Dynamic Transport Characteristics of Side-Coupled Double Quantum-Impurity Systems

TL;DR

This paper investigates the time-dependent transport properties of a double quantum-impurity system, revealing how coupling strength, interactions, and temperature influence current oscillations and quantum states.

Contribution

It provides a systematic analysis of dynamic transport in double quantum-impurity systems using hierarchical equations of motion, highlighting the effects of various parameters on current behavior and quantum states.

Findings

Transport current mimics a single quantum dot at low coupling.

Current oscillates due to temporal coherence when tunneling is coupled.

Oscillation frequency relates to applied step voltage.

Abstract

A systematic study is made on the time-dependent dynamic transport characteristics of the side-coupled double quantum-impurity system based on the hierarchical equations of motion. It is found that the transport current behaves like a single quantum dot when the coupling strength is low during tunneling or coulomb coupling. The dynamic current oscillates due to the temporal coherence of the electron tunneling device only when the tunneling transition is coupled. The oscillation frequency of the transport current is related to the step voltage applied by the lead, while the $T$, e-e interaction $U$ and the bandwidth $W$ have little influence. The amplitude of the current oscillation exists in positive correlation with $W$ and negative correlation with $U$. With the increase in coupling $t_{12}$ between impurities, the ground state of the system changes from a Kondo singlet of one impurity to a spin-singlet of two impurities. Moreover, lowering the temperature could promote the Kondo effect to intensify the oscillation of the dynamic current. When only the coulomb transition is coupled, it is found that the two split-off Hubbard peaks move upward and have different interference effects on the Kondo peak at the Fermi surface with the increase in $U_{12}$, from the dynamics point of view.