Multifold topological semimetals

TL;DR

This paper reviews recent advances in multifold topological semimetals, highlighting their unique band crossings, surface states, and the emergence of free fermionic excitations protected by crystal symmetries, with implications for quantum physics and technology.

Contribution

It provides a comprehensive overview of the theoretical predictions and experimental discoveries of multifold fermions and chiral semimetals, emphasizing their novel topological properties and symmetry protections.

Findings

Observation of multifold fermions in materials

Experimental realization of chiral topological semimetals

Potential for new quantum technological applications

Abstract

The discovery of topological semimetals with multifold band crossings has opened up a new and exciting frontier in the field of topological physics. These materials exhibit large Chern numbers, leading to long double Fermi arcs on their surfaces, which are protected by either crystal symmetries or topological order. The impact of these multifold crossings extends beyond surface science, as they are not constrained by the Poincar\'e classification of quasiparticles and only need to respect the crystal symmetry of one of the 1651 magnetic space groups. Consequently, we observe the emergence of free fermionic excitations in solid-state systems that have no high-energy counterparts, protected by non-symmorphic symmetries. In this work, we review the recent theoretical and experimental progress made in the field of multifold topological semimetals. We begin with the theoretical prediction of the so-called multifold fermions and discuss the subsequent discoveries of chiral and magnetic topological semimetals. Several experiments that have realized chiral semimetals in spectroscopic measurements are described, and we discuss the future prospects of this field. These exciting developments have the potential to deepen our understanding of the fundamental properties of quantum matter and inspire new technological applications in the future.