Abstract

Understanding the physics of low-dimensional systems and the operation of next-generation electronics will depend on our ability to measure the electrical properties of nanomaterials at terahertz frequencies (|[sim]|100|[nbsp]|GHz to 10|[nbsp]|THz). Single-walled carbon nanotubes are prototypical one-dimensional nanomaterials because of their unique band structure and long carrier mean free path. Although nanotube transistors have been studied at microwave frequencies (100|[nbsp]|MHz to 50|[nbsp]|GHz), no techniques currently exist to probe their terahertz response. Here, we describe the first terahertz electrical measurements of single-walled carbon nanotube transistors performed in the time domain. We observe a ballistic electron resonance that corresponds to the round-trip transit of an electron along the nanotube with a picosecond-scale period. The electron velocity is found to be constant and equal to the Fermi velocity, showing that the high-frequency electron response is dominated by single-particle excitations rather than collective plasmon modes. These results demonstrate a powerful new tool for directly probing picosecond electron motion in nanostructures.