Polarity‐Driven Atomic Displacements at the 2D Mg2TiO4‐MgO (001) Oxide Interface for Hosting Potential Interlayer Excitons. Issue 10 (3rd March 2023)

• Record Type: Journal Article
• Authors: Shin, Kidae; Eltinge, Stephen; Lee, Sangjae; Shin, Hyungki; Jiang, Juan; Hong, Hawoong; Davidson, Bruce A.; Zou, Ke; Ismail‐Beigi, Sohrab; Ahn, Charles H.; Walker, Frederick J.
• Is Part Of: Advanced materials interfaces. Volume 10:Issue 10(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-03
• Subjects: density functional theory -- interlayer excitons -- oxide thin film -- synchrotron X‐ray; Materials science -- Periodicals; 620.11
• DOI: 10.1002/admi.202202320
• Languages: English
• ISSNs: 2196-7350

Abstract

Abstract: Interlayer excitons in solid‐state systems have emerged as candidates for realizing novel platforms ranging from excitonic transistors and optical qubits to exciton condensates. Interlayer excitons have been discovered in 2D transition metal dichalcogenides, with large exciton binding energies and the ability to form various van der Waals heterostructures. Here, an oxide system consisting of a single unit cell of Mg2 TiO4 on MgO (001) is proposed as a platform for hosting interlayer excitons. Using a combination of density functional theory (DFT) calculations, molecular beam epitaxy growth, and in situ crystal truncation rod measurements, it is shown that the Mg2 TiO4 ‐MgO interface can be precisely controlled to yield an internal electric field suitable for hosting interlayer excitons. The atoms in the polar Mg2 TiO4 layers are observed to be displaced to reduce polarity at the interface with the non‐polar MgO (001) surface. Such polarity‐driven atomic displacements strongly affect electrostatics of the film and the interface, resulting in localization of filled and empty band‐edge states in different layers of the Mg2 TiO4 film. The DFT calculations suggest that the electronic structure is favorable for localization of photoexcited electrons in the bottom layer and holes in the top layer, which may bind to form interlayer exciton states. Abstract : 2D Mg2 TiO4 on MgO (001) is proposed as a transition metal oxide system for hosting interlayer excitons. Theoretical calculations predict localization of electrons and holes in the bottom and top Mg2 TiO4 layers respectively, which can bind to form interlayer excitons. The Mg2 TiO4 thin films are grown using molecular beam epitaxy and their crystal structure is determined with synchrotron X‐ray experiments.