Yb-based heavy-fermion metal situated close to a quantum critical point

Abstract

We report low-temperature thermodynamic, magnetic, and transport measurements on high-quality single crystals of the tetragonal heavy-fermion system ${\mathrm{YbIr}}_{2}{\mathrm{Si}}_{2}$. Depending on synthesis conditions it crystallizes either in the $I$-type body-centered ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$ or $P$-type ${\mathrm{CaBe}}_{2}{\mathrm{Ge}}_{2}$ structure. The $P$-type system has a low Kondo scale ${T}_{K}=2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and orders magnetically below 0.7 K whereas the $I$-type system remains paramagnetic and shows, above 0.5 K, a temperature dependence of the resistivity and the specific heat similar to that of ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$. In contrast to ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$ which exhibits non-Fermi-liquid behavior, ${\mathrm{YbIr}}_{2}{\mathrm{Si}}_{2}$ reaches a Landau Fermi-liquid state below 0.2 K and is thus ideally suited for pressure studies across the quantum critical point.