The dynamical coupling between spins and electrons on the femtosecond timescale in several materials is one of the subjects of several projects belonging to the Transregio-SFB TRR160. The overarching goal is to establish ways of converting ultrafast coherent spin dynamics into coherent charge dynamics and viceversa.
We are pursuing two different approaches:
- Antiferromagnetic semiconductors: In equilibrium, several antiferromagnetic semiconductors exhibit natural spin-electron coupling. In particular, the band-gap energy depends on the sublattice magnetization: the band-gap acquires a magnetic contribution called "magnetic blue shift". This phenomenon has already been experimentally confirmed in the antiferromagnetic semiconductor MnTe, extensively evaluated theoretically, and described in terms of a Hubbard-Kondo model (New Journal of Physics 22, 083029 (2020)). In our research, we will further investigate the connection between spins and band-gap in a time-resolved manner.
- Exciton-Magnon transition: In many dielectric antiferromagnets, a spectral feature can be observed below the absorption edge in the near-infrared spectral region, known as "exciton-magnon" transition. This is an electric dipole process in which electrons and magnons are simultaneously excited. In certain materials, high-energy magnons are involved in the exciton-magnon transition. This mechanism has already been employed to resonantly excite magnons at the edges of the Brillouin zone. This particular perturbation of the magnetic ground state is intense enough to drive a magnetic phase-transition on the femtosecond timescale (Nature Physics 14, 370-374 (2018)). In our research, we will further explore the exciton-magnon transition, for example with spectrally resolved optical and magneto-optical pump-probe experiments, even in strong magnetic fields.