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

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.

To download the article click on the link below:

http://arxiv.org/pdf/1201.5639.pdf

To download the Presentation click on the link below:

http://www.ncp.edu.pk/docs/iss/talks/Group_II/G2_D4_Dr_Gul_Rahman.pdf

2. Computation Models and Methods 

To search for the structural phase transition of FeSe, we considered different types of crystal structures, i.e., anti-PbO—commonly known as α-FeSe, as well as NiAs-, MnP-, CsCl-, and CuAu-type FeSe (see Fig. 1). These structures are related with each other, e.g., MnP-type FeSe can be considered as a deformed NiAs-type FeSe, changing the local hexagonal symmetry around the Fe atoms in the NiAs-type phase to tetrahedral results in the α-FeSe phase. The detailed structure relationship will be discussed in Sec. 3. 

.........