Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 21: FS: Quantum Criticality in Strongly Correlated Metals

TT 21.2: Topical Talk

Mittwoch, 24. März 2010, 10:10–10:50, H20

Tuning magnetic quantum phase transitions — •Hilbert v. Löhneysen — Karlsruher Institut für Technologie, Physikalisches Institut und Institut für Festkörperphysik, D-76021 Karlsruhe

In the canonical quantum-critical heavy-fermion system (HFS) CeCu_6−xAu_x, a quantum critical point (QCP) can be obtained as a function of Au concentration at x_c = 0.1 or, for x > x_c, by hydrostatic pressure p or magnetic field B. The different behavior of B and x tuning of the QCP inferred from specific heat and resistivity, is corroborated by inelastic neutron scattering probing critical fluctuations [1], indicating that the (B,x,p) phase diagram for T → 0 may exhibit several distinct phases. The Kondo temperature determined with UPS shows a sharp step at x_c, suggestive of a loss of complete Kondo screening [2]. 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 T_C up to 80 K is observed in epitaxial films whose properties can be "strain-tuned" by choosing different substrates [3].

[1] O. Stockert et al., Phys. Rev. Lett. 99, 237203 (2007)

[2] M. Klein et al., Phys. Rev. Lett. 101, 266404 (2008)

[3] D. Fuchs et al., Phys. Rev. B 75, 144402 (2007); B 77, 014434 (2008)