Dephasing dynamics of photoexcited state in correlated electron system

关联电子（CE）系统的光响应由于其超快动力学特性而备受关注。在本研究计划中，我们利用双脉冲简并四波混频（DFWM）研究了一维Mott绝缘体[Ni（chxn）_2Br]Br_2中光激发态的退相动力学，II）在二维有机导体中检测到超快光诱导绝缘体-金属跃迁（PIMT）（BEDT-TTF）_2X的中红外飞秒泵浦-探测光谱研究表明：（1）在强激发条件下，[Ni（chxn）_2Br]Br_2的DFWM信号出现了慢衰减分量（6ps），而对于弱激发仅可观察到亚ps分量。ii）强激发下慢衰变的温度依赖性不能用holon-doublon（h-d）团簇-光学声子相互作用来理解。动力学的温度依赖性可以概括如下：a）亚ps分量，其被检测为 ...更多信息 B）几个ps分量，当T> 100 K时变短。B）的弛豫过程可以用载流子与光学声子的相互作用来解释。然而，a）被认为与磁振子激发有关，因为衰变常数及其分数的温度依赖性类似于磁化率的温度依赖性。此外，对于B），虽然相互作用光学声子的频率被评估为与弱激发极限的频率相同，但是耦合常数小一个数量级。这些结果表明：1）强激发产生的h-d团簇被声子和磁振子散射，2）h-d团簇与光学声子之间的耦合常数被显著抑制，3）由此产生了反映磁振子散射的衰变（BEDT-TTF）_2X，超快、高效（>100个分子/光子）的光诱导绝缘体-金属跃迁。光致金属态的临界慢化和相干声子反映了光致畴的非均匀结构，这些结果将为三阶光学非线性和光致相变机制的超快CE开关器件材料的设计提供有用的信息。少

Photo-response of correlated electron (CE) system has attracted much attention because of their ultrafast dynamics aspects. In this research project, I) We have investigated dephasing dynamics of photoexcited state in one-dimesional Mott insulator [Ni(chxn)_2Br]Br_2 by using 2-pulse degenerative four-wave mixing (DFWM), II) ultrafast photoinduced insulator-to metal transition (PIMT) was detected in two-dimensional organic conductor (BEDT-TTF)_2X by mid-IR femtosecond pump-probe spectroscopy for the first time.I)In the DFWM study of [Ni(chxn)_2Br]Br_2, i) for strong excitation condition, the slower decay component (6 ps) of DFWM signal appears, while only sub-ps component is observable for the weak excitation. ii) A temperature dependence of the slow decay for the strong excitation can not be understood in terms of the holon-doublon (h-d) cluster-optical phonon interaction. The temperature dependence of the dynamics can be summarized as follows; a) sub-ps component, which is detected fo … More r T>30 K and becomes shorter for T<100 K, b) several ps component which becomes shorter for T >100 K. The relaxation process of b) can be explained by using the interaction between the carrier and the optical phonon. Nevertheless, the a) is suggested to be related to the magnon excitation since the temperature dependence of the decay constants and their fractions resemble the temperature dependence of the magnetic susceptibility. Moreover, for b), although, the frequency of the interacting optical phonon is evaluated to be same as that of for weak excitation limit, coupling constant is smaller for one order of magnitude. These results indicate that 1) h-d cluster, which is generated by the strong excitation, is scattered by phonon and magnon, 2) the coupling constant between the h-d cluster and optical phonon is markedly suppressed, 3) resultantly, decay reflecting the magnon scattering is considered to appear.II)In the research of the two-dimensional organic conductor (BEDT-TTF)_2X, ultrafast and efficient (>100 molecules /photon) photoinduced insulator-to metal transition was observed. The critical slowing down of the photoinduced metallic state and the coherent phonon reflecting the inhomogeneous structure of the photoinduced domain.Our results will provide the useful information for designing the material for ultarfast CE switching devise whose mechanisms are third order optical nonlinearity or photoinduced phase transition, respectively. Less