Single Crystal Studies of Charge Density Wave Physics in Quasi-1D Metals RNiC₂

Abstract

Ternary carbides RNiC2 (R = rare earths and Y) crystallize in the non-centrosymmetric orthorhombic CeNiC2-type structure, space group Amm2. These compounds attracted attention, because of various interesting properties such as superconductivity, magnetism, multiple charge density wave (CDW) transitions related to quasi-one-dimensional electronic features of RNiC2, and finally, a complex interplay of CDW order and rare earth magnetism in RNiC2 (see Ref. [1] for a review). Here, we report on crystal growth, crystallographic characteristics explored via single crystal XRD, as well as magnetic, thermodynamic, and electronic properties studied by a variety of techniques revealing orientation dependent, anisotropic features of selected RNiC2 single crystals. Based on heat capacity, thermal expansion and electrical resistivity studies, we analyse the nature of multiple CDW transitions occurring in RNiC2 crystals (e.g., orthorhombic to incommensurate CDW and incommensurate to commensurate CDW transitions). We discuss their relations to electronic and crystal structure changes and, employing Clausius-Clapeyron and generalized Ehrenfest relations, we discuss resulting pressure and strain dependencies of the observed CDW phases.