Intact quasiparticles at an unconventional quantum critical point

We report measurements of in-plane electrical and thermal transport properties in the limit T -> 0 near the unconventional quantum critical point in the heavy-fermion metal beta-YbAlB4. The high Kondo temperature T-K similar or equal to 200 K in this material allows us to probe transport extremely close to the critical point, at unusually small values of T/T-K < 5 x 10(-4). Here we find that the Wiedemann-Franz law is obeyed at the lowest temperatures, implying that the Landau quasiparticles remain intact in the critical region. At finite temperatures we observe a non-Fermi-liquid T-linear dependence of inelastic-scattering processes to energies lower than those previously accessed. These processes have a weaker temperature dependence than in comparable heavy fermion quantum critical systems, revealing a temperature scale of T similar to 0.3 K which signals a sudden change in the character of the inelastic scattering.