Experimental evidence for oxygen sublattice control in polar infinite layer SrCuO2

Area of Science:

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

Background:

• Theoretical studies predicted a critical thickness limit for polar cuprates, below which electrostatic instability drives a transition to a nonpolar state.
• Controlling the structure of complex oxide superlattices at the atomic level is crucial for understanding and tuning their physical properties.

Purpose of the Study:

• To experimentally demonstrate the predicted thickness-induced structural transformation in polar cuprates.
• To investigate the possibility of designing the oxygen sublattice and controlling the electronic structure by precise thickness reduction.
• To explore the electronic structure changes associated with the transition from planar to chainlike structures in SrCuO2/SrTiO3 superlattices.

Main Methods:

• Fabrication of SrCuO2/SrTiO3 superlattices with unit-cell precision.
• Structural characterization using X-ray diffraction (XRD) and high-resolution scanning transmission electron microscopy (HR-STEM).
• Electronic structure investigation via X-ray absorption spectroscopy (XAS).

Main Results:

• Successfully induced a structural transformation from a bulk planar to a chainlike structure by reducing the SrCuO2 repeat unit thickness.
• Demonstrated precise control over the oxygen sublattice arrangement during the structural transformation.
• Observed distinct electronic structure signatures in the chainlike phase, with preferential hole occupation in the Cu 3d(3z2-r2) orbital, differing from the planar phase.

Conclusions:

• The experimental results confirm the theoretical prediction of a thickness-driven transition to a nonpolar state in polar cuprates.
• Atomic-level control over superlattice thickness enables the design of specific structural motifs, such as chainlike arrangements.
• The observed changes in electronic structure highlight the strong coupling between structure and electronic properties in these materials, opening avenues for novel electronic device applications.