Study of temperature-dependent lattice parameter in the organic metal α-(ET)₂ KHg(SCN)₄

Each of the organic metals in the family α-(ET)₂XHg(SCN)₄, with X=K, NH₄, Tl, or Rb displays a correlated electron ground state at low-temperature. Although they are isostructural and exhibit almost identical band structures and Fermi surfaces, three of the salts have a low-temperature coexisting charge density wave (CDW) and metallic phase, while one (X=NH₄) has a superconducting ground state. To understand the nature of the density wave state, we studied α-(ET)₂KHg(SCN)₄ using elastic x-ray scattering at the Advanced Photon Source at Argonne National Laboratory. Here we will present preliminary temperature-dependent data for the lattice parameter (b-axis) at 296K, 104K, and 4K. In addition, we will discuss scattering data at 4 K to search for incommensurate CDW, below the thermodynamic phase transition at 8K. We will also use density-functional theory and the x-ray results at different temperatures to investigate changes in the band structure and calculate the Lindhard response function as a function of temperature to predict the amplitude and the orientation of the CDW.