# Overdamped antiferromagnetic strange metal state in Sr$_3$IrRuO$_7$

## TL;DR

This study reveals an overdamped antiferromagnetic strange metal state in Sr$_3$IrRuO$_7$, characterized by incoherent quasiparticles, linear resistivity, and overdamped spin excitations, bridging Mott insulator and quantum critical metal phases.

## Contribution

It identifies a novel overdamped antiferromagnetic strange metal phase in Sr$_3$IrRuO$_7$ with unique spin-charge dynamics and incoherent electronic structure.

## Key findings

- Lack of coherent quasiparticles in the intermediate phase.
- Linear temperature dependence of charge transport.
- Presence of overdamped magnetic excitations with a large energy scale.

## Abstract

The unconventional electronic ground state of Sr$_3$IrRuO$_7$ is explored via resonant x-ray scattering techniques and angle-resolved photoemission measurements. As the Ru content approaches $x=0.5$ in Sr$_3$(Ir$_{1-x}$Ru$_x$)$_2$O$_7$, intermediate to the $J_{eff}=1/2$ Mott state in Sr$_3$Ir$_2$O$_7$ and the quantum critical metal in Sr$_3$Ru$_2$O$_7$, a thermodynamically distinct metallic state emerges. The electronic structure of this intermediate phase lacks coherent quasiparticles, and charge transport exhibits a linear temperature dependence over a wide range of temperatures. Spin dynamics associated with the long-range antiferromagnetism of this phase show nearly local, overdamped magnetic excitations and an anomalously large energy scale of 200 meV---an energy far in excess of exchange energies present within either the Sr$_3$Ir$_2$O$_7$ or Sr$_3$Ru$_2$O$_7$ solid-solution endpoints. Overdamped quasiparticle dynamics driven by strong spin-charge coupling are proposed to explain the incoherent spectral features of the strange metal state in Sr$_3$IrRuO$_7$.