A STUDY OF INTERACTIONS BETWEEN ELEMENTARY EXCITATIONS IN TRANSITION METAL OXIDES BY MEANS OF FEMTOSECOND SPECTROSCOPY

我们研究了飞秒脉冲光掺杂引起的电子态的变化以及3d过渡金属氧化物中光激发态的弛豫动力学，以阐明声子和磁振子的相互作用以及磁相的弛豫过程。i）铜氧化物中CuO 2平面电子态的弛豫动力学。我们观察到光致光谱的变化，这是由光激发的载流子掺杂效应解释。磁振子的发射使光致隙内态在约1ps的时间内弛豫，这表明磁激发在强关联系统中起着至关重要的作用。ii）3d过渡金属氧化物薄膜的制备。利用激光烧蚀技术制备了多种氧化物薄膜，根据材料的不同，选择合适的衬底温度，可以制备出钴酸盐、镍酸盐和锰酸盐等过渡金属氧化物薄膜。本文研究了双交换铁磁体R_（0.6）S_（0.4）Mn_（0.3）薄膜的吸收光谱随温度的变化。我们已经发现，在可见光区的光激发强烈耦合与本地自旋排列在这些掺杂的锰酸盐。此外，我们还研究了飞秒脉冲激发引起的超快光谱变化。飞秒脉冲掺杂引起局部自旋取向的变化，并且在200 ps内形成顺磁畴，并且该畴在约100 ns内转换为铁磁畴。这是在强关联系统中首次观察到自旋的动力学行为和自旋的局域排列，并通过可见光的照射证明了自旋系统的可控性。这可能使我们将这些材料应用于具有光子模式的磁光器件。

We have investigated change in electronic states by photodoping with femtosecond pulses and relaxation dynamics of photoexcited states in 3d transition metal oxides in order to elucidate interactions with phonons and magnons and relaxation processes characteristic of magnetic phases.i) Relaxation dynamics of electronic states in CuO2 planes in cuprates. We have observed the photoinduced spectral change which is interpreted by the carrier doping effect by optical excitations. Optically induced in-gap states are relaxd in about 1 ps by emission of magnons, which indicates a crucial role of magnetic excitations in strongly correlated system.ii) Preparation of 3d transition metal oxides films. Using a laser ablation technique we have fabricated many kind of oxides films.Choosing an appropriate substrate temperature depending on materials we can fabricate transition metal oxides films such as cobaltates, nicklates and manganates.iii) Optical spectra and relaxation dynamics associated with magnetic transitions. Temperature dependence of absorption spectra for thin films of double-exchange ferromagnet R0.6S_r0.4Mn03 has been investigated with variation of the one-electron band width. We have found that optical excitations in the visible region strongly couples with the local spin alignments in these doped manganates. Furthermore, we have investigated ultrafast spectral change induced by femtosecond pulse excitations. The femtosecond pulse doping induces change in local spin alignments and the paramagnetic domain is formed in 200 ps and this domain is converted into the ferromagnetic domain in about 100 ns. This is the first observation of dynamical behaviors of spins and local spin alignments in strongly correlated systems and demonstrates the controllability of the spin systems by means of irradiation of visible light. This may lead us to apply these materials to magneto-optical devices with a photon-mode.