Pressure-induced transition from <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>J</mi><mi>eff</mi></msub><mo>=</mo><mrow></mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></math> to <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>S</mi><mo>=</mo><mrow></mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></math> states in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Cu</mi><msub><mi>Al</mi><mn>2</mn></msub><msub><mi mathvariant="normal">O</mi><mn>4</mn></msub></mrow></math>

Hwanbeom Cho; Choong H. Kim; Yongmoon Lee; Kazuki Komatsu; Byeong-Gwan Cho; Deok-Yong Cho; Taehun Kim; Chaebin Kim; Younghak Kim; Tae Yeong Koo; Yukio Noda; Hiroyuki Kagi; Daniel I. Khomskii; Donghoon Seoung; Je-Geun Park

doi:10.1103/PhysRevB.103.L081101

Letter

Pressure-induced transition from $J_{eff} = 1 / 2$ to $S = 1 / 2$ states in $Cu {Al}_{2} O_{4}$

Hwanbeom Cho ^1,2,3,*, Choong H. Kim ^2,3, Yongmoon Lee⁴, Kazuki Komatsu⁵, Byeong-Gwan Cho⁶, Deok-Yong Cho ⁷, Taehun Kim ^2,3,8, Chaebin Kim ^2,3,8, Younghak Kim ⁶ et al.

Tae Yeong Koo⁶, Yukio Noda ⁹, Hiroyuki Kagi⁵, Daniel I. Khomskii¹⁰, Donghoon Seoung ^11,†, and Je-Geun Park^2,3,8,12,‡

¹Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
²Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
³Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
⁴Department of Geological Sciences, Pusan National University, Busan 46241, Republic of Korea
⁵Geochemical Research Center, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
⁶Pohang Accelerator Laboratory, POSTECH, Pohang 37673, Republic of Korea
⁷IPIT & Department of Physics, Jeonbuk National University, Jeonju 54896, Republic of Korea
⁸Center for Quantum Materials, Seoul National University, Seoul 08826, Republic of Korea
⁹Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
¹⁰II. Physikalisches Institut, Universität zu Köln, D-50937 Köln, Germany
¹¹Department of Earth and Environmental Sciences, Chonnam National University, Gwangju 61186, Republic of Korea
¹²Institute of Applied Physics, Seoul National University, Seoul 08826, Republic of Korea

^*hwanbeom.cho@physics.ox.ac.uk
^†dseoung@jnu.ac.kr
^‡jgpark10@snu.ac.kr

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Phys. Rev. B 103, L081101 – Published 3 February, 2021

DOI: https://doi.org/10.1103/PhysRevB.103.L081101

Abstract

The spin-orbit entangled (SOE) $J_{eff}$ state has been a fertile ground to study quantum phenomena. Contrary to the conventional weakly correlated $J_{eff} = 1 / 2$ state of $4 d$ and $5 d$ transition metal compounds, the ground state of $Cu {Al}_{2} O_{4}$ hosts a $J_{eff} = 1 / 2$ state with a strong correlation of Coulomb $U$ . Here, we report that, surprisingly, ${Cu}^{2 +}$ ions of $Cu {Al}_{2} O_{4}$ overcome the otherwise usually strong Jahn-Teller distortion and instead stabilize the SOE state, although the cuprate has relatively small spin-orbit coupling. From the x-ray absorption spectroscopy and high-pressure x-ray diffraction studies, we obtained definite evidence of the $J_{eff} = 1 / 2$ state with a cubic lattice at ambient pressure. We also found the pressure-induced structural transition to a compressed tetragonal lattice consisting of the spin-only $S = 1 / 2$ state for pressure $P_{c} > 8 GPa$ . This phase transition from the Mott insulating $J_{eff} = 1 / 2$ to the $S = 1 / 2$ states is a unique phenomenon. Our study offers an example of the SOE $J_{eff}$ state under strong electron correlation and its pressure-induced transition to the $S = 1 / 2$ state.

Physical Review B

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Pressure-induced transition from $J_{eff} = 1 / 2$ to $S = 1 / 2$ states in $Cu {Al}_{2} O_{4}$

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Pressure-induced transition from Jeff=1/2 to S=1/2 states in CuAl2O4

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Pressure-induced transition from $J_{eff} = 1 / 2$ to $S = 1 / 2$ states in $Cu {Al}_{2} O_{4}$