Nonresonant nonlinear magnonics in an antiferromagnet

Gu-Feng Zhang; Sheikh Rubaiat Ul Haque; Kelson J. Kaj; Xiang Chen; Urban F. P. Seifert; Jingdi Zhang; Kevin A. Cremin; Leon Balents; Stephen D. Wilson; Richard D. Averitt

arXiv · 2411.10579

Nonresonant nonlinear magnonics in an antiferromagnet

Gu-Feng Zhang·Sheikh Rubaiat Ul Haque·Kelson J. Kaj·Xiang Chen·Urban F. P. Seifert·Jingdi Zhang·Kevin A. Cremin·Leon Balents·Stephen D. Wilson·Richard D. Averitt

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Abstract

Antiferromagnets exhibit rapid spin dynamics in a net zero magnetic background which enables novel spintronic applications and interrogation of many-body quantum phenomena. The layered antiferromagnet Sr$_2$IrO$_4$ hosts an exotic spin one-half Mott insulating state with an electronic gap arising from on-site Coulomb repulsion and strong spin-orbit coupling. This makes Sr$_2$IrO$_4$ an interesting candidate to interrogate dynamical attributes of the magnetic order using ultrafast laser pulses. We investigate the magnetization dynamics of Sr$_2$IrO$_4$ following circularly-polarized photoexcitation with below-gap mid-infrared (mid-IR -- 9 $\mu m$) and above-gap near-infrared (near-IR -- 1.3 $\mu m$) pulses. In both cases, we observe excitation of a zone-center coherent magnon mode featuring a 0.5 THz oscillation in the pump-induced Kerr-rotation signal. However, only below-gap excitation exhibits a helicity dependent response and linear (quadratic) scaling of the coherent magnon amplitude with excitation fluence (electric field). Moreover, below-gap excitation has a magnon generation efficiency that is at least two orders of magnitude greater in comparison to above-gap excitation. Our analysis indicates that the helicity dependence and enhanced generation efficiency arises from a unique one-photon two-magnon coupling mechanism for magnon generation. Thus, preferential spin-photon coupling without photoexcitation of electrons permits extremely efficient magnon generation. Our results reveal new possibilities for ultrafast control of antiferromagnets.

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Gu-Feng Zhang, Sheikh Rubaiat Ul Haque, Kelson J. Kaj, Xiang Chen, Urban F. P. Seifert, Jingdi Zhang, Kevin A. Cremin, Leon Balents, Stephen D. Wilson, Richard D. Averitt. 2024-11-15. Nonresonant nonlinear magnonics in an antiferromagnet. https://arxiv.org/abs/2411.10579

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