the P.J.-H. group was supported by AFOSR grant FA9550-16-1-0382, the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF9643, and Fundacion Ramon Areces. The development of new nanofabrication and characterization techniques enabling this work has been supported by the US DOE Office of Science, BES, under award DE-SC0019300. The development of the universal cryogenic platform used for scanning probe measurements is supported as part of the Energy Frontier Research Center on Programmable Quantum Materials funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0019443. The development of infrared nano-optics is supported by Vannevar Bush Faculty Fellowship to D.N.B., ONR-VB: N00014-19-1-2630. D.N.B. is Moore Investigator in Quantum Materials EPIQS #9455. This work also made use of the Materials Research Science and Engineering Center Shared Experimental Facilities supported by the National Science Foundation (NSF) (grant no. DMR-0819762). Support from the Materials Engineering and Processing programme of the National Science Foundation, award number CMMI 1538127 for hBN crystal growth is also greatly appreciated.
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