Disordered dimer state in electron-doped Sr$_{3}$Ir$_{2}$O$_{7}$

TL;DR

This study investigates spin excitations in electron-doped Sr$_{3}$Ir$_{2}$O$_{7}$, revealing a transition from long-range antiferromagnetism to a disordered dimer state with persistent gapped excitations and growing local moments.

Contribution

It provides new insights into the magnetic state of doped Sr$_{3}$Ir$_{2}$O$_{7}$, proposing a disordered dimer state as the key magnetic phase in the metallic regime.

Findings

Long-range antiferromagnetism vanishes with doping.

Gapped spin excitations persist in the metallic state.

Local magnetic moments grow with doping.

Abstract

Spin excitations are explored in the electron-doped spin-orbit Mott insulator (Sr$_{1-x}$La$_{x}$)$_3$Ir$_2$O$_7$. As this bilayer square lattice system is doped into the metallic regime, long-range antiferromagnetism vanishes, yet a spectrum of gapped spin excitation remains. Excitation lifetimes are strongly damped with increasing carrier concentration, and the energy integrated spectral weight becomes nearly momentum independent as static spin order is suppressed. Local magnetic moments, absent in the parent system, grow in metallic samples and approach values consistent with one $J=\frac{1}{2}$ impurity per electron doped. Our combined data suggest that the magnetic spectra of metallic (Sr$_{1-x}$La$_{x}$)$_3$Ir$_2$O$_7$ are best described by excitations out of a disordered dimer state.