Theoretical Research On Doping Effect Of Superconducting Magnesium Diboride

In chapter one,first,the history of superconductivity and its research progress are summarized,and some basic knowledge and notions on it are introduced also.Second, the crystal structure and electronic structure of magnesium diboride are shown, respectively.Last,why dopping of superconducting state of magnesium diboride can be my research point is answered.In chapter two,based on two-band model,the modulated potential function F is introduced according to BCS theory phenomenologically.The superconductivity transition temperature of superconductor Mg_1-xR_xB₂ and MgR_xB_2-xhave been studied by using the consistent method.The results of the calculations are in agreement with Refe.A maximum of the superconductivity critical temperature Tc is found at F=0.2,which is related to the doping elements,ratio of doping mass and the doping uniformity.These results provide a referable researching direction for us.In chapter three,the electronic structures and the DOS have been studied for doping superconductivity Mg_1-xR_xB₂.We use the unrestricted Hartree-Fock approximation to treat the correlation effect of the multiband Hubbard model and the real-space recursion method to calculate the density of states.Our study shows that the superconductivity transition temperature Tc can be improved a bit by doped D¹ electrons at concentration C＜0.11,and the density of fermi energy appeares a singularity at the dopping concentration C=0.11.After that,the density of fermi energy decreases with the dopping concentration C increasing.From the DOS comparison of these states,we conside it is because the electrons be located the states beneath the fermi energy.At the end of this thesis,the experiment of doping magnesium diboride is introduced.We don't get high and good superconductive material.It is showing that our experimental instruments which are relating to the researching of superconductivity must be improved in future.Meanwhile,our co-worker's recent experimental research result on the doping effect of magnesium diboride is given out in a brief way.