CeRu$ 4$Sn$ 6$: heavy fermions emerging from a Kondo-insulating state - Condensed Matter > Strongly Correlated ElectronsReport as inadecuate

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Abstract: The combination of low-temperature specific-heat andnuclear-magnetic-resonance NMR measurements reveals important information ofthe ground-state properties of CeRu$ 4$Sn$ 6$, which has been proposed as arare example of a tetragonal Kondo-insulator KI. The NMRspin-latticerelaxation rate $1-T 1$ deviates from the Korringa law below 100 Ksignaling the onset of an energy gap $\Delta E g1-k B \simeq 30$K. This gap isstable against magnetic fields up to 10 T. Below 10 K, however, unusuallow-energy excitations of in-gap states are observed, which depend strongly onthe field H. The specific heat C detects these excitations in the form of anenhanced Sommerfeld coefficient $\gamma = CT-T$ : In zero field, $\gamma$increases steeply below 5 K, reaching a maximum at 0.1 K, and then saturates at$\gamma = 0.6$ J-molK$^2$. This maximum is shifted to higher temperatures withincreasing field suggesting a residual density of states at the Fermi leveldeveloping a spin gap $\Delta E g2$. A simple model, based on two narrowquasiparticle bands located at the Fermi level - which cross the Fermi level inzero field at 0.022 states-meV f.u. - can account qualitatively as well asquantitatively for the measured observables. In particular, it is demonstratedthat fitting our data of both specific heat and NMR to the model, incorporatinga Ce magnetic moment of $\mu = \Delta E g1-\mu {0H} \simeq 1 \mu B$, leads tothe prediction of the field dependence of the gap. Our measurements rule outthe presence of a quantum critical point as the origin for the enhanced$\gamma$ in CeRu$ 4$Sn$ 6$ and suggest that this arises rather from correlated,residual in-gap states at the Fermi level. This work provides a fundamentalroute for future investigations into the phenomenon of narrow-gap formation inthe strongly correlated class of system

Author: E.M. BrĂ¼ning, M. Brando, M. Baenitz, A. Bentien, A.M. Strydom, R.E. Walstedt, F. Steglich

Source: https://arxiv.org/

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