Large Polarons as Key Quasiparticles in SrTiO_{3} and SrTiO_{3}-Based Heterostructures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Strontium titanate (SrTiO3) exhibits intriguing electronic phenomena, including superconductivity, despite its simple structure.
• The nature of quasiparticles governing SrTiO3's electronic and conduction properties remains incompletely understood.
• Understanding these quasiparticles is crucial for explaining collective phenomena in SrTiO3 and related heterostructures.

Purpose of the Study:

• To investigate the low-energy excitations in bulk SrTiO3 and LaAlO3/SrTiO3 two-dimensional electron gases (2DEGs).
• To elucidate the role of quasiparticles in the electronic and transport properties of SrTiO3-based systems.

Main Methods:

• Utilized Ti L3 edge resonant inelastic x-ray scattering (RIXS).
• Analyzed low-energy excitations in both bulk SrTiO3 and LaAlO3/SrTiO3 2DEG samples.

Main Results:

• Observed intense dd+phonon excitations, characteristic of polarons, across all studied samples.
• Detected a reduction in the electron-phonon coupling of the LO3 mode with increasing conductivity in SrTiO3.
• Found evidence of dynamic screening of large polaron self-induced polarization.

Conclusions:

• The low-temperature physics of SrTiO3 and SrTiO3-based 2DEGs is predominantly governed by large polaron quasiparticles.
• Dynamic screening plays a significant role in modulating the properties of these polarons.
• The findings provide critical insights into the fundamental electronic behavior of these quantum materials.