Does β-PbO₂ harbor topological states?

Area of Science:

• Solid State Physics
• Materials Science
• Computational Materials Science

Background:

• The electronic properties of beta-lead dioxide (β-PbO2) remain a subject of debate, with experimental and theoretical studies yielding conflicting results.
• Observed behaviors range from metallic to semiconducting, with reported band gaps varying significantly.
• Inconsistencies are particularly pronounced when considering topological states, which depend critically on electronic structure near the Fermi energy.

Purpose of the Study:

• To resolve the long-standing controversy surrounding the electronic properties and topological nature of β-PbO2.
• To accurately determine the electronic band structure and band gap of stoichiometric β-PbO2.
• To investigate the conditions under which β-PbO2 might exhibit semimetallic or topological states.

Main Methods:

• Employed a self-consistent density functional theory (DFT) + U approach for electronic structure calculations.
• Investigated the effects of applied strain on the electronic properties.
• Performed surface computations and considered spin-orbit coupling to assess topological protection.

Main Results:

• Stoichiometric β-PbO2 is found to be an indirect semiconductor with a band gap of approximately 0.8 eV, aligning with experimental observations.
• Significant strain (∼4%) is required to induce a nodal line semimetallic state, contrary to previous reports.
• The nodal line semimetallic state is not robust against spin-orbit coupling, and no topologically protected surface states were identified.

Conclusions:

• β-PbO2 is a topologically trivial material, consistent with experimental findings but contradicting some theoretical predictions.
• Previous claims of topological states in β-PbO2 are likely due to inaccuracies in describing bulk optical properties.
• This work provides a definitive electronic structure characterization, resolving ambiguities in β-PbO2 research.