Spin‐polarized transport through carbon nanotubes

Abstract

Published online zzz PACS 85.35. Kt, 81.07.De, Carbon nanotubes (CNT) belong to the most promising new materials which can in the near future revolutionize the conventional electronics. When sandwiched between ferromagnetic electrodes, the CNT behaves like a spacer in conventional spin-valves, leading quite often to a considerable giant magneto-resistance effect (GMR). This paper is devoted to reviewing some topics related to electron correlations in CNT. The main attention however is directed to the following effects essential for electron transport through nanotubes: (i) nanotube/electrode coupling and (ii) inter-tube interactions. It is shown that these effects may account for some recent experimental reports on GMR, including those on negative (inverse) GMR.Copyright line will be provided by the publisher 1 Introduction A particularly challenging class of materials for the future electronics are carbon nanotubes, i.e. graphite sheets rolled up in such a manner that they form very long and thin (in atomic scale) cylinders. Their length can be of the order of several micrometers whereas typical cross-sections of single wall carbon nanotubes (SWCNT) are a few nanometers in diameter, and roughly up to 10 times more for multi-wall carbon nanotubes (MWCNT) . Both the SWCNTs and MWCNTs have been attracting much attention of many researchers since they were discovered [1].It is now clear that the electronics based on conventional semiconducting devices (e.g. silicon technology) has faced fundamental limitations as far as further miniaturization is concerned. The reasons are various, including the fact that the relative amount of surface states -destructive for electronic transport properties -increases rapidly in 2-and 3-dimensional systems when their sizes are being reduced. Likewise, it is predicted that the SiO 2 layer in the MOSFET will be too thin soon (within 10 years or so) to retain its insulating properties [2]. So, there is much interest of physicists, technologists and engineers in new generation nano-scale devices, including molecular ones. The adopted approach is the so-called bottom up philosophy, aiming at designing electronic devices at the molecular level. In contrast to siliconbased devices, the molecular ones (incl. carbon nanotubes, CNT) can successfully cope with the more and more demanding miniaturization requirements without worsening their multi-functional properties. Most probably the CNTs are also good candidates for spintronics applications in view of their unusually long spin diffusion length. It is well-known that electrons can travel through carbon nanotubes up to many hundreds of nanometers, still keeping their momentum and spin orientation. So CNTs are believed to be useful in the near future microelectronics (or molecular electronics) as interconnects, and possibly also as active elements in integrated circuits. Physical properties of the CNTs connected to metallic electrodes depend critically on a quality of CNT/metal junctions, and may evolve with increasing transparencies of the j...

Theoretical studies of spin-dependent electrical transport through carbon nanotubes

“…Figure 2 shows how the GMR effect gets modified under the influence of Anderson-disorder. The obvious observations are that disorder destroys periodicity of GMR and decreases its absolute value from roughly 20% ( [17], [18]) down to a few per cent simultaneously reducing tendency of GMR to become negative. All these features are in accord with experimental data on GMR in multiwall carbon nanotubes (MWCNTs) with transparent ferromagnetic contacts [22,23].…”

Separating spin and charge transport in single-wall carbon nanotubes

“…It is nontrivial to explain these effects from spin transport only ͑they would require a sign change in the polarization at only one of the electrodes͒. 25 Another curiosity, often observed in nanotubes ͑although not by us͒, is the fact that the magnetoresistance increases before the external field has even changed sign. 2,5,14 The problem in the interpretation lies in the fact that many other phenomena, not related to spin, influence the magnetoresistance.…”

Remarks on theoretical modelling of spin-dependent electronic transport in carbon nanotubes and graphene

“…Refs. [8][9][10][11][12] are devoted to this problem. The GMR effect depends on chirality of the given graphitic struc- ture, as well as on its geometrical dimensions characterized by the so-called aspect ratio, A, equal to the ratio of the width (perimeter) of the graphene nanoribbon (nanotube) to the length.…”

“…In contrast, monolayer graphene sheets have no energy gap and consequently the corresponding OFF/ON ratio is much too high to exhibit a good FET performance. In specific conditions, the carbon-based structures can also behave as a Luttinger liquid or reveal the Kondo effect [10,18].…”