Electronic Properties of Carbon Nanotubes

Carbon nanotubes (CNTs) are quasi-one-dimensional allotropes of carbon that exhibit remarkable electronic properties arising from their precise atomic arrangement and dimensional confinement. Depending on the rolling vector of the graphene precursor, CNTs may behave as metals, semiconductors or zero-gap conductors. The band structure derives from the quantisation of electronic states around the nanotube circumference, producing discrete subbands whose energies depend on diameter and chirality. Semiconducting CNTs display direct band gaps inversely proportional to tube diameter, whereas metallic tubes may exhibit pseudogaps under symmetry breaking. Strong electron–electron interactions, augmented by reduced screening in one dimension, give rise to excitonic binding energies that can dominate optical and transport behaviour. Luttinger liquid theory has long been invoked to describe collective excitations, but recent findings suggest that correlated states, such as excitonic insulators, can emerge in nominally gapless tubes. External fields, strain and dielectric environment further modulate band gaps and conductance, enabling tunable transport characteristics. Applications range from field-effect transistors and photodetectors to quantum devices and sensors, where the interplay of chirality, environmental screening and electron correlation underpins device performance and dictates prospects for integration within existing semiconductor platforms.

Research from Nature Portfolio

Recent theoretical and experimental studies have demonstrated that zero-gap carbon nanotubes can host spontaneous excitonic ordering, whereby electron–hole pairs condense to open a small insulating gap that scales inversely with tube radius and is tunable via an axial magnetic field. Another line of work has shown that the transport band gap of individual suspended CNTs can be modulated by the surrounding dielectric medium, with increases in dielectric constant leading to reductions in gap energy by up to a third, thereby offering a non-invasive route to control electronic characteristics. Investigations into spin–orbit interactions reveal that the intrinsic chirality of single-walled tubes induces spin polarisation in electrical conductivity, with distinct behaviours observed for zigzag, armchair and chiral geometries as functions of temperature and frequency, pointing to opportunities in chiral-induced spin selectivity and spintronic applications.

Electronic Properties of Carbon Nanotubes publication trend

The graph below shows the total number of articles in electronic properties of carbon nanotubes across all publications each year (not limited to Nature Index journals).

Technical terms

Chirality: The geometric arrangement of carbon atoms in a nanotube determined by its (n,m) rolling indices, which dictates whether it behaves as a metal or semiconductor.

Band gap: The energy difference between the valence and conduction bands in a semiconductor or insulator, governing electrical conductivity and optical absorption.

Exciton: A bound state of an electron and a hole attracted by Coulomb interaction, whose binding energy is large in one-dimensional systems.

Dielectric screening: The reduction of effective Coulomb interactions between charged particles due to the polarisation of surrounding media.

Spin–orbit interaction: An intrinsic coupling between an electron’s spin and its orbital motion, influenced by the tube’s curvature and symmetry, affecting spin polarisation in transport.

References

1. Carbon-Related Materials: Graphene and Carbon Nanotubes in Semiconductor Applications and Design. Micromachines (2022).
2. Carbon nanotubes as excitonic insulators. Nature Communications (2017).
3. Theory of Electronic States and Transport in Carbon Nanotubes. Journal of the Physical Society of Japan (2005).
4. Giant modulation of the electronic band gap of carbon nanotubes by dielectric screening. Scientific Reports (2017).
5. Theoretical investigation of electronic bandgaps of semiconducting single-walled carbon nanotubes using semi-empirical self-consistent tight binding and ab-inito density functional methods. Journal of Physics Communications (2020).