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O: Fachverband Oberflächenphysik

O 97: Focus Session: SrTiO₃: A Versatile Material from Bulk Quantum Paraelectric to 2D Superconductor II (joint session TT/KFM/MA/O)

O 97.10: Talk

Thursday, March 21, 2024, 17:30–17:45, H 0104

Quasiparticle and excitonic properties of monolayer SrTiO₃ — •Lorenzo Varrassi¹, Peitao Liu², and Cesare Franchini^1,3 — ¹Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna — ²Shenyang National Laboratory for Materials Science, Institute of Metal Research — ³University of Vienna, Faculty of Physics and Center for Computational Materials Science, Vienna.

Recently, a breakthrough has been achieved with the synthesis of free-standing SrTiO₃ ultrathin films down to the monolayer limit[1]; its optical and excitonic properties remain however largely unexplored. This talk will provide insights on the quasiparticle and excitonic properties of monolayer SrTiO₃, employing many-body perturbation theory.

Our analysis[2] emphasizes the need to go beyond the diagonal GW approximation and include off-diagonal self-energy elements in order to obtain correct description of the orbital hybridizations. A fully satisfying description is achieved by treating non-locality in both exchange and correlation.

The optical properties are studied through the solution of the Bethe-Salpeter equation. We observe a significant enhancement of the excitonic effects with respect to the bulk phase, with a binding energy at the optical gap about four times greater. Furthermore, the two-dimensional polarizability at the long wavelength limit is dominated by two strongly bound excitonic peaks; their character is determined through the analysis of the excitonic wavefunctions.

[1] D. Ji et al., Nature 570 (2019) 87

[2] L. Varrassi et al., arxive:2303.14830 (2023)