Generation of Terahertz Radiation by Wave Mixing in Armchair Carbon Nanotubes

TL;DR

This paper theoretically investigates how mixing two electromagnetic waves can generate a direct current in armchair carbon nanotubes, proposing a method for terahertz radiation generation and electron relaxation time measurement.

Contribution

It presents a semiclassical Boltzmann equation analysis of DC generation in armchair CNTs by wave mixing, comparing results with zigzag CNTs and exploring phase shift effects.

Findings

Normalized current peaks are about 1.1 times higher in zigzag than armchair CNTs.

Current becomes positive when phase shift is between pi/2 and 3pi/2.

Armchair CNTs show greater normalized current than zigzag CNTs for certain conditions.

Abstract

Using semiclassical Boltzmann equation we have studied theoretically an effect of a direct current (DC) generation in undoped armchair carbon nanotube (CN) by mixing two coherent electromagnetic waves with commensurate frequencies i.e omega and 2 omega . We compared the results of the armchair with that of the zigzag carbon nanotubes for the same conditions (i.e. when the normalized current is plotted against the amplitude). Quantitatively they agree with each other except that the absolute value of the peaks of the current for zigzag is about 1.1 times that of the armchair. We noticed that the current is negative similar to that observed in zigzag CNs describing the same effect. However it is interesting to note that graph of normalized current against omega tau showed that the armchair is greater than that of the zigzag for about 1.1 times which is opposite. We also observed that when the phase shift theta lies between pi divided by 2 and 3 pi divided by 2 there is an inversion and the current becomes positive. We suggest the use of this approach for the generation of terahertz radiation and also for the determination of the relaxation time of electrons in carbon nanotubes.