Anomalous Coulomb-Enhanced Charge Transport in Triangular Triple Quantum Dots Systems

Abstract

Electron correlation and quantum interference are pivotal in mesoscopic transport. We theoretically study the nonequilibrium transport dynamics of a triangular triple quantum dot (TTQD) molecule connected to fermionic reservoirs using the exact hierarchical equations of motion (HEOM) formalism. We demonstrate a counter-intuitive transport signature where the stationary current is significantly enhanced by increasing the $U$, a behavior distinct from the suppression typically observed in linear quantum dot arrays. By analyzing the evolution of spectral functions, we attribute this enhancement to the interplay between Coulomb interaction-induced energy shifts and quantum interference effects unique to the triangular topology. We also explore how the circulation of chiral currents and electrode coupling strength modulates these interaction effects. Finally, we present a three-dimensional map of the transport current as a function of inter-dot tunneling ($t$) and Coulomb interaction ($U$), illustrating their combined effect on the current magnitude and its applications.

Figures (4)

• Figure 1: (a)Schematic diagrams of a triangular triple quantum dots (TTQDs) and a linear triple quantum dots (LTQDs), Quantum dot 1 and quantum dot 3 are connected to the left and right electrodes.(b)Comparison of the transport current as a function of the on-site Coulomb interaction $U$ for the TTQDs and LTQDs configurations. The filled markers on the TTQD curve denote the specific values of $U$ at which the spectral function $A(\omega)$ has been explicitly evaluated, with all other parameters held identical and the inter-dot hopping fixed at $t = 0.25meV$ .The other parameters are set as follows: $k_B T = 0.1meV$, $\Gamma =0.025meV$, $V=0.1meV$
• Figure 2: Spectral function $A(\omega)$ of the triangular triple quantum dot system in the vicinity of the Fermi level $\omega = 0$, computed at representative on-site Coulomb interaction $U$ selected from both the rising and the falling portions of the current curve in Fig. 1.
• Figure 3: (Transport current $I$ through the triangular triple quantum dot as a function of the on-site Coulomb interaction $U$, computed for several values of the lead-dot hybridization strength $\Gamma$.
• Figure 4: Three-dimensional representation of transport current as a function of interdot hopping amplitude t and on-site Coulomb repulsion U for the triangular triple quantum dot system. Yellow arrows indicate regions where transport current increases with growing U, demonstrating the counterintuitive enhancement effect. Blue arrows mark regions where further increases in U suppress the current due to Coulomb blockade effects. Red arrows highlight the trend that larger values of t require correspondingly larger values of U to achieve maximum transport current, revealing that the phenomenon is governed by the dimensionless ratio U over t. The plot demonstrates that interaction-enhanced transport occurs in an intermediate regime where U and t are comparable in magnitude.