Physics department (Colloquium)

Correlated electron pairs from photoexcited solids

Speaker : 助研究員 江正天 (中央研究院原子與分子科學研究所)
Location :
Time : 2021 / 03 / 05 14:10
In the search of novel functionalities of new materials, electron-electron interaction has shown to play an intriguing role. As an underlying mechanism for magnetism, superconductivity, as well as metal-to-insulator transitions [1,2], the interaction between electrons in solids has been widely studied by a variety of experimental methods. However, due to the lack of a simultaneous detection of two electrons in conventional experiments, it remains a challenge to unambiguously reveal and quantify the interaction between electrons in solids.

As a potential experimental approach to directly detect interacting electrons in solids, double photoemission (DPE) spectroscopy has been developed since decades [3,4]. In the DPE process, a pair of correlated electrons is excited upon the absorption of one single photon [5]. In this talk, a new laser-based DPE setup as well as the results on the correlated sp and d electrons in Ag, Cu and NiO will be presented [6]. On both Ag and Cu surfaces, dominant DPE signals result from the emission of a pair of d electrons. However, only on Ag the electron pairs with one sp and one d electrons are observed [7]. In contrast to the DPE spectra of Ag and Cu, on NiO the DPE intensity increases monotonically towards lower kinetic energies and provides a possible indication of multiple excitations of d electrons [6].

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[2] P. A. Lee, N. Nagaosa, and X.-G. Wen, Rev. Mod. Phys. 78, 17 (2006).
[3] C. Gazier and J. R. Prescott, Phys. Lett. 32A, 425(1970).
[4] F. O. Schumann, C. Winkler, and J. Kirschner, physica status solidi (b) 246, 1483 (2009). [5] J. Berakdar, Phys. Rev. B 58, 9808 (1998).
[6] C.-T. Chiang et al., Prog. Surf. Sci. 95, 100572 (2020).
[7] A. Trützschler, M. Huth, C.-T. Chiang et al., Phys. Rev. Lett. 118, 136401 (2017).