Unconventional crystal-field splitting in noncentrosymmetric BaTiO3 thin films

Yang Song, Xiaoran Liu, Fangdi Wen, M. Kareev, Ruyi Zhang, Yujuan Pei, Jiachang Bi, Padraic Shafer, Alpha T. N'Diaye, Elke Arenholz, Se Young Park, Yanwei Cao, J. Chakhalian

Research output: Contribution to journalArticlepeer-review

Abstract

Understanding the crystal-field splitting and orbital polarization in noncentrosymmetric systems such as ferroelectric materials is fundamentally important. In this study, taking BaTiO3 as a representative material, we investigate titanium crystal-field splitting and orbital polarization in noncentrosymmetric TiO6 octahedra with resonant x-ray linear dichroism at the Ti L2,3 edge. The high-quality BaTiO3 thin films were deposited on DyScO3 (110) single crystal substrates in a layer-by-layer way by pulsed laser deposition. The reflection high-energy electron diffraction and element specific x-ray absorption spectroscopy were performed to characterize the structural and electronic properties of the films. In sharp contrast to conventional crystal-field splitting and orbital configuration (dxz/dyz<dxy<d3z2-r2<dx2-y2 or dxy<dxz/dyz<dx2-y2<d3z2-r2) expected from compressive or tensile epitaxial strain, respectively, it is revealed that dxz, dyz, and dxy orbitals are nearly degenerate, whereas d3z2-r2 and dx2-y2 orbitals are split with an energy gap ∼100 meV in the epitaxial BaTiO3 films. We find that the unexpected degenerate orbitals dxz/dyz/dxy result from the competition between the orbital splitting induced by epitaxial strain and that induced by polar distortions of BaTiO3 films. Our results provide a route to manipulate orbital degree of freedom by switching electric polarization in ferroelectric materials.

Original languageEnglish (US)
Article number024413
JournalPhysical Review Materials
Volume4
Issue number2
DOIs
StatePublished - Feb 24 2020

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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