Strongly coupled charge-density wave transition in single-crystal Lu₅Ir₄Si₁₀

We report the observation of a strongly coupled first-order charge-density wave (CDW) transition in a high-quality single crystal of the intermetallic compound Lu₅Ir₄Si₁₀. The first-order nature is ascertained by a very narrow and huge cusp (360 J/mol K) in the specific heat. The susceptibility and the resistivity also show sharp jumps at the transition T_CDW=83K. The periodic lattice distortion associated with the CDW is exemplified by the formation of x-ray superlattice reflections along the tetragonal c^→ axis with ^→q ≈ (0, 0, 3/7)(T < 83K). Although our results are in accordance with a quasi-one-dimensional CDW scenario, the first-order transition suggests a strong interchain coupling. We propose Lu₅Ir₄Si₁₀ as a paradigm of such strong-coupling CDW systems.