Doping Evolution of Magnetic Order and Magnetic Excitations in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$

TL;DR

This study investigates how electron doping affects magnetic order and excitations in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$, revealing a transition from long-range antiferromagnetic order to a two-dimensional short-range state with suppressed magnetic anisotropy.

Contribution

It provides detailed doping-dependent insights into magnetic order evolution and excitations in a bilayer iridate using resonant X-ray scattering, highlighting the suppression of magnetic anisotropy and interlayer couplings.

Findings

Suppression of 3D long-range antiferromagnetic order with doping.

Transition to 2D short-range magnetic order at higher doping levels.

Magnetic excitations become damped and soften, with a collapsing magnon gap.

Abstract

We use resonant elastic and inelastic X-ray scattering at the Ir-$L_3$ edge to study the doping-dependent magnetic order, magnetic excitations and spin-orbit excitons in the electron-doped bilayer iridate (Sr$_{1-x}$La$_{x}$)$_3$Ir$_2$O$_7$ ($0 \leq x \leq 0.065$). With increasing doping $x$, the three-dimensional long range antiferromagnetic order is gradually suppressed and evolves into a three-dimensional short range order from $x = 0$ to $0.05$, followed by a transition to two-dimensional short range order between $x = 0.05$ and $0.065$. Following the evolution of the antiferromagnetic order, the magnetic excitations undergo damping, anisotropic softening and gap collapse, accompanied by weakly doping-dependent spin-orbit excitons. Therefore, we conclude that electron doping suppresses the magnetic anisotropy and interlayer couplings and drives (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ into a correlated metallic state hosting two-dimensional short range antiferromagnetic order and strong antiferromagnetic fluctuations of $J_{\text{eff}} = \frac{1}{2}$ moments, with the magnon gap strongly suppressed.