Breakdown of the Kondo effect at an antiferromagnetic instability

Frank Steglich

Max-Planck-Institute for Chemical Physics of Solids, Dresden, Germany


    Several heavy-fermion (HF) metals show low temperatures properties signaling a heavy Landau Fermi-liquid phase with composite quasiparticles. However, for an increasing number of such materials non-Fermi-liquid effects are observed. They arise due to a nearby quantum critical point (QCP), at which antiferromagnetic (AF) order is continuously suppressed. It is a fundamental open issue, whether the Landau quasiparticles persist in the vicinity of the QCP. Two types of HF QCPs have been established: (i) At a conventional QCP, spin-density wave order smoothly disappears giving way to three-dimensional quantum critical fluctuations. (ii) At an unconventional QCP the Kondo effect breaks down, as was inferred for CeCu6-xAux, CeRhIn5 under pressure and YbRh2Si2, with tetragonal ThCr2Si2 crystal structure. The properties of the latter compound will be discussed in this talk:

    Its very low Néel temperature (70 mK at B = 0) is continuously suppressed by applying a magnetic field Bc as small as 60 mT (B⊥c). Electrical transport and thermodynamic measurements have revealed multiple vanishing energy scales and, when the finite-T results are extrapolated to T->0, a discontinuity of the Fermi surface across the QCP. Direct evidence for this stems from low-T, low-field measurements of the Hall coefficient [1]. It is also implicated in, e.g., the unusual behavior of the thermoelectric power [2]. Combined heat and charge transport measurements highlight a violation of the Wiedemann-Franz law at the QCP [3]. This provides evidence for electronic quantum critical fluctuations which are naturally associated with the abrupt reconstruction of the Fermi surface that has been implicated by the measurements of the Hall coefficient.


[1] S. Friedemann et al., Proc. Natl. Acad. Sci. USA 107 (2010) 14547.

[2] S. Hartmann et al., Phys. Rev. Lett. 104 (2010) 096401.

[3] H. Pfau et al., to be published.

click the picture to download