GHz~THz Plasmonics using 1D Nanodevice
In bulk conductors, plasmonic resonance, in which electrons collectively slosh back and forth, occurs at optical frequencies. In contrast, in 1D conductors such as carbon nanotubes, plasmonic waves, the collective motion of electrons that propagate energy like in acoustic waves, can occur at GHz~THz frequencies due to the unique 1D electron transport physics, thus, can be available for electronics applications.
The 1D plasmonic wave, though predicted about 50 years ago, has yet to be observed. At Harvard, I initiated and developed an experiment that seeks to demonstrate the GHz~THz plasmonic waves, using carbon nanotubes and GaAs/AlGaAs quantum wires as 1D systems. This problem is remarkably interesting in a few ways. (1) From the circuit angle, plasmonic resonators made from 1D conductors would be smaller than EM resonators by orders of magnitude (as the plasmonic wave’s speed is hundreds of times smaller than the speed of light), thus, they could greatly reduce the size of GHz~THz integrated circuits. As 1D plasmonic resonators scale naturally well into THz frequencies, they can be especially useful in THz works. (2) From the fundamental physics viewpoint, electron-electron interactions in 1D, a significant topic in condensed matter physics, are intimately related to plasmonic waves, thus, my work may offer a frequency-domain method to examine the interacting electrons in 1D, e.g., to verify the Luttinger liquid (LL) model. (3) While nanoelectronics works are much focused on nanodevice-based transistors in the regime electrons do not show collective motion, my work examines the plasmonic behavior inherent in 1D devices, offering a new direction in nanoelectronics.
My experiment uses EM waves to excite plasmonic waves at one end of a carbon nanotube or a quantum wire, and detects the EM signal at the other device end, which is re-excited by the plasmonic waves. By analyzing the re-excited EM wave, the plasmonic waves can be observed and studied. The work is challenging, as the coupling strength of EM waves to 1D plasmonic waves is fundamentally on the order of the fine structure constant (~1/137). To overcome this, I have optimized the design of the plasmonic-EM interface. Our recent experiment with quantum wires shows promising results, which might hint the kinetic energy part of the plasmonic waves. We are in the process of conservatively confirming this speculation.
Plasmonic Circuits for THz Science & Technology
Building upon my PhD research, I plan to establish a program on THz circuits, where I will build THz circuits by exploiting the THz plasmonic waves in 1D nanodevices. Specifically, I seek to build a plasmonic-resonant THz detector with capability of spectral resolution (unlike the superconducting bolometers), and active plasmonic transistors that can potentially achieve THz generation and amplification. These THz circuits can have far-reaching impacts in many areas of science and technology, including biomedical or security imaging, semiconductor carrier dynamics study, gas sensing for environment, atmospheric monitoring, large-molecule chemistry, and submillimeter astronomy.