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Superconductivity at 52 K in hydrogen-substituted LaFeAsO(1-x)Hx under high pressure.

Takahashi H, Soeda H, Nukii M, Kawashima C, Nakanishi T, Iimura S, Muraba Y, Matsuishi S, Hosono H - Sci Rep (2015)

Bottom Line: Tc rises to 52 K at 6 GPa for the Tc-valley composition between the two Tc domes.On the other hand, the Tc of SmFeAsO1-x)Hx decreased continually, keeping its single-dome structure up to 15 GPa.The present findings strongly suggest that t(he main reason for realization of the Tc >50 K observed in RE-1111 compounds (RE: Pr, Sm, and Gd) at ambient pressure is the merging of SC1 and SC2.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, College of Humanities and Sciences, Nihon University, Tokyo, Japan.

ABSTRACT
The 1111-type iron-based superconductor LnFeAsO(1-x)Fx (Ln stands for lanthanide) is the first material with a Tc above 50 K, other than cuprate superconductors. Electron doping into LaFeAsO by H, rather than F, revealed a double-dome-shaped Tc-x diagram, with a first dome (SC1, 0.0550 K observed in RE-1111 compounds (RE: Pr, Sm, and Gd) at ambient pressure is the merging of SC1 and SC2.

No MeSH data available.


Phase diagram in hydrogen-doped 1111 materials.Superconductive phase diagrams for LnFeAsO1-xHx (Ln = La and Sm). A double-dome Tc(x) is observed in LaFeAsO1-xHx7. The two kinds of superconducting phases, SC1 and SC2, are thought to have different origins. The arrows show the maximum Tc, which shifts to the lightly-doped side in the order La to Sm. This shift in Tc-dome is observed for LnFeAsO1-xHx (Ln = La, Ce, Sm, and Gd) in the order La to Gd, i.e., in order of decreasing ionic radius.
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f1: Phase diagram in hydrogen-doped 1111 materials.Superconductive phase diagrams for LnFeAsO1-xHx (Ln = La and Sm). A double-dome Tc(x) is observed in LaFeAsO1-xHx7. The two kinds of superconducting phases, SC1 and SC2, are thought to have different origins. The arrows show the maximum Tc, which shifts to the lightly-doped side in the order La to Sm. This shift in Tc-dome is observed for LnFeAsO1-xHx (Ln = La, Ce, Sm, and Gd) in the order La to Gd, i.e., in order of decreasing ionic radius.

Mentions: Hydrogen-doped Ln-1111 materials were successfully synthesized using the high solubility limit of hydrogen7, covering the over-doped region, which has never been studied before because of the low solubility limit of fluorine. A combined study of neutron diffraction measurements with density functional calculations on LnFeAsO1-xDx demonstrated that these hydrogen atoms are incorporated as H− ions at the O2− sites. The hydrogen doping causes superconductivity as the same manner as fluorine doping for Sm8, Ce9 and La-11117, as shown in the previous studies. A complete single Tc dome is observed in Ce and Sm-11117, while a double-dome-shaped Tc curve is obtained in LaFeAsO1-xHx, which has hitherto not been observed for Ln-1111. The phase diagrams of LaFeAsO1-xHx and SmFeAsO1-xHx at ambient pressure are presented in Fig. 1. The Tc curve of the first dome (SC1) in the lightly-doped region almost coincides with the fluorine-doped La-1111. However, the second dome (SC2) in the heavily-doped region has the maximum Tc of 36 K at x = 0.36, which is higher than that of SC1. The SC2 is far from the magnetic phase of x = 0. This finding suggests that the rigid-band picture does not hold in the highly-doped region710 because the size and shape of hole pocket on the Fermi surface differs fairly from those of the electron pockets. Thus, orbital fluctuation and/or spin fluctuation resulting from another have been proposed recently as the superconductivity mechanism in the highly-doped region10. In addition, a new antiferromagnetic phase was recently discovered by NMR11 and neutron diffraction measurements12 in the over-doped region (x = ~0.5) in LaFeAsO1-xHx, where the Tc of the SC2 vanishes. This magnetic phase is expected to be the key to understanding the appearance of the second Tc dome.


Superconductivity at 52 K in hydrogen-substituted LaFeAsO(1-x)Hx under high pressure.

Takahashi H, Soeda H, Nukii M, Kawashima C, Nakanishi T, Iimura S, Muraba Y, Matsuishi S, Hosono H - Sci Rep (2015)

Phase diagram in hydrogen-doped 1111 materials.Superconductive phase diagrams for LnFeAsO1-xHx (Ln = La and Sm). A double-dome Tc(x) is observed in LaFeAsO1-xHx7. The two kinds of superconducting phases, SC1 and SC2, are thought to have different origins. The arrows show the maximum Tc, which shifts to the lightly-doped side in the order La to Sm. This shift in Tc-dome is observed for LnFeAsO1-xHx (Ln = La, Ce, Sm, and Gd) in the order La to Gd, i.e., in order of decreasing ionic radius.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296289&req=5

f1: Phase diagram in hydrogen-doped 1111 materials.Superconductive phase diagrams for LnFeAsO1-xHx (Ln = La and Sm). A double-dome Tc(x) is observed in LaFeAsO1-xHx7. The two kinds of superconducting phases, SC1 and SC2, are thought to have different origins. The arrows show the maximum Tc, which shifts to the lightly-doped side in the order La to Sm. This shift in Tc-dome is observed for LnFeAsO1-xHx (Ln = La, Ce, Sm, and Gd) in the order La to Gd, i.e., in order of decreasing ionic radius.
Mentions: Hydrogen-doped Ln-1111 materials were successfully synthesized using the high solubility limit of hydrogen7, covering the over-doped region, which has never been studied before because of the low solubility limit of fluorine. A combined study of neutron diffraction measurements with density functional calculations on LnFeAsO1-xDx demonstrated that these hydrogen atoms are incorporated as H− ions at the O2− sites. The hydrogen doping causes superconductivity as the same manner as fluorine doping for Sm8, Ce9 and La-11117, as shown in the previous studies. A complete single Tc dome is observed in Ce and Sm-11117, while a double-dome-shaped Tc curve is obtained in LaFeAsO1-xHx, which has hitherto not been observed for Ln-1111. The phase diagrams of LaFeAsO1-xHx and SmFeAsO1-xHx at ambient pressure are presented in Fig. 1. The Tc curve of the first dome (SC1) in the lightly-doped region almost coincides with the fluorine-doped La-1111. However, the second dome (SC2) in the heavily-doped region has the maximum Tc of 36 K at x = 0.36, which is higher than that of SC1. The SC2 is far from the magnetic phase of x = 0. This finding suggests that the rigid-band picture does not hold in the highly-doped region710 because the size and shape of hole pocket on the Fermi surface differs fairly from those of the electron pockets. Thus, orbital fluctuation and/or spin fluctuation resulting from another have been proposed recently as the superconductivity mechanism in the highly-doped region10. In addition, a new antiferromagnetic phase was recently discovered by NMR11 and neutron diffraction measurements12 in the over-doped region (x = ~0.5) in LaFeAsO1-xHx, where the Tc of the SC2 vanishes. This magnetic phase is expected to be the key to understanding the appearance of the second Tc dome.

Bottom Line: Tc rises to 52 K at 6 GPa for the Tc-valley composition between the two Tc domes.On the other hand, the Tc of SmFeAsO1-x)Hx decreased continually, keeping its single-dome structure up to 15 GPa.The present findings strongly suggest that t(he main reason for realization of the Tc >50 K observed in RE-1111 compounds (RE: Pr, Sm, and Gd) at ambient pressure is the merging of SC1 and SC2.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, College of Humanities and Sciences, Nihon University, Tokyo, Japan.

ABSTRACT
The 1111-type iron-based superconductor LnFeAsO(1-x)Fx (Ln stands for lanthanide) is the first material with a Tc above 50 K, other than cuprate superconductors. Electron doping into LaFeAsO by H, rather than F, revealed a double-dome-shaped Tc-x diagram, with a first dome (SC1, 0.0550 K observed in RE-1111 compounds (RE: Pr, Sm, and Gd) at ambient pressure is the merging of SC1 and SC2.

No MeSH data available.