  The great practical utility has motivated extensive efforts to discover
ultra-low resistance electrical conductors and superconductors in ambience.
Here we report the observation of vanishingly small electrical resistance at
the ambient temperature and pressure conditions in films and pellets of a
nanostructured material that is composed of silver particles embedded into a
gold matrix. Upon cooling below a sample-specific temperature scale ($T_{C}$)
as high as $286$ K, the film resistance drops below $\sim 2\mu\Omega$, being
limited by measurement uncertainty. The corresponding resistivity ($\sim
10^{-12}$ $\Omega$.m) is at least four orders of magnitude below that of
elemental noble metals, such as gold, silver or copper. Furthermore, the
samples become strongly diamagnetic below $T_{C}$, with volume susceptibilities
as low as -0.056. We additionally describe methods to tune $T_{C}$ to
temperatures much higher than room temperature.
