Electronic nematicity revealed by torque magnetometry in $\mathrm{Eu}{\mathrm{Fe}}_{2}({\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}{)}_{2}$

Electronic nematicity revealed by torque magnetometry in $Eu {Fe}_{2} ({As}_{1 - x} P_{x})_{2}$

Xiaofeng Xu, W. H. Jiao, N. Zhou, Y. K. Li, B. Chen, C. Cao, Jianhui Dai, A. F. Bangura, and Guanghan Cao

Phys. Rev. B 89, 104517 – Published 26 March 2014

Abstract

Electronic nematics, an electron orientational order which breaks the underlying rotational symmetry, were observed in iron pnictide superconductors several years after their discovery. However, the universality of the doping dependence of this phase and its relation to other symmetry-breaking orders (such as superconductivity) in distinct families of iron pnictides remain outstanding questions. Here we use torque magnetometry as a probe to study the rotational symmetry breaking in $Eu {Fe}_{2} ({As}_{1 - x} P_{x})_{2}$ without introducing external pressure. The nematic phase is found to proliferate well above the structural transition and to persist into the superconducting regime at optimal doping, after which it becomes absent or very weak, in sharp contrast to the behavior observed in $Ba {Fe}_{2} ({As}_{1 - x} P_{x})_{2}$ . These measurements suggest a putative quantum nematic transition near optimal doping under the superconducting dome.

Received 27 January 2014
Revised 14 March 2014

DOI:https://doi.org/10.1103/PhysRevB.89.104517

Authors & Affiliations

Xiaofeng Xu^1,*, W. H. Jiao², N. Zhou¹, Y. K. Li¹, B. Chen^3,1, C. Cao¹, Jianhui Dai¹, A. F. Bangura⁴, and Guanghan Cao²

¹Department of Physics, Hangzhou Normal University, Hangzhou 310036, China
²State Key Laboratory of Silicon Materials and Department of Physics, Zhejiang University, Hangzhou 310027, China
³Department of Physics, University of Shanghai for Science & Technology, Shanghai, China
⁴RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan

^*xiaofeng.xu@hznu.edu.cn

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Vol. 89, Iss. 10 — 1 March 2014

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Figure 1
Angular dependence of magnetic torque with fields rotating in the $a b$ plane of the EuFe $_{2}$ As $_{2}$ parent compound. (a) Schematic of the field orientation in the setup. Note that the $x$ and $y$ axes do not necessarily denote the crystal $a$ axis and $b$ axis due to the lack of knowledge about the crystalline axes in the plane, which, however, does not affect our conclusions in the text. (b), (c) Angular dependence of the torque above (b) and below (c) the nematic onset temperature $T^{*}$ . (d) Temperature dependence of the amplitude $A$ [see Eq. (1)]. (e) Contour plot of the torque as a function of both temperature and angle. Note that the torques are renormalized to the maximal values at each temperature. (f) Zero-field resistivity for the strain-free sample.
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Figure 2
Angular dependence of the torque when fields are rotating out of the plane of the EuFe $_{2}$ As $_{2}$ parent compound. (a), (b) Angular torque at various temperatures. (c) Torque amplitude $A$ as a function of temperature.
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Figure 3
Angular dependence of magnetic torque with fields rotating in the $a b$ plane of an underdoped sample ( $x = 0.18$ ). (a), (b) Angular dependence of the torque above (a) and below (b) the nematic onset temperature $T^{*} \sim 140$ K. (c) Temperature dependence of the amplitude $A$ . (d) Contour plot of the torque as a function of both temperature and angle. Note that the torques are renormalized to the maximal values at each temperature. (e) Zero-field resistivity for the strain-free sample.
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Figure 4
Angular dependence of magnetic torque with fields rotating in the $a b$ plane of the optimal doping sample ( $x = 0.20$ ). (a), (b) Angular dependence of the torque above (a) and below (b) the nematic onset temperature $T^{*} \sim 100$ K. (c) Temperature dependence of the amplitude $A$ . (d) Contour plot of the torque as a function of both temperature and angle. Note that the torques are renormalized to the maximal values at each temperature. To best visualize the changes below $T^{*}$ , the data window is set to from angle 0 $^{\circ}$ to angle 180 $^{\circ}$ . (e) Zero-field resistivity for the strain-free sample. The dashed (red) line is the linear guideline.
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Figure 5
Angular dependence of the torque for fields rotating in the $a b$ plane of the overdoped sample ( $x = 0.24$ ). (a), (b) Angular torque at different temperatures. (c) Summary of the resultant amplitude $A$ at each temperature studied. (d) Contour plot of the renormalized torque as a function of temperature and angle. (e) Zero-field resistivity for the strain-free sample.
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Figure 6
Resultant phase diagram of EuFe $_{2}$ (As $_{1 - x}$ P $_{x}$ ) $_{2}$ as derived collectively from our measurements and previous studies. For simplicity, we neglect the fine spin structure of Eu $^{2 +}$ , including that in the superconducting state, which was recently reported in Refs. [21] and [24].
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Physical Review B

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Electronic nematicity revealed by torque magnetometry in $Eu {Fe}_{2} ({As}_{1 - x} P_{x})_{2}$

Xiaofeng Xu, W. H. Jiao, N. Zhou, Y. K. Li, B. Chen, C. Cao, Jianhui Dai, A. F. Bangura, and Guanghan Cao

Phys. Rev. B 89, 104517 – Published 26 March 2014

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Electronic nematicity revealed by torque magnetometry in EuFe2(As1−xPx)2

Xiaofeng Xu, W. H. Jiao, N. Zhou, Y. K. Li, B. Chen, C. Cao, Jianhui Dai, A. F. Bangura, and Guanghan Cao

Phys. Rev. B 89, 104517 – Published 26 March 2014

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Electronic nematicity revealed by torque magnetometry in $Eu {Fe}_{2} ({As}_{1 - x} P_{x})_{2}$