High-order harmonics at MHz: light for correlated electrons

Wednesday, 16 March 2016, at 11:15 in Y36 J33

The interaction between electrons plays an important role in solid state physics ranging from magnetism to superconductivity. Nevertheless, a direct access to investigate electron-electron interaction is rarely demonstrated experimentally. One of the most straightforward method to observe electron correlation is the double photoemission (DPE) spectroscopy, where a pair of correlated electrons are emitted upon the absorption of one single photon [1]. In strong contrast to conventional ARPES experiments, DPE spectroscopy probes electron correlation more directly since both of the two interacting electrons can be analyzed angle- and energy-resolved. In this talk we will present DPE spectroscopy at surfaces and explore the two-dimensional energy distribution of correlated photoelectron pairs. In addition, the development of our high-order harmonic generation (HHG) light source will be introduced [2,3]. The compact HHG light source operating at megahertz repetition rates delivers a photon energy from 15 to 40 eV and is combined with a pair of time-of-flight spectrometers. As examples we will show the spectra of photoelectron pairs from Ag(001) and Cu(111) in comparison to the strongly correlated material NiO. The characteristic signature of electron correlation in DPE specifically related to their valence band structure will be discussed.

[1] M. Huth et al., Appl. Phys. Lett. 104, 061602 (2014)
[2] C.-T. Chiang et al., New J. Phys. 17, 013035 (2015)
[3] C.-T. Chiang et al., J. Electron Spectrosc. Relat. Phenom. 200, 15 (2015)