Abstract
We provide experimental evidence for unconventional superconductivity in a newly synthesized three-dimensional nearly antiferromagnetic metal, LaAg1 − xMnx, and report results that indicate that the antiferromagnetic spin-fluctuation-mediated pairing may have a direct bearing on this phenomenon. Compared to the heavy-fermion systems, the superconducting transition temperature is nearly 10 times higher, superconductivity is robust against impurities and the specific-heat anomaly associated with the superconducting transition is extremely weak, or even absent. Our results are consistent with certain previously reported theoretical criteria for observing antiferromagnetic spin-fluctuation-mediated superconductivity at elevated temperatures.