The topology of a topological material can be encoded in its surface states.These surface states can only be removed by a bulk topological quantum phasetransition into a trivial phase. Here we use photoemission spectroscopy toimage the formation of protected surface states in a topological insulator aswe chemically tune the system through a topological transition. Surprisingly,we discover an exotic spin-momentum locked, gapped surface state in the trivialphase that shares many important properties with the actual topological surfacestate in anticipation of the change of topology. Using a spin-resolvedmeasurement, we show that apart from a surface band-gap these states developspin textures similar to the topological surface states well-before thetransition. Our results offer a general paradigm for understanding how surfacestates in topological phases arise and are suggestive for future realizing Weylarcs, condensed matter supersymmetry and other fascinating phenomena in thevicinity of topological quantum criticality.
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