Intrinsic polaron formation and influence on the surface chemical properties

Michele Reticcioli (U of Vienna)

Dec 13. 2019, 09:40 — 10:20

Uncompensated charge at the surface boundary of polar materials is conventionally expected to form a two dimensional electron gas (2DEG), as a result of the alternating charged-plane stacking in the ionic crystals, interrupted by the surface cut. By means of density-functional theory calculations and surface-sensitive experiments, we propose a different paradigm able to accommodate the uncompensated charge in a more effective way, establishing a more favorable ground state for the system, that is the polaron formation. In fact, the intrinsic uncompensated charge tends to spontaneously localize and form polarons, rather than a 2DEG. Only beyond the critical polaron density, excess charge arising from external doping or defects starts to build a 2DEG. Here, we show how polarons and 2DEG compete on the polar KTaO3(001) surface. Unrevealing the mechanism behind the accommodation of the uncompensated charge is extremely important for technological applications, since the formation of localized charge rather than a dispersed gas drastically alters the materials functionality: Here, the effects on the chemical properties of KTaO3 are shown by analyzing the CO adsorption.

Further Information
ESI Boltzmann Lecture Hall
Associated Event:
Polarons in the 21st Century (Workshop)
Jozef Devreese (U Antwerpen)
Cesare Franchini (U of Vienna)
Georg Kresse (U of Vienna)
Jacques Tempere (U Antwerpen)