時間・スピン・角度分解光電子分光装置の開発と光スピントロニクス研究への応用

抄録

We have developed a high-repetition-rate time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) system that employs a 10.7 eV vacuum-ultraviolet laser generated from a Yb-doped fiber chirped-pulse-amplification source operating at 1 MHz. When combined with very-low-energy-electron-diffraction (VLEED) type spin polarimeter, the high-repetition-rate laser pulses effectively suppress space-charge broadening while enabling efficient spin detection, thereby overcoming the long-standing limitations of tr-SARPES. As a demonstration, we investigated the electronic structure of surface states including unoccupied states above the Fermi level on Bi(111), and achieved a direct, spin- and momentum-resolved visualization of pure spin currents generated immediately after photoexcitation in the topological insulator Sb₂Te₃. The present tr-SARPES apparatus provides a powerful platform for exploring opto-spintronics.