Visualizing phase transitions in Weyl semimetal materials

Weyl semimetals are characterized by pairs of bulk Weyl nodes of opposite chirality, whose surface projections are connected by Fermi arcs. Many of these materials exhibit a high degree of tunability, which opens the possibility for driving topological phase transitions through various modalities. I will present our angle-resolved photoemission spectroscopy (ARPES) studies on two classes of Weyl semimetals, which demonstrate sometimes unexpected changes in band structure that occur when driving topologically relevant phase transitions. The first, WTe₂, is a 2D material where a structural (and topological) phase transition can be driven by shear displacements of adjacent layers, and we show how this shear displacement can be driven by electron doping and visualized via changing surface states. I will also discuss our work on Co₃Sn₂S₂, a magnetic Weyl semimetal, where ferromagnetism and electronic correlations conspire to produce a rich phase diagram.