Synthesis and electronic properties of Ruddlesden-Popper strontium iridate epitaxial thin films stabilized by control of growth kinetics

TL;DR

This study demonstrates the controlled synthesis of Ruddlesden-Popper Sr-iridate thin films via pulsed laser deposition, highlighting the role of oxygen partial pressure and growth kinetics in stabilizing different phases and revealing their electronic structures.

Contribution

It introduces a kinetic control method for stabilizing various RP phases of Sr-iridates, expanding synthesis possibilities beyond thermodynamic limits.

Findings

Oxygen partial pressure critically influences phase stabilization.

Strong spin-orbit coupling observed in electronic structure.

Kinetic control enables synthesis of higher RP members.

Abstract

We report on the selective fabrication of high-quality Sr$_2$IrO$_4$ and SrIrO$_3$ epitaxial thin films from a single polycrystalline Sr$_2$IrO$_4$ target by pulsed laser deposition. Using a combination of X-ray diffraction and photoemission spectroscopy characterizations, we discover that within a relatively narrow range of substrate temperature, the oxygen partial pressure plays a critical role in the cation stoichiometric ratio of the films, and triggers the stabilization of different Ruddlesden-Popper (RP) phases. Resonant X-ray absorption spectroscopy measurements taken at the Ir $L$-edge and the O $K$-edge demonstrate the presence of strong spin-orbit coupling, and reveal the electronic and orbital structures of both compounds. These results suggest that in addition to the conventional thermodynamics consideration, higher members of the Sr$_{n+1}$Ir$_n$O$_{3n+1}$ series can possibly be achieved by kinetic control away from the thermodynamic limit. These findings offer a new approach to the synthesis of ultra-thin films of the RP series of iridates and can be extended to other complex oxides with layered structure.