The quantum ferromagnetic transition in a clean Kondo lattice is discontinuous

Abstract

The Kondo-lattice model, which couples a lattice of localized magnetic moments to conduction electrons, is often used to describe heavy-fermion systems. Because of the interplay between Kondo physics and magnetic order it displays very complex behavior and is notoriously hard to solve. The ferromagnetic Kondo-lattice model, with a ferromagnetic coupling between the local moments, describes a phase transition from a paramagnetic phase to a ferromagnetic one as a function of either temperature or the ferromagnetic local-moment coupling. At zero temperature, this is a quantum phase transition that has received considerable attention. It has been theoretically described to be continuous, or second order. Here we show that this belief is mistaken; in the absence of quenched disorder the quantum phase transition is first order, in agreement with experiments, as is the corresponding transition in other metallic ferromagnets.

Continuous ferromagnetic quantum phase transition on an anisotropic Kondo lattice

“…The recent discovery of a ferromagnetic (FM) quantum critical point (QCP) in the clean heavy fermion compound CeRh 6 Ge 4 under hydrostatic pressure [1] has stimulated intensive interest in clarifying its underlying mechanism. According to prevailing theories, FM quantum phase transitions (QPTs) in heavy fermion systems, as manifested in UGe 2 [2] and URhAl [3], are typically first order because of some soft modes associated with the electron Fermi surfaces [4,5]. A continuous FM QPT had previously been observed in YbNi 4 (P 0.92 As 0.08 ) 2 [6,7], but might be due to disorder introduced by chemical substitution.…”