Electronic switching of topology in LaSbTe

In the past two decades, various classes of topological materials have been discovered, yet the deliberate control of topology in a single material remains largely unexplored. Here we demonstrate full experimental control over the topological nodal loop in the square-net material LaSb_xTe_2-x by chemical substitution and electron doping. Using angle-resolved photoemission spectroscopy, we show that changing the antimony concentration x from 0.86 to 1.0 in the bulk opens a gap larger than 400 meV in the nodal loop. Symmetry analysis establishes that this effect originates from the breaking of n glide symmetry in the square-net layer. The same topological phase transition can also be driven reversibly on the surface of LaSb_xTe_2-x by in situ chemical gating via potassium deposition, enabling on-demand switching of topology. The control parameter for both the bulk and surface transition is the electron concentration, providing a pathway towards applications based on switching topology by electrostatic gating.