Multiple charge density waves compete in ternary rare-earth nickel carbides, R NiC2(R :Y ,Dy ,Ho ,and Er )

Single-crystal x-ray-diffraction experiments and electrical resistivity measurements were performed on intermetallic compounds of formula R NiC₂ [rare earth (R ): Y, Dy, Ho, and Er]. In the series of diffraction studies, we found three kinds of satellite reflections that had different wave vectors [incommensurate q_{1 i c}:(0.5 ,0.5 +η ,0 ) and commensurate q_{1 c}:(0.5 ,0.5 ,0 ) and q_{2 c}:(0.5 ,0.5 ,0.5 ) ] at temperatures where their resistivities show anomalies, such as a hump, a sharp increase, or a dent. Satellite reflections with nearly identical wave vectors have also been reported in R NiC₂ composed of earlier lanthanide atoms (GdNiC₂ and TbNiC₂). These results indicate the formation of a charge density wave (CDW) also in R NiC₂ studied in this paper. We found strong competition between the q_{1 i c} and the q_{2 c} CDWs in DyNiC₂ and YNiC₂, and that only the q_{2 c} CDW existed in HoNiC₂ and ErNiC₂. Based on the results obtained in the present paper and those of SmNiC₂,GdNiC₂ , and TbNiC₂ reported before, we discuss the CDW transitions in the R NiC₂ family.