A New Kind Of Topological Insulator-the Study Of Two Dimensional Pb Material Via First Principle Calculation

As a new state of materials, topological insulators (TIs) have attracted a lot of attention in both condense matter physics and material science. This kind of material has an insulating bulk phase just like ordinary insulators, but on the edge/surface, there exist gapless edge/surface states and they are protected by time-reversal symmetry and immune to scattering by nonmagnetic impurities or crystal defects. It is this kind of wonderful feature that make TI a promising candidate for realizing spintronics and low-dissipation devices. However, TIs fabricated by experiments or predicted by theoretical calculation show little bulk gap and their edge/surface states can only be observed in a ultra-low temperature which limits TIs’realization and application. Thus, take advantage of material calculation in material design and properties research to find a type of huge gap TI is of important significance. The contents of this thesis are shown blow:In the first chapter, the concept of TIs was presented, including the research course from Hall effect to Quantum spin hall effect and the underlying theoretical foundation.In the second chapter, the background information on first-principle calculation method based on density function theory was introduced. Including kinds of exchange-correlation functional (local density approximation (LDA), generalized gradient approximation (GGA) and hybrid functional, e.g.) and some mostly common first-principle codes.In the third chapter, I studied the system of pristine 2D Pb and Pb layer decorated by chemical functional groups. The optimum geometry structure of Pb layer was obtained through relationships between their total energy and lattice constants, and then their band structures with and without SOC were calculated and analyzed.In the fourth chapter, I took Pb-H as an example to study the influence of strain on Pb system’s electronic properties. After that, I provided the band structure of Pb honeycomb layer’s nanoribbon. At last, a suitable substrate to stabilize the Pb layer was found and its band structure was also calculated.In the fifth chapter, projects above were summarized and prospect about the future research work was carried out.