engleski

Unconventional superconductivity and quantum magnetism in π-electron molecular systems

Molecular solids whose cooperative electronic properties are based purely on π-electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. In our search for novel conducting and magnetic functionalities, we have been exploring the electronic properties of such materials in which the active components of the extended structures are π-electron open-shell molecular units. These systems crystallise in architectures of varied dimensionality ranging from one- to three-dimensions and encompass molecular metals and superconductors such as the alkali fullerides, which provide the highest Tc (38 K) [1] and highest Hc2 (>90 T) [2] together with 3D Mott insulating quantum spin liquids (QSL) in alkali-doped polyaromatic hydrocarbons [3, 4]. In this contribution, we focus on some recent work on the structures and physical properties of selected mixed valence rare-earth fullerene- based architectures with stoichiometry RE2.75C60. These materials constitute an intriguing, essentially unique class of strongly correlated electron systems because, in addition to the highly correlated cation (rare-earth) sublattice [5], they also accommodate the electronically active anion (C60) sublattice [6]. The occurrence of temperature- and pressure-driven valence transitions and giant negative thermal expansion effects and the systematic tuning of the electronic response by both isovalent and aliovalent metal substitution are being systematically mapped out by a combination of structural (synchrotron X-ray diffraction) and spectroscopic (Raman spectroscopy, synchrotron X-ray absorption spectroscopy, resonant inelastic X-ray scattering) techniques at both ambient and elevated pressures (Fig. 1). In addition, the isolation and characterization of binary superconductors with nominal composition Ca6C60 (Fig. 2) have led to the prospect of coexisting superconductivity and Kondo phenomena by co- intercalation of alkaline earth anions in rare- earth fullerides. [1] A. Y. Ganin et al., Nature Mater. 7, 367 (2008). [2] Y. Kasahara et al., Nature Commun. 8, 14467 (2017). [3] Y. Takabayashi et al., Nature Chem. 9, 635 (2017). [4] F. D. Romero et al., Nature Chem. 9, 644 (2017). [5] J. Arvanitidis et al., Nature 425, 599 (2003). [6] R. H. Zadik et al., Science Adv. 1, e1500059 (2015).

Superconductivity ; Magnetism ; XRD ; XANES

nije evidentirano