Gapless spin liquid in a square-kagome lattice antiferromagnet

Masayoshi Fujihala; Katsuhiro Morita; Richard Mole; Setsuo Mitsuda; Takami Tohyama; Shin-Ichiro Yano; Dehong Yu; Shigetoshi Sota; Tomohiko Kuwai; Akihiro Koda; Hirotaka Okabe; Hua Lee; Shinichi Itoh; Takafumi Hawai; Takatsugu Masuda; Hajime Sagayama; Akira Matsuo; Koichi Kindo; Seiko Ohira-Kawamura; Kenji Nakajima

doi:10.1038/s41467-020-17235-z

Gapless spin liquid in a square-kagome lattice antiferromagnet

Nat Commun. 2020 Jul 9;11(1):3429. doi: 10.1038/s41467-020-17235-z.

Authors

Masayoshi Fujihala¹, Katsuhiro Morita², Richard Mole³, Setsuo Mitsuda⁴, Takami Tohyama⁵, Shin-Ichiro Yano⁶, Dehong Yu³, Shigetoshi Sota⁷, Tomohiko Kuwai⁸, Akihiro Koda⁹, Hirotaka Okabe⁹, Hua Lee⁹, Shinichi Itoh¹⁰, Takafumi Hawai¹⁰, Takatsugu Masuda¹¹, Hajime Sagayama¹², Akira Matsuo¹³, Koichi Kindo¹³, Seiko Ohira-Kawamura¹⁴, Kenji Nakajima¹⁴

Affiliations

¹ Tokyo University of Science, Department of Physics, Tokyo, 162-8601, Japan. fujihara@nsmsmac4.ph.kagu.tus.ac.jp.
² Tokyo University of Science, Department of Applied Physics, Tokyo, 125-8585, Japan. katsuhiro.morita@rs.tus.ac.jp.
³ Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2232, Australia.
⁴ Tokyo University of Science, Department of Physics, Tokyo, 162-8601, Japan.
⁵ Tokyo University of Science, Department of Applied Physics, Tokyo, 125-8585, Japan.
⁶ National Synchrotron Radiation Research Center, Hsinchu, 30077, Taiwan.
⁷ Computational Materials Science Research Team, RIKEN Center for Computational Science, Kobe, Hyogo, 650-0047, Japan.
⁸ Graduate School of Science and Engineering, University of Toyama, Toyama, 930-8555, Japan.
⁹ Muon Science Laboratory and Condensed Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organisation, 1-1 Oho, Tsukuba, 305-0801, Japan.
¹⁰ Neutron Science Division, Institute of Materials Structure Science, High Energy Accelerator Research Organisation, 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan.
¹¹ Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
¹² Synchrotron Radiation Science Division 1 and Center for Integrative Quantum Beam Science, Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan.
¹³ International MegaGauss Science Laboratory, Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
¹⁴ Materials and Life Science Division, J-PARC Center, Tokai, Ibaraki, 319-1195, Japan.

Abstract

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu₆AlBiO₄(SO₄)₅Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state.