High tunability of the soft mode in strained SrTiO(3)/DyScO(3) multilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Epitaxial multilayers offer tunable electronic and optical properties.
• Strontium titanate (SrTiO3) is a prominent perovskite oxide with ferroelectric characteristics.
• Dysprosium scandate (DyScO3) serves as a substrate influencing film properties through strain.

Purpose of the Study:

• Investigate the terahertz (THz) and sub-THz spectral response of SrTiO3/DyScO3 epitaxial multilayers.
• Determine the effect of strain and electrical bias on the ferroelectric soft mode.
• Develop a model to explain the observed tunability and properties of the soft mode.

Main Methods:

• Time-domain terahertz spectroscopy at room temperature.
• Fabrication of SrTiO3/DyScO3 multilayers with varying bilayer thickness (10-100 nm) on DyScO3 substrates.
• Application of electrical bias to probe mode hardening and coupling.

Main Results:

• Tensile strain in SrTiO3 films shifts the ferroelectric soft mode frequency downwards by ~25-45 cm⁻¹.
• Electrical bias causes significant hardening of the soft mode.
• A linear coupling between the soft mode and a relaxation-type excitation at 10 cm⁻¹ was observed.
• The THz response is primarily governed by the soft mode eigenfrequency.

Conclusions:

• The study demonstrates the tunability of THz properties in SrTiO3/DyScO3 multilayers via strain engineering.
• A phenomenological model successfully describes the behavior of the ferroelectric soft mode in the THz range.
• These findings are crucial for developing novel THz devices based on ferroelectric multilayers.