Electron transport in nanoscale junctions with local anharmonic modes

Area of Science:

• Quantum dots and molecular electronics
• Condensed matter physics
• Electron transport phenomena

Background:

• Electron transport through nanojunctions is crucial for molecular electronics.
• Understanding interactions between electrons and local systems (impurities, modes, spins) is key.
• Existing models like Anderson-Holstein and spin-fermion offer frameworks for these studies.

Purpose of the Study:

• To compare electron transport characteristics in the Anderson-Holstein and spin-fermion models.
• To investigate the presence of Franck-Condon blockade and nonlinear phenomena in these models.
• To analyze the behavior under different temperature and coupling regimes.

Main Methods:

• Utilized a shift transformation for perturbative expansion in the tunneling matrix element.
• Employed kinetic rate equation formalism for high-temperature, weak coupling analysis.
• Examined the low-temperature quantum adiabatic limit of the dissipative spin-fermion model.

Main Results:

• The spin-fermion model lacks the Franck-Condon blockade analog found in the Anderson-Holstein model.
• Nonlinear functionalities such as bistability and hysteresis were observed in the Anderson-Holstein model at the mean-field level.
• These nonlinear effects were absent in the spin-fermion model at the mean-field level.

Conclusions:

• The spin-fermion model exhibits distinct transport properties compared to the Anderson-Holstein model, particularly concerning blockade phenomena.
• The choice of model significantly impacts the prediction of nonlinear electronic functionalities in nanojunctions.
• Further research is needed to fully elucidate the behavior of these systems across various physical regimes.