Ferroelectric Topological Matter for Manipulation of Weyl Fermions – FERROTOP

This project aims to bring together ferroelectricity and topology to create a new class of material named Ferroelectric Topological Insulators (FerroTis). They will be launched and developped using the narrow gap IV-VI semiconductors and employed for the manipulation of Weyl fermions.

The IV-VI materials will be grown by molecular beam epitaxy and their complex electronic structure revealed by angle-resolved photoemission spectroscopy, magnetooptics and quantum transport. Beside the usual IV-VI alloys, the novel quaternary system (Pb,Ge,Sn)Se will be developped as one promising FerroTi.

Weyl physics appears when fermions are massless with a well-definite chirality. Interestingly, this relativistic behavior emerges in topological matter when the inversion symmetry is broken by ferroelectricity. In the usual topological IV-VI systems, the gap closes at well defined values of internal or external tuning parameters (alloy composition, temperature, strain...) and then reopens with band symmetry inversion. We will demonstrate that in the FerroTis, this picture is radically different since a metallic phase protected by Weyl nodes persists over a large interval of the tuning parameters. We will study how Weyl-semimetal phase appears in FerroTis under the ferroelectric distortion.

Our project will open exciting perspectives for fundamental physics (chiral anomaly, Fermi arcs, axion...) and paves the way for novel devices in non-dissipative electronics and in spintronics (efficient spin-to-charge current conversion). It is also timely for the realisation of the proposed "chiral qubit" for quantum computing.