Metallicity, Spin-Splitting and Magnetism on an Oxide Surface

by Nicholas Plumb (PSI)

Tuesday 19 May 2015, 14:00 → 15:00 Europe/Stockholm

Nordita East (last minute change)

n recent years, transition metal oxide thin films and interfaces have been at the frontier of developing next-generation multifunctional devices. The hope – and challenge – is to wield the rich, complex, and often poorly understood behaviors emergent in oxide systems in order to achieve coupling and control over various phases such as superconductivity, colossal magnetoresistance, metal-insulator transitions, multiferroicity, and so on. SrTiO3 (STO) is a crucial player in this game, serving as the most common substrate for oxide film growth, and quite often being found to exhibit low-dimensional conductivity (and even sometimes magnetism or superconductivity) at various film interfaces. All of this is surprising, since in bulk STO is a nonmagnetic insulator with a ~3 eV bandgap. Attempts to better understand such complex behaviors eventually led to the discovery that a metallic surface state can actually form atop bare STO. I will present some of the latest findings from this surface state using angle-resolved photoemission spectroscopy (ARPES). We have uncovered a number of remarkable properties of its electronic structure: a mixture of 2D and nonbulklike 3D carriers in the near-surface region inhabiting a unique form of spatio-orbital ordering; universality of the surface electron dispersion and carrier density with respect to diverse sample preparations; intriguing photosensitive behavior; and giant “Rashba-like” spin-splitting combined with an implicit magnetic order. The findings give insights into many related oxide surface and interface systems while illustrating the rich and powerful phenomena that can arise when STO plays host to confined metallic states. They also highlight the outstanding experimental and theoretical challenges in understanding these systems.