Structural properties, magnetic order and electronic transport in single crystalline UPt2Si2

We present a detailed comparison of the physical properties of as-cast and annealed single crystalline UPt₂Si₂, a compound whose properties we have shown to be governed by strain disorder on the Pt/Si ligand sites. Contrary to common knowledge, and to our surprise, from our data we do not observe a significant improvement of the physical properties of UPt₂Si₂ upon annealing at 900 °C for one week. We attribute this to the specific way the strain disorder is produced in UPt₂Si₂ by presenting evidence that it results from a first order phase transition at ambient temperatures. We discuss the implications of such phase transitions occurring at comparatively low temperatures for the ground state properties of heavy fermion systems and related correlated electron materials.