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 chi(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 in 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.