Abstract
Ab-initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant
inelastic x-ray scattering, showed an anomalous thermal softening of the M5- phonon mode in
B2-ordered FeTi that could not be explained by phonon-phonon interactions or electron-phonon
interactions calculated at low temperatures. A computational investigation showed that the Fermi
surface undergoes a novel thermally-driven electronic topological transition, in which new features
of the Fermi surface arise at elevated temperatures. The thermally-induced electronic topological
transition causes an increased electronic screening for the atom displacements in the M5- phonon
mode, and an adiabatic electron-phonon interaction with an unusual temperature dependence.
