Quantum Interference Effects In Transport Research Articles

Novel Quantum Interference Effects in Transport through Molecular Radicals

We investigate electronic transport through molecular radicals and predict a correlation-induced transmission node arising from destructive interference between transport contributions from different charge states of the molecule. This quantum interference effect has no single-particle analog and cannot be described by effective single-particle theories. Large errors in the thermoelectric properties and nonlinear current-voltage response of molecular radical junctions are introduced when the complementary wave and particle aspects of the electron are not properly treated. A method to accurately calculate the low-energy transport through a radical-based junction using an Anderson model is given.

Quantum interference effects and spin-orbit interaction in quasi-one-dimensional wires and rings.

We study two kinds of quantum interference effects in transport--the Aharonov-Bohm effect and the weak-localization effect--in quasi-one-dimensional wires and rings to address issues concerning the phase-coherence length, spin-orbit scattering, and the flux cancellation mechanism which is predicted to be present when the elastic mean free path exceeds the sample width. Our devices are fabricated on GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As and pseudomorphic ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure materials and the experiments carried out at 0.4--20 K temperatures. In the GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As devices which exhibit no significant spin-orbit scattering, we were able to extract a phase-coherence length ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$ from the amplitude of the Aharonov-Bohm magnetoresistance oscillations in different sized rings. We find it to be in agreement with ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$ deduced from the weak-localization data in parallel wires when the one-dimensional weak-localization theory including the flux cancellation mechanism is used to fit the data. We therefore unambiguously establish that the same ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$ governs the behavior of the two quantum interference phenomena of Aharonov-Bohm oscillations and weak localization, and that the flux cancellation is in force. In the pseudomorphic ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure devices which exhibit strong spin-orbit interaction effects, ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$ exceeds the spin-orbit-scattering length at low temperatures. The amplitude of Aharonov-Bohm oscillations can only be explained by introducing reduction factors due to spin-orbit scattering.