Fermi surface is at the heart of our understanding of the properties of metals and strongly correlated many-body systems. An abrupt change in the Fermi surface topology, also called Lifshitz transition, can leads to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. While Lifshitz transitions have been demonstrated for a broad range of materials using equilibrium tuning of macroscopic
parameters like strain, doping, pressure, and temperature, a nonequilibrium route towardu ltrafast and transient switching of the Fermi surface topology has not been demonstrated yet. Using time-resolved multidimensional photoemission spectroscopy combined with TDDFT+U simulations, we demonstrate a scheme based on ultrafast laser-driven band renormalization that drives a Lifshitz transition in the topological type-II Weyl semimetal Td-MoTe2, due to transient modification of effective electron-electron interactions.

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