Thermally induced electronic topological transition in FeTi

Figure: Experimental FeTi phonon DOS curves. The neutron weighted DOS curves were obtained from inelastic neutron scattering measurements and the Fe partial DOS curves from nuclear resonant inelastic x-ray scattering measurements at HPCAT. Error bars are from counting statistics.
Figure: Experimental FeTi phonon DOS curves. The neutron weighted DOS curves were obtained from inelastic neutron scattering measurements and the Fe partial DOS curves from nuclear resonant inelastic x-ray scattering measurements at HPCAT. Error bars are from counting statistics.

Electronic topological transition (ETT), where new features occur in the topology of the Fermi surface, has strong influences on structural, mechanical, and electronic properties of materials. Recent nuclear resonant inelastic x-ray scattering experiments at HPCAT strongly support a thermally driven ETT that drives anomalous changes in phonon dynamics. The thermally induced ETT in FeTi 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. This behavior is consistent with the atomic displacement pattern, in which (110) planes slide in opposite [110] directions. From the phonon polarization vectors, it is found that the magnitude of the Fe displacement is at least twice as that of Ti. [F. C. yang et al, Phys. Rev. Lett., 117, 076402, (2016)]