Non-Fermi liquid state bounded by a possible electronic topological transition in ZrZn ₂

We report high-precision magnetic and transport measurements of ZrZn ₂ and present a phase diagram as a function of pressure and magnetic field. The paramagnetic phase is found to be divided into two regions at T ≃ 0 by a possible electronic topological transition (i.e., a non-symmetry breaking transition) known as the Lifshitz transition, and the two regions are characterized by Fermi and non-Fermi liquid behaviors. These results strongly suggest that the non-Fermi liquid state exists as a stable phase distinguished from the Fermi liquid by the Fermi surface topology. As a possible origin of the non-Fermi liquid behavior, an antiferromagnetic fluctuation arising from the Fermi surface nesting is discussed.