STM studies of a Weyl semiconductor*

Topological phases of matter are at the frontier of scientific research and have a potential to become a building block of future electronic devices. Using scanning tunneling microscopy (STM) we probe a Weyl semiconductor material and reveal defect-free atomically flat surfaces with an energy gap of We observe that the atomic surfaces separated by a monolayer step edge exhibit a switch of the intensity of the tunneling spectrum below and above the Fermi level and develop a gap difference of  at 4.2 K, thus effectively realizing AB stacking sequence of atomic layers. Temperature dependent STM measurements on AB surfaces show spectroscopic contrast weakening and gap difference shrinkage with the increasing temperature. The results of our STM study indicate a surprising electronic AB stacking of layers, possibly linked to the presence of a phonon-induced instability in the material.