High-density two-dimensional small polaron gas in a delta-doped Mott insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Strongly Correlated Electron Systems

Background:

• Heterointerfaces in complex oxides are crucial for studying strongly correlated materials.
• Metal-insulator transitions (MITs) and polaron formation are influenced by dimensionality and electron correlations.
• Mott insulators near quantum critical points are sensitive to band filling and disorder.

Purpose of the Study:

• To investigate delta-doped Mott insulators as a disorder-free system to explore electron correlations and dimensionality.
• To examine the transport properties of a two-dimensional system created by delta-doping GdTiO3 with SrO.
• To compare experimental conductivity data with theoretical predictions of small polaron transport.

Main Methods:

• Epitaxial growth of delta-doped GdTiO3 films by substituting GdO planes with SrO monolayers.
• Measurement of DC and optical conductivity.
• Analysis of transport phenomena in the context of small polaron models.

Main Results:

• Successful creation of a two-dimensional system with high planar doping density (~7 × 10^14 cm^-2) in delta-doped GdTiO3.
• Observation of thermally activated DC and optical conductivity in the delta-doped layer.
• Quantitative agreement between experimental conductivity and small polaron transport predictions.

Conclusions:

• Delta-doping provides a route to create disorder-free Mott insulating systems for fundamental studies.
• The delta-doped SrO layer in GdTiO3 behaves as a two-dimensional system dominated by small polaron transport.
• This work offers new insights into electron correlations and dimensionality effects in condensed matter.