3 research outputs found
Valence effect on the thermopower of Eu systems
We investigated the thermoelectric transport properties of EuNi2P2 and
EuIr2Si2 in order to evaluate the relevance of Kondo interaction and valence
fluctuations in these materials. While the thermal conductivities behave
conventionally, the thermopower curves exhibit large values with pronounced
maxima as typically observed in Ce- and Yb-based heavy-fermion materials.
However, neither the positions of these maxima nor the absolute thermopower
values at low temperature are in line with the heavy-fermion scenario and the
moderately enhanced effective charge carrier masses. Instead, we may relate the
thermopower in our materials to the temperature-dependent Eu valence by taking
into account changes in the chemical potential. Our analysis confirms that
valence fluctuations play an important role in EuNi2P2 and EuIr2Si2.Comment: 7 pages, 3 figure
Single-ion Kondo Scaling of the Coherent Fermi Liquid Regime in Ce1-xLaxNi2Ge2
Thermodynamic and transport properties of the La-diluted Kondo lattice
CeNi2Ge2 were studied in a wide temperature range. The Ce-rich alloys
Ce1-xLaxNi2Ge2 were found to exhibit distinct features of the coherent heavy
Fermi liquid. At intermediate compositions (0.7 <= x <= 0.9) non-Fermi liquid
properties have been observed, followed by the local Fermi liquid behavior in
the dilute limit. The 4f-electron contribution to the specific heat was found
to follow the predictions of the Kondo impurity model both in the local as well
as coherent regimes, with the characteristic Kondo temperature decreasing
rapidly from about 30 K for the parent compound CeNi2Ge2 to about 1K in the
most dilute samples. The specific heat does not show any evidence for the
emergence of a new characteristic energy scale related to the formation of the
coherent Kondo lattice.Comment: to appear in Physical Review Letter
Unexpected differences between surface and bulk spectroscopic and implied Kondo properties of heavy fermion CeRh2Si2
Ultra-violet angle-resolved photoemission spectroscopy (UV-ARPES) was used to explore the temperature dependence of the Ce-4f spectral responses for surface and bulk in the antiferromagnetic Kondo lattice CeRh2Si2. Spectra were taken from Ce- and Si-terminated surfaces in a wide temperature range, and reveal characteristic 4f patterns for weakly (surface) and strongly (bulk) hybridized Ce, respectively. The temperature dependence of the Fermi level peak differs strongly for both cases implying that the effective Kondo temperature at the surface and bulk can be rather distinct. The greatly reduced crystal–electric-field (CEF) splitting at the surface gives reason to believe that the surface may exhibit a larger effective Kondo temperature because of a higher local-moment effective degeneracy. Further, the hybridization processes could strongly affect the 4f peak intensity at the Fermi level. We derived the k-resolved dispersion of the Kondo peak which is also found to be distinct due to different sets of itinerant bands to which the 4f states of surface and bulk Ce are coupled. Overall our study brings into reach the ultimate goal of quantitatively testing many-body theories that link spectroscopy and transport properties, for both the bulk and the surface, separately. It also allows for a direct insight into the broader problem of Kondo lattices with two different local-moment sublattices, providing some understanding of why the cross-talking between the two Kondo effects is weak