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By comparing photoemission spectroscopy with a non-perturbative dynamical mean field theory extension to many-body ab initio calculations, we show in the prominent case of pentacene crystals that an excellent agreement with experiment for the bandwidth, dispersion and lifetime of the hole carrier bands can be achieved in organic semiconductors provided that one properly accounts for the coupling to molecular vibrational modes and the presence of disorder. Our findings rationalize the growing experimental evidence that even the best band structure theories based on a many-body treatment of electronic interactions cannot reproduce the experimental photoemission data in this important class of materials.
When electrons are subject to a potential with two incommensurate periods, translational invariance is lost, and no periodic band structure is expected. However, model calculations based on nearly free one-dimensional electrons and experimental results from high-resolution photoemission spectroscopy on a quasi-one-dimensional material do show dispersing band states with signatures of both periodicities. Apparent band structures are generated by the nonuniform distribution of electronic spectral weight over the complex eigenvalue spectrum.
Angle-resolved photoemission (ARPES) on the quasi-one-dimensional conductor (TaSe4)(2)I shows a hidden Fermi-surface crossing in its metallic state and the opening of a Peierls gap at low temperatures, The underlying quasiparticles have vanishing spectral weight and extremely short coherence lengths. They are interpreted as polarons in the strong-coupling adiabatic Lin-Lit, and almost all their ARPES weight is incoherent. These observations suggest a scenario where the long-standing contradictions between ARPES and other experiments on Peierls materials could be resolved.
High-resolution angle-resolved photoemission spectroscopy (ARPES) on the quasi-one-dimensional Peierls system K0.3MoO3 reveals a "hidden" open Fermi surface and band features displaying the symmetry properties of the underlying lattice. However, the ARPES line shapes and optical data suggest that the corresponding quasiparticles are heavily renormalized by strong electron-phonon interactions. The temperature dependence of the leading edge of the mostly incoherent spectrum bears signatures of the Peierls transition at T-P=180 K and of pretransitional fluctuations.
High-resolution angle-resolved photoemission data show that a metal-insulator Mott transition occurs at the surface of the quasi-two-dimensional compound 1T-TaSe2. The transition is driven by the narrowing of the Ta 5d band induced by a temperature-dependent modulation of the atomic positions. A dynamical mean-field theory calculation of the spectral function of the half-filled Hubbard model captures the main qualitative feature of the data, namely, the rapid transfer of spectral weight from the observed quasiparticle peak at the Fermi surface to the Hubbard bands, as the correlation gap opens up.
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