Heavy-electron behavior in single-crystal YbNi2B2C.

Abstract

We have measured the magnetic susceptibility, specific heat, and electrical resistivity on single crystals of the intermetallic borocarbide Yb${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$C. An enhanced linear contribution is observed in the specific heat with a Sommerfeld coefficient of 530 mJ/mol ${\mathrm{K}}^{2}$, indicative of a heavy-electron system with a Kondo temperature \ensuremath{\sim}10 K. The magnetic susceptibility, which is anisotropic and Curie-Weiss-like at high temperatures, is also consistent with our interpretation of a strongly correlated ground state at low temperatures and crystal-electric-field excitations at higher temperatures. At $T=1.8$ K, the Wilson ratio is determined to be 0.85 using the high-temperature effective moment. The resistivity shows a quadratic temperature dependence below 1.5 K with a ${T}^{2}$ coefficient of 1.2 \ensuremath{\mu}\ensuremath{\Omega} cm ${\mathrm{K}}^{\ensuremath{-}2}$. Unlike the other members of the series $R{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}(R=\mathrm{Y},\phantom{\rule{0ex}{0ex}}\mathrm{G}\mathrm{d}\ensuremath{-}\mathrm{L}\mathrm{u})$, Yb${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$C does not order above our lowest measurement temperature of 0.34 K. The suppression of superconductivity in Yb${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$C is consistent with a significantly enhanced hybridization between the conduction electrons and the $4f$ states.