2004, Max Planck Institute for Chemical Physics of Solids
Sparn, Günter; Gegenwart, Philipp; Sichelschmidt, Jörg; Coleman, Piers; Custers, Jeroen; Deppe, Micha; Ferstl, Julia; Geibel, Christoph; Grosche, Friedrich Malte; Neumaier, Karl; Pépin, Catherine; Steglich, Frank; Tokiwa, Yoshifumi; Trovarelli, Octavio; Voevodin, Vladimir; Wilhelm, Heribert; Yuan, Huiqiu
All developments achieved to date in the fields of medical-, information- and sensor- technology are based on models which are well established in physics and chemistry and which reflect the state of knowledge of fundamental research until the middle of the last century. Further progress, however, seems to be possible only if we learn to understand a new state of condensed matter, which can not be described within the context of the established models. This new state is dominated by quantum phenomena. Quantum phenomena come into play, when spatial dimensions become smaller than the wavelength of light (nano-technology) or when extremely strong correlations build up among the electrons of the solid (Quantum Hall Effect, Collossal Magnetoresistance, High Temperature Superconductivity (HTSC)). Here we report two outstanding discoveries which could be particularly important for the understanding of the HTSC. At the heart of the description of HTSC lies the assumption that superconductivity is created by coupling the charge carriers via magnetic fluctuations. In CeCu2Si2, a compound whose properties are related to those of HTSC, we not only have found hints towards the existence of a magnetic coupling mechanism but furthermore, for the first time, have been able to collect evidence for the existence of an additional, completely new coupling mechanism. The second discovery concerns the physical properties of a strongly correlated electron system (YbRh2Si2) in the vicinity of the magnetic quantum critical point. In YbRh2Si2 the strongly interacting charge carriers can not be treated within the concept of weakly interacting heavy quasi particles, as it is successfully done in heavy electron metals away from quantum criticality. In contrast to hitherto models, the quasiparticles in YbRh2Si2 seem to disintegrate into a charge part (current) and a spin part (magnetism) when approaching the quantum critical point.