arXiv1998
We derive an effective 1D theory from the Hamiltonian of the 3D system which consists of a mesoscopic conductor and reservoirs. We assume that the many-body interaction have the same magnitude in the conductor as that in the reservoirs, in contrast to the previous theories which made the ad hoc assumption that the many-body interaction were absent in the reservoirs. We show the following: (i) The effective potentials of impurities and two-body interaction for the 1D modes become weaker as $x$ goes away from the conductor. (ii) On the other hand, the interaction between the 1D and the reservoir modes is important in the reservoir regions, where the reservoir modes excite and attenuate the 1D modes through the interaction. (iii) As a result, the current $\hat I_1$ of the 1D modes is not conserved, whereas the total current $\hat I$ is of course conserved. (iv) For any steady state the total current $\bra I \ket$, its equilibrium fluctuation $\bra δI^2 \ket^{eq}$ at low frequency, and non-equilibrium fluctuation $\bra δI^2 \ket^{noneq}$ at low frequency, of the original system are independent of $x$, whereas $\bra δI^2 \ket^{eq}$ and $\bra δI^2 \ket^{noneq}$ at higher frequencies may depend on $x$. (v) Utilizing this property, we can evaluate $\bra I \ket$, $\bra δI^2 \ket^{eq}$, and $\bra δI^2 \ket^{noneq}$ at low frequency from those of the 1D current $\hat I_1$. (vi) In general, the transmittance $T$ in the Landauer formula should be evaluated from a single-body Hamiltonian which includes a Hartree potential created by the density deformation which is caused by the external bias.