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Register a new userMagnetic susceptibility of YbRh2Si2 and YbIr2Si2 on the basis of a localized 4f electron approach
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Added by
J\\\"org Sichelschmidt
Publication date
2008
fields
Physics
and research's language is
English
Authors
A.S. Kutuzov
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We consider the local properties of the Yb3+ ion in the crystal electric field in the Kondo lattice compounds YbRh2Si2 and YbIr2Si2. 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-Fermi-liquid behaviour for these materials.
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The CeIn3-xSnx cubic heavy fermion system presents an antiferromagnetic transition at T_N = 10 K, for x = 0, that decreases continuously down to 0 K upon Sn substitution at a critical concentration of x_c ~ 0.65. In the vicinity of T_N -> 0 the system shows non-Fermi liquid behavior due to antiferromagnetic critical fluctuations. For a high Sn content, x > 2.2, intermediate valence effects are present. In this work we show that Gd3+-doped electron spin resonance (ESR) probes a change in the character of the Ce 4f electron, as a function of Sn substitution. The Gd3+ ESR results indicate a transition of the Ce 4f spin behavior from localized to itinerant. Near the quantum critical point, on the antiferromagnetic side of the magnetic phase diagram, both localized and itinerant behaviors coexist.
Magnetic-field-induced changes of the Fermi surface play a central role in theories of the exotic quantum criticality of YbRh2Si2. We have carried out de Haas-van Alphen measurements in the magnetic-field range 8 T <= H <= 16 T, and directly observe field dependence of the extremal Fermi surface areas. Our data support the theory that a low-field large Fermi surface, including the Yb 4f quasihole, is increasingly spin split until a majority-spin branch undergoes a Lifshitz transition and disappears at H0 ~ 10 T, without requiring 4f localization at H0.
We report thermoelectric and resitivity measurements of antiferromagnetic heavy fermion compound YRh2Si2 at low temperatures down and under high magnetic field. At low temperature, the thermoelectric power and the resistivity present several distinct anomalies as a function of field around H_0 ~ 9.5 T when the magnetic polarization reaches a critical value. The anomalies are accompanied with a change of sign from negative at low magnetic field to positive at high field (H>H_0) and are resulting from a Lifshitz-type topological transition of the Fermi surface. A logarithmic divergence of S/T at T to 0 K just above H_0 (H=11.5 T) is quite comparable to the well known divergence of S/T in the temperature range above the antiferromagnetic order at H=0 T referred to as non Fermi liquid behavior. The transition will be compared to the well characterized Fermi surface change in CeRu2Si2 at its pseudo-metamagnetic transition.
We report the temperature- and magnetic-field-dependent optical conductivity spectra of the heavy electron metal YbIr$_2$Si$_2$. Upon cooling below the Kondo temperature ($T_{rm K}$), we observed a typical charge dynamics that is expected for a formation of a coherent heavy quasiparticle state. We obtained a good fitting of the Drude weight of the heavy quasiparticles by applying a modified Drude formula with a photon energy dependence of the quasiparticle scattering rate that shows a similar power-law behavior as the temperature dependence of the electrical resistivity. By applying a magnetic field of 6T below $T_{rm K}$, we found a weakening of the effective dynamical mass enhancement by about 12% in agreement with the expected decrease of the $4f$-conduction electron hybridization on magnetic field.
We present the field and temperature behavior of the narrow Electron Spin Resonance (ESR) response in YbRh2Si2 well below the single ion Kondo temperature. The ESR g factor reflects a Kondo-like field and temperature evolution of the Yb3+ magnetism. Measurements towards low temperatures (>0.5K) 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.
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