Banda, J., D. Hafner, J. F. Landaeta, E. Hassinger, K. Mitsumoto, M. Giovannini, J. G. Sereni, C. Geibel, and M. Brando. "Electronuclear Quantum Criticality." arXiv (2023): 2308.15294.
Abstract: We present here a rare example of electronuclear quantum criticality in a metal. The compound YbCu4.6Au0.4 is located at an unconventional quantum critical point (QCP). In this material the relevant Kondo and RKKY exchange interactions are very weak, of the order of 1 K. Furthermore, there is strong competition between antiferromagnetic and ferromagnetic correlations, possibly due to geometrical frustration within the fcc Yb sublattice. This causes strong spin fluctuations which prevent the system to order magnetically. Because of the very low Kondo temperature the Yb3+ 4f-electrons couple weakly with the conduction electrons allowing the coupling to the nuclear moments of the 171Yb and 173Yb isotopes to become important. Thus, the quantum critical fluctuations observed at the QCP do not originate from purely electronic states but from entangled electronuclear states. This is evidenced by the anomalous temperature and field dependence of the specific heat at low temperatures.
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Romero, M. A., A. A. Aligia, J. G. Sereni, and G. Nieva. "Interpretation of experimental results on Kondo systems with crystal field." Journal of Physics: Condensed Matter 26 (2014): 025602. http://dx.doi.org/10.1088/0953-8984/26/2/025602 (accessed December 6, 2023).
Abstract: We present a simple approach to calculate the thermodynamic properties of single Kondo impurities including orbital degeneracy and crystal field effects (CFE) by extending a previous proposal by K. D. Schotte and U. Schotte [Physics Lett. A 55, 38 (1975)]. Comparison with exact solutions for the specific heat of a quartet ground state split into two doublets shows deviations below $10\%$ in absence of CFE and a quantitative agreement for moderate or large CFE. As an application, we fit the measured specific heat of the compounds CeCu$2$Ge$2$, CePd${3}$Si${0.3}$, CePdAl, CePt, Yb$2$Pd$2$Sn and YbCo$2$Zn${20}$. The agreement between theory and experiment is very good or excellent depending on the compound, except at very low temperatures due to the presence of magnetic correlations (not accounted in the model).
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Sereni, J. G. First observation of Ce volume collapse in CeN., 2017.
Abstract: On the occasion of the 80th anniversary of the first observation of Ce volume collapse in CeN a remembrance of the implications of that transcendent event is presented, along with a review of the knowledge of Ce physical properties available at that time. Coincident anniversary corresponds to the first proposal for Ce as a mix valence element, motivating to briefly review how the valence instability of Ce was investigated since that time.
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