Structural, electronic, and dynamical properties of the tetragonal and collapsed tetragonal phases of KFe2As2

Compounds with a tetragonal ThCr2Si2-type structure are characterized by the possibility of the isostructural phase transition from the tetragonal phase to the collapsed tetragonal phase induced by the external pressure. An example of a compound with such a phase transition is KFe2As2, which belongs...

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Bibliographic Details
Published in:Physical review. B 2019-04, Vol.99 (13), p.134103
Main Authors: Ptok, Andrzej, Sternik, Małgorzata, Kapcia, Konrad Jerzy, Piekarz, Przemysław
Format: Article
Language:English
Subjects:
Cooper pairs
External pressure
Fermi surfaces
Iron
Lattice parameters
Lattice vibration
Orbitals
Phase transitions
Phonons
Pressure dependence
Properties (attributes)
Qualitative analysis
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Summary:Compounds with a tetragonal ThCr2Si2-type structure are characterized by the possibility of the isostructural phase transition from the tetragonal phase to the collapsed tetragonal phase induced by the external pressure. An example of a compound with such a phase transition is KFe2As2, which belongs to the family of the iron-based superconductors. In this paper, we investigate the effects of the phase transition on the structural, electronic, and dynamical properties of this compound. Performing the ab initio calculations, we reproduce the dependence of the lattice constants on pressure and analyze the changes of the interatomic distances in the tetragonal and collapsed tetragonal phases. Using the tight binding model with maximally localized Wannier orbitals, we calculate and discuss the influence of pressure on the electronic band structure as well as on the shape of the Fermi surface. We found a precursor of the phase transition in the form of enhancement of overlapping between two Wannier orbitals of As atoms. In order to better understand the superconducting properties of KFe2As2, we study the orbital-projected Cooper pairs susceptibility as a function of pressure. We found a decrease of susceptibility with the increasing pressure in a good qualitative agreement with experimental observation. The structural transition also influences the phonon spectrum of KFe2As2, which exhibits pronounced changes induced by pressure. Some phonon modes related with the vibrations of Fe and As atoms show an anomalous, nonmonotonic dependence on pressure close to the phase transition.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.99.134103