Dr. Cheng-Tien Chiang focuses on the electronic structure at surfaces and interfaces of transition metals and their oxides. In these systems, the interaction between localized d electrons as well as the interplay between the d and sp electrons play dominant roles. To observe these effects directly in experiments, he uses angle-resolved photoelectron spectroscopy (ARPES) with time- and spin-resolution. By using laser-based ARPES, Dr. Chiang discovered unexpected magnetic dichroic effects from optically excited quantum well states and the strongly spin-dependent nonlinear photoemission processes. These findings can be applied to the real space imaging of magnetic domains and are currently further explored on the femtosecond time scale.

Moreover, Dr. Chiang has developed a new widely tunable vacuum-ultraviolet light source using high-order harmonic generation (HHG) at megahertz repetition rates, which benchmarks a significant progress toward the most efficient laboratory ARPES technique. In the invited paper in J. Electron Spectrosc. Relat. Phenomena (2015) as well as in the invited book chapter of Reference Module of Elsevier (2017), Dr. Chiang summarized this development and gave an overview of the importance of HHG-based ARPES. Furthermore, Dr. Chiang applied the HHG light source to double photoemission (DPE) experiments, which allow the band-resolved analysis of correlated electron pairs in solids for the first time. These HHG-based DPE experiments not only pave the way to a systematic study of interacting electrons in strongly correlated systems such as high-temperature superconductors, but will also allow access to the dynamics of electron pairs in solids.

The laboratory has been built since November 2019. Details can be found at https://ufss.iams.sinica.edu.tw .