Giant Bulk Photovoltaic Effect in Two-Dimensional Topological Ferroelectric Semimetal

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Ferroelectric (FE) metals are of significant interest due to their unique combination of ferroelectricity and metallic properties.
• These materials allow for polarization control of band topology near the Fermi level.
• The scarcity of known ferroelectric metals necessitates the search for new candidates.

Purpose of the Study:

• To identify novel two-dimensional (2D) ferroelectric metal candidates.
• To investigate the ferroelectric, topological, and photovoltaic properties of these materials.
• To explore their potential for multifunctional nanoelectronic and optoelectronic applications.

Main Methods:

• Utilizing first-principles calculations to predict material properties.
• Employing symmetry analysis to understand topological characteristics.
• Investigating polarization, switching barriers, and band topology.

Main Results:

• Identification of three 2D ferroelectric metal candidates: XO monolayers (X = Nb, Ta, Rh).
• These materials exhibit considerable out-of-plane polarization and moderate switching barriers, with RhO showing significant polarization (5.68 pC/m).
• The XO monolayers are ferroelectric topological semimetals with symmetry-protected Weyl points and nontrivial edge states, alongside a large intrinsic bulk photovoltaic effect (BPVE).

Conclusions:

• XO monolayers represent a versatile 2D platform integrating switchable ferroelectricity, topological semimetal behavior, and a giant BPVE.
• These properties enable potential multifunctional nanoelectronic and optoelectronic applications.
• The BPVE can be further enhanced via charge doping and strain engineering.