Nature of the charge carriers in LaAlO ₃ -SrTiO ₃ oxide heterostructures probed using hard X-ray photoelectron spectroscopy

Abstract

PACS 79.60.-i-Photoemission and photoelectron spectra PACS 79.60.Jv-Interfaces; heterostructures; nanostructures PACS 73.20.-r-Electron states at surfaces and interfaces Abstract-A proper investigation of the valence band electronic structure is the essential first step towards understanding the intriguing coexistence of several exotic electronic phases like ferromagnetism and superconductivity, in LaAlO3-SrTiO3 heterostructures. In order to comprehend the electronic structure across the LaAlO3-SrTiO3 oxide interface, a detailed valence band investigation has been carried out using variable energy Hard X-ray Photoelectron Spectroscopy and signatures of both low-energy coherent and high-energy features have been observed in the valence band spectra. Our combined experimental and theoretical study suggests that the charge carriers at the interface are only weakly correlated and the high-energy feature does not arise from the lower Hubbard band. Instead, this high-energy feature is attributed to in-gap states induced by oxygen vacancies and possible polaron formation.