  The thermal conductivity measurements have been performed on the
heavy-fermion compound YbRh2Si2 down to 0.04 K and under magnetic fields
through a quantum critical point (QCP) at Bc = 0.66 T || c-axis. In the limit
as T -> 0, we find that the Wiedemann-Franz law is satisfied within
experimental error at the QCP despite the destruction of the standard signature
of Fermi liquid. Our results place strong constraints on models that attempt to
describe the nature of unconventional quantum criticality of YbRh2Si2.
