Giant Spin Gap and Magnon Localization in the Disordered Heisenberg Antiferromagnet Sr2Ir1-xRuxO4

TL;DR

This study investigates how disorder introduced by Ru doping in Sr2IrO4 creates a giant spin gap and localizes magnons, revealing the robustness of the Ir Jeff=1/2 state and the impact of local anisotropy on magnetic excitations.

Contribution

It demonstrates the emergence of a large magnetic gap and magnon localization in disordered Sr2Ir1-xRuxO4, combining experiments and first-principles calculations to explain the effects of Ru-induced disorder.

Findings

Magnetic gap exceeds 40 meV at x=0.27 and grows with Ru concentration.

Ir Jeff=1/2 state remains stable up to x=0.77 despite disorder.

Magnetic excitations are well reproduced by a disordered Heisenberg model with suppressed ferromagnetic coupling.

Abstract

We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr2Ir1-xRuxO4. A gigantic magnetic gap greater than 40 meV opens at x = 0.27 and increases with Ru concentration, rendering the dispersive magnetic excitations in Sr2IrO4 almost momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir Jeff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest neighbor ferromagnetic coupling.