Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides  

作　　者：Yuki Kobayashi Christian Heide Hamed Koochaki Kelardeh Amalya Johnson Fang Liu Tony F.Heinz David A.Reis Shambhu Ghimire 

机构地区：[1]Stanford PULSE Institute,SLAC National Accelerator Laboratory,Menlo Park,CA 94025,USA [2]Department of Applied Physics,Stanford University,Stanford,CA 94305,USA [3]Max Planck Institute for the Physics of Complex Systems,Nöthnitzer Str.38,01187 Dresden,Germany [4]Department of Materials Science and Engineering,Stanford University,Stanford,CA 94305,USA [5]Department of Chemistry,Stanford University,Stanford,CA 94305,USA [6]Department of Photon Science,Stanford University,Stanford,CA 94305,USA

出　　处：《Ultrafast Science》2021年第1期39-47,共9页超快科学（英文）

基　　金：supported by the US Department of Energy,Office of Science,Basic Energy Sciences,Chemical Sciences,Geosciences,and Biosciences Division through the AMOS program.F.L.was supported by a Terman Fellowship and startup funds from the Department of Chemistry at Stanford University.Y.K.acknowledges support from the UrbanekChodorow Fellowship from Stanford University.C.H.acknowledges support from the W.M.Keck Foundation and a Humboldt Research Fellowship.

摘　　要：We present a systematic study of the crystal-orientation dependence of high-harmonic generation in monolayer transition-metal dichalcogenides,WS2 and MoSe2,subjected to intense linearly polarized midinfrared laser fields.The measured spectra consist of both odd-and even-order harmonics,with a high-energy cutoff extending beyond the 15th order for a laser-field strength around~1 V/nm.In WS2,we find that the polarization direction of the odd-order harmonics smoothly follows that of the laser field irrespective of the crystal orientation,whereas the direction of the even-order harmonics is fixed by the crystal mirror planes.Furthermore,the polarization of the even-order harmonics shows a flip in the course of crystal rotation when the laser field lies between two of the crystal mirror planes.By numerically solving the semiconductor Bloch equations for a gapped-graphene model,we qualitatively reproduce these experimental features and find the polarization flipping to be associated with a significant contribution from interband polarization.In contrast,high-harmonic signals from MoSe2 exhibit deviations from the laser-field following of oddorder harmonics and crystal-mirror-plane following of even-order harmonics.We attribute these differences to the competing roles of the intraband and interband contributions,including the deflection of the electron-hole trajectories by nonparabolic crystal bands.

关 键 词：POLARIZATION HARMONICS mirror 

分 类 号：TN2[电子电信—物理电子学]