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The present focus on quantum critical phenomena in correlated matter is driven by the puzzling enigma concerning the origin of unconventional superconductivity (SC). In a weak coupling picture, the magnetic ordering is a spin density wave (SDW) induced by Fermi surface (FS) nesting of itinerant electrons. Consequently, superconductivity results from pair scattering between the electron - and holelike FS pockets. A drastically different viewpoint proposes that magnetism and superconductivity develop out of localized moments which are generated by strong electron - electron correlations (strong coupling limit). The similarities in the superconducting phase diagrams of correlated materials tempt us to believe that there may be a certain fundamental aspects shared between the iron pnictides, chalcogenides, cuprate superconductors and the HF materials. Against this backdrop, heavy Fermion (HF) materials acquire a new significance. This class of materials is inherent close to a magnetic quantum phase transition frequently in conjunction with emergence of unconventional superconductivity [1]. Recently it was shown that strong and weak coupling scenarios are complementary if taking into account the "dimensionality" of the critical fluctuations which in most cases mirrors the structural dimensionality of the compound [2-4]. In this presentation I will discuss the global phase diagram of heavy fermions with an experimental focus on the CenTmIn3n+2m (T = transition metal, n = 1, 2,..; m = 0, 1,..) family. This family is predestinated in order to understand how magnetism and superconductivity is influenced when going from 3D to 2D HF structures. CenTmIn3n+2m compounds display both attributes with cubic CeIn3 at the 3D and CeCoIn5 as an example of the opposite (2D) end of the series. I will present first results on single crystals of two new members Ce3PdIn11 and Ce3PtIn11 located in between [5]. At ambient pressure superconductivity emerges in the complex antiferromagnetic state below Tc = 0.42 K (Tc = 0.32 K) in Ce3PdIn11 (Ce3PtIn11). Both phenomena coexist in a wide range of the pressure - temperature phase diagrams. The critical pressure where TN -> 0 and Tc is maximum equals pc ~= 1.6 GPa. [1] H. von Löhneysen et al., Rev. Mod. Phys. 79, 1015 - 1075 (2007). [2] Q. Si, Physica B 378-380, 23 (2008) [3] J. Custers et al. Phys. Rev. Lett. 104, 186402 (2010) [4] J. Custers et al. Nature Mat. 11, 189 (2012) [5] J. Prokleska et al. submitted to Science (2013)

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Dr. Jeroen Custers, Charles University, Prague
Seminar Room of the Institute of Physics II (R201)
Contact: Mohsen Abd-Elmeguid