Researches On The Spin-orbit Coupling Effect And De Hass-van Alphen Effect Of Noncentrosymmetric Superconductors

The topical of superconductor has been a significant subject in condensed matter physics since its discovery decades ago. The scientists classified the materials according to their phase transition types, superconductive temperatures, magnetic properties and interaction strength in order to study the theories systematically. A new heavy-fermion superconductor CePt3Si was discovered in 2004 whose crystalline structure doesn't contain a space-reversal-invariant center. By the intensive study of it,more unusual physical properties related to its special structure have been exhibited .Many traditional superconductors were restudied and novel ones are being researched in this new aspect. Various theorems are proposed based on the experimental reports on specific heat, phase transition, etc. The density-functional theory has always been an useful method in calculations of electronic structures. The ab-initio calculation process can describe the particular interaction called "antisymmetric spin-orbital coupling" effect which is different from the term in normal Hamiltonian. The main contents and conclusions of this thesis are as follows:1. We calculate the electronic structure and optical properties of newly discovered superconductor CaIr2 based on full-potential local orbital and linear augmented plane waves methods. The densities of states (DOS) near Fermi level are contributed by d-electrons of Ir. The number of Fermi surfaces is four including two hole-pockets and two electron-pockets without including SOC which jump to fourteen in the situation of spin-polarization. The SOC effect changes the energy levels and adds another three pairs of Fermi surfaces in this system, causing a topological transition of Fermi surfaces (TTFS). In this thesis I have preformed a series of de Haas-van Alphen(dHvA) effect simulations on the calculated band structures as guidance for the research on the following materials. The optical properties data shows that the intra-band light absorption turns inter-band type when the energy of incident light reaches 1.45eV.2. The same properties of noncentrosymmetric superconductor (NCS) Re6Hf have been calculated as well. The d-d interaction dominates near Fermi level according to the results of bands and DOS. The electronic structures affected by ASOC indicate that even the magnetic moment of system yields zero, the polarization DOS are asymmetric. The number of Fermi surfaces is five without ASOC which increases to 8 after considering of it, suggesting the ASOC effect only splits two surfaces instead of lifting or declining the bands near Fermi level. The energy splitting due to ASOC has been estimated to be 34 meV and 44 meV,respectively. The plasma frequency is 1.84 eV and the optical absorption transition point locates near 1.4 eV.3. At last the electronic structures of NCS LaNiC2 considered as a two-gap superconductor has been calculated and discussed. The splitting in two bands crossing Fermi level turn out to be 62.9 meV and 27. 5meV. By Introducing the difference of polarization DOS like that in Re6Hf, we find some regular transitions between them following the increase of energy. There exist two Fermi surfaces without ASOC and the second one is particularly small. They turns only four after adding the ASOC effect. Two reasons may be responsible to it: Firstly the relatively simple crystalline structure makes the DOS locate in clearly discrete energy ranges. New surfaces wouldn't appear even the bands were lifted. Secondly the weight of heavy atoms is not high, resulting in a comparatively weak interaction which may not change the bands to a great extend. We also make the dHvA simulation on it and get some interesting results.