Teaching

Topics: Topological systems, Anomalous transport, nonlinear phenomena, THz radiation, Magnetotransport

The emergent functions of topological materials revolve around the formation of band structures near the Fermi level, resembling the linear Dirac and Weyl fermionic dispersions introduced a century ago in the high-energy physics context. In particular, Weyl semimetals were first discovered experimentally in 2014 in TaAs, and from that moment there has been a rush for the study of their anomalous transport properties associated to their non-trivial topology. Topological semimetals are important due to their 3D nature of the Weyl/Dirac electrons, that appears both on the surface and the bulk band structure.

The thesis project will focus upon the study of the plethora of different spectroscopic responses that can appear in these systems, mainly nonlinear ones, with the possibility to research them both from a theoretical and an experimental point of view:

Theoretical Master Thesis: Many quantum effects in transport, like the quantum Hall effect or the chiral anomaly, emerge from the complexity that resides in the topological nature of the single-electron band structure in a periodic lattice. The thesis project will focus upon the development of conductivity models for the description of nonlinear interband responses and magnetotransport of the Weyl/Dirac cones in topological semimetals. Topics ranging from the Berry phase theory and topological phase transitions, up to the many body Keldysh and density matrix formalism will be tackled for the study of the quasiparticles transport at equilibrium and outside equilibrium.

Experimental Master Thesis: THz radiation (1 THz= 300 um= 4 meV=30 cm^-1) is the main spectroscopic source for the study of the Weyl electrons behaviour in topological semimetals. The spectroscopic importance of THz resides in its capability to scan not only the low energy features of quantum materials, but also the phononic and roto-vibrational excitations of many condensed matter and biological systems. In recent years, the technology to produce and detect THz has seen a rapid development, however it is still lagging behind any other frequency interval (THz gap). The thesis project will focus upon the study of the Weyl electrons transport in novel topological semimetals, with the goal to highlight their nonlinear behaviour and tunability at the presence of external magnetic fields (magnetotransport, chiral anomaly) and chemical potential control. These studies will try to find a way to exploit the predicted properties of these materials as a starting point for the development of novel THz electro-optical systems.

For info contact: luca.tomarchio@uniroma1.it or stefano.lupi@roma1.infn.it