- The paper establishes the discovery of spin-1 and charge-2 Dirac nodes in CoSi, evidenced by non-contractible surface Fermi arcs observed via ARPES.
- Experimental ARPES mapping validates theoretical predictions by confirming the high Chern numbers and robust chiral nature of these nodes.
- The findings open new avenues for exploring topologically protected states with potential applications in quantum computing and advanced electronics.
New Classes of Chiral Topological Nodes in CoSi
Zhicheng Rao et al. report the experimental observation of novel chiral topological nodes in the material CoSi, distinct from the historically characterized Weyl nodes. This work delineates two unconventional types of chiral nodes—spin-1 nodes and charge-2 Dirac nodes—and highlights their role in generating non-contractible surface Fermi arcs, using angle-resolved photoemission spectroscopy (ARPES).
Overview
Chiral topological nodes are established band crossing points in momentum space carrying nonzero Chern numbers. These nodes manifest unique surface states known as Fermi arcs. In contrast to the extensively studied Weyl nodes, the paper proposes and confirms the existence of spin-1 and charge-2 Dirac nodes in CoSi using ARPES, a powerful technique for mapping electronic band structures.
Experimental Findings
- Crystal Structure and Nodes: CoSi, characterized by a simple cubic crystal structure, houses both spin-1 and charge-2 Dirac nodes at the high-symmetry points Γ and R of the Brillouin zone (BZ). These nodes are protected and enforced by the crystal symmetries, leading to projections on the (001) surface BZ that form a path traversing the entire surface—a stark deviation from the small separations between Weyl point pairs.
- Non-Contractible Surface Fermi Arcs: The ARPES measurements reveal that the surface Fermi arcs connecting the projections of the spin-1 and charge-2 nodes form an unbroken path on the (001) surface. This finding distinguishes these surface states from those traditionally noted in Weyl semimetals, which typically form small, contractible arcs due to the limited separation between Weyl points.
- Consistency with Theoretical Predictions: Experimental observations align well with theoretical calculations. The calculated and observed band structures, particularly the Chern numbers associated with the nodes, corroborate the robust chiral nature of the spin-1 and charge-2 nodes in CoSi. This experimental validation fills a significant gap between theoretical anticipations and experimental realizations.
Implications and Future Directions
The paper expands the current understanding of chiral quasiparticles beyond the confines of Weyl fermions by providing robust experimental evidence for spin-1 and charge-2 Dirac nodes. These findings imply that other similar topological features could exist undiscovered in different material systems, potentially leading to the unearthing of novel electronic properties and states.
The chiral nature and the associated topological protection of spin-1 and charge-2 nodes hold promise for future developments in quantum computing and electronics, where robust quasiparticle excitations can be pivotal. Moreover, these experimental insights could fuel theoretical exploration into more complex topological phases and the interaction between these nodes under various symmetry-breaking conditions.
In conclusion, this paper presents a significant advancement in the field of topological materials by identifying new classes of chiral topological nodes in CoSi. It sets a precedent for further experimentation and theoretical modeling of exotic fermionic quasiparticles in condensed matter systems. The insights herein also present avenues for deploying such materials in emerging technological applications where stability and non-trivial band topology play critical roles.