Rotation of reflectivity anisotropy due to uniaxial strain along ${[110]}_{\mathrm{tetr}}$ in the electron-doped Fe-based superconductor $\mathrm{Ba}{({\mathrm{Fe}}_{0.955}{\mathrm{Co}}_{0.045})}_{2}{\mathrm{As}}_{2}$

Rotation of reflectivity anisotropy due to uniaxial strain along ${[110]}_{tetr}$ in the electron-doped Fe-based superconductor $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$

Inho Kwak, Soonsang Huh, Min-Cheol Lee, Younsik Kim, Bumjoo Lee, Y. S. Lee, C. W. Seo, Byung Cheol Park, Thomas Wolf, Changyoung Kim, Tae Won Noh, and K. W. Kim

Phys. Rev. B 101, 165136 – Published 27 April 2020

Abstract

We present a strain-dependent time-resolved reflectometry experiment on $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$ in the nematic state. Uniaxial external pressure has usually been applied to obtain a single nematic domain. However, reflectivity with and without pumping under uniaxial strain along ${[110]}_{tetr}$ reveals an unexpected nematicity of which $C_{4}$ symmetry-breaking orientation is rotated by $20^{\circ}$ . Our observation suggests a microscopic coexistence of $B_{2 g}$ and $B_{1 g}$ nematicity under uniaxial strain and possibly of an $X Y$ -type nematic order in the electron-doped iron pnictide.

Received 16 December 2019
Revised 28 February 2020
Accepted 25 March 2020

DOI:https://doi.org/10.1103/PhysRevB.101.165136

Physics Subject Headings (PhySH)

Nematic order

Iron-based superconductors Superconductors

Reflectivity Ultrafast pump-probe spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Inho Kwak ^1,2, Soonsang Huh ^1,2, Min-Cheol Lee ^1,2, Younsik Kim^1,2, Bumjoo Lee^1,2, Y. S. Lee³, C. W. Seo³, Byung Cheol Park^1,2, Thomas Wolf⁴, Changyoung Kim^1,2, Tae Won Noh ^1,2,*, and K. W. Kim ^3,†

¹Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Republic of Korea
²Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
³Department of Physics, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
⁴Institute of Solid State Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany

^*Corresponding author: twnoh@snu.ac.kr
^†Corresponding author: kyungwan.kim@gmail.com

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 101, Iss. 16 — 15 April 2020

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Strain-dependent transient reflectivity measurements of $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$ single crystals. Experimental schematics (a) of the isotropic strain condition and (d) of the uniaxial strain condition. Probe polarization dependent evolution of the transient reflectivity $Δ R / R$ measured as a function of delay time $τ_{d}$ at 30 K (b) under isotropic strain and (e) under uniaxial strain. The poled axis of the piezoelectric stack is aligned parallel to ${[110]}_{tetr}$ crystal orientation. Polar axis plot of the transient reflectivity at $τ_{d} = 0.2$ ps as a function of the probe polarization (c) under isotropic strain and (f) under uniaxial strain. Incident fluences were set to be $120 μ J / {cm}^{2}$ for pump and $20 μ J / {cm}^{2}$ for probe at the experiment under isotropic strain, and $39 μ J / {cm}^{2}$ for pump and $1.2 μ J / {cm}^{2}$ for probe under uniaxial strain.
Reuse & Permissions
Figure 2
Reflectivity anisotropy of $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$ under uniaxial strain along ${[110]}_{tetr}$ normalized by the maximum value of the reflectivity anisotropy in the equilibrium state at 30 K. (a) Reflectivity anisotropy $δ R / {| δ R |}_{Max}^{eq}$ measured as functions of $θ$ in the equilibrium state without pump (blue solid line) and in the nonequilibrium state at $τ_{d} = 0.2$ ps after pumping (red solid line). Fluences were set to be $41 μ J / {cm}^{2}$ for pump and $5 μ J / {cm}^{2}$ for probe. The incident probe polarizations of $θ = 0^{\circ}$ and $90^{\circ}$ were parallel to the Fe-Fe bonding directions. (b) Time transient of the reflectivity anisotropy $δ R / {| δ R |}_{Max}^{eq}$ measured as a function of delay time $τ_{d}$ at the incident probe polarization of $θ = 69^{\circ}$ . A dashed vertical line indicates $τ_{d} = 0.2$ ps.
Reuse & Permissions
Figure 3
(a) Transient anisotropy change normalized by equilibrium anisotropy $Δ (δ R) / {| δ R |}_{Max}^{eq}$ measured as a function of the incident probe polarization $θ$ and the delay time $τ_{d}$ at 30 K under uniaxial strain. Fluences were set to be $41 μ J / {cm}^{2}$ for pump and $5 μ J / {cm}^{2}$ for probe. (b) Transient anisotropy change $Δ (δ R) / R$ measured as functions of the incident probe polarization at $τ_{d} = 0.2$ ps with pump fluences of $41 μ J / {cm}^{2}$ (blue solid line) and $1000 μ J / {cm}^{2}$ (red dashed line), respectively. They were normalized by the maximum values of respective fluence conditions. (c) Transient anisotropy change normalized by equilibrium anisotropy ${| Δ (δ R) |}_{Max} / {| δ R |}_{Max}^{eq}$ measured as a function of the pump fluence. Isotropic-strain results (open circle) were obtained from difference between the maximum and the minimum values of the transient reflectivity $Δ R_{Max} (90^{\circ}) - Δ R_{Min} (0^{\circ})$ in Fig. 1. They were scaled to fit to the uniaxial-strain results (open square). A gray solid line is a simple saturation function of ${| Δ (δ R) |}_{Max} / {| δ R |}_{Max} = A (1 - e^{- Φ / Φ_{sat}})$ , where $Φ$ is the incident pump fluence, $Φ_{sat} = 59 μ J / {cm}^{2}$ , and $A = 0.77$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Rotation of reflectivity anisotropy due to uniaxial strain along ${[110]}_{tetr}$ in the electron-doped Fe-based superconductor $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$

Inho Kwak, Soonsang Huh, Min-Cheol Lee, Younsik Kim, Bumjoo Lee, Y. S. Lee, C. W. Seo, Byung Cheol Park, Thomas Wolf, Changyoung Kim, Tae Won Noh, and K. W. Kim

Phys. Rev. B 101, 165136 – Published 27 April 2020

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Rotation of reflectivity anisotropy due to uniaxial strain along [110]tetr in the electron-doped Fe-based superconductor Ba(Fe0.955Co0.045)2As2

Inho Kwak, Soonsang Huh, Min-Cheol Lee, Younsik Kim, Bumjoo Lee, Y. S. Lee, C. W. Seo, Byung Cheol Park, Thomas Wolf, Changyoung Kim, Tae Won Noh, and K. W. Kim

Phys. Rev. B 101, 165136 – Published 27 April 2020

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Rotation of reflectivity anisotropy due to uniaxial strain along ${[110]}_{tetr}$ in the electron-doped Fe-based superconductor $Ba {({Fe}_{0.955} {Co}_{0.045})}_{2} {As}_{2}$