Ab initio prediction of pressure-induced structural phase transition of superconducting FeSe

Gul Rahman 

Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan

In Gee Kim 

Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea E-mail: igkim@postech.ac.kr

Arthur J. Freeman 

Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, U. S. A.

Abstract:

External pressure driven phase transitions of FeSe are predicted using ab initio calculations. The calculations reveal that α-FeSe takes transitions to NiAs-type, MnP-type, and CsCl-type FeSe. Transitions from NiAs-type to MnP-type and CsCl-type FeSe is also predicted. MnP-type FeSe is also found to be able to transform to CsCl-type FeSe, which is easier from α-FeSe than the transition to MnP-type FeSe, but comparable to the transition from NiAstype FeSe. The calculated electronic structures show that all phases of FeSe are metallic, but the ionic interaction between Fe-Se bonds becomes stronger and the covalent interaction becomes weaker when the structural phase transition occurs from α-FeSe to the other phases of FeSe. The experimentally observed decrease in Tc of superconducting α-FeSe at high pressure may be due to a structural/magnetic instability, which exists at high pressure. The results suggest us to increase the Tc of α-FeSe if such phase transitions are frustrated by suitable methods.

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https://arxiv.org/pdf/1201.5639.pdf