| Description |
Heavy fermion metals are often characterized by a variety of relevant energy scales and competing interactions which may result in such fascinating phenomena as quantum criticality and unconventional superconductivity. Therefore, these materials have advanced to suitable model systems by means of which electronic interactions can be studied in detail. This will be discussed for two classes of heavy fermion metals, YbRh2Si2 and CeMIns (M = Co, Ir), with focus on the former family of compounds.
First, results of detailed magnetotransport investigations on YbRh2Si2 will be described within the so-called local quantum critical scenario [1]. Here, an additional energy scale is related to the critical breakdown of the Kondo screening. The experimental hallmark of this breakdown is a crossover in the Hall coefficient indicating a Fermi surface reconstruction [2]. By application of chemical pressure through doping Yb(Rh1-xMx)2Si2 (M = Co, Ir) this Fermi surface reconstruction can be detached from the antiferromagnetic quantum critical point [3].
We also present very recent STM and STS at low temperature conducted on YbRh2Si2. The topography confirms an excellent low temperature in situ cleave of the single crystals. The hybridization of conduction and 4f electrons results in a gap-like feature in the tunneling conductance. In addition, the crystal field excitations are unambiguously reflected by STS for the first time. A strongly temperature dependent peak in tunneling conductance is attributed to a resonance resulting from the Kondo lattice.
In the CeMIns class of compounds the relation between superconductivity and anti ferro¬magnetism will be discussed. Through Cd-doping into CeCoIns, anti ferromagnetic order can be established. For the specific case of CeCo(InO.92SCd0075)S neutron scattering, magnetotransport and heat capacity measurements on identical samples have been combined to comprehensively map out the phase diagram [4]. Moreover, from these data we infer that both types of order, superconductivity and antiferromagnetism, not only coexist on a microscopic scale but, more importantly, mutually influence each other indicating a common origin.
|