Giant oscillating thermopower at oxide interfaces

Area of Science:

• Condensed Matter Physics
• Materials Science
• Oxide Heterostructures

Background:

• The nature of charge carriers at the LaAlO3/SrTiO3 interface is crucial for understanding charge confinement in oxide heterostructures.
• Previous studies have explored the electronic properties of this interface, but a complete picture of charge carrier behavior remains elusive.

Purpose of the Study:

• To investigate the electronic structure of the LaAlO3/SrTiO3 interface at low temperatures using thermopower measurements.
• To understand the role of gate field in modulating the charge carrier behavior and electronic states.

Main Methods:

• Low-temperature thermopower measurements as a function of gate voltage applied to the LaAlO3/SrTiO3 heterostructure.
• Analysis of thermopower magnitude and oscillations to probe the electronic structure and charge density.

Main Results:

• Under negative gate voltage, thermopower exhibited large negative values (10^4-10^5 microVK^-1), indicating a phonon-drag contribution.
• Regular oscillations in thermopower as a function of gate voltage were observed, correlating with Fermi level descent.
• These oscillations provide evidence for a dense array of localized states at the bottom of the Ti 3d conduction band.

Conclusions:

• The study provides direct evidence for a localized Anderson tail in the two-dimensional electron liquid at the LaAlO3/SrTiO3 interface.
• Thermopower measurements are a powerful tool for probing electronic states and charge carrier localization in oxide heterostructures.