摘要:
本文利用时间分辨光谱技术,系统研究了飞秒激光诱导YMnO3薄膜中Mn^3＋离子3d轨道跃迁的 载流子动力学过程.当抽运光子能量为1.7 eV,对应于Mn^3＋离子的3d轨道跃迁, 抽运-探测零延迟时间处的透射率变化随着温度的降低逐渐减小. 这起源于低温下短程反铁磁有序诱导Mn3＋离子d-d能级发生＂蓝移＂. 载流子弛豫过程由快、慢两个过程组成,分别对应于电子-声子相互作用和自旋-声子相互作用. 实验发现,当温度低于80 K,电子-声子热化时间显著增加,表明低温下电子-声子的 耦合强度受长程反铁磁有序的影响.
Abstract:
Photoinduced carrier dynamic behavior of the Mn^3＋ 3d resonance excitation of YMnO3 thin film is studied by the femtosecond time resolved spectroscopy. The photon energy of the pump pulse is tuned to 1.70 eV, which is corresponding to the Mn^3＋ 3d energy level at room temperature. With resonant excitation, the transient transmission signals at the zero-delay time gradually increase with temperature increasing. The temperature dependent transmission change results from the blue shift of the Mn3＋ 3d energy level, which is believed to originate from the short-range antiferromagnetic order in YMnO3 film. In addition, the fast and slow relaxations of the transient signal arise from electronic-phonon and phonon-spin interactions, respectively. When the temperature is lower than TN, the relaxation time of the fast process increases significantly, which indicates that the strength of electronic-phonon coupling is restrained by the long-range antiferromagnetic order.
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