Quasi one-dimensional Ta₂Se₈I under pressure: From Weyl semimetal to superconductor

Structurally chiral Ta₂Se₈I shows a Fermi surface purely composed by the cones of Weyl nodes close to the chemical potential, resulting in quasi one-dimensional physics. Most intriguing is the formation of a charge-density wave that gaps the Fermi surface Weyl points just below room temperature. The phase mode of the charge-density wave realizes axion electrodynamics, together with excotic magnetoelectric responses. Here, we present a study on the electronic properties of Ta₂Se₈I under pressure. Increasing pressure lowers this charge-density wave transition temperature and eventually introduces superconductivity. We show how the Fermi surface evolves when compressing the unit cell, deviating from its originally quasi one-dimensional form. For larger pressures, coupling between the Ta-Se-chains increases, eventually leading to the break-down of the charge density wave transition. We present the ab initio electronic structure for unit cells compressed by external pressure, phonon instabilities and the implication for the electromagnetic response in equilibrium. Further, we find that signatures of the topological chiral anomaly appear in the non-linear optical response of the phase mode.