Correlation and Spin Dynamics in Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have been in the focus of research and technology in an unprecedented broad field of science. Their mechanical as well as electronic properties, which are determined by the local arrangement of their sp hybridized carbon atoms, such that their character is either insulating, or semiconducting or metallic are exceptional. They are ideal one-dimensional (1D) conductors with unusual transport properties such as e.g. ballistic transport in metallic tubes. Semiconducting tubes are a very promising system for molecular electronics in which recently already a CMOS integrated circuit was successfully implemented. On the other hand SWCNT exhibit in many aspects properties of 1D quantum systems and are therefore one of the most promising materials to study tunable correlation effects, including spin interactions. The latter renders SWCNT functionalized by filling to be one of the promising candidates for future spin based quantum computers. Since the discovery of SWCNTs one of the most serious problems for science and applications particularly in the field of electronics was the preparation-immanent mixture of semiconducting and metallic nanotubes. The aim of the project is to overcome this problem and clearly elucidate the different behavior of semiconducting and metallic SWCNTs regarding electron correlation and spin dynamics. This will be done by using fully separated sets of semiconducting and metallic tubes as they became available very recently on the bulk scale from the laboratory of the project partners in Japan. This material is unique so far and allows for the first time to study bulk samples of metallic and semiconducting SWCNTs separately. This will be also a break through regarding the properties of functionalized SWCNT since these samples allow us to perform unique experiments on fully separated tubes with respect to their modification in the transport character. Firstly, the separated samples will be characterized regarding sample morphology, diameter distribution and optical properties by transmission electron microscopy, x- ray diffraction and optical techniques (Raman, optical absorption). Using functionalization with different fillers and intercalants the electronic transport properties of the separated SWCNT will be then modified in a controlled manner. The existence of the optical window in the tube absorption will allow for an analysis of many different filler species including the spin carrying systems. Photoemission and x-ray absorption will allow studying the influence of functionalization on the electronic properties of the separated tubes. For the first time the transition from a 1D metallic Tomonaga-Luttinger liquid (TLL) ground state to a normal Fermi liquid will be followed in detail in purely metallic tubes as a function of doping and the semiconductor-metal transition will be followed in doped semiconducting tubes. On the other hand, studying semiconducting SWCNT filled with metals will enable us to produce isolated and protected novel 1D metal wires in a controlled manner and analyze their properties utilizing resonant photoemission across metal core edges. In the case of spin resonance this will give also a breakthrough for the 1D interaction of the electron and nuclear spins with the conduction electrons or, if the latter are absent, with other spins in the tubes. The clear-cut experiments will allow for a clean theoretical treatment of the experiments and thus provide a so far unreached understanding of spin dynamics in linear chains. The TLL character is expected to show up in the interaction behavior for the metallic tubes. For the first time, information on RKKY interaction for a 1D electron system will be obtained. Similar new information will be obtained for the nuclear spin interaction. Since there is a well known charge transfer between filling, inner and outer tubes direct interaction can be expected. Summarizing, in the frame of this project we will unravel the underlying electron and spin coupling mechanisms in these correlated systems of functionalized purely metallic viz. purely semiconducting SWCNT. These novel results will be key for assessing the application potential of these 1D quantum systems.

Single-walled carbon nanotubes (SWCNTs) have been in the focus of research and technology, covering an unprecedented broad field of science. Their mechanical and electronic properties, which are determined by the local arrangement of their sp2 hybridized carbon atoms, are exceptional. Their character is either insulating, semiconducting or metallic. They are ideal one-dimensional (1D) conductors with unusual transport properties such as e.g. ballistic transport in metallic tubes. On the other hand, semiconducting tubes are a very promising system for nanoelectronics, which have been even successfully, implemented 2013 in a carbon nanotube computer. Additionally, SWCNT exhibit in many aspects properties of 1D quantum systems and are therefore one of the most promising materials to study tuneable correlation effects, including spin interactions. The latter renders SWCNT functionalized by filling to be one of the promising candidates for future spin based quantum computers as well as for biomedical applications. The project "Correlation and Spin Dynamics in Carbon Nanotubes" clearly elucidated the different behaviour of semiconducting and metallic SWCNTs regarding electron correlation and spin dynamics. This was done by using, on the bulk scale, pristine fully separated sets of semiconducting and metallic tubes as well as doped tubes after controlled substitution and filling reactions. This enabled us to modify the electronic transport and magnetic properties of the separated SWCNT in a controlled manner. Selected highlights of the project cover the first disentanglement of the exact correlated 1D electronic and magnetic structure of SWCNTs as a function of metallicity. With respect to filled SWCNTs we achieved the exact determination and control of the local charge transfer and local magnetic moments and the optimization of the photoluminescence quantum yield towards biocompatible near infrared sensors for ferrocene filled SWCNT. This study was complemented by a detailed analysis of the properties of 1D nanowires of Gd, Eu and ErCl3 nanowires which are modified by the quantum confinement inside SWCNTs. For substitutional doping we made great progress regarding the control of B and N substitution tailoring the bonding environment and doping level. In addition, we were able to determine the underlying adsorption process of nitroxides on metallicity sorted ultrapure nanotubes revealing an unexpected physisorption process and novel reaction kinetics. This is crucial for their application potential as environmental sensors. Summarizing, in the frame of this project we were able to unravel underlying electron and spin coupling mechanisms in these correlated systems of functionalized purely metallic viz. purely semiconducting SWCNT. These novel results will be a key for assessing the potential of SWCNTs in nanoelectronics, biomedical applications and as environmental sensors.