Magnetism and superconductivity of compacted micro- and nanogranular Platinum

Compared to their bulk counterparts, micro- and nanogranular materials can reveal a diverse physical appearance. In particular, their magnetic and superconducting behaviour can be drastically influenced. As a prominent example, the superconductivity of compacted granular Pt will be presented.
Pt has been cooled down to an equilibrium temperature of phonons, electrons and nuclear magnetic moments of 1.5 µK, lower than all other materials so far [1]. However, superconductivity has not been observed in bulk Pt. Surprisingly, superconductivity occurs in compacted microgranular Pt [2]. The weakened impurity magnetism in powdered Pt (spin glass behaviour at mK temperatures) may play the crucial role in adjusting the balance between electron-phonon interaction and competing magnetic interactions. As a proof, we have also investigated Pt powders with a higher impurity content observing lower Tc values. In addition, low frequency phonons from the Pt surface could influence the electron-phonon interaction. In further investigated nanoscale Pt powders, the superconducting transition temperature is about 20 times larger than detected in the micrometer sized grains [3].

[1] W. Wendler, T. Herrmannsdörfer, S. Rehmann, F. Pobell, Europhys. Lett. 38, 619 (1997)
[2] R. König, A. Schindler, T. Herrmannsdörfer, Phys. Rev. Lett. 82, 4528 (1999)
[3] A. Schindler et al., Europhys. Lett. 58, 885 (2002)