Kondo Universal Scaling for a Quantum Dot Coupled to Superconducting Leads

Buizert, C.; Oiwa, A.; Shibata, Kenji; Hirakawa, Kazuomi; Tarucha, Seigo

doi:10.1103/physrevlett.99.136806

Cited by 109 publications

(115 citation statements)

References 27 publications

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“…Carbon nanotubes (CNTs) have proved to be well suited for the observation of both Kondo effect 6,7,14,18 and ABS 4 because they fulfill three basic requirements: (i) At low enough temperatures (below 4 K) they behave as QDs whereby electron occupancy can be electrostatically tuned. (ii) Good S-X coupling with conventional superconductors (that can be turned into the normal state with a moderate magnetic field) were recently achieved, 2,3 and (iii) there is a possibility of simultaneous weak coupling to a probe that allows tunneling spectroscopy of ABS.…”

Section: A Sample Fabrication and Characterizationmentioning

confidence: 99%

“…The interest in such new materials relies on the wealth of different phenomena they present (Kondo effect, 6,7 spin-orbit coupling, [8][9][10] Luttinger liquid behavior 11 ) and their interplay when coupled to superconducting reservoirs. Further interest in this field has been prompted by recent theoretical predictions on the existence of Majorana fermions at the edge of a S-X structure, where X is a one-dimensional semiconductor with strong spin-orbit interaction.…”

Section: Introductionmentioning

confidence: 99%

“…6,7,[14][15][16][17][18] In this work, instead of relying on transport through a QD, we perform tunneling spectroscopy of a single QD (coupled to a superconducting reservoir) in order to investigate this interplay in a direct way. In particular, we explore how the Kondo resonance, observed when the QD's occupancy is odd and the reservoir is in the normal state, is replaced by ABS within the gap as the reservoir becomes superconducting.…”

Section: Introductionmentioning

confidence: 99%

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To Screen or Not to Screen, That is the Question!

Maurand¹,

Schönenberger²

2013

Physics

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We performed tunneling spectroscopy of a carbon nanotube quantum dot (QD) coupled to a metallic reservoir either in the normal or in the superconducting state. We explore how the Kondo resonance, observed when the QD's occupancy is odd and the reservoir is normal, evolves towards Andreev bound states (ABS) in the superconducting state. Within this regime, the ABS spectrum observed is consistent with a quantum phase transition from a singlet to a degenerate magnetic doublet ground state, in quantitative agreement with a single-level Anderson model with superconducting leads.

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Section: A Sample Fabrication and Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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To Screen or Not to Screen, That is the Question!

Maurand¹,

Schönenberger²

2013

Physics

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“…In the past years, quantum dots (QDs) coupled to superconducting leads have been widely explored as tunable Josephson junctions [6,7], or as building blocks of Cooper-pair splitters [8][9][10]. Hybrid superconductor-QD devices also constitute versatile platforms for studying fundamental issues, such as the physics of the Andreev bound states (ABS) [11][12][13] or the interplay between the Kondo effect and the superconducting proximity effect [14][15][16][17][18][19][20][21][22][23][24].…”

mentioning

confidence: 99%

Zero-Bias Anomaly in a Nanowire Quantum Dot Coupled to Superconductors

et al. 2012

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We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminium superconducting leads. By varying the superconducting gap, ∆, with a magnetic field, B, we investigated the transition from strong coupling, ∆ ≪ TK, to weak coupling, ∆ ≫ TK, where TK is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust sub-gap structures at bias voltages between ∆ and 2∆. For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intra-gap quasiparticle states, and the finite-bias sub-gap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnelspectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures.

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“…Experimentally, supercurrents through quantum dots formed in carbon nanotubes [26], InAs nanowires [27], InAs quantum dots [28], and graphene [29] have been observed, making them potential candidates to observe the many-particle Majorana modes. We therefore suggest that many-particle Majorana modes may become standard in practical applications of Majorana physics.…”

mentioning

confidence: 99%

Localized Many-Particle Majorana Modes with Vanishing Time-Reversal Symmetry Breaking in Double Quantum Dots

Wright

Veldhorst

2013

Phys. Rev. Lett.

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We introduce the concept of spinful many-particle Majorana modes with local odd operator products, thereby preserving their local statistics. We consider a superconductor -double quantum dot system where these modes can arise with negligible Zeeman splitting when Coulomb interactions are present. We find a reverse Mottinsulator transition, where the even and odd parity bands become degenerate. Above this transition, Majorana operators move the system between the odd parity ground state, associated with elastic co-tunneling, and the even parity ground state, associated with crossed Andreev reflection. These Majorana modes are described in terms of one, three and five operator products. Parity conservation results in a 4π periodic supercurrent in the even state and no supercurrent in the odd state.The prediction for the existence of Majorana modes [1] has attracted enormous attention in condensed matter physics [2][3][4][5][6][7]. Allured by the possibility of constructing topological qubits for quantum computation [2,4], a plethora of schemes promising the positive identification of Majorana modes has emerged [8][9][10][11][12]. Although superconductors are a natural habitat of chargeless quasiparticles, spin degeneracy in standard s-wave superconductors prevents the appearance of localized Majorana modes. Effective spinless p-wave superconductors can be realized using strong spin-orbit coupling, for example at the interface of a superconductor and a topological insulator [5], or in semiconducting nanowires in the presence of Zeeman and Rashba fields [6,7]. Experimentally, supercurrents [13], Fraunhofer patterns and Shapiro steps [14], SQUIDs [15], and zero bias conductance peaks [16] have been observed in topological insulator systems, which, together with the zero bias conductance peaks in nanowire systems [17], provide prospects for the observation of the Majorana mode, but to date, no conclusive evidence has been observed.Superconductor -quantum dot systems are also proposed to realize Majorana modes [11,18,19], by including spin-orbit coupling [11], or in the presence of anisotropic magnetic fields [19]. Although quantum dots have several advantages, the strong spin-orbit or anisotropic magnetic fields required forms a major hurdle and limits material flexibility. For example, anisotropic magnetic fields only result in spinless localized Majorana modes in fields E Z ≫ ∆ ∼ t, with ∆ the induced superconducting gap and t the inter-site hopping. Here, generalizing the proposal of Ref.[19] to strongly correlated quantum dots, we show that in the presence of small anisotropic magnetic fields, E Z ∼ k B T , a new arena emerges: the concept of spinful many-particle Majorana modes. These Majorana modes are localized in their odd operator products, and thereby preserve the local statistics of spinless proposals [20]. Furthermore, this demonstrates that interactions can greatly relax the constraints of large Zeeman splitting and large spin FIG. 1: (a) Schematic representation of the device. Two superconductors (with p...

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Kondo Universal Scaling for a Quantum Dot Coupled to Superconducting Leads

Cited by 109 publications

References 27 publications

To Screen or Not to Screen, That is the Question!

To Screen or Not to Screen, That is the Question!

Zero-Bias Anomaly in a Nanowire Quantum Dot Coupled to Superconductors

Localized Many-Particle Majorana Modes with Vanishing Time-Reversal Symmetry Breaking in Double Quantum Dots

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