Atomic-scale observation of localized phonons at FeSe/SrTiO₃ interface

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Superconductivity in single unit-cell FeSe grown on SrTiO3 exhibits enhanced transition temperatures.
• Interfacial phonon modes and electron-phonon coupling are hypothesized to drive this enhancement.
• Direct experimental observation of these interfacial phonon modes has been challenging due to complex interface structures.

Purpose of the Study:

• To directly characterize the atomic structure and phonon modes at the FeSe/SrTiO3 interface.
• To elucidate the role of interfacial phonons in the superconductivity enhancement of FeSe films.
• To establish a structure-phonon relationship at the unique FeSe/SrTiO3 interface.

Main Methods:

• Atomically resolved imaging using an electron microscope.
• Electron energy loss spectroscopy (EELS) for phonon mode characterization.
• Ab initio calculations to determine electron-phonon interactions.

Main Results:

• Identification of several phonon modes highly localized (~1.3 nm) at the Ti-O terminated interface.
• Observation of a specific phonon mode (~83 meV) exhibiting strong interactions with FeSe electrons.
• Direct correlation between interfacial structure and localized phonon behavior.

Conclusions:

• Localized interfacial phonon modes exist at the FeSe/SrTiO3 interface.
• Strong electron-phonon coupling involving these modes contributes to superconductivity enhancement.
• Provides crucial insights into the mechanism behind interface-induced superconductivity in FeSe/SrTiO3.