Nature of the charge carriers in LaAlO₃-SrTiO₃ oxide heterostructures probed using hard X-ray photoelectron spectroscopy

¹ Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India
² Deutsches Elektronen-Synchrotron DESY - Notkestrasse 85, D-22607 Hamburg, Germany
³ Université Grenoble Alpes - F-38000 Grenoble, France
⁴ CEA, LITEN - 17 rue des Martyrs, F-38054 Grenoble, France
⁵ Department of Physics, University of Tokyo - Tokyo 113-0033, Japan
⁶ Max-Plank-Institute for Solid State Research - Stuttgart D-70569, Germany
⁷ RIKEN Center for Emergent Matter Science (CEMS) - Saitama 351-0198, Japan
⁸ Centre de Physique Theorique, Ecole Polytechnique, CNRS UMR 7644 - F-91128 Palaiseau, France

^(a) sarma@sscu.iisc.ernet.in

Received: 24 August 2018
Accepted: 28 August 2018

Abstract

A proper investigation of the valence band electronic structure is the essential first step towards understanding the intriguing co-existence 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 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.