Steady state conductance in a double quantum dot array: the nonequilibrium equation-of-motion Green function approach

Area of Science:

• Quantum physics
• Condensed matter physics
• Mesoscopic physics

Background:

• Steady-state charge transport through quantum dot arrays is crucial for nanoelectronic devices.
• The equation-of-motion (EOM) approach using nonequilibrium Green functions (NEGF) is widely used but relies on approximations.
• The accuracy of EOM closures for complex systems like double quantum dots remains an open question.

Purpose of the Study:

• To investigate and compare the accuracy of different approximations (closures) within the EOM-NEGF formalism for double quantum dot systems.
• To develop and validate new closures for improved accuracy in modeling quantum transport.
• To provide a reliable method for analyzing transport properties in interacting quantum dot systems.

Main Methods:

• Utilized the equation-of-motion approach to the nonequilibrium Green functions (EOM-NEGF) formalism.
• Investigated four distinct closure approximations: two extended from single quantum dot models and two newly developed ones.
• Compared results for differential conductance with a benchmark master equation approach, valid for weak system-lead couplings and high temperatures.

Main Results:

• All four closures accurately described transport properties for single quantum dots (Coulomb blockade).
• Significant discrepancies arose among the closures when applied to the double quantum dot system.
• Only one of the newly developed closures yielded satisfactory agreement with the benchmark method for the double quantum dot array.

Conclusions:

• The choice of closure approximation is critical for the accuracy of EOM-NEGF in multi-component quantum systems.
• The developed closure provides a more reliable description of steady-state transport in double quantum dots.
• This work offers a pathway to apply EOM-NEGF to more complex models with strong electronic interactions, advancing the study of nanoscale electronic devices.