Abstract
Analyzing temperature dependent photoemission (PE) data of the ferromagnetic Kondo-lattice (KL) system YbNiSn in the light of the Periodic Anderson model (PAM) we show that the KL behavior is not limited to temperatures below a temperature T_K, defined empirically from resistivity and specificic heat measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE spectra reveal a 4f-derived Fermi level peak, which reflects contributions from the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn this peak has an unusual temperature dependence: With decreasing temperature a steady linear increase of intensity is observed which extends over a large interval ranging from 100 K down to 1 K without showing any peculiarities in the region of T_K ~ TC= 5.6 K. In the light of the single-impurity Anderson model (SIAM) this intensity variation reflects a linear increase of 4f occupancy with decreasing temperature, indicating an onset of Kondo screening at temperatures above 100 K. Within the PAM this phenomenon could be described by a non-Fermi liquid like T- linear damping of the self-energy which accounts phenomenologically for the feedback from the closely spaced CEF-states.
Highlights
Intermetallic rare-earth (RE) systems based on Ce, Eu, or Yb form a prototype of strongly correlated electron systems, where the interplay between almost localized 4f and itinerant valence states results in a wealth of extraordinary phenomena
Within the periodic Anderson model (PAM) this phenomenon could be described by a non-Fermi-liquid-like T - linear damping of the self-energy which accounts phenomenologically for the feedback from the closely spaced crystal electric field (CEF) states
The KL model has the same relation to the PAM as the single site Kondo model to the single-impurity Anderson model (SIAM): They are linked via the Schrieffer-Wolff transformation [5], valid when the state of Yb is almost trivalent
Summary
Intermetallic rare-earth (RE) systems based on Ce, Eu, or Yb form a prototype of strongly correlated electron systems, where the interplay between almost localized 4f and itinerant valence states results in a wealth of extraordinary phenomena. As a stoichiometric material with a low level of defects, YbNiSn broadens the range of experimental techniques available for studies of the QCP, such as quantum oscillations in the electrical resistivity and magnetization and photoemission (PE). The nearest neighbors of a Yb atom are four Yb atoms located at the vertices of a much distorted tetrahedron; two of them are at the distance of 3.552 A (shown in the polyhedra in Fig. 1) and the other two at 3.797 A. a six-axis CARVING manipulator with high angular precision which is ideally suited for ARPES experiments down to 10 K. The temperature-dependent measurements were performed always going from high to low temperatures in order to avoid fast sample aging
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