Resolving interfacial charge transfer in titanate superlattices using resonant x-ray reflectometry

Area of Science:

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

Background:

• Oxide heterostructures exhibit tunable interfacial states driven by charge transfer.
• Probing buried interfaces requires high-resolution depth-dependent electronic structure measurements.
• Existing techniques struggle to resolve physics at buried interfaces with atomic precision.

Purpose of the Study:

• To develop and apply a technique for visualizing buried interfacial charge transfer in oxide superlattices.
• To achieve single unit cell precision in depth profiling of electronic structure.
• To investigate charge transfer mechanisms at the polar-nonpolar SmTiO3/SrTiO3 interface.

Main Methods:

• Linearly polarized resonant X-ray reflectometry (RXR) was employed.
• Valence depth profiles were extracted for SmTiO3 (SmTO)/SrTiO3 (STO) heterostructures.
• STO quantum wells with thicknesses down to a single SrO plane were analyzed.

Main Results:

• RXR successfully visualized charge transfer at the SmTO/STO interface with single unit cell precision.
• An electrostatic discontinuity transferred approximately half an electron per unit cell from SmO to STO.
• Charge transfer was observed as suppressed t2g absorption peaks and absent superlattice peaks.

Conclusions:

• RXR is highly sensitive to electronic reconstruction within single unit cell layers.
• RXR is established as a powerful method for characterizing buried oxide interfaces.
• The study provides insights into interfacial electronic states in oxide superlattices.