Experimental control of Tc in AlB2-type compounds using an applied voltage

We utilize the van de Pauw technique combined with Density Functional Theory to show that an external voltage applied to superconducting AlB2-type compounds, such as MgB2 and Mg(B1.9C0.1), effects substantive changes in transition temperature due to modification of electronic band structure. An applied voltage results in a symmetric split of degenerate sigma bands in MgB2 similar to that calculated for atom displacement along the B-B bond aligned with E2g phonon mode directions. For AlB2, similar splitting of sigma bands occurs albeit with higher voltage requirement compared to MgB2. Experimental data show that Tc values for MgB2 and Mg(B1.9C0.1) reduce consistently with increased increments of applied voltage. Zero resistance is limited by an upper applied voltage depending on the compound.