Quantum fluctuation driven first-order phase transition in weak ferromagnetic metals

Abstract

In a local Fermi liquid (LFL), we show that there is a line of weak first-order phase transitions between the ferromagnetic and paramagnetic phases due to purely quantum fluctuations. We predict that an instability towards superconductivity is only possible in the ferromagnetic state. At T = 0 we find a point on the phase diagram where all three phases meet and we call this a quantum triple point (QTP). A simple application of the Gibbs phase rule shows that only these three phases can meet at the QTP. This provides a natural explanation of the absence of superconductivity at this point coming from the paramagnetic side of the phase diagram, as observed in the recently discovered ferromagnetic superconductor, UGe ₂.

Acknowledgements

We gratefully acknowledge discussions with A.V. Balatsky, K.B. Blagoev, B. Chakraborty, A.V. Chubukov, J.R. Engelbrecht, D. Morr, and especially, Prof. G.E. Brown. K.S.B. would like to acknowledge the Aspen Center for Physics where some of the ideas presented here were formulated. This work was done with the support of DOE Grants No. DEFG0297ER45636 and No. 60202ER63404.