Theory of Tunneling Spectroscopy in a Mn$_{12}$ Single-Electron Transistor by Density-Functional Theory Methods

TL;DR

This paper develops a density-functional theory approach to analyze spin-dependent tunneling transport in a Mn12 molecular magnet, revealing how spin multiplet transitions influence conductance and can cause negative differential conductance.

Contribution

It introduces a practical method to construct many-body wavefunctions from Kohn-Sham orbitals for transport calculations in magnetic molecules.

Findings

Tunneling conductance peaks correspond to spin multiplet transitions.

Spin multiplet energy splittings significantly impact transport properties.

Negative differential conductance can arise from the orbital degrees of freedom.

Abstract

We consider tunneling transport through a Mn$_{12}$ molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wavefunctions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.