Emerging Two-Dimensional Conductivity at the Interface between Mott and Band Insulators

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Interfaces between band insulators and conductors are well-researched.
• Interfaces involving Mott insulators, like LaTiO3, and band insulators, like KTaO3, remain less understood.
• Existing models for interfacial conductivity do not fully explain phenomena in Mott insulator systems.

Purpose of the Study:

• To investigate the interfacial conductivity mechanism at LaTiO3/KTaO3 heterostructures.
• To explore the role of crystal structure and oxygen octahedra tilting in interfacial electronic properties.
• To elucidate the origins of conductivity and superconductivity in these specific interfaces.

Main Methods:

• First-principles calculations were employed to simulate (001), (110), and (111) interfaces.
• Analysis focused on electronic band structure and charge transfer dynamics.
• Investigated the influence of oxygen octahedra tilting on material properties.

Main Results:

• A novel interfacial conductivity mechanism was identified, distinct from those in polar wide-band insulators.
• Matching of oxygen octahedra tilting between LaTiO3 and KTaO3 is the key factor for conductivity.
• A small band gap in LaTiO3, sensitive to crystal structure, leads to metallization and charge transfer from Ti to Ta.

Conclusions:

• The findings provide a new understanding of conductivity at Mott insulator interfaces.
• Explains conductivity in LaTiO3/KTaO3 (110) interfaces where polar arguments fail.
• Offers insights into the emergence of superconductivity in related heterostructures.