Magnetic-Field Induced Quantum Critical Point in YbRh₂Si₂

We report low-temperature calorimetric, magnetic, and resistivity measurements on the antiferromagnetic (AF) heavy- fermion metal YbRh2Si2 ( T-N=70 mK) as a function of magnetic field B. While for fields exceeding the critical value B-c0 at which T-N-->0 the low-temperature resistivity shows an AT(2) dependence, a 1/(B-B-c0) divergence of A(B) upon reducing B to B-c0 suggests singular scattering at the whole Fermi surface and a divergence of the heavy quasiparticle mass. The observations are interpreted in terms of a new type of quantum critical point separating a weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state