Protection of excited spin states by a superconducting energy gap

The latest concepts for quantum computing and data storage envision to address and manipulate single spins. A limitation for single atoms or molecules in contact to a metal surface are the short lifetime of excited spin states, typically picoseconds, due to the exchange of energy and angular momentum with the itinerant electrons of the substrate [1-4]. Here we show that paramagnetic molecules on a superconducting substrate exhibit excited spin states with a lifetime of approximately 10 ns. We ascribe this increase in lifetime by orders of magnitude to the depletion of electronic states within the energy gap at the Fermi level. This prohibits pathways of energy relaxation into the substrate and allows for electrically pumping the magnetic molecule into higher spin states, making superconducting substrates premium candidates for spin manipulation. We further show that the proximity of the scanning tunneling microscope tip modifies the magnetic anisotropy.