[Back]

M. Cordin, P. Amann, A. Menzel, E. Bertel, S. Diehl, J. Redinger, C. Franchini:
"Comment on "Cleavage surface of the BaFe_2-xCo_xAs₂ and Fe_ySe_1-xTex Superconductors: A combined STM plus LEED study"";
Physical Review B, 86 (2012), 1674011 - 1674015.

Massee et al. [ Phys. Rev. B 80 140507 (2009)] found on the cleavage planes of BaFe2−xCoxAs2 two different long-range ordered structures, i.e., a (2×1) phase present only after cleavage at low temperature and a √2×√2 phase observed after cleavage at room temperature. These results apply generally to 122 Fe-based superconductors, but have been discussed controversially [for a summary of the conflicting views, see Hoffman Rep. Prog. Phys. 74 124513 (2011)]. Here we support the interpretation of Massee et al. In addition, we argue that the existence of different long-range ordered structures corresponding to the same coverage in different temperature regimes is associated with the melting of a charge density wave and removal of an associated periodic lattice distortion (CDW/PLD) in the substrate as T is increased. At sufficiently low temperature the fluctuating CDW/PLD order parameter is stabilized by the adsorbate in a lock-in type mechanism. Accordingly, we interpret the surface structures observed on the 122 Fe pnictide surfaces as evidence for the presence of CDW fluctuations at low temperature, but with a wave vector differing from that of the antiferromagnetic spin-density fluctuations.