Physical Properties Of Low Dimensional Systems Based On Synchrotron Radiation Experiments

In this thesis, I have investigated the fundamental physical properties of several low dimensional systems by using inelastic x-ray sacattering (IXS) and angle resovled photoemission spectroscopy (ARPES) techniques. According to the dimensionality, I will first introduce the works about the small organic molecular system which can be considerd as zero dimensional system, and then I will talk about one dimensional system-inorganic chain SrCuO and orgnic chain TTF-TCNQ. In the end, I will introduce my work about the 2D cuprate superconductor Bi2201 system.We pioneered the study of exciton behavior in organic molecular systems with IXS. Combined with quantum chemical calculations based on ZINDO /SCI, which produce theoretical spetra in good agreement with experiments, we found that the lowest Frenkel exciton in a small molecule can be confined to only a fraction of the molecule, instead of extending over the entire molecule. The dispersion of this exciton is about 130 meV. Moreover, we present a clear experimental counterexample to prove that the momentum structure of the dynamic structure factor is NOT straightforwardly associated with the size of the exciton, providing strong experimental evidence for a critical theoretical claim.For the study of the quasi 1D Mott insulator SrCuO, unlike previous studies, we performed the resonant inelastic x-ray scattering (RIXS) experiments at the Cu 1s to 3d edge, obtaining more direct information on the electronic excitations involving the Cu 3d orbitals. The energy loss spectra indicate that the lowest peak is around 2．0 eV, which is 0．6 eV smaller than the lowest energy peak obtained at the 1s to 4p edge. The feature exhibits a total dispersion of about 0．2 eV with a periodicity ofπ. Comparison of the data with optical results supports the interpretation of the data as being from dd excitation.In the ARPES study of another one dimensional system-organic conductor TTF-TCNQ. I observed some anomalous phenomena. For example, there is a very deep pseudogap about 100meV and very broad "quasiparticle" peak in the spectra. Moreover, in such a 1D system, the temperature and energy dependence of the electron scattering rate exhibits Fermi liquid like behavior, in consistence with the resistivity measurements. These raised serious questions on the microscopic properties of such a system with both strong electron-electron interaction and electron-phonon interaction.Previous experimental studies on cuprate superconcutor have been mostly focusing on the anomalous, and certainly interesting, underdoped regime. On the other hand, although to be validated by experiments, the overdoped half of the phase diagram, particularly the heavily overdoped regime, is considered to be a "normal" metal regime where correlations are negligible. The electronic structure in this regime was seldom studied. To build a comprehensive picture of high temperature superconductivity, it is crucial to study the properties of the entire overdoped regime, particularly the heavily overdoped regime. We explore the electronic structure in the heavily overdoped regime of the single-layer cuprate superconductor BiPbSrCuO. We found that the nodal quasiparticle behavior is dominated mostly by phonons, while the antinodal quasiparticle line shape is dominated by spin fluctuations. Moreover, while long range spin fluctuations diminish at very high doping, the local magnetic fluctuations still dominate the quasiparticle dispersion, and the system exhibits a strange metal behavior in the entire overdoped regime.Our results indicate that there are plenty of interesting physical phenomena and unresolved problems in the low dimensional systems. By utilizing the powerful tools based on synchrotron radiation, we can understand the complications in the low dimensional system better. Moreover, it is often that we always can find new and more fundamental problems when we resolve old questions.