Splitting efficiency and interference effects in a Cooper pair splitter based on a triple quantum dot with ferromagnetic contacts

Abstract

We theoretically study the spin-resolved subgap transport properties of a Cooper pair splitter based on a triple quantum dot attached to superconducting and ferromagnetic leads. Using the Keldysh Green's function formalism, we analyze the dependence of the Andreev conductance, Cooper pair splitting efficiency, and tunnel magnetoresistance on the gate and bias voltages applied to the system. We show that the system's transport properties are strongly affected by spin dependence of tunneling processes and quantum interference between different local and nonlocal Andreev reflections. We also study the effects of finite hopping between the side quantum dots on the Andreev current. This allows for identifying the optimal conditions for enhancing the Cooper pair splitting efficiency of the device. We find that the splitting efficiency exhibits a nonmonotonic dependence on the degree of spin polarization of the leads and the magnitude and type of hopping between the dots. An almost perfect splitting efficiency is predicted in the nonlinear response regime when the energies of the side quantum dots are tuned to the energies of the corresponding Andreev bound states. In addition, we analyzed features of the tunnel magnetoresistance (TMR) for a wide range of the gate and bias voltages, as well as for different model parameters, finding the corresponding sign changes of the TMR in certain transport regimes. The mechanisms leading to these effects are thoroughly discussed. arXiv:1805.11130v1 [cond-mat.mes-hall]

Long-range Cooper pair splitting by chiral Majorana edge states

“…The basic structure of such devices consists of a superconducting region (S) connected to two normal electrodes (N) separated by a distance of the order of the superconducting coherence length ξ 0 . Various designs include intermediate quantum dots [30][31][32][33][34][35][36][37][38][39], anisotropic superconductivity [2,11,[40][41][42], and some devices have been realized experimentally [14,15,17,19,22,[32][33][34]. For subgap voltages, CARs compete with local Andreev reflections (AR) and elastic co-tunneling (EC) between electrodes.…”

Current cross-correlations and waiting time distributions in Andreev transport through Cooper pair splitters based on a triple quantum dot system

“…35 To capture and understand the role of quantum interference, a three-site model has been put forward, where the central part is coupled to superconductor, while the left and right arms of the splitter are modeled by remaining two separate sites. [35][36][37] The transport properties of such three-site models are however still rather unexplored. The purpose of this paper is therefore to advance further the understanding of the Andreev transport in CPS based on triple quantum dots.…”

Nonlocal thermoelectricity in a Cooper-pair splitter

“…The competing process of local Andreev reflection (LAR), where the electrons tunnel into the same lead, does not directly contribute to the spatially nonlocal entanglement. In order to increase the CAR fraction of the current and minimize the effect of LAR, different strategies have been adopted such as employing ferromagnetic leads, [20][21][22][23][24] or including quantum dots with large intradot Coulomb repulsion. [25][26][27][28][29][30][31][32] In double quantum dots with finite Coulomb repulsion, it has been discussed the possibility to induce spatially nonlocal entanglement and manipulate its symmetry by involving only the LAR process even without the nonlocal coupling.…”