Reduction of superconducting transition temperature and flux pinning in and C codoped MgB_2 with insight from first-principles calculations

摘要

We report for the first time the Al and C codoping effect on the structures and superconductivity in MgB_2. It was found that both the lattice parameters and the T_c decreased monotonically with increasing doping level of both Al and C. The T_c dropped to 27.5 and 7 K for x=0.2 and for x =0.4, respectively. The reduction of T_c for the codoping was found to be quicker than for individual Al doping and slower than for individual C doping at the same doping levels. First-principles calculations indicated that the observed decrease in T_c for the codoped MgB_2 can be understood in terms of a band filling effect due to the electron doping by both Al and C. However, it is suggested that other factors may also play a role in the T_c reduction in the real Mg_(1-x)Al_xB_(2-x)C_x. samples. Furthermore, the Al and C codoping also reduces J_c and weakens flux pinning in MgB_2.