First-principles analysis of electron correlation, spin ordering and phonons in the normal state of FeSe1-x

Kumar, Anil and Kumar, Pradeep and Waghmare, Umesh V and Sood, AK (2010) First-principles analysis of electron correlation, spin ordering and phonons in the normal state of FeSe1-x. In: Journal of Physics: Condensed Matter, 22 (38).

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Abstract

We present first-principles density-functional-theory-based calculations to determine the effects of the strength of on-site electron correlation, magnetic ordering, pressure and Se vacancies on phonon frequencies and electronic structure of FeSe1-x. The theoretical equilibrium structure (lattice parameters) of FeSe depends sensitively on the value of the Hubbard parameter U of on-site correlation and magnetic ordering. Our results suggest that there is a competition between different antiferromagnetic states due to comparable magnetic exchange couplings between first- and second-neighbor Fe sites. As a result, a short range order of stripe antiferromagnetic type is shown to be relevant to the normal state of FeSe at low temperature. We show that there is a strong spin-phonon coupling in FeSe (comparable to its superconducting transition temperature) as reflected in large changes in the frequencies of certain phonons with different magnetic ordering, which is used to explain the observed hardening of a Raman-active phonon at temperatures (similar to 100 K) where magnetic ordering sets in. The symmetry of the stripe antiferromagnetic phase permits an induced stress with orthorhombic symmetry, leading to orthorhombic strain as a secondary order parameter at the temperature of magnetic ordering. The presence of Se vacancies in FeSe gives rise to a large peak in the density of states near the Fermi energy, which could enhance the superconducting transition temperature within the BCS-like picture.

Item Type:	Journal Article
Publication:	Journal of Physics: Condensed Matter
Publisher:	Institute of Physics
Additional Information:	Copyright of this article belongs to Institute of Physics.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	27 Sep 2010 11:18
Last Modified:	27 Sep 2010 11:18
URI:	http://eprints.iisc.ac.in/id/eprint/32469

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