Effect of Electron Correlations on Magnetic Excitations in the Isovalently Doped Iron-Based Superconductor $\mathrm{Ba}({\mathrm{Fe}}_{1\mathbf{\ensuremath{-}}x}{\mathrm{Ru}}_{x}{)}_{2}{\mathrm{As}}_{2}$

Effect of Electron Correlations on Magnetic Excitations in the Isovalently Doped Iron-Based Superconductor $Ba ({Fe}_{1 - x} {Ru}_{x})_{2} {As}_{2}$

Jun Zhao, C. R. Rotundu, K. Marty, M. Matsuda, Y. Zhao, C. Setty, E. Bourret-Courchesne, Jiangping Hu, and R. J. Birgeneau

Phys. Rev. Lett. 110, 147003 – Published 5 April 2013

Abstract

Magnetic correlations in isovalently doped $Ba ({Fe}_{1 - x} {Ru}_{x})_{2} {As}_{2}$ ( $x = 0.25$ , $T_{c} = 14.5 K$ ; $x = 0.35$ , $T_{c} = 20 K$ ) are studied by elastic and inelastic neutron scattering techniques. A relatively large superconducting spin gap accompanied by a weak resonance mode is observed in the superconducting state in both samples. In the normal state, the magnetic excitation intensity is dramatically reduced with increasing Ru doping toward the optimally doped regime. Our results favor that the weakening of the electron-electron correlations by Ru doping is responsible for the dampening of the resonance mode, as well as the suppression of the normal state antiferromagnetic correlations near the optimally doped regime in this system.

Received 12 January 2012

DOI:https://doi.org/10.1103/PhysRevLett.110.147003

Authors & Affiliations

Jun Zhao^1,2,3, C. R. Rotundu⁴, K. Marty⁵, M. Matsuda⁵, Y. Zhao^6,7, C. Setty⁸, E. Bourret-Courchesne⁴, Jiangping Hu⁸, and R. J. Birgeneau^2,9

¹Department of Physics, and Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, People’s Republic of China
²Department of Physics, University of California, Berkeley, California 94720, USA
³Miller Institute for Basic Research in Science, Berkeley, California 94720, USA
⁴Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁵Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁶NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
⁷Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
⁸Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
⁹Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA

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Vol. 110, Iss. 14 — 5 April 2013

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Figure 1
(a) Schematic phase diagram of $Ba ({Fe}_{1 - x} M_{x})_{2} {As}_{2}$ $M = Ru$ , Co, Rh. The blue filled circles denote the $T_{c}$ and $T_{N}$ of the underdoped $Ba ({Fe}_{0.75} {Ru}_{0.25})_{2} {As}_{2}$ sample; the red filled circle denotes the $T_{c}$ of optimally doped $Ba ({Fe}_{0.65} {Ru}_{0.35})_{2} {As}_{2}$ sample [3, 16]. The blue dotted line and magenta dashed line denote the Néel temperatures of $Ba ({Fe}_{1 - x} {Co}_{x})_{2} {As}_{2}$ and $Ba ({Fe}_{1 - x} {Rh}_{x})_{2} {As}_{2}$ , respectively [34]. (b) Temperature dependence of the intensity of magnetic Bragg peak ( $1 / 2$ , $1 / 2$ , 3) of the underdoped $Ba ({Fe}_{0.75} {Ru}_{0.25})_{2} {As}_{2}$ sample. The error bars indicate one standard deviation throughout the Letter.Reuse & Permissions
Figure 2
Magnetic excitations in the $T_{c} = 14.5 K$ sample. (a), (b) Constant energy scans near ( $1 / 2$ , $1 / 2$ , 1) below and above $T_{c}$ ; linear backgrounds are subtracted. (c), (d) $L$ scans at 2.5 and 6 meV. (e) Temperature dependence of the dynamic susceptibility at ( $1 / 2$ , $1 / 2$ , 1) with $E = 2.5 meV$ , which clearly shows a kink at $T_{c}$ . The thermal population factor is corrected here. (f) Temperature dependence of the dynamical spin correlation length at 2.5 meV, which also displays a kink at $T_{c}$ . The dynamical correlation length is estimated as $1 / HWHM$ , where HWHM is the half width at half maximum of $Q$ scans deconvoluted with the instrumental resolution.Reuse & Permissions
Figure 3
Magnetic excitations in the $T_{c} = 20 K$ sample. (a)–(c) Constant energy scans near ( $1 / 2$ , $1 / 2$ , 1) below and above $T_{c}$ ; linear backgrounds are subtracted. (d) Temperature dependence of magnetic excitation intensity at ( $1 / 2$ , $1 / 2$ , 1) with $ℏ ω = 8 meV$ , which clearly shows a kink at $T_{c}$ .Reuse & Permissions
Figure 4
(a), (b) Imaginary part of the dynamic susceptibility $χ^{''} (Q, ω)$ in the superconducting state (2 K) and normal state (25 K) of the $T_{c} = 14.5 K$ sample. The data were obtained by correcting the thermal population factor. (c),(d) Temperature difference plots of the dynamic susceptibility between 2 K and 25 K at $Q = (1 / 2, 1 / 2, 1)$ and $Q = (1 / 2, 1 / 2, 0)$ of the $T_{c} = 14.5 K$ sample. (e), (f) Imaginary part of the dynamic susceptibility $χ^{''} (Q, ω)$ in the superconducting state and normal state of the $T_{c} = 20 K$ sample. (g),(h) Temperature difference plots of the dynamic susceptibility between 2 K and 25 K at $Q = (1 / 2, 1 / 2, 1)$ and $Q = (1 / 2, 1 / 2, 0)$ of the $T_{c} = 20 K$ sample. The shaded area denotes the spectral weight change below and above $T_{c}$ . In both samples, the energy dependent background measured near $Q = (0.7, 0.7, L)$ are subtracted and all magnetic intensities are normalized to absolute units with acoustic phonons.Reuse & Permissions

Physical Review Letters

Effect of Electron Correlations on Magnetic Excitations in the Isovalently Doped Iron-Based Superconductor Ba(Fe1−xRux)2As2

Jun Zhao, C. R. Rotundu, K. Marty, M. Matsuda, Y. Zhao, C. Setty, E. Bourret-Courchesne, Jiangping Hu, and R. J. Birgeneau

Phys. Rev. Lett. 110, 147003 – Published 5 April 2013

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Effect of Electron Correlations on Magnetic Excitations in the Isovalently Doped Iron-Based Superconductor $Ba ({Fe}_{1 - x} {Ru}_{x})_{2} {As}_{2}$