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$_x$Te$_{2-x}$ by chemical substitution and electron doping. Using angle-resolved photoemission spectroscopy (ARPES), we show that changing the antimony concentration x from 0.9 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 \textit{n} glide symmetry in the square-net layer. Remarkably, the same topological phase transition can also be driven reversibly on the surface of LaSb$_x$Te$_{2-x}$ by \textit{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.