Orbital character effects in the photon energy and polarization dependence of pure C60 photoemission

Recent direct experimental observation of multiple highly-dispersive C$_{60}$ valence bands has allowed for a detailed analysis of the unique photoemission traits of these features through photon energy- and polarization-dependent measurements. Previously obscured dispersions and strong photoemission traits are now revealed by specific light polarizations. The observed intensity effects prove the locking in place of the C$_{60}$ molecules at low temperatures and the existence of an orientational order imposed by the substrate chosen. Most importantly, photon energy- and polarization-dependent effects are shown to be intimately linked with the orbital character of the C$_{60}$ band manifolds which allows for a more precise determination of the orbital character within the HOMO-2. Our observations and analysis provide important considerations for the connection between molecular and crystalline C$_{60}$ electronic structure, past and future band structure studies, and for increasingly popular C$_{60}$ electronic device applications, especially those making use of heterostructures

Linearly dispersive bands at the onset of correlations in Kx_xC60_{60} films

Molecular crystals are a flexible platform to induce novel electronic phases. Due to the weak forces between molecules, intermolecular distances can be varied over relatively larger ranges than interatomic distances in atomic crystals. On the other hand, the hopping terms are generally small, which results in narrow bands, strong correlations and heavy electrons. Here, by growing K$_x$C$_{60}$ fullerides on hexagonal layered Bi$_2$Se$_3$, we show that upon doping the series undergoes a Mott transition from a molecular insulator to a correlated metal, and an in-gap state evolves into highly dispersive Dirac-like fermions at half filling, where superconductivity occurs. This picture challenges the commonly accepted description of the low energy quasiparticles as appearing from a gradual electron doping of the conduction states, and suggests an intriguing parallel with the more famous family of the cuprate superconductors. More in general, it indicates that molecular crystals offer a viable route to engineer electron-electron interactions.Comment: 5 pages, 4 figures. Accepted at Physical Review Researc

Observation of highly dispersive bands in pure thin film C60_{60}

While long-theorized, the direct observation of multiple highly dispersive C$_{60}$ valence bands has eluded researchers for more than two decades due to a variety of intrinsic and extrinsic factors. Here we report a realization of multiple highly dispersive (330-520 meV) valence bands in pure thin film C$_{60}$ on a novel substrate--the three-dimensional topological insulator Bi$_{2}$Se$_{3}$--through the use of angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. The effects of this novel substrate reducing C$_{60}$ rotational disorder are discussed. Our results provide important considerations for past and future band structure studies as well as the increasingly popular C$_{60}$ electronic device applications, especially those making use of heterostructures.Comment: 7 pages, 4 figure

Orbital Character Effects in the Photon Energy and Polarization Dependence of Pure C60 Photoemission.

Recent direct experimental observation of multiple highly dispersive C60 valence bands has allowed for a detailed analysis of the unusual photoemission traits of these features through photon energy- and polarization-dependent measurements. Previously obscured dispersions and strong photoemission traits are now revealed by specific light polarizations. The observed intensity effects prove the locking in place of the C60 molecules at low temperatures and the existence of an orientational order imposed by the substrate chosen. Most importantly, photon energy- and polarization-dependent effects are shown to be intimately linked with the orbital character of the C60 band manifolds which allow for a more precise determination of the orbital character within the third highest occupied molecular orbital (HOMO-2). Our observations and analysis provide important considerations for the connection between molecular and crystalline C60 electronic structure, past and future band structure studies, and for increasingly popular C60 electronic device applications, especially those making use of heterostructures

Polarization dependent photoemission as a probe of the magnetic ground state in the van der Waals ferromagnet VI3

Van der Waals ferromagnets are thrilling materials from both a fundamental and technological point of view. VI3 is an interesting example, with a complex magnetism that differentiates it from the first reported Cr based layered ferromagnets. Here, we show in an indirect way through angle resolved photoemission spectroscopy experiments, the importance of spin-orbit coupling setting the electronic properties of this material. Our light polarized photoemission measurements point to a ground state with a half-filled e ± ′ doublet, where a gap opening is triggered by spin-orbit coupling enhanced by electronic correlations