Transport through Magnetic Molecules with Spin-Vibron Interaction

Abstract

Electronic transport through single-molecule devices is a powerful spectroscopic tool to probe various degrees of freedom at the nanoscopic level. Among these degrees of freedom, molecular vibrations are of particular relevance since they can result in drastic effects such as transport blockade. While the effect of the interaction between the molecular charge and vibrations on transport through a single magnetic molecule has already been characterized, additional research, especially from the theoretical perspective, is still required to examine the vibrations’ coupling to the molecular spin and its impact on the magnetic anisotropy. For this reason, the aim of this thesis is to provide and scrutinize a theoretical model for transport through a single magnetic molecule that takes into account the threefold interplay between charge, spin and molecular vibrations. For a quantum mechanical treatment, the real-time diagrammatic technique is employed to study transport in the sequential tunneling regime. However, exploiting Bloch-like equations, it is proven that coherent superpositions do not influence transport for a molecule embedded between nonmagnetic electrodes. Consequently, using classical rate equations with Fermi golden rule is sufficient to capture the full picture. Based on this approach, it is shown that the coupling of the molecular vibrations modulates the magnetic anisotropy of a molecule along both the uniaxial and transverse directions, which results in various implications on transport properties, most notably transport blockade. This demonstrates yet another possibility to modify the magnetic properties of molecules by controlling the vibrational excitations. For instance, the anisotropy barrier can be enhanced to potentially improve the stability of a magnetic molecule as a nanoscopic memory element.