The group of Majed Chergui at EPFL, along with national and international colleagues, have
shed light on this long - standing question by using a combination of cutting - edge experimental methods: steady - state angle - resolved photoemission spectroscopy (ARPES), which maps the energetics of the electrons along the different axis in the solid; spectroscopic ellipsometry, which determines the optical properties of the solid with high accuracy; and ultrafast two - dimensional deep - ultraviolet spectroscopy, used for the
first time in the study of materials, along with state - of - the - art
first - principles theoretical
tools.