Protection of excited spin states by a superconducting energy gap

• Published in: Nature physics 2013-12, Vol.9 (12), p.765-768
• Main Authors: Heinrich, B. W., Braun, L., Pascual, J. I., Franke, K. J.
• Format: Article
• Language: English
• Subjects: 639/766/119/1001; 639/766/119/1003; 639/766/119/997; Anisotropy; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Contact angle; Data storage; Depletion; Exchange; Excitation; Fermi level; letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Substrates; Superconductivity; Superconductors; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2794

When a paramagnetic molecule is placed on a superconducting surface the lifetime of its spin excitations increases dramatically. This effect, caused by the depletion of the electronic states within the energy gap at the Fermi level, could find application in coherent spin manipulation. The latest concepts for quantum computing and data storage rely on the addressing and manipulation of single spins. A limitation for single atoms or molecules in contact with a metal surface is 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 , 2 , 3 , 4 . Here we show that paramagnetic molecules on a superconducting substrate exhibit excited spin states with a lifetime of τ ≈10 ns. We ascribe this increase in lifetime by orders of magnitude to the depletion of electronic states around the Fermi level in the superconductor. This prohibits pathways of energy relaxation into the substrate and allows the magnetic molecule to be electrically pumped into higher spin states, making superconducting substrates prime candidates for spin manipulation. We further show that the proximity of the scanning tunnelling microscope tip modifies the magnetic anisotropy.