Abstract. We develop a theoretical basis for understanding the spin relaxation processes in Kondo lattice systems with heavy fermions as experimentally observed by electron spin resonance (ESR). The Kondo effect leads to a common energy scale that regulates a logarithmic divergence of different spin kinetic coefficients and supports a collective spin motion of the Kondo ions with conduction electrons. We find that the relaxation rate of a collective spin mode is greatly reduced due to a mutual cancellation of all the divergent contributions even in the case of the strongly anisotropic Kondo interaction. The contribution to the ESR linewidth caused by the local magnetic field distribution is subject to motional narrowing supported by ferromagnetic correlations. The developed theoretical model successfully explains the ESR data of YbRh2Si2 in terms of their dependence on temperature and magnetic field.
We consider the local properties of the Yb 3+ ion in the crystal electric field in the Kondo lattice compounds YbRh 2 Si 2 and YbIr 2 Si 2 . On this basis we have calculated the magnetic susceptibility taking into account the Kondo interaction in the simplest molecular field approximation. The resulting Curie-Weiss law and Van Vleck susceptibilities could be excellently fitted to experimental results in a wide temperature interval where thermodynamic and transport properties show non-Fermiliquid behaviour for these materials.
We present the field and temperature behavior of the narrow Electron Spin Resonance (ESR) response in YbRh 2 Si 2 well below the single ion Kondo temperature. The ESR g-factor reflects a Kondo-like field and temperature evolution of the Yb 3+ magnetism. Measurements towards low temperatures (> 0.6K) have shown distinct crossover anomalies of the ESR parameters upon approaching the regime of a well defined heavy Fermi liquid. Comparison with the field dependence of specific heat and electrical resistivity reveal that the ESR parameters can be related to quasiparticle mass and cross section and, hence, contain inherent heavy electron properties.Copyright line will be provided by the publisher 1 Introduction The heavy fermion metal YbRh 2 Si 2 has proven to display a variety of unusual low temperature electronic properties which are related to the interplay between the Kondo interaction of Yb 3+ 4f spin / conduction electron spin and the indirect magnetic RKKY interaction of the 4f spins. It is located very close to a magnetic instability where a weak antiferromagnetic long range order below 70 mK is suppressed by a magnetic field of B c = 60 mT. In the vicinity of such a magnetic field induced quantum critical point and at low temperature (T ) pronounced non-Fermi liquid behavior is observed as evidenced by a divergence of the electronic specic heat and electrical resistivity ρ ∝ T . At higher fields electronic specific heat C, magnetic susceptibility, and ρ show Landau-Fermi liquid (LFL) behavior with a renormalized electronic mass and quasiparticle scattering [1]. YbRh 2 Si 2 is one of a few Kondo lattice compounds where a welldefined Electron Spin Resonance (ESR) signal allows to directly characterize the spin dynamics of the Kondo ion.
The tetragonal crystal electric field parameters for Yb 3+ ion in YbRh 2 Si 2 are determined from the analysis of the literature data on angle-resolved photoemission, inelastic neutron scattering and electron paramagnetic resonance. q k O J [19] as follow:
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