We report on the first direct observation of a transition from a Tomonaga-Luttinger liquid to a Fermi liquid behavior in potassium intercalated mats of single wall carbon nanotubes (SWCNT). Using high resolution photoemission spectroscopy an analysis of the spectral shape near the Fermi level reveals a Tomonaga-Luttinger liquid power law scaling in the density of states for the pristine sample and for low dopant concentration. As soon as the doping is high enough to fill bands of the semiconducting tubes a distinct transition to a bundle of only metallic SWCNT with a scaling behavior of a normal Fermi liquid occurs. This can be explained by a strong screening of the Coulomb interaction between charge carriers and/or an increased hopping matrix element between the tubes.PACS numbers: 73.63.Fg The charge transport properties of carbon nanotubes have been investigated intensively over the last years since they represent an archetype of a one dimensional system [1,2,3]. For such metallic systems, conventional Fermi-liquid (FL) theory fails since even the smallest interaction between the charge carriers leads to very strong correlation effects. Correlation effects are one of the central research areas in solid state physics and therefore one-dimensional metals are a paradigm for solids, where a breakdown of the FL theory due to many-body problems is expected. Under certain conditions a one-dimensional metal forms a Tomonaga-Luttinger liquid (TLL) which shows peculiar behavior such as spin charge separation and interaction dependent exponents in the density of states, correlation function and momentum distribution of the electrons [1,2,4,5]. Results from transport measurements through junctions between metals and individual metallic carbon nanotubes as well as between carbon nanotubes have been extensively analyzed in the framework of a tunnelling into or between TLL [6,7,8]. Recently, the electronic density of states (DOS) of the valence band electrons of mats of single wall carbon nanotubes (SWCNT) was directly monitored by angle integrated high resolution photoemission experiments [9]. The spectral function and the temperature dependence of the intensity at the Fermi level exhibited a power law dependence with exponents of 0.46 and 0.48 respectively which are identical within experimental error. This value yields a TLL parameter g = 0.18 in very good agreement with theoretical predictions [1, 2] and consistent with transport experiments through carbon nanotubes between normal metals [8]. This photoemission study clearly evidenced that metallic SWCNT within a bundle of SWCNT can be described within TLL theory regarding their low energy properties, without uncertainties regarding their contacting. However, there is still an open question regarding the amount of metallic SWCNT within a bundle of SWCNT. The interaction within a bundle could yield to the opening of a small gap in all SWCNT [10]. Hence all SWCNT would be narrow gap semiconductors which could not be described within TLL theory. On the other hand, tigh...
High filling of single wall carbon nanotubes (SWCNT) with C60 and C70 fullerenes in solvent is reported at temperatures as low as 69 o C. A 2 hour long refluxing in n-hexane of the mixture of the fullerene and SWCNT results in a high yield of C60,C70@SWCNT, fullerene peapod, material. The peapod filling is characterized by TEM, Raman and electron energy loss spectroscopy and X-ray scattering. We applied the method to synthesize the temperature sensitive (N@C60:C60)@SWCNT as proved by electron spin resonance spectroscopy. The solvent prepared peapod samples can be transformed to double walled nanotubes enabling a high yield and industrially scalable production of DWCNT.
The electronic properties of matter are on the nanometer scale strongly influenced by its local environment. The site-dependent electronic properties in composites of semiconducting and metallic matter are at the heart of establishing molecular electronics. Our combined theoretical and experimental investigations comprise first-principles calculations, resonant x-ray absorption as well as core-level and valence-band photoemission on pristine and potassium intercalated bundles of mixtures of semiconducting and metallic single-wall carbon nanotubes. We present a coherent picture of the archetypical changes in the site selective electronic properties of this tunable semiconductor/metal hybrid system.
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