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The electronic structure of transition metal compounds research and modulation

Author: ZhaoJiaFeng
Tutor: FengDongLai
School: Fudan University
Course: Condensed Matter Physics
Keywords: Transition metal compound ARPES Molecular beam epitaxy Electronic structure
CLC: O561
Type: PhD thesis
Year: 2009
Downloads: 231
Quote: 2
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Abstract


Transition metals include 3B to 12B from the periodic table group 10, this type of feature is the common element is not filled d orbitals, thus forming compounds exhibit significantly different from the other elements in the optical, electrical, magnetic performance of many other aspects of the nature of novelty. And these strange properties on temperature, doping, pressure and other adjustable parameters are very sensitive to the formation of many colorful phase diagram: for example transition metal disulfide compounds in a typical charge density wave and superconductivity coexist behavior; manganese oxide compounds of the metal. insulator phase diagram in disguise;, and new iron-based superconductors spin density wave and superconductivity coexist phase diagram. The phase diagram is behind a wealth of physical information and may have broad practical prospects, thus becoming the current condensed matter physics research focus. However, the singular characteristic d-electron band theory of the traditional transition metal compounds in the study had already lapsed, experimental measurements become understood that all these bizarre nature of the most direct and effective means of experimental methods for such systems such as scanning tunneling microscope ( STM) and angle-resolved photoemission spectroscopy (ARPES), etc. In the last decade been a huge development. Modern technology has ARPES measurements are not limited to the band gap of the solid, through the data for further analysis, we can simultaneously obtain the energy of valence electrons in a solid, moving direction and scattering properties, and thus within the solid band , rail, etc. gives a comprehensive understanding. The first half of this paper introduces the use of optical spectroscopy Tsz classic transition metal disulfide compound 1T-Cu x TiSe 2 and the new iron-based superconductor BaFe < sub> 2-x Co x As 2 measurements and results are as follows: 1, for a wide range controversial 1T-TiSe 2 < / sub> of 2 × 2 × 2 charge density wave mechanism gives a reasonable explanation and a reasonable understanding of the phase diagram of the doped samples: the use of angle-resolved photoemission spectroscopy on the electronic structure of such samples doped with a systematic study of changes; observed chemical potential uplift in line with the doping just band model, while the valence charge density wave caused by doping with folded significant repression. Through the Fermi energy at the Ti 3d energy band spectrum analysis weights 3d band has been intercalated copper atoms from the filling, which provides for the production of superconducting necessary conditions. Comprehensive our analysis, we propose 1T-TiSe2 behavior of the charge density wave originated in electron - hole interaction between band and the valence band by influencing the energy saving system. With doping to enhance the chemical potential, one charge - hole interaction is significantly weakened, suppressed charge density wave: Fermi surface density of states on the other hand be increased, resulting in superconductivity. Our experiments using the doped samples, the source of controversy for the past, the band and the density of states from two angles make a reasonable explanation to solve a long-standing debate. 2, of a new type of superconductor BaFe2-xCoxAs2, obtained for the sample and the energy band structure changes with doping, observed electron doping and doping to M different points of Γ. For the above sample of one hand we marvel photoelectron spectroscopy powerful means of this experiment, it also let us lament because of its surface-sensitive, current areas of research can also be limited to the cleavage of bulk samples. Interestingly, many of the same samples such as La1-xSrxMnO3 other, unable to cleave only to give up. In order to expand our field of research but also for the further promotion of photoelectron spectroscopy for the following attempts: 1, oxide molecular beam epitaxy and angle-resolved photoelectron spectroscopy combined with organic, independent design with the photoelectron spectrometer design and construction work. Completed a chilled and dry evaporation source design and production: design and finished ozone purification system. Currently located at Fudan University oxide molecular beam epitaxy system structures has entered the end, in the commissioning phase. 2, funded by the ICTP in Italy during the exchange. LSMO system involved in the molecular beam epitaxial growth, La 1-x Sr x MnO 3 As Its unique magnetic and electrical properties, is the next generation magnetic storage materials popular candidate. With the MBE method, we can grow PLD than the conventional means such as a single crystal of higher quality, and thanks to the Layer by layer growth pattern, we can make the interface of the top manual optimization of its Curie temperature impact greatly exceeded our expectations.

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