Mode softening and phononic-crystal-like behavior of FeSe

We present a first-principles pseudopotential study on lattice dynamics of binary iron-based superconductor FeSe in both tetragonal nonmagnetic (NM) phase and orthorhombic striped antiferromagnetic (SAF) phase. It is found that significant softening of phonon modes induced by spin-phonon coupling in FeSe may increase the electron-phonon coupling strength. Moreover, we discover and report that an evident phononic-crystal-like behavior exists in FeSe, exhibiting absolute frequency gap in the range of 187 cm(-1) < omega < 210 cm(-1) in SAF phase, may manipulate and control phonon propagation, and have good application foreground. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626590]