Hilbert v. Löhneysen
Karlsruher Institut für Technologie, Physikalisches Institut und Institut für Festkörperphysik, 76031 Karlsruhe
Quantum phase transitions can be tuned by a non-thermal control parameter such as pressure, magnetic field, or chemical composition. In the canonical quantum-critical heavy-fermion system (HFS) CeCu6-xAux, a quantum critical point (QCP) can be obtained as a function of Au concentration at xc = 0.1 or, for x > xc, by hydrostatic pressure or magnetic field. The different behavior of field tuning vs. composition tuning of the QCP, evidenced by specific heat and resistivity measurements, is corroborated by inelastic neutron scattering experiments probing critical fluctuations . This may indicate that the (B,x,p) phase diagram for T → 0 may exhibit several distinct phases. The Kondo temperature determined by ultraviolet photoelectron spectroscopy exhibits a distinct step near xc, suggestive of a loss of complete Kondo screening .
Implications for QCP models for HFS will be discussed. - Uniaxial stress imposed on epitaxially grown LaCoO3 films leads to the stabilization of a high-spin state, as opposed to bulk LaCoO3 which is non-magnetic with S = 0 for T → 0. Unexpectedly, ferromagnetism with TC up to 80 K is observed in epitaxial films whose properties can be "strain-tuned" by choosing different substrates .
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