Quantum criticality and the α/δ puzzle

Abstract

In an overview of the elemental actinides, Np and Pu stand out due to their anomalously low melting temperatures and the variety of complex phase transitions that occur in these elements and their alloys as a result of relatively modest changes in temperature and pressure. In this paper, we suggest a novel explanation based on an analogy between the evolution of the actinide ground state as a function of spin-orbit coupling and the behaviour of thin film superconductors in a magnetic field. The key point is that, in metals with a low carrier density, spin-orbit interactions give rise to low energy monopole-like solitons with quantised spin currents, which play much the same role as Abrikosov vortices in thin film superconductors. In Np and alpha-Pu, these solitons form an ordered solid, while, in impurity stabilised delta-Pu, they form a pair condensate. This provides a simple explanation for the heretofore unexplained phenomenology of alpha-delta transition. Near room temperature delta-Pu represents a novel form of condensed matter: a ‘Planckian metal’ analogous to the quark-gluon plasma.

Keywords:

• actinides
• spin-orbit
• high Tc

Acknowledgements

The author is very grateful for conversations with M. Fluss, S. Hecker, J. Lashley, S. McCall, K. Moore, P. Soderlind and J. Zaanen. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.