Gapless spin liquid in a square-kagome lattice antiferromagnet

• Published in: Nature communications 2020-07, Vol.11 (1), p.3429-3429, Article 3429
• Main Authors: Fujihala, Masayoshi, Morita, Katsuhiro, Mole, Richard, Mitsuda, Setsuo, Tohyama, Takami, Yano, Shin-ichiro, Yu, Dehong, Sota, Shigetoshi, Kuwai, Tomohiko, Koda, Akihiro, Okabe, Hirotaka, Lee, Hua, Itoh, Shinichi, Hawai, Takafumi, Masuda, Takatsugu, Sagayama, Hajime, Matsuo, Akira, Kindo, Koichi, Ohira-Kawamura, Seiko, Nakajima, Kenji
• Format: Article
• Language: English
• Subjects: 639/766/119/997; 639/766/119/999; Antiferromagnetism; Condensed matter physics; Crystal structure; Experimental methods; Frustrated magnetism; Heat exchange; Heisenberg theory; Humanities and Social Sciences; Inelastic scattering; Kagome lattice; Laboratories; Low temperature; Magnetic fields; Magnetic permeability; Magnetic susceptibility; Magnetism; multidisciplinary; Muon spin relaxation; Nearest-neighbor; Neutron scattering; Phase transitions; Physics; Playgrounds; Radiation; Science; Science (multidisciplinary); Solid state physics; Spin liquid; Statistical models
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-17235-z

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, KCu 6 AlBiO 4 (SO 4 ) 5 Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation ( μ SR), 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. There exist many theoretical models of frustrated quantum magnetism, most of which lack convincing experimental realisations. Here the authors combine several experimental methods to argue that KCu 6 AlBiO 4 (SO 4 ) 5 Cl behaves as a square-kagome-lattice quantum Heisenberg antiferromagnet.