Quantum Phase Transitions in an Yb-based Semiconductor YbCuS<sub>2</sub> with an Effective Spin-1/2 Zigzag Chain
Yudai Ohmagari, Takahiro Onimaru, Yu Yamane, Yasuyuki Shimura, Kazunori Umeo, T. Takabatake, Hitoshi Sato, Naoki Kikugawa, Taichi Terashima, Hishiro T. Hirose, Shinya Uji
Abstract
Magnetic properties of an Yb-based semiconductor YbCuS2 with a zigzag chain of Yb3+ ions were studied. The Curie–Weiss behavior of the magnetic susceptibility χ(T) indicates antiferromagnetic interaction and an isolated Kramers doublet ground state with effective spin-1/2. Magnetic specific heat Cm/T exhibits a sharp peak at TO = 0.95 K, where the magnetic entropy is 20% of R ln 2, indicating strong magnetic fluctuations. In magnetic fields, TO is robust for B < 4 T, and it shifts to higher temperatures but reverses downward for B ≥ 7 T. Below TO, a magnetization plateau manifests itself at around 6 T which is followed by transitions at 9.1 and 15.6 T. The phase diagram suggests that nontrivial phases arise from magnetic frustration in the Yb zigzag chain.