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Ab-initio prediction of pressure induced superconductivity in potassium

Authors: A. Sanna, C. Franchini, A. Floris, G. Profeta, N.N. Lathiotakis, M. Lueders, M.A.L. Marques, E.K.U. Gross, A. Continenza, and S. Massidda

Ref.: Phys. Rev. B 73, 144512 (2006)

Abstract: We report first principles calculations of the superconducting properties of fcc potassium under high pressure. Using a completely ab-initio method we predict a superconducting phase transition at 18 GPa. A maximum critical temperature of about 2 K is observed around 23 GPa, the pressure at which the crossover between the fcc phase and the K III structure experimentally occurs. At higher pressure, when the fcc phase is experimentally unstable, we find, in the phononically stable range, values of T_c up to 11 K. In order to understand the underlying mechanisms inducing superconductivity in potassium, we study the effect of pressure on the electronic and vibrational properties, showing a progressive phonon softening near the K point of the Brillouin zone and a concomitant enhancement of the electron-phonon coupling constant lambda. Interestingly, we find that the pressure induced s-d charge transfer causes an increasing anisotropy of the superconducting gap Delta. Although similar to dense Li in many respects, K displays interesting peculiar features.

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