Phys. Rev. B 104, L161103 (2021) - Magnetic structure of the topological semimetal ${\mathrm{YbMnSb}}

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Magnetic structure of the topological semimetal ${YbMnSb}_{2}$

Jian-Rui Soh, Siobhan M. Tobin, Hao Su, Ivica Zivkovic, Bachir Ouladdiaf, Anne Stunault, J. Alberto Rodríguez-Velamazán, Ketty Beauvois, Yanfeng Guo, and Andrew T. Boothroyd

Phys. Rev. B 104, L161103 – Published 5 October 2021

Abstract

The antiferromagnetic (AFM) semimetal ${YbMnSb}_{2}$ has recently been identified as a candidate topological material, driven by time-reversal symmetry breaking. Depending on the ordered arrangement of Mn spins below the Néel temperature, $T_{N} = 345 K$ , the electronic bands near the Fermi energy can either have a Dirac node, a Weyl node, or a nodal line. We have investigated the ground state magnetic structure of ${YbMnSb}_{2}$ using unpolarized and polarized single crystal neutron diffraction. We find that the Mn moments lie along the $c$ axis of the $P 4 / n m m$ space group and are arranged in a $C$ -type AFM structure, which implies the existence of gapped Dirac nodes near the Fermi level. The results highlight how different magnetic structures can critically affect the topological nature of fermions in semimetals.

Received 8 July 2021
Accepted 10 September 2021

DOI:https://doi.org/10.1103/PhysRevB.104.L161103

Physics Subject Headings (PhySH)

First-principles calculations Magnetic order Topological materials

Neutron scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jian-Rui Soh ¹, Siobhan M. Tobin ², Hao Su³, Ivica Zivkovic¹, Bachir Ouladdiaf⁴, Anne Stunault⁴, J. Alberto Rodríguez-Velamazán⁴, Ketty Beauvois⁴, Yanfeng Guo ³, and Andrew T. Boothroyd ²

¹Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
²Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, United Kingdom
³School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
⁴Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, F-38042 Grenoble Cedex 9, France

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Vol. 104, Iss. 16 — 15 October 2021

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Figure 1
(a) Two unit cells of ${YbMnSb}_{2}$ as described by the space group $P 4 / n m m$ with cell parameters $a = b = 4.31 (2) Å$ , $c = 10.85 (1) Å$ at $T = 400 K$ . The square Sb layers (at $z = 0$ and $c$ ) are predicted to host different types of topological fermions, depending on the magnetic structure of the Mn magnetic sublattice. (b)–(e) show different Mn magnetic structures and the corresponding predicted topology of the electronic bands: (b) $G$ -type AFM with in-plane Mn moments stabilizes a line node in the electronic bands; (c) $C$ -type AFM with in-plane moments gives rise to Dirac nodes with a small gap; (d) a canted $C$ -type AFM order gives rise to topologically protected Weyl nodes; (e) $C$ -type AFM with moments along $c$ stabilizes a gapped Dirac state.
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Figure 2
(a) Temperature dependent magnetization curves of ${YbMnSb}_{2}$ measured with a field $μ_{0} H = 3 T$ applied parallel and perpendicular to the crystal $c$ axis. The bifurcation of the curves below $T_{N} = 345 (1) K$ indicates the onset of AFM order. (b) Integrated intensity of the 100 magnetic reflection measured by neutron diffraction. (c) Temperature dependence of the in-plane resistivity of ${YbMnSb}_{2}$ , displaying metallic conductivity for $T < T_{N}$ .
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Figure 3
(a) Reciprocal space representation of the $h k l$ reflections that were measured on the D10 instrument. The blue and red points correspond to reflections which are allowed and forbidden, respectively, by the $P 4 / n m m$ space group. (b) Comparison of measured ( $I_{obs}$ ) and calculated ( $I_{calc}$ ) integrated intensities from the structural refinement in the paramagnetic phase of ${YbMnSb}_{2}$ at $T = 400 K$ . (c)–(e) compare $I_{obs}$ and $I_{calc}$ for the $T = 2 K$ data refined against structural models with $G$ -type AFM, $C$ -AFM (moments in plane), and $C$ -AFM (moments along $c$ ), respectively.
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Figure 4
(a) Unpolarized neutrons were used on the D10 instrument (ILL), with the scattering vector $Q$ along $00 l$ . (b) Since magnetic neutron diffraction is sensitive to the component of $M$ perpendicular to $Q$ , namely $M_{⊥}$ , a canting of the Mn moments away from the crystal $c$ axis will produce a magnetic contribution to the nuclear Bragg reflections along $00 l$ . (c) The temperature dependence of the integrated intensities of the 001 and the 002 reflections. The line corresponds to the fit to the Debye-Waller factor.
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Figure 5
(a) To access the $(h 0 l)$ reflections in the half-polarized experimental setup on D3, a ${YbMnSb}_{2}$ single crystal was aligned with the crystal $b$ axis normal to the horizontal scattering plane. The incident neutrons are polarized along $z$ ( $P_{i} ∥ z$ ) and the scattered neutron polarization $P_{f}$ is not analyzed. (b) Reciprocal space plot of the measured reflections (blue spheres) in the $(h 0 l)$ scattering plane. (c) Measured flipping ratios (blue circles) along with the calculated $R$ for zero in-plane moment (dashed line) and several nonzero values up to $0.03 μ_{B}$ (colored bars).
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Figure 6
Ab initio electronic dispersion of ${YbMnSb}_{2}$ along in-plane high symmetry directions. The calculation assumes the magnetic structure determined in this study.
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Physical Review B

covering condensed matter and materials physics

Magnetic structure of the topological semimetal ${YbMnSb}_{2}$

Jian-Rui Soh, Siobhan M. Tobin, Hao Su, Ivica Zivkovic, Bachir Ouladdiaf, Anne Stunault, J. Alberto Rodríguez-Velamazán, Ketty Beauvois, Yanfeng Guo, and Andrew T. Boothroyd

Phys. Rev. B 104, L161103 – Published 5 October 2021

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Physical Review B

covering condensed matter and materials physics

Magnetic structure of the topological semimetal YbMnSb2

Jian-Rui Soh, Siobhan M. Tobin, Hao Su, Ivica Zivkovic, Bachir Ouladdiaf, Anne Stunault, J. Alberto Rodríguez-Velamazán, Ketty Beauvois, Yanfeng Guo, and Andrew T. Boothroyd

Phys. Rev. B 104, L161103 – Published 5 October 2021

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Magnetic structure of the topological semimetal ${YbMnSb}_{2}$