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SUMMARY:Introduction to two-photon photoemission on NiTe2\, Dr. Cheng-Tien
  Chiang [江正天]\, IAMS Academia Sinica
DTSTART:20260324T053000Z
DTEND:20260324T110000Z
DTSTAMP:20260420T131700Z
UID:indico-event-177@indico.phys.nthu.edu.tw
DESCRIPTION:Since its first demonstration in 1964 [1\,2]\, two-photon phot
 oemission (2PPE) spectroscopy at surfaces has become an efficient combinat
 ion of femtosecond lasers with conventional angle-resolved photoelectronsp
 ectroscopy (ARPES)\, allowing direct access to the ultrafast electron dyna
 mics with energy and momentum resolution [3\,4]. In strong contrast to con
 ventional ARPES as well as the advanced time-resolved ARPES measurements\,
  in the 2PPE experiments the photon energy is specifically chosen to be lo
 wer than the surface work function in order to greatly suppress the one-ph
 oton photoemission process[5]. As a consequence\, each photoelectron can o
 nly obtain sufficient energy to escape from the surface upon the absorptio
 n of two photons. Besides the clear signatures of valence band electronic 
 structure in the 2PPE spectra [6]\, the two-photon excitation pathway can 
 go through unoccupied electronic states\, thereby providing the straightfo
 rward detection of conduction band electronic structure of semiconductors 
 [7]\, topological insulators [8]\, and strongly correlated materials [9]. 
 In this talk\, 2PPE spectroscopy and our recent development of first 2PPE 
 experiments in Taiwan will bepresented. As a specific example\, the moment
 um patterns of photoelectrons from the 2PPE processes on NiTe2 single crys
 tals\, which have been kindly provided by Prof. Chin Shan Lue and Dr. Chia
 -Nung Kuo at the Department of Physics\, National Cheng Kung University\, 
 will be demonstrated [10]. Hereby we have identified the momentum patterns
  of the spin-orbit split Te 5px\,y valence bands in NiTe2. As outlook\, hi
 gher-order photoemission processes involving three photons will be discuss
 ed [11].[1] H. Sonnenberg\, H. Heffner\, and W. Spicer\, Appl. Phys. Lett.
  5\, 95 (1964).[2] M. C. Teich\, J. M. Schroeer\, and G. J. Wolga\, Phys. 
 Rev. Lett. 13\, 611 (1964).[3] H. Petek and S. Ogawa\, Prog. Surf. Sci. 56
 \, 239 (1997).[4] M. Weinelt\, J. Phys. Condens. Matter 14\, R1099 (2002).
 [5] J. H. Bechtel\, W. L. Smith\, and N. Bloembergen\, Phys. Rev. B 15\, 4
 557 (1977).[6] A. Li et al.\, Phys. Rev. B 105\, 075105 (2022).[7] H. Tani
 mura et al.\, Phys. Rev. B 100\, 035201 (2019).[8] J. A. Sobota et al.\, P
 hys. Rev. Lett. 111\, 136802 (2013).[9] K. Gillmeister et al.\, Nat. Commu
 n. 11\, 4095 (2020).[10] M. Singh et al.\, Appl. Phys. Lett. 128\, 031601 
 (2026).[11] F. Bisio et al.\, J. Phys.: Condens. Matter 23\, 485002 (2011)
 .\n\nhttps://indico.phys.nthu.edu.tw/event/177/
LOCATION:Physics/124
URL:https://indico.phys.nthu.edu.tw/event/177/
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