Gavin Lucsik

Major: Physics & Mathematics

Mentors: Jack Tregidga, John Harter

Topological Phase Transitions in Ferroelectric-Like Superconductor SrAuBi 

The ternary half-Heusler compound, CaAuBi, when transformed to the LiGaGe-type crystal structure under pressure has been proposed to host both Dirac and Weyl points in momentum space. In a homologous compound, SrAuBi, surface superconductivity has been demonstrated yet it's topological properties are not well understood. Here we investigate alloying between these neighboring compounds to classify the topological phase of the superconducting ferroelectric, SrAuBi, and map its topological phase transition boundaries as a function of the doping parameter, x, in the alloy Sr_(1-x)Ca_(x)AuBi. We find a gapless Dirac & Weyl semimetal state for several compositions that correlate to topologically distinct phases. We formalize our first-principles calculations using a kp theory approach to derive a low-energy effective Hamiltonian describing the Dirac semimetal state in SrAuBi.