Emergence of superconductivity in the canonical heavy-electron metal YbRh₂Si₂

The smooth disappearance of antiferromagnetic order in strongly correlated metals commonly furnishes the development of unconventional superconductivity. The canonical heavy-electron compound YbRh₂Si₂ seems to represent an apparent exception from this quantum critical paradigm in that it is not a superconductor at temperature T ? 10 millikelvin (mK). Here we report magnetic and calorimetric measurements on YbRh₂Si₂, down to temperatures as low as T ? 1 mK. The data reveal the development of nuclear antiferromagnetic order slightly above 2 mK and of heavy-electron superconductivity almost concomitantly with this order. Our results demonstrate that superconductivity in the vicinity of quantum criticality is a general phenomenon.