Since the initial predictions for the existence of Weyl fermions in condensed matter, many different experimental techniques have confirmed the existence of Weyl semimetals. Among these techniques, optical responses have shown a variety of effects associated with the existence of Weyl fermions. In chiral crystals, we find a new type of fermions protected by crystal symmetries - the chiral multifold fermions - that can be understood as a higher-spin generalization of Weyl fermions.

This work analyzes how multifold fermions interact with light and highlights the power of optical responses to identify and characterize multifold fermions and the materials hosting them. In particular, we find optical selection rules, compute the linear optical response of all chiral multifold fermions, and analyze the non-linear optical responses and their relation to the presence of topological bands.

Finally, the research presented here analyzes the theoretical foundations and experimentalfeatures of optical responses of two multifold semimetals, RhSi and CoSi, connecting the observed features with the theoretical predictions and demonstrating the power of optical responses to understand real-life multifold semimetals.

Auteur

I was born in Murcia, Spain. I completed my Bachelor's degree in Physics and my Master's degree in Theoretical Physics at the Complutense University of Madrid. During my Master's degree, I specialized in gauge theories. I wrote my Master's thesis on perturbative quantization of a non-abelian gauge theory focusing on high-energy physics.

Shortly after this, I became more interested in the Condensed Matter realm during my studies at the Autonomous University of Barcelona. I joined Dr. Adolfo G. Grushin's group at Néel Institute in Grenoble to do my Ph.D. in Condensed Matter Physics, working on theoretical aspects of topological materials. During this time, I developed the work presented in this thesis: a theoretical characterization of optical responses in multifold semimetals in close collaboration with experimentalists.

I am currently working on optical responses of superconducting phases as a postdoctoral researcher at the Donostia International Physics Center in Dr. Fernando de Juan's group.