First principles correspondence of a second type of phonon anomaly along [211] to the Fermi nesting features and associated electron-phonon interactions in Ni$_2$FeGa

Abstract

First principles calculation supports the occurence of a phonon anomaly along [211] in Ni$_2$FeGa that was observed experimentally for the first time as structural modulations along [211] direction. Fermi surface scans have been performed in both austenite and martensite phase to observe the possible Fermi nesting features in the system. The magnitude of observed Fermi surface nesting vectors in (211) plane exactly match the phonon anomaly wavevectors along [211] direction. Electron-phonon calculations in the austenite phase shows that there is significant electron-phonon coupling in the system which may arise out of the lattice coupling between lower acoustic phonon modes and higher optical phonon modes and also because of strong Fermi surface nesting features observed in the system.