Non-Fermi Liquid Behavior of Correlated Fermions in Applied Field

Abstract

We have determined an instability of the Fermi-liquid state of almost localized fermions in an applied magnetic ffeld. It is proposed that a transition to a strongly correlated fermions (statistical-spin-liquid) state takes place at that point. The resultant magnetization curve and the field dependence of the specific heat are calculated and compared with those for CeRu 2 Si2 .PACS numbers: 71.27.+a, 71.30.+h, 71.10.FóThe metallic state close to Mott-Hubbard localization is commonly regarded as a Fermi-liquid state of correlated fermions [1]. The quasiparticles in this liquid have spin-dependent effective masses (if the band fllling n # 1), and experience a nonlinear molecular field in the spin polarized state [2]. The principal question is: what happens for n # 1 if we apply a magnetic field and the number of double occupancy d2 --> 0, i.e. magnetization m Ξ n↑ -n ↓ --> n? Does it transform gradually into a gas of fermions with one spin direction up or a non-Fermi liquid state comes into play before the system saturates magnetically?The purpose of this paper is to demonstrate that at the point of instability of the almost localized Fermi liquid (ALFL) a transition to the spin liquid state takes place. Consequently, we calculate the magnetization curve exhibiting a mixed itinerant-localized behavior, as well as the applied field dependence of the linear specific heat coeímcient γ Ξ C/T across the transition. In Fig. 1a we have displayed the field dependence of the double occupancy d2 Ξ (ni↑ni↓) in the narrow band of correlated fermions, for three different relative temperatures t Ξ kBT/W (W is the bare band width, U/Uc is the relative magnitude of interaction, U = 2W and n is the band filling). At the points of instability (marked by the dashed lines) there is a metamagnetic transition, associated with a jump in d 2 and magnetization m. For the fields h = μΒ Η a /W beyond this point (h = hc) w e o b t a i n a n o n p h y s i c a l values of d2 < 0, so the ALFL state is unstable. On the physical grounds one can visualize the state d2 = 0 as a liquid of itinerant spins, since the hopping takes place only via empty lattice sites. Therefore, we proposed [3] that such a state (323)