Transport properties of MgB2 single crystals doped with electrons and holes Original Research Article

The thermoelectric power of C, Mn, C:Li, and Al:Li substituted MgB2 single crystals has been investigated in the temperature range 10–300 K. Both the in-plane (Sab) and the out-of-plane (Sc) thermopowers are positive for the non-substituted crystal and both Sab and Sc change a sign for crystals doped with electrons where C is substituted for B in the amount larger than 5 at%. When Li is substituted for Mg, the π band rather than the σ band is doped with holes and the doping effects are much more subtle. The anisotropy ratio of the non-substituted crystal Sab/Sc≈3 and this ratio is strongly reduced by the substitution of C. Isovalent magnetic Mn ions, which substitute for Mg with a drastic reduction of Tc, do not influence the values and temperature dependences of both Sab and Sc.