Atomic‐Scale Metal–Insulator Transition in SrRuO₃ Ultrathin Films Triggered by Surface Termination Conversion

Abstract

The metal–insulator transition (MIT) in transition‐metal‐oxide is fertile ground for exploring intriguing physics and potential device applications. Here, an atomic‐scale MIT triggered by surface termination conversion in SrRuO3 ultrathin films is reported. Uniform and effective termination engineering at the SrRuO3(001) surface can be realized via a self‐limiting water‐leaching process. As the surface termination converts from SrO to RuO2, a highly insulating and nonferromagnetic phase emerges within the topmost SrRuO3 monolayer. Such a spatially confined MIT is corroborated by systematic characterizations on electrical transport, magnetism, and scanning tunneling spectroscopy. Density functional theory calculations and X‐ray linear dichroism further suggest that the surface termination conversion breaks the local octahedral symmetry of the crystal field. The resultant modulation in 4d orbital occupancy stabilizes a nonferromagnetic insulating surface state. This work introduces a new paradigm to stimulate and tune exotic functionalities of oxide heterostructures with atomic precision.

Coupling Charge and Topological Reconstructions at Polar Oxide Interfaces

“…In this sense, the system considered here offers a pleasing simplicity and a more direct approach toward controlling the topology in ultrathin SrRuO 3 and potentially other correlated metals. Our results are also of relevance to the scenario of uncapped SrRuO 3 films [83], where dangling bonds at the surface can manifest as a charged electrostatic boundary condition [38], albeit complicated by the unavoidable interaction with adsorbed ambient chemical species.…”

“…This is a surprising observation since, due to the highly volatile nature of the Ru x O y species, the SrO termination has been argued to be more stable in oxidizing conditions [35,36]. The in situ stabilization demonstrated here poses a substantial advantage over ex situ approaches and is a promising mechanism that invites further exploration [37,38]. Irrespective of its origin, the observed LaO=RuO 2 =SrO interface has important consequences for the Ru charge state, with on the SRO side Sr 2þ requiring Ru 4þ and on the LAO side La 3þ requiring Ru 3þ for charge neutrality.…”

Manipulating Surface Termination of Perovskite Manganate for Oxygen Activation

“…The surface engineering of perovskite oxides is now an intense and challenging area of research. [16,17] Neagu et al pioneered the concept of perovskite exsolution, namely that B-site cations migrate from the bulk structure to the surface under a reducing atmosphere and finally precipitate into metal or alloy nanoparticles. [18] This method not only increases the number of B-site active sites on the surface but also contributes to a stronger metal-oxide interface.…”

Direct Observation and Control of Surface Termination in Perovskite Oxide Heterostructures

“…These results show our ability to study characteristics of thin film growth that were previously speculated upon but never directly observed, such as termination switching events and dynamic layer-rearrangement, which occur on a timescale comparable to the deposition rate. [26][27][28][29][30][31][32][33][34][35][36][37] This demonstration dramatically broadens the knowledge of atomic scale composition and provides unprecedented control over the quality of complex oxide heterostructures which can be synthesized using epitaxial growth techniques such as PLD.…”