Generation of terahertz radiation by wave mixing in armchair carbon nanotubes

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 and . 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 θ lies between and 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