Gapless spin liquid in a square-kagome lattice antiferromagnet
Masayoshi Fujihala, Katsuhiro Morita, Richard A. Mole, Setsuo Mitsuda, Takami Tohyama, Shin-ichiro Yano, Dehong Yu, Shigetoshi Sota, Tomohiko Kuwai, A. Koda, Hirotaka Okabe, Hua Lee, Shinichi Itoh, Takafumi Hawai, Takatsugu Masuda, Hajime Sagayama, Akira Matsuo, Koichi Kindo, Seiko Ohira‐Kawamura, Kenji Nakajima
Abstract
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, 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.