Thermally Driven Electronic Topological Transition in FeTi

Area of Science:

• Condensed matter physics
• Materials science
• Computational physics

Background:

• Phonon behavior in B2-ordered FeTi exhibits anomalous thermal softening of the M_{5}^{-} mode.
• Existing models of phonon-phonon and electron-phonon interactions at low temperatures fail to explain this phenomenon.

Purpose of the Study:

• To investigate the underlying mechanism responsible for the anomalous thermal softening of the M_{5}^{-} phonon mode in B2-ordered FeTi.
• To elucidate the role of electronic structure and temperature-dependent effects.

Main Methods:

• Ab initio molecular dynamics simulations.
• Inelastic neutron scattering (INS).
• Nuclear resonant inelastic X-ray scattering (NRIXS).
• Computational investigation of the Fermi surface and electronic topological transitions.

Main Results:

• Observed anomalous thermal softening of the M_{5}^{-} phonon mode in B2-ordered FeTi.
• Identified a novel thermally driven electronic topological transition (ETT) in the Fermi surface at elevated temperatures.
• Demonstrated that the ETT leads to increased electronic screening and an unusual temperature dependence of the adiabatic electron-phonon interaction.

Conclusions:

• The anomalous thermal softening is attributed to a temperature-induced electronic topological transition.
• The findings reveal a new mechanism linking electronic structure evolution with lattice dynamics.
• This study provides a deeper understanding of thermal properties in intermetallic compounds like FeTi.