Interplay of staggered SC with CDW in a fully polarized ferromagnet

Abstract

We have studied the competition of charge density waves (CDW) and superconductivity (SC) in a fully polarized ferromagnetic (FM) medium. Motivation for this study was the observation of SC deep in the FM state of UGe 2. Assuming the spins frozen, there are four possible SC order parameters in the triplet channel both at zone center (i.e. with zero total momentum) and at zone boundary (i.e. staggered SC) that may compete with four possible CDW order parameters forming 16 different pairs of competing states. Emphasis is given on the proper consideration of the effect of particle-hole asymmetry that may simulate the effect of pressure in UGe 2. Four different systems of coupled self consistent gap equations describe four different competing pairs of CDW and SC order parameters. We focus here on the situations in which staggered SC is a possible state and we study the influence of particle-hole asymmetry on its competition with charge density waves. We obtain cases in which CDW and staggered SC coexist as well as cascades of transitions induced by particle-hole asymmetry that exhibit striking similarities with those seen in UGe 2 by applying pressure. Our analysis suggests that SC in UGe 2 is staggered competing with a CDW.