Quantum Phase Transitions in an Yb-based Semiconductor YbCuS2 with an Effective Spin-1=2 Zigzag Chain.

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 C_m=T exhibits a sharp peak at T_O = 0.95 K, where the magnetic entropy is 20% of R ln 2, indicating strong magnetic fluctuations. In magnetic fields, T_O is robust for B < 4 T, and it shifts to higher temperatures but reverses downward for B ≥ 7 T. Below T_O, 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. [ABSTRACT FROM AUTHOR]