Magnetic-Field Induced Quantum Critical Point inYbRh2Si2

We report low-temperature calorimetric, magnetic, and resistivity measurements on the antiferromagnetic (AF) heavy-fermion metal ${\mathrm{Y}\mathrm{b}\mathrm{R}\mathrm{h}}_2{\mathrm{S}\mathrm{i}}_2$ ($T_N=70\mathrm{m}\mathrm{K}$) as a function of magnetic field $B$. While for fields exceeding the critical value $B_{c0}$ at which $T_N\to 0$ the low-temperature resistivity shows an $A{T}^2$ dependence, a $1/(B-B_{c0})$ divergence of $A\left(B\right)$ 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.