- A new experiment shows nano-circuits can produce motions directly from an electrical current.
- Researchers use carbon nanotubes to build such circuits.
The electron-phonon interaction is one of the fundamental interactions of quasiparticles in solids. It plays a crucial role in several physical phenomena and contributes to the self-energy of an electron.
The extreme limit of electron-phonon coupling can be represented by a single-electron transistor embedded in a nanomechanical resonator. This could enable rapid and sensitive measurements.
Recently, a team of researchers at the University of Oxford and Lancaster University developed a nano-electronic circuit that vibrates itself without any external force. This shows that nano-circuits can produce motions directly from an electrical current.
How Did They Create This Device?
Researchers used a carbon nanotube, an extremely thin wire with a diameter of approximately 3 nanometers. To put this in context, a guitar string is about 100,000 times thicker than this carbon nanotube.
The nanotube was stamped across metallic contact electrodes and cooled to a temperature of 25 mK (0.025 degrees above absolute zero). The middle part of the nanotube was free to vibrate.
The vibration could be detected by passing an electric current through the tube and measuring variations in electrical resistance.
The research team found that the nanotube vibrates when it is forced into motion via an oscillating voltage. This is similar to the vibration of a guitar string (when it is plucked).
They then performed the experiment one more time without the forcing voltage. The results were quite surprising this time. Under certain scenarios, the nanotube vibrated of its own accord. The tiny guitar string was playing itself.
What’s Causing The Vibrations?
Strings of a regular size guitar
In such a small instrument, each electron (from electrical current) plays a significant role. Individual electrons hop one by one onto the nanotube and give a tiny, random push to each other. By carefully controlling specific parameters, it is possible to synchronize and produce an oscillation.
Since the carbon nanotube is hundreds of thousands of times thinner than guitar string, it vibrates at a higher frequency. It oscillates into the ultrasound range so you can’t hear it without using a sound-amplifying device.
Researchers assigned a note to this ‘nano-electronic guitar’: It oscillates at a frequency of 231 MHz, so it is an A string, pinched 21 octaves above normal tuning.
The oscillating nano circuit can be used to measure the viscosity of quantum fluids and amplify tiny forces such as in novel microscopes.
Further development from this circuit could replace the single-electron transistor with a coherent two-level system such as a double quantum dot, a superconducting single-electron transistor. This will also enable the examination of complex phenomena in the fully quantum limit.