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Abstract:
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.
