Triple point fermions in ferroelectric GeTe

TL;DR

This paper reports the discovery of triple-point and type-II Weyl fermions in ferroelectric GeTe, revealing complex topological electronic structures and spin textures with potential for novel condensed matter phenomena.

Contribution

It demonstrates the existence of multiple non-trivial topological fermions in ferroelectric GeTe using combined experimental and theoretical methods.

Findings

Identification of triple-point and type-II Weyl fermions in GeTe

Observation of unique spin textures around triple points

Spin winding numbers linked to symmetry properties

Abstract

Ferroelectric GeTe is unveiled to exhibit an intriguing multiple non-trivial topology of the electronic band structure due to the existence of triple-point and type-II Weyl fermions, which goes well beyond the giant Rashba spin splitting controlled by external fields as previously reported. Using spin- and angle-resolved photoemission spectroscopy combined with ab initio density functional theory, the unique spin texture around the triple point caused by the crossing of one spin degenerate and two spin-split bands along the ferroelectric crystal axis is derived. This consistently reveals spin winding numbers that are coupled with time reversal symmetry and Lorentz invariance, which are found to be equal for both triple-point pairs in the Brillouin zone. The rich manifold of effects opens up promising perspectives for studying non-trivial phenomena and multi-component fermions in condensed matter systems.