Acoustic phonon instabilities in Fe_1.06Te studied by inelastic neutron scattering

The advent of superconductivity in iron pnictides and the iron chalcogenides family of compounds has triggered an active stream of novel 2D materials [1]. Specifically, this field intends to investigate the high Tc superconductors by tuning parameters such as chemical doping or external pressure [2,3]. The uniqueness of Fe-based superconductors lies in the layered crystal structure where magnetic iron ions reside in a tetrahedral coordination at room temperature. Here, we present inelastic neutron scattering results of Fe_1+xTe which is isostructural to Fe (Se,Te) family of superconducting compounds. Fe_1+xTe is composed of edge-sharing FeTe₄ tetrahedra held by weak van der Waals interactions and the concentration of interstitial Fe²⁺ ion plays a crucial role in tuning the magnetic properties [2]. Below the Neel temperature of 75 K, it undergoes a structural phase transition from tetragonal (P4/nmm) to monoclinic (P2₁/m) symmetry [3]. We examine the acoustic phonon instabilities associated with this transition and compare with the results of pnictide materials.

[1] V. Gnezdilov et al., PRB 83, 245127 (2011) [2] C. Stock et al., PRB 84, 045124 (2011) [3] E.E. Rodriguez et al., PRB 84, 064403 (2011).