Ultrasensitive strain modulation of terahertz magnons at a magnetic phase transition

TL;DR

This study demonstrates that applying uniaxial strain to Ca$_2$RuO$_4$ can dramatically alter its THz magnon spectrum near a magnetic phase transition, enabling highly sensitive control for magnonic applications.

Contribution

It reveals that strain can induce significant changes in magnon energies and magnetic states in Ca$_2$RuO$_4$, with a detailed theoretical explanation of the underlying mechanisms.

Findings

Magnon energies change by over 10% (~0.3 THz) across the strain-induced phase transition.

Strain controls the sign of interlayer interactions and magnetic ground states.

Theoretical analysis links magnon energy shifts to spin-orbital electron configurations.

Abstract

Antiferromagnets typically host spin-wave (magnon) excitations in the terahertz (THz) regime, offering a promising platform for high-speed magnonic information technologies. Harnessing these excitations requires sensitive control of their spectral properties. Here we use resonant x-ray diffraction and Raman scattering to demonstrate uniaxial-strain control of the antiferromagnetic (AFM) ground state and THz magnon excitations in the layered Mott insulator Ca$_2$RuO$_4$. Although the states separated by the strain-induced phase transition differ only by the sign of the weak and partially frustrated interlayer interaction, their magnon energies differ by more than 10% (~ 0.3 THz). Our theoretical analysis explains this surprising observation by tracing the origin of both the sign reversal of the interlayer coupling and the magnon energy to the spin-orbital composition of the Ru valence electrons. The extreme strain sensitivity of the THz magnon energy near a magnetic phase transition opens up pathways towards a new generation of transition-edge magnonic devices.