Magnetoresistance in Spin-Polarized Transport through a Carbon Nanotube

TL;DR

This theoretical study explores how magnetoresistance in spin-polarized transport through a finite carbon nanotube varies with Fermi energy and electrode coupling, revealing oscillations and conditions for negative MR.

Contribution

The paper provides a detailed theoretical analysis of magnetoresistance behavior in finite CNTs, highlighting the effects of energy level resonances and coupling asymmetries on MR.

Findings

MR oscillates with Fermi energy due to discrete energy levels.

Negative MR occurs under strong coupling asymmetry.

MR dips are positive in symmetric coupling cases.

Abstract

We report on our theoretical study of the magnetoresistance in spin polarized transport through a finite carbon nanotube (CNT). Varying the Fermi energy of a CNT and the relative strength of couplings to two ferromagnetic (FM) electrodes, we studied the conductance as well as the magnetoresistance (MR). Due to resonant transport through discrete energy levels in a finite CNT, the conductance and MR are oscillating as a function of the CNT Fermi energy. The MR is peaked at the conductance valleys and dipped close to the conductance peaks. When couplings to two FM electrodes are asymmetric, the MR dips become negative under a rather strong asymmetry. When couplings are more or less symmetric, the MR dips remain positive except for a very strong coupling case. Under strong coupling case, the line broadening is significant and transport channels through neighboring energy levels in a CNT interfere with each other, leading to the negative MR.