The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal-SWNT and SWNT-SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

A universal set of third-nearest-neighbor tight-binding ͑TB͒ parameters is presented for calculation of the quasiparticle ͑QP͒ dispersion of N stacked sp 2 graphene layers ͑N =1. . .ϱ͒ with AB stacking sequence. The present TB parameters are fit to ab initio calculations on the GW level and are universal, allowing to describe the whole "experimental" band structure with one set of parameters. This is important for describing both low-energy electronic transport and high-energy optical properties of graphene layers. The QP bands are strongly renormalized by electron-electron interactions, which results in a 20% increase in the nearest-neighbor in-plane and out-of-plane TB parameters when compared to band structure from density-functional theory. With the new set of TB parameters we determine the Fermi surface and evaluate exciton energies, charge carrier plasmon frequencies, and the conductivities which are relevant for recent angle-resolved photoemission, optical, electron energy loss, and transport measurements. A comparision of these quantitities to experiments yields an excellent agreement. Furthermore we discuss the transition from few-layer graphene to graphite and a semimetal to metal transition in a TB framework.

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The full three-dimensional dispersion of the bands, Fermi velocities, and effective masses are measured with angle-resolved photoemission spectroscopy and compared to first-principles calculations. The band structure by density-functional theory underestimates the slope of the bands and the trigonal warping effect. Including electron-electron correlation on the level of the GW approximation, however, yields remarkable improvement in the vicinity of the Fermi level. This demonstrates the breakdown of the independent electron picture in semimetallic graphite and points toward a pronounced role of electron correlation for the interpretation of transport experiments and double-resonant Raman scattering for a wide range of carbon based materials. Recently graphene has been investigated as a prototype system to address basic questions of quantum mechanics [1-3] (relativistic Dirac fermions) as well as for high speed semimetal field effect transistors in emerging nanoelectronic devices [4]. Many of these results are based on its peculiar electronic properties, i.e., an isotropic and linear dispersion close to the Fermi level (E F ). In low dimensional and strongly anisotropic systems correlation effects play a crucial role in understanding and describing the electronic band structure. Kinks in the quasiparticle (QP) dispersions and lifetimes were observed and interpreted as band renormalization due to electron-phonon [5] and electron-plasmon [6] interactions and band-structure effects [7]. Its electronic properties are also very sensitive to stacking and the number of layers [8]. In bilayer graphene a gap that could be tuned by doping was observed [9]. For few-layer graphene, the parent compound, graphite, is the key to understanding these new phenomena. Interlayer coupling in an AB stacking sequence leads to the formation of electron and hole pockets responsible for the semimetallic character in graphite. The linear dispersion is broken and only if we have an AA stacking the linear dispersion remains. Nevertheless, at the H point of graphite [2] the band dispersion is close to linear and has been interpreted as Dirac-fermion-like. Much less is known about the quantitative description of electron-electron correlations in these graphitic systems. Angle-resolved photoemission (ARPES) studies indicated that local density approximation (LDA) gives a dispersion that is too flat and a scaling has to be applied in order to fit the experimental dispersion of few-layer graphene and graphite. [15] for Raman scattering in graphene and graphite. Furthermore, it is important to know the exact k z dispersion, because it is responsible for the conductivity perpendicular to the graphene layers.In this Letter we report on a combined ARPES and theoretical ab initio QP study of the three-dimensional band structure and the Fermi surface in graphite single crystals. ARPES is best for studying correlations since it probes the complex self-energy function which contains the electronic interactions. We elucidate the full electronic QP disper...

The inherent structure of single-walled carbon nanotubes ͑SWCNTs͒ provides them tremendous value as archetypical one-dimensional ͑1D͒ solids, which exhibit van Hove singularities in their local density of states, Tomonaga-Luttinger liquid behavior, ballistic transport properties, and in many other aspects, features of 1D quantum systems, which allow the study of fundamental problems. Therefore, unraveling the signature of their peculiar electronic structure as pristine material is a prerequisite for tracing any modification. Here, we show the disentanglement of the unique 1D features and bonding environments in clean metallicity sorted nanotube films. The photoemission and x-ray absorption responses unambiguously reveal how the fine structure in the C1s edge and photoemission valence band separately discerns the SWCNT metallic and semiconducting nature. This has crucial implications for applications allowing for instance finding the limit of maximum conductivity in transparent electrodes or the uniformity of power transistors, among others.

Tweaking the properties of carbon nanotubes is a prerequisite for their practical applications.Here we demonstrate fine-tuning the electronic properties of single-wall carbon nanotubes via filling with ferrocene molecules. The evolution of the bonding and charge transfer within the tube is demonstrated via chemical reaction of the ferrocene filler ending up as secondary inner tube. The charge transfer nature is interpreted well within density functional theory. This work gives the first direct observation of a fine-tuned continuous amphoteric doping of single-wall carbon nanotubes.

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Black phosphorus intercalation compounds (BPICs) with alkali metals (namely: K and Na) have been synthesized in bulk by solid‐state as well as vapor‐phase reactions. By means of a combination of in situ X‐ray diffraction, Raman spectroscopy, and DFT calculations the structural behavior of the BPICs at different intercalation stages has been demonstrated for the first time. Our results provide a glimpse into the very first steps of a new family of intercalation compounds, with a distinct behavior as compared to its graphite analogues (GICs), showing a remarkable structural complexity and a dynamic behavior.