Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate $\mathrm{L}{\mathrm{i}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}$

Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate $L i_{2} Ru O_{3}$

Seokhwan Yun, Ki Hoon Lee, Se Young Park, Teck-Yee Tan, Junghwan Park, Soonmin Kang, D. I. Khomskii, Younjung Jo, and Je-Geun Park

Phys. Rev. B 100, 165119 – Published 14 October 2019

Abstract

$L i_{2} Ru O_{3}$ undergoes a structural transition at a relatively high temperature of 550 K with a distinct dimerization of Ru-Ru bonds on the otherwise isotropic honeycomb lattice. It exhibits a unique herringbone dimerization pattern with an unusually large value of bond shrinkage, about $\sim 0.5 Å$ . However, many questions still remain about its origin and its effect on the physical properties. In this work, using high-quality single crystals we investigated the anisotropy of resistivity (ρ) and magnetic susceptibility (χ) to find a very clear anisotropy: $ρ_{c^{*}} > ρ_{b} > ρ_{a}$ and $χ_{b} > χ_{a} > χ_{c^{*}}$ . We also carried out density functional calculations for possible theoretical interpretations, and concluded that this anisotropic behavior is due to the correlation effects combined with the unique orbital structure and the dimerization of Ru $4 d$ bands.

Received 20 March 2019
Revised 26 July 2019

DOI:https://doi.org/10.1103/PhysRevB.100.165119

Physics Subject Headings (PhySH)

Strongly correlated systems

Crystal growth Magnetization measurements Resistivity measurements Susceptibility measurements X-ray diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Seokhwan Yun^1,2, Ki Hoon Lee^1,2, Se Young Park^1,2, Teck-Yee Tan², Junghwan Park³, Soonmin Kang^1,2, D. I. Khomskii⁴, Younjung Jo^5,*, and Je-Geun Park ^1,2,†

¹Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
²Center for Correlated Electron System, Institute for Basic Science (IBS), Seoul 08826, Korea
³Samsung SDI Co. Ltd., Yongin 17084, Korea
⁴II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany
⁵Department of Physics, Kyungpook National University, Daegu 41566, Korea

^*Corresponding author: jophy@knu.ac.kr
^†jgpark10@snu.ac.kr

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Vol. 100, Iss. 16 — 15 October 2019

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Figure 1
(a) Single crystal refinement results of the $L i_{2} Ru O_{3}$ single-crystal. The inset shows a typical hexagonal single crystal. (b) $L i_{2} Ru O_{3}$ at room temperature, viewed along the perpendicular direction to the Ru honeycomb layer in the $ab$ plane. The yellow and green spheres represent the Ru and Li ions, respectively. The blue polygons represent the oxygen octahedrons. There are two unequal Ru–Ru bonds, i.e., dimerized bonds (red) and two other bonds (yellow) with similar lengths. (c) X-ray diffraction image in the $(h k 0)$ plane of single-crystal $L i_{2} Ru O_{3}$ with no sign of twinning.
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Figure 2
Temperature dependence of (a) the intensity of the (101) peak and (b) the $b / a$ ratio of the lattice parameters. The blue dashed line represents the value of $b / a \sim \sqrt{3}$ , a value found for the honeycomb structure with an almost ideal honeycomb lattice. The inset shows an illustration of the ideal hexagonal honeycomb structure.
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Figure 3
The photographs of (a) two-probe contact and (b) four-probe contact on the single-crystal $L i_{2} Ru O_{3}$ (c) Resistivity of the $L i_{2} Ru O_{3}$ single-crystal as a function of temperature in the range of 5–650 K, along the $a$ - (green), $b$ - (red), and $c$ *- (blue) crystal axes. The dashed lines in the range of 5–300 K are for the data taken on another samples to check the reproducibility of the results. The inset shows the Arrhenius plots of the resistivity curves from 300 to 650 K. (d) Four-probe resistivity measurement along the $b$ axis in the range of 300–630 K, with heating (red) and cooling (blue). The inset shows the Arrhenius plot of the cooling curves.
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Figure 4
(a) Susceptibilities of the $c$ *-axis-aligned single crystals as a function of temperature in the range of 2–300 K, along the out-of-plane ( $χ_{c^{*}}$ , circles ) and in-plane ( $χ_{a b}$ , squares ) directions; the inset shows the sample used for the measurement. (b) Angular-dependent torque measurement at fixed ϕ angles from $ϕ_{b a} = 0^{\circ}$ ( $b$ axis) to $ϕ_{b a} = 90^{\circ}$ ( $a$ axis). (c) Fitted amplitudes from the data with $ab$ rotation. The inset illustrates the crystal axes and rotating angles of the sample.
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Figure 5
(a) DFT band structure: upper six bands are from antibonding states and lower six bands are from bonding states. (b) Various points in the first Brillouin zone of the $L i_{2} Ru O_{3}$ (c) Resistivity divided by $ρ_{c^{*}}$ at 100 K with varying chemical potential. The green line represents $ρ_{a} / ρ_{c^{*}}$ , while the red line represents $ρ_{b} / ρ_{c^{*}}$ .
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Physical Review B

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Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate $L i_{2} Ru O_{3}$

Seokhwan Yun, Ki Hoon Lee, Se Young Park, Teck-Yee Tan, Junghwan Park, Soonmin Kang, D. I. Khomskii, Younjung Jo, and Je-Geun Park

Phys. Rev. B 100, 165119 – Published 14 October 2019

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Physical Review B

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Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate Li2RuO3

Seokhwan Yun, Ki Hoon Lee, Se Young Park, Teck-Yee Tan, Junghwan Park, Soonmin Kang, D. I. Khomskii, Younjung Jo, and Je-Geun Park

Phys. Rev. B 100, 165119 – Published 14 October 2019

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Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate $L i_{2} Ru O_{3}$