Events

Department of Magnetic Reseach Seminar

Charge-spin response and collective excitations in Weyl semimetals

dr Sayandip Ghosh

Uniwersytet Techniczny w Dreźnie (TU Dresden)

Weyl semimetals are characterized by unconventional electromagnetic response. Towards its understanding, I will discuss all components of the frequency- and wave-vector-dependent charge-spin linear-response tensor of Weyl fermions, and their analytical expressions. The spin-momentum locking of the Weyl Hamiltonian leads to a coupling between charge and longitudinal spin fluctuations, while transverse spin fluctuations remain decoupled from the charge. Based on the response tensor, I will present the low-energy collective excitations of interacting Weyl fermions. For a local Hubbard interaction, the charge-spin coupling leads to a dramatic change of the zero-sound dispersion: its velocity becomes independent of the interaction strength and the chemical potential and is given solely by the Fermi velocity. In the presence of long-range Coulomb interactions, the coupling transforms the plasmon modes into spin plasmons. I will show that for a model with two Weyl nodes, the collective modes are strongly affected by the presence of parallel static electric and magnetic fields, due to the chiral anomaly. In particular, their dispersion goes through a singularity as the chemical potential of one of the Weyl cones is tuned through the Weyl node. I will also discuss possible experiments that could provide smoking-gun evidence for Weyl physics.