Orbital-Active Dirac Materials from the Symmetry Principle

Abstract

Dirac materials, starting with graphene, have drawn tremendous research interest in the past decade. Instead of focusing on the $p_z$ orbital as in graphene, we move a step further and study orbital-active Dirac materials, where the orbital degrees of freedom transform as a two-dimensional irreducible representation of the lattice point group. Examples of orbital-active Dirac materials occur in a broad class of systems, including transition-metal-oxide heterostructures, transition-metal dichalcogenide monolayers, germanene, stanene, and optical lattices. Different systems are unified based on symmetry principles. The band structure of orbital-active Dirac materials features Dirac cones at $K(K^{\prime })$ and quadratic band touching points at $\Gamma$, regardless of the origin of the orbital degrees of freedom. In the strong anisotropy limit, i.e., when the $\pi$-bonding can be neglected, flat bands appear due to the destructive interference. These features make orbital-active Dirac materials an even wider playground for searching for exotic states of matter, such as the Dirac semi-metal, ferromagnetism, Wigner crystallization, quantum spin Hall state, and quantum anomalous Hall state.

14 pages, 5 figures

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Cited by in corpus (2)

• Quantum many-body scars with unconventional superconducting pairing symmetries via multibody interactions
• Orbital homology of p and t2g orbitals in models and materials