Nature of electrons from oxygen vacancies and polar catastrophe at LaAlO3/SrTiO3 interfaces

TL;DR

This study investigates the electronic properties at LaAlO3/SrTiO3 interfaces, revealing that electrons from oxygen vacancies are localized and magnetic, while those from the polar field are weakly localized and non-magnetic, with implications for understanding low-temperature transport phenomena.

Contribution

It provides a comparative magnetotransport analysis distinguishing the roles of oxygen vacancy electrons and polar field electrons at LaAlO3/SrTiO3 interfaces.

Findings

Electrons from oxygen vacancies are localized and magnetic at low temperatures.

Electrons from the polar field are weakly localized and non-magnetic.

Magnetotransport behavior varies between amorphous and crystalline heterostructures.

Abstract

The relative significance of quantum conductivity correction and magnetic nature of electrons in understanding the intriguing low-temperature resistivity minimum and negative magnetoresistance of the two-dimensional electron gas at LaAlO3/SrTiO3 interfaces has been a long outstanding issue since its discovery. Here we report a comparative magnetotransport study on amorphous and oxygen-annealed crystalline LaAlO3/SrTiO3 heterostructures at a relatively high-temperature range, where the orbital scattering is largely suppressed by thermal fluctuations. Despite of a predominantly negative out-of-plane magnetoresistance effect for both, the magnetotransport is isotropic for amorphous LaAlO3/SrTiO3 while strongly anisotropic and well falls into a two-dimensional quantum correction frame for annealed crystalline LaAlO3/SrTiO3. These results clearly indicate that a large portion of electrons from oxygen vacancies are localized at low temperatures, serving as magnetic centers, while the electrons from the polar field are only weakly localized due to constructive interference between time-reversed electron paths in the clean limit and no signature of magnetic nature is visible.