Using single-crystal neutron and x-ray diffraction, we discovered a charge density wave (CDW) below 320 K, which accounts for the long-sought origin of the heat capacity and resistivity anomalies in ${\mathrm{UPt}}_2{\mathrm{Si}}_2$. The modulation wave vector, ${\mathit{Q}}_{\mathrm{mod}}$, is intriguingly similar to the incommensurate wave vector of ${\mathrm{URu}}_2{\mathrm{Si}}_2$. ${\mathit{Q}}_{\mathrm{mod}}$ shows an unusual temperature dependence, shifting from commensurate to incommensurate position upon cooling and becoming locked at aproximately (0.42 0 0) near 180 K. Bulk measurements indicate a crossover toward a correlated coherent state around the same temperature, suggesting an interplay between the CDW and Kondo-lattice-like coherence before coexisting antiferromagnetic order sets in at $T_{\mathrm{N}}=35$ K.

• Received 20 September 2019
• Revised 29 June 2020
• Accepted 29 June 2020
• Corrected 1 October 2020

DOI:https://doi.org/10.1103/PhysRevB.102.041112