Field-induced phases in UPt₂Si₂

The tetragonal compound UPt₂Si₂ has been characterized as a moderately mass-enhanced system with an antiferromagnetic (AFM) ground state below T_N = 32 K. Here, we present an extensive study of the behavior in high magnetic fields.We have performed pulsed field magnetization and static field resistivity measurements on single crystalline samples UPt₂Si₂. Along the crystallographic a axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 40 T, possibly indicating a first-order transition. Along the crystallographic c axis, in magnetic fields of B ≥ 24 T, we find distinct anomalies in both properties. From our analysis of the data we can distinguish new high-field phases above the AFM ground state. We discuss the emergence of these new phases in the context of Fermi surface effects and the possible occurrence of a Lifshitz or electronic topological transition, this in contrast to previous modelings of UPt₂Si₂ based on crystal electric field effects.