Kondo-enhanced Andreev transport in single self-assembled InAs quantum dots contacted with normal and superconducting leads

Deacon, Russell; Tanaka, Yoïchi; Oiwa, A.; Sakano, Rui; Yoshida, Kenji; Shibata, Kenji; Hirakawa, Kazuhiko; Tarucha, Seigo

doi:10.1103/physrevb.81.121308

Cited by 89 publications

(82 citation statements)

References 35 publications

(34 reference statements)

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“…[1][2][3][4][5] These transition energies appear as features in the tunneling spectra, below the superconducting gap ∆. 'N-QD-S' systems were realized by evaporating contacts on top of carbon nanotubes, 6,7 self-assembled dots, 8 and semiconducting nanorwires (NWs). 9,10 These systems allow for gate-tunability of the dot chemical potential, generating a transition between two distinct ground states: An even parity, Cooper-pair-like singlet, and an odd parity, single-electron doublet.…”

Section: Introductionmentioning

confidence: 99%

Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers

et al. 2019

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Quantum dots proximity-coupled to superconductors are attractive research platforms due to the intricate interplay between the single-electron nature of the dot and the many body nature of the superconducting state. These have been studied mostly using nanowires and carbon nanotubes, which allow a combination of tunability and proximity. Here we report a new type of quantum dot which allows proximity to a broad range of superconducting systems. The dots are realized as embedded defects within semiconducting tunnel barriers in van-der-Waals layers. By placing such layers on top of thin NbSe 2 , we can probe the Andreev bound state spectra of such dots up to high in-plane magnetic fields without observing effects of a diminishing superconducting gap. As tunnel junctions defined on NbSe 2 have a hard gap, we can map the sub-gap spectra without background related to the rest of the junction. We find that the proximitized defect states invariably have a singlet ground state, manifest in the Zeeman splitting of the sub-gap excitation. We also find, in some cases, bound states which converge to zero energy and remain there. We discuss the role of the spin-orbit 1 arXiv:1906.01215v1 [cond-mat.supr-con] 4 Jun 2019 term, present both in the barrier and the superconductor, in the realization of such topologically trivial zero-energy states.

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Section: Introductionmentioning

confidence: 99%

Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers

et al. 2019

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“…Individual localized Yu-Shiba-Rusinov (YSR) states have been observed both by scanning tunneling spectroscopy of magnetic atoms like Mn or Cr adsorbed on superconducting Pb or Nb substrates, [4][5][6][7][8] and as subgap states in Coulomb blockaded quantum dots (QD) coupled to superconducting (S) leads. [9][10][11][12][13][14][15][16][17] The quantum dot realization is based on the spin-1/2 of oddoccupation charge states, and is therefore free of most of the material dependent complications for adatoms on a surface, like mixed valence, higher spin, and magnetic anisotropy. Furthermore, the quantum dot system allows for electrical tunability of the particle-hole asymmetry and, to some extent, the exchange coupling between the spin on the quantum dot and the quasiparticles in the superconductor, which makes it an ideal system for studying the properties of individual YSR states.…”

Section: Introductionmentioning

confidence: 99%

Yu-Shiba-Rusinov states in phase-biased superconductor–quantum dot–superconductor junctions

et al. 2015

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We study the effects of a phase difference on Yu-Shiba-Rusinov (YSR) states in a spinful Coulombblockaded quantum dot contacted by a superconducting loop. In the limit where charging energy is larger than the superconducting gap, we determine the subgap excitation spectrum, the corresponding supercurrent, and the differential conductance as measured by a normal-metal tunnel probe. In absence of a phase difference only one linear combination of the superconductor lead electrons couples to the spin, which gives a single YSR state. With finite phase difference, however, it is effectively a two-channel scattering problem and therefore an additional state emerges from the gap edge. The energy of the phase-dependent YSR states depend on the gate voltage and one state can cross zero energy twice inside the valley with odd occupancy. These crossings are shifted by the phase difference towards the charge degeneracy points, corresponding to larger exchange couplings. Moreover, the zero-energy crossings give rise to resonant peaks in the differential conductance with magnitude 4e 2 /h. Finally, we demonstrate that the quantum fluctuations of the dot spin do not alter qualitatively any of the results.

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“…In the strong coupling regime, the Coulomb correlations on QD may give rise to another interesting phenomenon, namely the Kondo effect [5,6]. In the proximity with S, the Kondo peak can be enhanced and the conductance can reach the value 4e 2 /h [7,8]. However, this occurs only for the Coulomb correlations properly adjusted to the asymmetry in the couplings to N and S lead [9].…”

Section: Introductionmentioning

confidence: 94%

Andreev Conductance through a Quantum Dot Strongly Coupled to Ferromagnetic and Superconducting Leads

Wójcik

Weymann

2017

Acta Phys. Pol. A

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We analyze the Andreev conductance through a quantum dot strongly coupled to one ferromagnetic and one superconducting lead. The transmission due to the Andreev reflection is obtained from the numerical renormalization group method. We show that at low temperatures, depending on the dot level position, the Andreev conductance exhibits a peak at zero bias due to the Kondo effect, which can be split by the exchange field due to spin-dependent coupling to ferromagnetic lead.

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Kondo-enhanced Andreev transport in single self-assembled InAs quantum dots contacted with normal and superconducting leads

Cited by 89 publications

References 35 publications

Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers

Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers

Yu-Shiba-Rusinov states in phase-biased superconductor–quantum dot–superconductor junctions

Andreev Conductance through a Quantum Dot Strongly Coupled to Ferromagnetic and Superconducting Leads

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