Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Band Alignment Tuning from Charge Transfer in Epitaxial SrIrO$_3$/SrCoO$_3$ Superlattices

Jibril Ahammad, Brian B. Opatosky, Tanzila Tasnim, John W. Freeland, Gabriel Calderon Ortiz, Jinwoo Hwang, Gaurab Rimal, Boris Kiefer, Ryan B. Comes

Abstract

Understanding charge transfer at oxide interfaces is crucial for designing materials with emergent electronic and magnetic properties, especially in systems where strong electron correlations and spin-orbit coupling coexist. SrIrO$_3$/SrCoO$_3$ (SIO/SCO) superlattices offer a unique platform to explore these effects due to their contrasting electronic structures and magnetic behaviors. Building on past theory based on continuity of O 2p band alignment, we employ density functional theory (DFT) to model electron transfer from Ir to Co across the SIO/SCO interface. To characterize these effects, we synthesized epitaxial SIO/SCO superlattices via molecular beam epitaxy. Structural and transport measurements confirmed high crystallinity, metallic behavior, and suppression of Kondo scattering that has been reported in uniform SIO films. Further characterization via X-ray absorption spectroscopy (XAS) revealed orbital anisotropy and valence changes consistent with interfacial charge transfer. Co K- and L$_{2,3}$-edge and Ir L$_2$-edge spectra verified electron donation from Ir to Co, stabilizing the perovskite SCO phase and tuning the electronic structure of SIO via hole-doping. O K-edge XAS showed band alignment shifts in the SIO layer consistent with DFT predictions. Our work here provides a pathway for engineering oxide heterostructures with tailored magnetic and electronic properties.

Band Alignment Tuning from Charge Transfer in Epitaxial SrIrO$_3$/SrCoO$_3$ Superlattices

Abstract

Understanding charge transfer at oxide interfaces is crucial for designing materials with emergent electronic and magnetic properties, especially in systems where strong electron correlations and spin-orbit coupling coexist. SrIrO/SrCoO (SIO/SCO) superlattices offer a unique platform to explore these effects due to their contrasting electronic structures and magnetic behaviors. Building on past theory based on continuity of O 2p band alignment, we employ density functional theory (DFT) to model electron transfer from Ir to Co across the SIO/SCO interface. To characterize these effects, we synthesized epitaxial SIO/SCO superlattices via molecular beam epitaxy. Structural and transport measurements confirmed high crystallinity, metallic behavior, and suppression of Kondo scattering that has been reported in uniform SIO films. Further characterization via X-ray absorption spectroscopy (XAS) revealed orbital anisotropy and valence changes consistent with interfacial charge transfer. Co K- and L-edge and Ir L-edge spectra verified electron donation from Ir to Co, stabilizing the perovskite SCO phase and tuning the electronic structure of SIO via hole-doping. O K-edge XAS showed band alignment shifts in the SIO layer consistent with DFT predictions. Our work here provides a pathway for engineering oxide heterostructures with tailored magnetic and electronic properties.

Paper Structure

This paper contains 14 sections, 14 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Computational Modeling
  3. Experimental Methods
  4. Results and Discussions
  5. Conclusions
  6. Data Availability
  7. Acknowledgements
  8. Supplementary Crystal Structure of the Superlattice films
  9. Density Functional Theory
  10. Sr$_2$CoIrO$_{6}$ Growth and Characterization
  11. X-ray linear dichroism (XLD)
  12. Co K Pre-edge fitting
  13. XAS Co L-edge and O K-edge
  14. Electrical Transport Methods

Figures (14)

  • Figure 1: (a) Structural model of 2 unit cell (u.c.) SrIrO$_3$/2 u.c. SrCoO$_3$ superlattice with Ir octahedra shown in gold and Co octahedra shown in blue; (b)Layer-resolved partial density of states of O 2p, Co 3d, and Ir 5d. The Fermi level is denoted by gray solid line, superlattice O 2p band centers for each layer are denoted by red lines, and bulk O 2p band centers for SrIrO$_3$ and SrCoO$_3$ are denoted by black dotted lines in the relevant regions.
  • Figure 2: (a) RHEED, (b) STEM, (c) RSM of a representative superlattice (SIO/SCO=6/4 uc), (d) XRD of all three superlattices (XRR in inset).
  • Figure 3: Temperature-dependent resistivity for superlattice samples and reference SrCoO$_3$/LaAlO$_3$ and SrIrO$_3$/LSAT samples.
  • Figure 4: XAS Co $K$-edge data for the superlattice films (a), (c) In-plane data (normalized spectra and their first derivatives); (b),(d) Out-of-plane data (normalized spectra and their first derivatives).
  • Figure 5: Polarization dependent-XAS data of superlattices compared with a reference SrIrO$_3$ film: (a) Co L-edge, (b) Ir L$_2$-edge, and (c) O K-edge. All spectra were collected in the fluorescence yield detection mode.
  • ...and 9 more figures