Spectroscopic evidence for polaronic behaviour of the strong spin-orbit insulator Sr$_3$Ir$_2$O$_7$

TL;DR

This study uses temperature-dependent angle-resolved photoemission to reveal polaronic behavior in Sr$_3$Ir$_2$O$_7$, linking its insulating state to strong electron-boson interactions similar to cuprates.

Contribution

It provides spectroscopic evidence of polaronic ground state behavior in Sr$_3$Ir$_2$O$_7$, connecting 5d iridates with 3d cuprates through electron-boson coupling.

Findings

Sr$_3$Ir$_2$O$_7$ is a narrow-gap correlated insulator.

Spectral features indicate a polaronic ground state.

Similar behavior observed in Sr$_2$IrO$_4$.

Abstract

We investigate the bilayer Ruddlesden-Popper iridate Sr$_3$Ir$_2$O$_7$ by temperature-dependent angle-resolved photoemission. We find a narrow-gap correlated insulator, with spectral features indicative of a polaronic ground state, strikingly similar to that observed previously for the parent compounds of the cuprate superconductors. We additionally observe similar behaviour for the single-layer cousin Sr$_2$IrO$_4$, indicating that strong electron-boson coupling dominates the low-energy excitations of this exotic family of materials, and providing a microscopic link between the insulating ground states of the seemingly-disparate 3d cuprates and 5d iridates.