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

TL;DR

This study demonstrates that applying an external voltage to AlB2-type superconductors like MgB2 can significantly alter their electronic structure and transition temperature, with experimental and theoretical evidence showing a reduction in Tc.

Contribution

It introduces a novel method of controlling superconducting transition temperatures through external voltage, combining experimental measurements with density functional theory calculations.

Findings

Applied voltage causes band splitting similar to atomic displacement.

Tc decreases with increasing applied voltage.

Upper voltage limit prevents zero resistance state.

Abstract

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.