Upon femtosecond-laser stimulation, generally materials are expected to recover back to their thermal-equilibrium conditions, with only a few exceptions reported. Here, we demonstrate that deviation from the thermal-equilibrium pathway can be induced in canonical 3D antiferromagnetically (AFM) ordered ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ by a single 100-fs-laser pulse, appearing as losing long-range magnetic correlation along one direction into a glassy condition. We further discover a “critical-threshold ordering” behavior for fluence above approximately $12\mathrm{mJ}/{\mathrm{cm}}^2$, which we show corresponds to the smallest thermodynamically stable $c$-axis correlation length needed to maintain long-range quasi-two-dimensional AFM order. We suggest that this behavior arises from the crystalline anisotropy of the magnetic-exchange parameters in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, whose strengths are associated with distinctly different timescales. As a result, they play out very differently in the ultrafast recovery processes, compared with the thermal-equilibrium evolution. Thus, our observations are expected to be relevant to a wide range of problems in the nonequilibrium behavior of low-dimensional magnets and other related ordering phenomena.

中文翻译：

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Sr2IrO4 准二维磁序的单激光脉冲驱动热极限

在飞秒激光刺激下，通常材料会恢复到它们的热平衡条件，只有少数例外报告。在这里，我们证明了可以在规范的 3D 反铁磁 (AFM) 有序中诱导偏离热平衡路径${锶}_2{\mathrm{氧化铁}}_4$由单个 100 飞秒激光脉冲产生，表现为沿一个方向失去长程磁相关性，变为玻璃态。我们进一步发现了通量高于近似值的“临界阈值排序”行为$12\mathrm{兆焦耳}/{\mathrm{厘米}}^2$，我们显示对应于最小的热力学稳定 $C$维持长程准二维 AFM 顺序所需的轴相关长度。我们认为这种行为是由磁交换参数的结晶各向异性引起的${锶}_2{\mathrm{氧化铁}}_4$，其优势与明显不同的时间尺度相关联。因此，与热平衡演化相比，它们在超快恢复过程中的表现非常不同。因此，我们的观察预计与低维磁体的非平衡行为和其他相关排序现象中的广泛问题有关。