Breakup of Heavy Fermions on the Brink of “PhaseA” inCeCu2Si2

Abstract

We report resistivity, $\rho \left(T\right)$, and specific-heat, $C\left(T\right)$, results on near stoichiometric $\mathrm{CeCu}{}_2{\mathrm{Si}}_2$ samples, in the vicinity of a quantum critical point (QCP). The latter is defined by $T_A\to 0$, where $T_A\lesssim 0.8\mathrm{K}$ marks the transition into a spin-density–wave-type “phase $A$” which competes with heavy-fermion superconductivity below $T_c\approx 0.65\mathrm{K}$. Upon approaching the QCP, $\rho \left(T\right)$ and $C\left(T\right)$ behave very disparately, suggesting a breakup of the heavy quasiparticles. Very surprising observations are being made for samples with $T_A>0\mathrm{}$ also.