Scanning Tunneling Microscopy Study Of The Charge Ordering In One Dimensional System And Pnictide Superconductors

Recently, the one-dimensional nanomaterials and the strongly correlated materials have attracted intensive attentions in condensed matter physics. Comparing to the ground state of the traditional Fermi liquid, the physical properties are quite unique because of the enhanced interaction between electron, spin, and lattice in these materials. Charge ordering is one of the interesting physical phenomena. The charge density wave in one dimensional system and the charge ordering are closely related to each other.However, there have been few researches on the charge ordering, especially in micro scale. In this thesis, scanning tunneling microscope with extremely high resolution is used to study the charge ordering in one-dimensional chain and the strongly correlated iron-based superconductors. Studying the charge ordering in micro scale is useful in deeper understanding the properties and function of charge ordering in these systems.After introduction of the basic principle of the scanning tunneling microscope (STM), we briefly describe the physical properties of one-dimensional system and some high-temperature superconducting materials as well as some studies carried out on these systems using STM.In the next part, through the STM and the first-principles theoretical studies, because the soliton, we characterize the precise atomic structure of topological soliton which is one of the important elementary excitations of the1D CDWs in Indium chains. Variable-temperature measurements of the soliton population allow us to determine the soliton formation energy and activation energy. We demonstrate the local electric field enhances the soliton dynamics. The last part is the interaction between two solitons.We describe the charge inhomogeneity on Si (111)-(8×2)-In surface and find out that this is mainly caused by the defects on the surface. Further researches show that the electric field on tip has an effect on some unusual reconstructed area. And the electric field can be controlled by current and voltage between the tip and sample to tune the charger ordering area.Self-assembly of quasi-one dimensional pentacene molecular chains are realized on Si(111) surface using the atomic chain structures of the well-defined Si(111)-(4×1)-In surface reconstruction as templates. The positive results suggest that this approach might be applied to grow organic hetero-nanostructures on decorated semiconductor surfaces.The structure and electronic property at the cleaved (001) surfaces of the newly discovered pnictide super-conductors BaFe2-xCoxAs2with x ranging from0to0.32are systematically investigated by scanning tunneling microscopy. A (?)×(?) surface structure is revealed for all the compounds. And it is identified to be Ba layer with half Ba atoms lifted off by combination. We prove this by theoretical simulation. Charge inhomogeneity is observed at this (?)×(?) surface associated with an energy gap of about30meV for all the compounds. Another1×1reconstruction is also reported in this part.