Linear bands, zero-momentum Weyl semimetal, and topological transition in skutterudite-structure pnictides

Abstract

It was reported earlier [Phys. Rev. Lett. 106, 056401 (2011)] that the skutterudite structure compound CoSb${}_3$ displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three dimensional crystal, (2) the band critical point occurs at $k$=0, and (3) linear bands are degenerate with conventional (massive) bands at the critical point (before inclusion of spin-orbit coupling). Further interest arises because the critical point separates a conventional (trivial) phase from a topological phase. In the native cubic structure this is a zero-gap topological semimetal; we show how spin-orbit coupling and uniaxial strain converts the system to a topological insulator (TI). We also analyze the origin of the linear band in this class of materials, which is the characteristic that makes them potentially useful in thermoelectric applications or possibly as transparent conductors. We characterize the formal charge as Co${}^{+}$ $d^8$, consistent with the gap, with its $\bar{3}$ site symmetry, and with its lack of moment. The Sb states are characterized as $p_x$ (separately, $p_y$) $\sigma$-bonded $S{b}_4$ ring states occupied and the corresponding antibonding states empty. The remaining (locally) $p_z$ orbitals form molecular orbitals with definite parity centered on the empty $2a$ site in the skutterudite structure. Eight such orbitals must be occupied; the one giving the linear band is an odd orbital singlet $A_{2u}$ at the zone center. We observe that the provocative linearity of the band within the gap is a consequence of the aforementioned near-degeneracy, which is also responsible for the small band gap.

arXiv comment10 pages, 7 figures

References in corpus (14)

• The electronic properties of graphene
• Topological Insulators
• Topological insulators and superconductors
• Berry Phase Effects on Electronic Properties
• Topological Insulators in Three Dimensions
• Topological Field Theory of Time-Reversal Invariant Insulators
• Chern semi-metal and Quantized Anomalous Hall Effect in HgCr2Se4
• Model Hamiltonian for Topological Insulators
• Quantum Spin Hall Effect in Inverted Type II Semiconductors
• Half-metallic semiDirac point generated by quantum confinement in TiO${}_2$/VO${}_2$ nanostructures
• Tight-binding modeling and low-energy behavior of the semi-Dirac point
• Topological insulators in filled skutterudites
• Metal-insulator transition through a semi-Dirac point in oxide nanostructures: VO${}_2$ (001) layers confined within TiO${}_2$
• Dirac Point Degenerate with Massive Bands at a Topological Quantum Critical Point

Cited by in corpus (5)

• A large new family of filled skutterudites stabilized by electron count
• Electronic Structure and Lattice Dynamics in the FeSb${}_3$ Skutterudite from Density Functional Theory
• Role of Hydrogen in the Electronic Properties of CaFeAsH-based Superconductors
• Symmetry-enforced Fermi degeneracy in topological semimetal RhSb${}_3$
• Self-regulated growth of candidate topological superconducting parkerite by molecular beam epitaxy