Spin-dependent electronic hybridization in a rope of carbon nanotubes

Abstract

We demonstrate single-electron addition to different strands of a carbon nanotube rope. Anticrossings of anomalous conductance peaks occur in quantum transport measurements through the parallel quantum dots forming on the individual strands. We determine the magnitude and the sign of the hybridization as well as the Coulomb interaction between the carbon nanotube quantum dots, finding that the bonding states dominate the transport. In a magnetic field the hybridization is shown to be selectively suppressed due to spin effects. Molecular electronics and spintronics aim at exploiting the chemical versatility of molecules to control charge and magnetism in nanoscale devices. However, the assembly of molecular structures in junctions for electric and magnetic manipulation is a challenging task.1-4 Carbon nanotubes (CNTs) are particularly promising as building blocks of new devices for nanoelectronics, 5-8 which exhibit interesting spin properties 9-12 and can be useful for quantum information processing.13,14 Fundamental aspects of single-molecule devices require an understanding of strong perturbations by environmental effects, for example, the interaction with contacts or neighboring molecules. 15 These interactions can, in principle, be studied on a single-molecule level using scanning probe techniques as for instance scanning near-field optical microscopy, 16 tip-enhanced Raman spectroscopy 17,18 or scanning tunneling spectroscopy (STS). 19 However, in situ characterization of actual devices, for example, field-effect transistors, is difficult to implement and only STS can detect spin-dependent phenomena.As an alternative approach, one may exploit the differential electrostatic gating effect, which was found to occur for contacted CNTs filled with fullerenes 20 and for single molecules in nanojunctions. 15 In this respect, bundled CNTs are interesting: Within a rope one expects the strands to be at a different potential and to respond differently to the external electric fields due to electrostatic effects. 21 Low-temperature transport spectroscopy is sensitive to these potential variations on the sub-meV scale, allowing the study of interactions between coupled nanoscale conductors.In this Rapid Communication we show that transport spectroscopy can resolve both charge addition to individual strands of a single CNT rope as well as the coupling between these strands caused by molecular interactions. We determine the hybridization and the electrostatic interaction between parallel quantum dots (QDs) forming on the different strands. We extract both the magnitude and the sign of the hybridization and find that current transport occurs via the bonding states of the coupled QD system. Furthermore, by applying a magnetic field the electronic hybridization is selectively suppressed due to spin effects. This offers prospects for accessing individual charge and spin degrees of freedom in coupled carbon-based molecular systems.The CNTs of the reported device were grown on a Si/SiO 2 substrate by chemical vapor deposition ...

Parallel carbon nanotube quantum dots and their interactions

“…The experimentally observed shift of resonances can be explained with the model developed previously. 36 This confirms its potential to fully describe a system of several parallel quantum dots which exhibit a tunnel coupling as well as a capacitive coupling.…”

“…36 Here, we report on the same device, focusing, however, on the off-resonance case in order to create a complete picture of the manifold of effects that can arise in a system of parallel coupled quantum dots. Tuning the system from in-resonance to off-resonance cases is possible by a differential gating effect which enables one to shift the dot potentials relative to each other.…”

“…Previously, we reported on a selective hybridization of in-resonance spin states in a magnetic field. 36 Here, on the other hand, we use the transport data at high magnetic field to extract relative tunnel rates and discuss their effect on the stability diagram. In addition, we present the influence of a capacitive coupling on a main resonance.…”

Fermionic superoperators for zero-temperature nonlinear transport: Real-time perturbation theory and renormalization group for Anderson quantum dots

“…In fact, kinks in SET resonances are often observed in various types of quantum dot systems. [66][67][68][69] Our calculations indicate that tunnel-induced renormalization is a possible mechanism for their occurrence, but other (e.g., electrostatic) mechanisms 70,71 should not be ruled out in an experimental situation. However, for strong coupling, it is physically not unexpected that when ICT sets on, the level renormalization significantly changes, resulting in such a kink.…”

Interaction effects in electric transport through self-assembled molecular monolayers

“…In other mesoscopic systems, U is likely much smaller (U = 0.15−0.4 meV between strands of nanotubes within a nanotube rope was found in recent experiments 22,23 ), but can still dominate the transport physics at low temperatures.…”