Prominent features in the optical spectrum of materials can be
deeply connected to its electronic structure.
Triggering an ultrafast change using ultrashort laser pulses may lead
to the excitation of coherent phonon modes, such as in the case of
the type-II Weyl semimetal WTe2, where these collective vibrations
lead to a periodic change of the band structure. We examine the
impact on the effective mass of the electron and hole pockets
through broadband white light and X-ray diffraction and discuss the
consequences on WTe2’s magnetoresistance and topological
properties.
Alternatively, resonant excitations via specific band transitions may
lead to a control of element-specific electronic configurations.
FeCr2S4 is a spinel ferrimagnet where the magneto-optical Kerr
rotation peaks in correspondence of the intra-atomic Fe d-d
transitions in the mid-infrared. We show how a resonant excitation
of the material through this pathway leads to a significantly different
timescale of the magneto-optical dynamics compared to the non
resonant case and discuss its impact on the superexchange
interaction within the system.