Low-temperature properties of CeRu4Sn6 from NMR and specific heat measurements: Heavy fermions emerging from a Kondo-insulating state

E. M. Brüning, M. Brando, M. Baenitz, A. Bentien, A. M. Strydom, R. E. Walstedt, F. Steglich

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25 Citations (Scopus)


The combination of low-temperature specific heat and nuclear-magnetic- resonance (NMR) measurements reveals important information on the ground-state properties of CeRu4Sn6, which has been proposed as a rare example of a tetragonal Kondo insulator (KI). The NMR spin-lattice-relaxation rate 1/ T1 deviates from the Korringa law below 100 K signaling the onset of an energy gap Δ Eg1 / kB ≈30K. This gap is stable against magnetic fields up to 10 T. Below 10 K, however, unusual low-energy excitations of in-gap states are observed, which depend strongly on the field H. The specific heat C detects these excitations in the form of an enhanced Sommerfeld coefficient γ=C (T) /T: in zero field, γ increases steeply below 5 K, reaching a maximum at 0.1 K, and then saturates at γ≈0.6J/ K2 mol. Upon increasing field, this maximum is shifted to higher temperatures with an overall reduction in γ, suggesting a residual density of states at the Fermi level developing a spin (pseudo-)gap Δ Eg2. A simple model, based on two narrow quasiparticle bands located at the Fermi level-which cross the Fermi level in zero field at 0.022 states/meVf.u.-can account qualitatively as well as quantitatively for the measured observables. In particular, it is demonstrated that fitting this model, incorporating a Ce magnetic moment of μ=Δ Eg1 / μ0 H≈1 μB, to our data of both specific heat and NMR leads to the prediction of the field dependence of the gap. Our measurements rule out the presence of a quantum critical point as the origin for the enhanced γ in CeRu4Sn6 and suggest that this arises rather from correlated, residual in-gap states at the Fermi level. This work provides a fundamental route for future investigations into the phenomenon of narrow-gap formation in the strongly correlated class of systems.

Original languageEnglish
Article number125115
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number12
Publication statusPublished - 15 Sept 2010

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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