  Scanning tunnelling microscopy and low energy electron diffraction show a
dimerization-like reconstruction in the one-dimensional atomic chains on
Bi(114) at low temperatures. While one-dimensional systems are generally
unstable against such a distortion, its observation is not expected for this
particular surface, since there are several factors that should prevent it: One
is the particular spin texture of the Fermi surface, which resembles a
one-dimensional topological state, and spin protection should hence prevent the
formation of the reconstruction. The second is the very short nesting vector $2
k_F$, which is inconsistent with the observed lattice distortion. A
nesting-driven mechanism of the reconstruction is indeed excluded by the
absence of any changes in the electronic structure near the Fermi surface, as
observed by angle-resolved photoemission spectroscopy. However, distinct
changes in the electronic structure at higher binding energies are found to
accompany the structural phase transition. This, as well as the observed short
correlation length of the pairing distortion, suggest that the transition is of
the strong coupling type and driven by phonon entropy rather than electronic
entropy.
