Possible structural quantum phase transition in UCr_2-xRu_xSi₂

We report an investigation of the structural, thermodynamic, and electrical transport properties of the chemical substitution series UCr_2-xRu_xSi₂. UCr₂Si₂ is an unusual Kondo lattice metal that shows antiferromagnetism at T_N = 27 K, a structural phase transition from tetragonal (I4/mmm) to triclinic (P) near T_s = 210 K, and a so-far unidentified phase transition near T_M = 275 K. Cr → Ru substitution results both in expansion of the unit cell volume and filling of the d-shell, causes T_N and T_S to be suppressed to zero temperature near x_cr ≈ 0.075 and 0.13, respectively. In contrast, T_M disappears immediately with small amount of Ru. In the critical region, there is evidence for non-Fermi liquid behavior, (i) a weak logarithmic divergence in the electronic component of the heat capacity divided by temperature and (ii) a sub-quadratic temperature dependence of the electrical resistivity. Thus, we suggest that this may be a model system for studying a lattice instability at zero temperature, its relationship to a nearby antiferromagnetic quantum phase transition, and the resulting impact on electronic properties and lattice modes in a strongly correlated electron metal.