Single-crystal study of the charge density wave metal LuNiC2

Abstract

We report on single crystal growth, single crystal x-ray diffraction, physical properties and density functional theory (DFT) electronic structure as well as Fermi surface calculations for two ternary carbides, LuCoC2 and LuNiC2. Electrical resistivity measurements reveal for LuNiC2 a charge density wave (CDW) transition at T_{CDW}~ 450 K and, for T > T_{CDW}, a significant anisotropy of the electrical resistivity, which is lowest along the orthorhombic a-axis. The analysis of x-ray superstructure reflections suggest a commensurate CDW state with a Peierls-type distortion of the Ni atom periodicity along the orthorhombic a-axis. DFT calculations based on the CDW modulated monoclinic structure model of LuNiC2 as compared to results of the orthorhombic parent-type reveal the formation of a partial CDW gap at the Fermi level which reduces the electronic density of states from N(E_{F})= 1.03 states/eV f.u. without CDW to N(E_{F})= 0.46 states/eV f.u. in the CDW state. The corresponding bare DFT Sommerfeld value of the latter, gamma_{DFT}^{CDW}= 0.90 mJ/molK^2, reaches reasonable agreement with the experimental value gamma= 0.83(5) mJ/mol\,K^2 of LuNiC2. LuCoC2 displays a simple metallic behavior with neither CDW ordering nor superconductivity above 0.4 K. Its experimental Sommerfeld coefficient, gamma= 5.9 (1) mJ/molK^2, is in realistic correspondence with the calculated, bare Sommerfeld coefficient, gamma_{DFT}= 3.82 mJ/molK^2, of orthorhombic LuCoC2.