Laser-based photoemission on correlated electrons
Cheng-Tien Chiang1*
1Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
* Presenter:Cheng-Tien Chiang,
Laser-based photoemission spectroscopy and microscopy have been developed into power tools for studying magnetism. In combination with the magnetic dichroism [1] and the spin detection of photoelectrons [2], the spin-polarized electronic structure as well as the domain structure of magnetic materials can be sensitively measured. However, as one of the most important driving forces for magnetism in solids, electron-electron interaction could be rarely measured directly and is one of the most difficult processes to be calculated in theory. In order to directly probe the interaction between electrons in solids, double photoemission (DPE) spectroscopy has been developed since decades [3]. In this talk, band-resolved DPE experiments using a femtosecond laser and a pair of time-of-flight electron spectrometers will be presented [4].

In the DPE process, a pair of electrons are emitted upon the absorption of one single photon. Each of the electrons can be analyzed with energy and momentum resolution. DPE experiments haven been performed on Ag(001) and Cu(111) surfaces as paradigmatic metallic systems [5]. On both Ag and Cu surfaces, dominant DPE signals with a pair of d electrons are observed. In strong contrast, electron pairs consisting of one sp and one d electron are observed only on Ag(001). These results are compared with DPE experiments on the strongly correlated antiferromagnetic NiO films and provide indications for a band-dependent physical picture of electron-electron interaction in solids [3,4].

[1] C.-T. Chiang et al., Phys. Rev. Lett. 103, 077601 (2009); Phys. Rev. B 81, 115130 (2010).
[2] C.-T. Chiang et al., Phys. Rev. B 85, 165137 (2012).
[3] C.-T. Chiang et al., Prog. Surf. Sci. 95, 100572 (2020).
[4] M. Huth, C.-T. Chiang et al., Appl. Phys. Lett. 104, 061602 (2014).
[5] A. Tr├╝tzschler, M. Huth, C.-T. Chiang et al., Phys. Rev. Lett. 118, 136401 (2017).

Keywords: photoemission, correlated electrons, electronic structure, femtosecond laser, electron spectroscopy