Anomalous effect of Li-Al codoping in MgB2: A simple explanation

By means of first-principles calculations we investigate the possibility that coincorporation of Li and Al in MgB2 could result in an effective "isoelectronic" doping, such as to introduce chemical and structural disorder while leaving unchanged the occupation of the sigma and pi bands. Our results show that the effect on electronic structure of codoping in MgB2 is far from trivial, and shed light on the experimental findings indicating a scarce contribution of Li to the superconducting properties of Mg1-x(AlLi)(x)B-2. The latter result has often been unnecessarily interpreted in terms of the experimental difficulty of actually incorporating Li into the samples.