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

为了阐明与声子和磁振子的相互作用以及磁相的弛豫过程特征，我们研究了飞秒脉冲光掺杂在三维过渡金属氧化物中的电子态变化和光激发态的弛豫动力学。i)铜酸盐中CuO2平面中电子态的弛豫动力学。我们观察到光致光谱变化，这种变化可以用光激发的载流子掺杂效应来解释。通过发射磁振子，光诱导隙内态弛豫约1ps，这表明磁激励在强相关体系中起着至关重要的作用。ii)三维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。选择合适的衬底温度取决于材料，我们可以制造过渡金属氧化物薄膜，如钴酸盐，镍酸盐和锰酸盐。iii)与磁跃迁相关的光谱和弛豫动力学。研究了双交换铁磁体R0.6S_r0.4Mn03薄膜吸收光谱随单电子带宽度变化的温度依赖性。我们发现在这些掺杂的锰酸盐中，可见光区的光激发与局部自旋排列强烈耦合。此外，我们还研究了飞秒脉冲激发引起的超快光谱变化。飞秒脉冲掺杂导致局部自旋排列发生变化，在200 ps内形成顺磁畴，在100 ns左右转变为铁磁畴。这是第一次观察到强相关系统中自旋和局部自旋排列的动力学行为，并通过可见光照射证明了自旋系统的可控性。这可能导致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.