Resonant four-photon photoemission from SnSe_(2)(001)  

作　　者：Chengxiang Jiao Kai Huang Hongli Guo Xingxia Cui Qing Yuan Cancan Lou Guangqiang Mei Chunlong Wu Nan Xu Limin Cao Min Feng 

机构地区：[1]School of Physics and Technology and Key Laboratory of Artificial Micro-and Nano-Structures of Ministry of Education,Wuhan University,Wuhan 430072,China [2]Department of Physics and Astronomy,California State University Northridge,Northridge,CA 91330-8268,USA [3]Institute for Advanced Study,Wuhan University,Wuhan 430072,China

出　　处：《Frontiers of physics》2024年第3期83-92,共10页物理学前沿（英文版）

基　　金：the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XD30000000);the National Key R&D Program of China(Grant Nos.2018YFA0305802 and 2017YFA0303500);the National Natural Science Foundation of China(Grant No.11774267).Calculations were performed at the supercomputing center of WHU of China.

摘　　要：High-order nonlinear multiphoton absorption is usually inefficient,but can be enhanced by designing resonant excitations between occupied and unoccupied energy levels.We conducted angle-resolved multi-photon photoemission(mPPE)studies on the SnSe_(2)(001)surfaces excited by ultrashort laser pulses.By tuning photon energy and light polarization,we demonstrate the presence of a resonant four-photon photoemission(4PPE)process involving the occupied valence band(VB),the unoccupied second conduction band(CB2)and the unoccupied image-potential state(IPs)of SnSe_(2).In this 4PPE process,VB electrons of SnSe_(2) are resonantly excited into CB2 by adsorbing two photons,followed by the adsorption of another photon to populate the n=1 IPs before being emitted out to the vacuum by adsorbing one more photon.This results in a double-resonant 4PPE process,which exhibits approximately a 40 times enhancement in photoemission yields compared to cases where one of the resonant pathways,CB2→IPs,is inhibited by involving a virtual state instead of the IPs in the 4PPE.The double-resonant 4PPE process efficiently excite the bulk VB electrons outside the vacuum,like taking advantage of resonant“ladders”through two real empty electronic states of SnSe_(2).Our results highlight the important applications of mPPE in probing the band-structure,particularly the unoccupied states,of recently emerging main group dichalcogenide semiconductors.Furthermore,the discovered resonant mPPE process contributes to the exploration of their promising optoelectronic applications.

关 键 词：multi-photon photoemission four-photon photoemission SnSe_(2) unoccupied states resonant excitation 

分 类 号：O43[机械工程—光学工程]