Principal Investigator Nuh Gedik
Angle resolved photoemission spectroscopy (ARPES) is a powerful tool for mapping the electronic bandstructure of solids by measuring the energy and momentum of photoemitted electrons. In our lab we use UV laser pulses and a time-of-flight spectrometer, which simultaneously measures the photoemitted electron energy by its flight time, and momentum Kx and Ky using a 2D position-sensitive-detector. As a result, 3D intensity spectra I(E,Kx,Ky) are obtained.
We can also look for circular dichroism, which is the difference in the ARPES intensity spectrum obtained with right- vs. left-circularly polarized light. In some materials, such as the topological insulator Bi2Se3, this can be a sensitive measure of the electron spin orientation in momentum space (below left). The ultrafast dynamics of electrons can also be resolved by performing ARPES in a pump-probe scheme. An 80 fs ultrafast laser pulse pumps the sample to initiate electronic excitation and the excited system is then probed by the delayed UV pulse that photoemits electrons for the ARPES measurement. By sweeping the delay time t between the two pulses while collecting the 3D intensity spectra I(E,Kx,Ky), we obtain a 3D movie of I(E,Kx,Ky,t) that captures electrons’ dynamics in the solids on femtosecond time scale (below right for Bi2Se3).