Carbon nanotubes (CNTs) are potential candidates for use in nanoelectronics due to their outstanding electrical and mechanical properties. Especially in high-frequency device applications, not only the averaged current characteristics such as impedance but also the current fluctuation such as shot noise are essential. Until recently, the current fluctuation has been considered mere noise being an obstacle to signal detection, but recent developments in nonequilibrium statistical mechanics with respect to current fluctuations such as the fluctuation theorem (FT) and the thermodynamic uncertainty relation (TUR) suggest that they can be controllable signals and useful information. In addition to formal frameworks of the nonequilibrium statistical mechanics, it is desirable to development new theoretical and computational methods that allows quantitative evaluation of current fluctuations in a specific target material with high precisely.

In this study, we provide a new simulation method that can simulate the time-dependent current flowing through a material on an atomistic level. Furthermore, we apply the new method to CNTs and evaluate the averaged current, the current fluctuation (current variance) and higher orders of cumulant expansion. Fig. 1(a) shows the time-dependent current in metallic (5,5) carbon nanotubes with three typical lengths of L=51 nm, 281 nm and 2,757 nm at T=300 K, where L=281 nm is almost the mean free path L_m of electrons in the (5,5) CNTs due to the electron-phonon scattering. As we can easily expect, the averaged current <J>decreases with increasing L. On the other hand, the current fluctuation, i.e., the variance σ²=<(J-<J>)²>, increases monotonically with L and exhibits the maximum near L=L_m(=281 nm) as shown in Fig.1(b). The new finding is extremely instructive in controlling the current noise of CNT-based electric devices. Furthermore, to give a physical interpretation of the new finding, we perform theoretical analysis based on the quantum scattering theory combined with Buttiker’s fictitious probe method [1] that can incorporates the electron-phonon scattering effects phenomenologically. The details are presented in the presentation.

Reference

[1] M. Büttiker, IBM J. Res Dev., 32, 63 (1988).