Topological semimetals predicted from first-principles calculations.

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science
• Solid State Physics

Background:

• Topological semimetals (TSMs) represent novel quantum states of matter distinct from topological insulators.
• TSMs are characterized by topologically stable Fermi surfaces that may enclose band crossing points, known as Dirac cone-like energy nodes.
• Distinctions between TSM types arise from the degeneracy and momentum-space distribution of these nodal points.

Purpose of the Study:

• To provide a theoretical overview of three primary types of topological semimetals: Dirac semimetals (DSMs), Weyl semimetals (WSMs), and node-line semimetals (NLSMs).
• To highlight the challenges and importance of realizing these topological quantum states for both fundamental research and technological applications.
• To summarize the family of TSMs and elucidate their interrelationships.

Main Methods:

• Theoretical prediction and analysis of topological semimetal properties.
• Review of existing theoretical and experimental studies on DSMs, WSMs, and NLSMs.
• Classification and comparison of different TSM types based on their electronic band structures and topological characteristics.

Main Results:

• Theoretical predictions for DSMs (Na3Bi, Cd3As2) and their experimental verification.
• Theoretical prediction of nonmagnetic WSMs in the TaAs family, leading to extensive experimental research.
• Theoretical proposal of a 3D carbon crystal and Cu3PdN as potential NLSM candidates.

Conclusions:

• Topological semimetals, including DSMs, WSMs, and NLSMs, are crucial new states of quantum matter.
• The realization and study of TSMs are vital for advancing fundamental science and developing future technologies.
• A comprehensive understanding of the TSM family and their relationships is essential for continued progress in the field.