Angle-resolved photoemission study of USb2 the 5f band struc(2)

Single crystal antiferromagnetic USb2 was studied at 15K by angle-resolved photoemission with an overall energy resolution of 24 meV. The measurements unambiguously show the dispersion of extremely narrow bands situated near the Fermi level. The peak at th

1.Introduction

The unusual properties of heavy fermion compounds have attracted considerable attention during the last two decades and several theoretical approaches have been developed in order to explain the large effective mass of the conduction electrons. It is well established that it is the f-electrons which are responsible for an effective mass enhancement and thus features that are specific to heavy fermion materials. The heavy fermion and antiferromagnetic ground states are both singlet states and similar in that the f-moment is compensated ostensibly by either a screening cloud of conduction electrons (heavy fermion) or an f-moment of opposite spin on an adjacent site (antiferromagnet). Photoemission techniques, which are capable of providing detailed information regarding the binding energy of the 5f electron band, as well as the dispersion and hybridization with the conduction band, are an especially valuable tool for evaluation of the various theoretical models.

U and Ce heavy fermion compounds exhibit similar bulk properties (magnetic susceptibility, resistivity and indications of enhanced mass), thus one might expect similarities in their electronic structures and similar theoretical models to be capable of explaining their heavy fermion behavior. The Single Impurity Model (SIM) [1 - 4] and the Periodic Anderson Model (PAM) [5, 6] have been the basic computational approaches, although many other models like the charge polaron model [7] or the two-electron band model [8] also address properties beyond one-electron models.

In the SIM model, f-electrons are treated as completely localized impurities in the sea of conduction electrons. This model assumes only slight hybridization with ligand conduction bands, which results in a non-dispersive f-levels. The second prediction of the model is that the PES f-electron weight scales with characteristic temperature. The shortcomings of this treatment of the PES data for correlated electron systems have been well documented [9 - 12].

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