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Fanoa??Andreev and Fanoa??Majorana Correspondence in Quantum Dot Hybrid Structures
摘要： A correspondence on the single-electron transport properties between systems of different nature, a topological quantum system and a (conventional) non-topological one, is demonstrated. Specifically, the equivalence between the Fano resonances obtained in T-shaped double quantum dot system coupled to a superconducting lead (QD–QD–S) and a topological superconductor ring nanowire (QD–MBSs) is presented. The non-zero value of the Fano (anti)resonance in the conductance of the QD-MBSs systems is shown as a consequence of a complex Fano factor qM, which is equivalent to the complex Fano factor qS of the QD–QD–S. The complex nature of qS is understood as a sign of a phase introduced by the superconducting lead in the QD–QD–S. It is because of this phase that the correspondence between the QD–QD–S and the QD–MBSs is possible. It is believed that these results can help to reveal the importance of the Fano interference process toward the understanding of the role of the superconductor lead in the QD–QD–S system as well as giving a clear signature of the presence of MBS’s in the topological system.
关键词： Majorana bound states,proximity effects,Andreev reflection,(anti)fano resonances,topological superconductors
更新于2025-09-23 15:19:57
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Tunable nonlocal valley-entangled Cooper pair splitter realized in bilayer-graphene van der Waals spin valves
摘要： We investigate the Cooper pair splitting based on crossed Andreev reflection in a two-dimensional narrow superconductor coupled to two leads, where the two leads are van der Waals (vdW) spin valves formed by inserting bilayer graphene (BLG) between two antiparallel insulating ferromagnetic layers. In this BLG-based n-type vdW spin valve/superconductor/p-type vdW spin valve junction with edge-contact geometry, when controlling the Fermi energy and the interlayer electric field in BLG independently by top- and bottom-gate voltages in the vdW spin valve region, we first demonstrate that the two electrons of perfect Cooper pair splitting can remain nonlocal valley entanglement. This effect can be explained as follows: When both the two antiparallel insulating ferromagnetic layers and the interlayer electric field are taken into account, BLG exhibits a spin-splitting but valley-degenerate band gap near the Dirac point. Thus, our setups allow the Cooper pair in the BCS scenario to serve as a natural source of valley entanglement. We further predict large oscillations of cross conductance as a function of the doping of the superconductor, the junction length, and the bias voltage. Our results may provide a tool for realizing fast nonlocal switching of the valley-entanglement state.
关键词： valley entanglement,crossed Andreev reflection,Cooper pair splitting,van der Waals spin valves,bilayer graphene
更新于2025-09-19 17:13:59
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Fano-Andreev effect in a parallel double quantum dot structure
摘要： We investigate the Andreev reflection in a parallel double quantum dot structure, by considering one metallic lead coupled to one s-wave superconductor through the quantum dots. It is found that if an arm of this system provides the reference channel for the Andreev reflection, the Fano line shapes will have opportunities to appear in the linear conductance spectra and can be reversed by adjusting the dot level or local magnetic flux. To present the underlying physics, we obtain the Fano form of the linear conductance expression. Despite the complicated structural parameters, the property of the Fano effect is clearly shown. We believe that the results of this work will help us to understand the Fano interference in the Andreev reflection process.
关键词： quantum dots,Andreev reflection,superconductivity,Fano effect,quantum interference
更新于2025-09-11 14:15:04