Doping dependence of the superconductivity of (Ca${}_{1\ensuremath{-}x}$Na${}_{x}$)Fe${}_{2}$As${}_{2}$

Doping dependence of the superconductivity of (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$

K. Zhao, Q. Q. Liu, X. C. Wang, Z. Deng, Y. X. Lv, J. L. Zhu, F. Y. Li, and C. Q. Jin

Phys. Rev. B 84, 184534 – Published 29 November 2011

Abstract

Single-crystalline CaFe $_{2}$ As $_{2}$ and (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ polycrystals (0 < $x$ < 0.66) are synthesized and characterized using structural, magnetic, electronic transport, and heat capacity measurements. These measurements show that the structural/magnetic phase transition in CaFe $_{2}$ As $_{2}$ at 165 K is monotonically suppressed by the Na doping and that superconductivity can be realized over a wide doping region. For 0.3 < $x$ < 0.36, the magnetic susceptibilities indicate the possible coexistence of the spin density wave (SDW) and superconductivity. Superconducting phases corresponding to the Na doping level in (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ for nominal $x$ $=$ 0.36, 0.4, 0.5, 0.6, and 0.66, with $T c$ $=$ 17, 19, 22, 33, and 34 K, respectively, are identified. The effects of the magnetic field on the superconductivity transitions for $x$ $=$ 0.66 samples are studied from which high upper critical fields $H_{c 2}$ ≈ 103 T is deduced. A phase diagram of the SDW and superconductivity as a function of the doping level is thus presented.

Received 2 December 2010

DOI:https://doi.org/10.1103/PhysRevB.84.184534

Authors & Affiliations

K. Zhao, Q. Q. Liu, X. C. Wang, Z. Deng, Y. X. Lv, J. L. Zhu, F. Y. Li, and C. Q. Jin^*

Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

^*jin@iphy.ac.cn

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Vol. 84, Iss. 18 — 1 November 2011

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Figure 1
(a) X-ray diffractions of the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ polycrystals for $x$ $=$ 0, 0.1, 0.2, 0.3, 0.36, 0.4, 0.5, 0.6, and 0.66. (b) Rietveld refinements of the x-ray diffractions of the CaFe $_{2}$ As $_{2}$ polycrystals with space group I4/mmm resulting in $a$ $=$ 3.8907 Å and $c$ $=$ 11.7212 Å with $R_{wp}$ $=$ 6.16% and $R p$ $=$ 3.74%, respectively. (c) Rietveld refinements of the x-ray diffractions of the (Ca $_{0.64}$ Na $_{0.36}$ )Fe $_{2}$ As $_{2}$ polycrystals with space group I4/mmm resulting in $a$ $=$ 3.8590 Å and $c$ $=$ 12.0155 Å with $R_{wp}$ $=$ 6.81% and $R p$ $=$ 4.33%, respectively. (d) Rietveld refinements of the x-ray diffractions of the (Ca $_{0.5}$ Na $_{0.5}$ )Fe $_{2}$ As $_{2}$ polycrystals with space group I4/mmm resulting in $a$ $=$ 3.8510 Å and $c$ $=$ 12.0874 Å with $R_{wp}$ $=$ 7.14% and $R p$ $=$ 4.35%, respectively.Reuse & Permissions
Figure 2
Lattice parameters and volumes of the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ polycrystals for $x$ $=$ 0, 0.1, 0.2, 0.3, 0.36, 0.4, 0.5, 0.6, and 0.66, respectively.Reuse & Permissions
Figure 3
(a) Temperature-dependent magnetic susceptibility curves of the CaFe $_{2}$ As $_{2}$ single crystal for $H$ // $a b$ and the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ for $x$ $=$ 0.1, 0.2, and 0.3 with a magnetic field of $H$ $=$ 5 T. (upper inset) Enlarged magnetic susceptibility curves around 135 K. (b) $R$ ( $T$ )/ $R$ (200 K) versus $T$ of (Ca $_{0.9}$ Na $_{0.1}$ )Fe $_{2}$ As $_{2}$ . (inset) d( $R$ ( $T$ )/ $R$ (200 K))/d $T$ versus $T$ . (c) Temperature-dependent magnetic susceptibility curves of the (Ca $_{0.68}$ Na $_{0.32}$ )Fe $_{2}$ As $_{2}$ and (Ca $_{0.67}$ Na $_{0.33}$ )Fe $_{2}$ As $_{2}$ with a magnetic field of $H$ $=$ 5 T. (lower inset) Magnetic susceptibilities [χ( $T$ )] of the (Ca $_{0.68}$ Na $_{0.32}$ )Fe $_{2}$ As $_{2}$ and (Ca $_{0.67}$ Na $_{0.33}$ )Fe $_{2}$ As $_{2}$ measured in a magnetic field $H$ $=$ 30 Oe with both ZFC and FC modes. (d) Magnetic susceptibilities [χ( $T$ )] of the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ for $x$ $=$ 0.36, 0.4, 0.5, 0.6, and 0.66 measured in a magnetic field $H$ $=$ 30 Oe with both ZFC and FC modes.Reuse & Permissions
Figure 4
(a) Temperature-dependent electrical resistivity curves of the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ for $x$ $=$ 0.36, 0.5, and 0.66. (upper inset) $R$ ( $T$ )/ $R$ (300 K) and d( $R$ ( $T$ )/ $R$ (300 K))/d $T$ versus $T$ for (Ca $_{0.34}$ Na $_{0.66}$ )Fe $_{2}$ As $_{2}$ around $T c$ . (b) Effects of the magnetic field on the superconductivity transition of the (Ca $_{0 . . 34}$ Na $_{0.66}$ )Fe $_{2}$ As $_{2}$ with $H$ $=$ 1, 3, 5, and 9 T.Reuse & Permissions
Figure 5
(a) Temperature-dependent specific heat of the (Ca $_{0.64}$ Na $_{0.36}$ )Fe $_{2}$ As $_{2}$ with $H$ $=$ 0 and 5 T. (upper inset) Δ $C$ (C-Cn)/ $T$ versus $T c$ . (b) Temperature-dependent specific heat of the (Ca $_{0.5}$ Na $_{0.5}$ )Fe $_{2}$ As $_{2}$ with $H$ $=$ 0 and 5 T. (upper inset) Δ $C$ ( $C$ - $C n$ )/ $T$ versus $T c$ . (c) Temperature-dependent specific heat of the (Ca $_{0.34}$ Na $_{0.66}$ )Fe $_{2}$ As $_{2}$ with $H$ $=$ 0 and 5 T. (upper inset) Δ $C$ ( $C$ - $C n$ )/ $T$ versus $T c$ .Reuse & Permissions
Figure 6
Phase diagrams of the (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$ system. $T c$ denotes the superconductivity transition temperature, and $T s$ represents the structural and magnetic transitions.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Doping dependence of the superconductivity of (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$

K. Zhao, Q. Q. Liu, X. C. Wang, Z. Deng, Y. X. Lv, J. L. Zhu, F. Y. Li, and C. Q. Jin

Phys. Rev. B 84, 184534 – Published 29 November 2011

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Physical Review B

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Doping dependence of the superconductivity of (Ca1−xNax)Fe2As2

K. Zhao, Q. Q. Liu, X. C. Wang, Z. Deng, Y. X. Lv, J. L. Zhu, F. Y. Li, and C. Q. Jin

Phys. Rev. B 84, 184534 – Published 29 November 2011

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Doping dependence of the superconductivity of (Ca $_{1 - x}$ Na $_{x}$ )Fe $_{2}$ As $_{2}$