Jahn-Teller orbital glass state in the expanded fcc Cs3C60 fulleride

The most expanded fcc-structured alkali fulleride, Cs3C60, is a Mott insulator at ambient pressure because of the weak overlap between the frontier t1u molecular orbitals of the C603− anions. It has a severely disordered antiferromagnetic ground state that becomes a superconductor with a high critical temperature, Tc of 35 K upon compression. The effect of the localised t1u3 electronic configuration on the properties of the material is not well-understood. Here we study the relationship between the intrinsic crystallographic C603− orientational disorder and the molecular Jahn–Teller (JT) effect dynamics in the Mott insulating state. The high-resolution 13C magic-angle-spinning (MAS) NMR spectrum at room temperature comprises three peaks in the intensity ratio 1:2:2 consistent with the presence of three crystallographically-inequivalent carbon sites in the fcc unit cell and revealing that the JT-effect dynamics are fast on the NMR time-scale of 10−5 s despite the presence of the frozen-in C603− merohedral disorder disclosed by the 133Cs MAS NMR fine splitting of the tetrahedral and octahedral 133Cs resonances. Cooling to sub-liquid-nitrogen temperatures leads to severe broadening of both the 13C and 133Cs MAS NMR multiplets, which provides the signature of an increased number of inequivalent 13C and 133Cs sites. This is attributed to the freezing out of the C603− JT dynamics and the development of a t1u electronic orbital glass state guided by the merohedral disorder of the fcc structure. The observation of the dynamic and static JT effect in the Mott insulating state of the metrically cubic but merohedrally disordered Cs3C60 fulleride in different temperature ranges reveals the intimate relation between charge localization, magnetic ground state, lifting of electronic degeneracy, and orientational disorder in these strongly-correlated systems

Spin frustration and magnetic ordering in theS=12molecular antiferromagnetfcc−Cs3C60

We have investigated the low-temperature magnetic state of face-centered-cubic (fcc) Cs3C60, a Mott insulator and the first molecular analog of a geometrically frustrated Heisenberg fcc antiferromagnet with S=1/2 spins. Specific heat studies reveal the presence of both long-range antiferromagnetic ordering and a magnetically disordered state below TN=2.2 K, which is in agreement with local probe experiments. These results together with the strongly suppressed TN are unexpected for conventional atom-based fcc antiferromagnets, implying that the fulleride molecular degrees of freedom give rise to the unique magnetic ground state

Evidence for phase formation in potassium intercalated 1,2;8,9-dibenzopentacene

We have prepared potassium intercalated 1,2;8,9-dibenzopentacene films under vacuum conditions. The evolution of the electronic excitation spectra upon potassium addition as measured using electron energy-loss spectroscopy clearly indicate the formation of particular doped phases with compositions K$_x$dibenzopentacene ($x$ = 1,2,3). Moreover, the stability of these phases as a function of temperature has been explored. Finally, the electronic excitation spectra also give insight into the electronic ground state of the potassium doped 1,2;8,9-dibenzopentacene films.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with arXiv:1201.200

Anisotropic fluctuations and quasiparticle excitations in FeSe0:5Te0:5

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Methylaminated Potassium Fulleride, (CH3NH2)K3C60: Towards Hyperexpanded Fulleride Lattices

Co-intercalation of methylamine molecules into the cubic K3C60 lattice affords the fulleride (CH3NH2)K3C60, which was characterized by Raman and MAS 13C and 1H NMR spectroscopy. The high-resolution synchrotron X-ray powder diffraction technique was employed to determine its crystal structure at ambient temperature. We find that CH3NH2 bonds to K+ ions residing in the pseudo-octahedral interstices, thereby providing an efficient and facile route to hyperexpanded close-packed strongly anisotropic fulleride lattices, while retaining the electronic contact between the C603- anions. Preliminary evidence for the occurrence of a transition to an antiferromagnetic state at low temperature is also presented, consistent with the proximity of the present system to the metal-insulator boundary of the electronic phase diagram of C603- fullerides

The covalent functionalization of few-layered MoTe2 thin films with iodonium salts

Covalent functionalization of 2D materials provides a tailored approach towards tuning of their chemical, optical, and electronic properties making the search for new ways to graft small molecules important. Herein, the reaction with (3,5-bis(trifluoromethyl)phenyl)iodonium salt is revealed as an effective strategy for functionalization of MoTe2 thin films. Upon decomposition of the salt, the generated radicals graft covalently as aryl-(CF3)2 groups at the surface of both metallic (1T’) and semiconducting (2H) polymorphs of MoTe2. Remarkably, the reactivity of the salt is governed by the electronic structure of the given polymorph. While the functionalization of the metallic MoTe2 occurs spontaneously, the semiconducting MoTe2 requires activation by light. The reaction proceeds with the elimination of oxide from the original films yielding the functionalized products that remain protected in ambient conditions, presenting a viable solution to the ageing of MoTe2 in air