Influence of Coulomb Correlations on Nonequilibrium Quantum Transport in a Quadruple Quantum-Dot Structure

Abstract

The description of quantum transport in a quadruple quantum-dot structure (QQD) is proposed taking into account the Coulomb correlations and nonzero bias voltages. To achieve this goal the combination of nonequilibrium Green's functions and equation-ofmotion technique is used. It is shown that the anisotropy of kinetic processes in the QQD leads to negative differential conductance (NDC). The reason of the effect is an interplay of the Fano resonances which are induced by the interdot Coulomb correlations. Different ways to increase the peak-to-valley ratio related to the observed NDC are discussed. IntroductionTechnological development in recent decades allowed the experimental study of systems of few-electron quantum dots [1,2]. In these structures the occupation of each dot and the interaction between them are governed by the electric fields of gate electrodes.Since the lifetime of single-electron spin state, a spin qubit, in semiconducting quantum dot is relatively long, such objects are attractive for storage and processing of quantum information [3,4]. The research of quantum-dot complexes in this direction is necessary to create a scalable architecture of spin qubits [5,6].Intra-and interdot Coulomb interactions are the key factors determining different many-particle effects in the systems of quantum dots. They are being considered as a

Level anticrossing effect in single-level or multilevel double quantum dots: Electrical conductance, zero-frequency charge susceptibility and Seebeck coefficient

“…The zero-frequency charge susceptibility χ c (0) and the total DQD occupancy N = N 1 + N 2 are calculated from Eqs. (48) and (49). The calculations are performed in the linear response regime, i.e.…”

“…From the theoretical side, the electrical transport properties in DQD have been widely studied and the approaches to model them are mainly based on the use of Master equations for the density matrix [38][39][40][41][42][43] or on the use of Keldysh Green function methods [44][45][46][47][48][49] which becomes es-sential when one wants to treat out-of-equilibrium situations. The overall evolution of the linear conductance as a function of gate voltages is well understood within a classical theory along which the DQD is modeled as a network of resistors and capacitors which mimic the tunnel and electrostatic couplings between dots and leads [4][5][6] : (i) at weak interdot coupling, conductance peaks are observed at the nodes of a square lattice, (ii) at intermediate interdot coupling, pairs of triple-points arise at the boundaries between the regions with different electron occupancy in the dots to form a honeycomb lattice in the plane (ε 1 , ε 2 ), where ε 1 and ε 2 are the energy levels of the two dots, and (iii) at strong interdot coupling, the triple-point separation reaches its maximum and the DQD behaves as a single dot with an occupancy N 1 + N 2 , where N 1 and N 2 are the average number of electrons in the dots 1 and 2 respectively.…”