Evidence of a Kondo Destroying Quantum Critical Point in YbRh₂Si₂

The heavy-fermion metal YbRh₂Si₂ is a weak antiferromagnet below TN = 0.07 K. Application of a low magnetic field Bc = 0.06 T (⊥ c) is sufficient to continuously suppress the antiferromagnetic (AF) order. Below T ≈ 10 K, the Sommerfeld coefficient of the electronic specific heat γ(T) exhibits a logarithmic divergence. At $T < 0.3$ K, γ(T) ~ T-ε (ε: 0.3 - 0.4), while the electrical resistivity ρ(T) = ρ₀ + aT (ρ₀: residual resistivity). Upon extrapolating finite-T data of transport and thermodynamic quantities to $T = 0$, one observes (i) a vanishing of the "Fermi surface crossover" scale T*(B), (ii) an abrupt jump of the initial Hall coefficient RH(B) and (iii) a violation of the Wiedemann Franz law at B = Bc, the field-induced quantum critical point (QCP). These observations are interpreted as evidence of a critical destruction of the heavy quasiparticles, i.e., propagating Kondo singlets, at the QCP of this material.