The Impact of Geometric Blockade on Thermoelectric Transport in Triangular Triple Quantum Dots

TL;DR

The paper examines thermoelectric transport in a triangular triple quantum dot (TTQD) system coupled to two reservoirs, focusing on a geometric blockade that arises from $C_{3v}$ symmetry. Using the nonperturbative hierarchical equations of motion (HEOM), the authors quantify how inter-dot coupling $t_{13}$ and symmetry breaking influence the Seebeck coefficient and the thermoelectric figure of merit $ZT$ in the linear response regime. They show that, at low temperature, lifting the blockade via symmetry breaking markedly enhances heat currents relative to charge currents, leading to a high $ZT$ (up to ~4.46) and a pronounced thermopower, with a nontrivial dependence on $U$ and $T$ tied to spectral-function evolution. The work highlights geometry as a powerful control parameter for nanoscale thermoelectrics and provides a detailed link between energy filtering, quantum interference, and many-body correlations in TTQDs.

Abstract

We investigate the transport properties of a triangular triple quantum dot (TTQD) system connected with two reservoirs under linear response regime. By employing the hierarchical equations of motion(HEOM), we compute the thermopower and thermoelectric figure of merit. The impact of interaction scheme among three quantum dots on the thermopower is thoroughly analyzed, while the thermoelectric current and spectral function throughout this process are also elaborated. Our results reveal that, under low-temperature conditions, the alleviation of the geometric blockade in the TTQD system leads to a significantly faster enhancement of the heat current compared to the electric current. This phenomenon consequently elevates the thermopower, resulting in a remarkably high thermoelectric figure of merit.

Figures (4)

• Figure 1: (a)Quantum dot 1 and quantum dot 3 are connected to the left and right electrodes.The coupling strength between each electrode and the quantum dot is 0.2 meV.(b)shows how the thermoelectric parameters change with the intradot tunneling strength $t_{13}$ . The black line indicates the Seebeck coefficient, while the red line indicates the $ZT$ value. The tunneling strength $t_{13}$ranges from 0 to 1 meV. The other parameters are set as follows: $U = 1 \, \text{meV}$, $\epsilon = -0.5 \, \text{meV}$, $t_{12} = t_{23} = 0.4 \, \text{meV}$, and $k_B T = 0.04 \, \text{meV}$
• Figure 2: shows the relationship between the electronic heat current and the voltage induced electron current as $t_{13}$ varies. The red line represents the current under a temperature difference between the electrodes, while the black line represents the current under a voltage difference. Other parameters are: $k_B T = 0.04 \, \text{meV}$, $\Delta T = 0.004 \, \text{meV}$, $\Delta V = 0.004 \, \text{meV}$; $t_{12} = t_{23} = 0.4 \, \text{meV}$, $U = 1 \, \text{meV}$, $\epsilon = -0.5 \, \text{meV}$
• Figure 3: (a) Local spectrum function of quantum dot 1 under different coupling strengths between quantum dots 1 and 3, in the presence of a temperature difference between the left and right electrodes. The inset shows the variation of the horizontal coordinate difference between the split peaks with respect to $t_{13}$.(b) Local spectrum function of quantum dot 1 in the presence of a potential difference between the left and right electrodes.
• Figure 4: (a) and (b) show how the thermoelectric parameters change with the T, (c) and (d) show how the thermoelectric parameters change with the U