  Topological phase transitions are typically associated with the formation of
gapless states. Spontaneous symmetry breaking can lead to a gap opening thereby
obliterating the topological nature of the system. Here we highlight a
completely different destiny for a topological transition in presence of
interaction. Solving a Bernevig-Hughes-Zhang model with local interaction, we
show that dynamical quantum fluctuations can lead to the opening of a gap
without any symmetry breaking. As we vary the interaction and the bare mass of
the model, the continuous gapless topological transition turns into a
first-order one, associated with the presence of massive Dirac fermion at the
transition point showing a Gross-Neveu critical behaviour near the quantum
critical endpoint. We identify the gap opening as a condensed matter analog of
the Coleman-Weinberg mechanism of mass generation.
