Transport properties of a gated nanostructure depend crucially on the coupling of its states to the states of electrodes. In the case of a single quantum dot the coupling, for a given quantum state, is constant or can be slightly modified by additional gating. In this paper we consider a concentric dot-ring nanostructure (DRN) and show that its transport properties can be drastically modified due to the unique geometry. We calculate the dc current through a DRN in the Coulomb blockade regime and show that it can efficiently work as a single-electron transistor (SET) or a current rectifier. In both cases the transport characteristics strongly depend on the details of the confinement potential. The calculations are carried out for low and high bias regime, the latter being especially interesting in the context of current rectification due to fast relaxation processes.
We investigate the inhomogeneous Rashba chain coupled to a superconducting substrate, hosting the Majorana quasiparticles near its edges. We discuss its subgap spectrum and study how robust are the zero-energy quasiparticles against the diagonal and off-diagonal disorder. Studying the Z2 topological invariant we show that disorder induced transition from the topologically non-trivial to trivial phases is manifested by characteristic features in the spatially-resolved quasiparticle spectrum at zero energy. We provide evidence for the non-local nature of the zero-energy Majorana quasiparticles, that are well preserved upon partitioning the chain into separate pieces. Even though the Majorana quasiparticles are not completely immune to inhomogeneity we show that they can spread onto other (normal) nanoscopic objects via the proximity effect.
We discuss the quantum dot-ring nanostructure (DRN) as canonical example of a nanosystem, for which the interelectronic interactions can be evaluated exactly. The system has been selected due to its tunability, i.e., its electron wave functions can be modified much easier than in, e.g., quantum dots. We determine many-particle states for Ne = 2 and 3 electrons and calculate the 3- and 4-state interaction parameters, and discuss their importance. For that purpose, we combine the first- and second-quantization schemes and hence are able to single out the component single-particle contributions to the resultant many-particle state. The method provides both the ground- and the first-excited-state energies, as the exact diagonalization of the many-particle Hamiltonian is carried out. DRN provides one of the few examples for which one can determine theoretically all interaction microscopic parameters to a high accuracy. Thus the evolution of the single-particle vs. many-particle contributions to each state and its energy can be determined and tested with the increasing system size. In this manner, we contribute to the wave-function engineering with the interactions included for those few-electron systems.
Performing Monte Carlo simulations we study the temperature dependent self-organization of magnetic moments coupled to itinerant electrons in a finite-size one-dimensional nanostructure proximitized to a superconducting reservoir. At low temperature an effective interaction between the localized magnetic moments, that is mediated by itinerant electrons, leads to their helical ordering. This ordering, in turn, affects the itinerant electrons, inducing the topologically nontrivial superconducting phase that hosts the Majorana modes. In a wide range of system parameters, the spatial periodicity of a spiral order that minimizes the ground state energy turns out to promote the topological phase. We determine the correlation length of such spiral order and study how it is reduced by thermal fluctuations. This reduction is accompanied by suppression of the topological gap (which separates the zero-energy mode from continuum), setting the upper (critical) temperature for existence of the Majorana quasiparticles. Monte Carlo simulations do not rely on any ansatz for configurations of the localized moments, therefore they can be performed for arbitrary model parameters, also beyond the perturbative regime. arXiv:1902.06750v1 [cond-mat.mes-hall]
Within the formalism of the Keldysh Green's functions we investigate long-range response of an anisotropic XY chain to the local magnetic field. This field couples to a single spin on a selected lattice site. The system is driven out of equilibrium by a coupling to two semi-infinite XX spin chains. We demonstrate that the longrange response becomes enhanced by a few orders of magnitude upon application of nonequilibrium conditions. This enhancement does not occur in the isotropic XX chain. Our results agree with the recently predicted nonequilibrium-driven long-range magnetic correlations ͓T. Prosen and I. Pižorn, Phys. Rev. Lett. 101, 105701 ͑2008͔͒. We argue that this effect may be observed in quasi-one-dimensional triplet superconductors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.