Single Pair of Weyl Points in Nonmagnetic Crystals

Abstract

Topological semimetal states having the minimal number, i.e., only a single pair, of Weyl points are desirable for the study of effects associated with chiral topological charges. So far, the search for such states is focused on magnetic spinful systems. Here, we find that nonmagnetic spinless systems can host a class of single-pair-Weyl-point (SP-WP) states, where the two Weyl points are located at two high-symmetry time-reversal-invariant momenta. We identify 32 candidate space groups that host such states, and we show that the chiral charge of each Weyl point in the SP-WP state must be an even integer. Besides achieving the minimal number, Weyl points in SP-WP states are far separated in momentum space, making the physics of each individual point better exposed. The large separation combined with the even topological charge lead to extended surface Fermi loops with a non-contractible winding topology on the surface Brillouin zone torus, distinct from conventional Weyl semimetals. We confirm our proposal in the phonon spectra of two concrete materials TlBO${}_2$ and KNiIO${}_6$. Our finding applies to a wide range of systems, including electronic, phononic, and various artificial systems. It offers a new direction for the search of ideal platforms to study chiral particles.

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• Recipe for single-pair-Weyl-points phonons carrying the same chiral charges
• Engineering the in-plane anomalous Hall effect in Cd${}_3$As${}_2$ thin films
• Observation of Single Pair of Type-III Weyl Points in Sonic Crystals
• Landau level spectrum and magneto-optical conductivity in tilted Weyl semimetal
• Chiral phonons in binary compounds $A$Bi ($A$ = K, Rb, Cs) with P2${}_1$/c structure
• Twist-Induced Effects on Weyl Pairs in Magnetized Graphene Nanoribbons
• Phonon Weyl points and chiral edge modes with unconventional Fermi arcs in NbSi${}_2$
• Ferroelectrically Controlled Chirality Switching of Weyl Quasiparticles