High Efficiency CVD Graphene-lead (Pb) Cooper Pair Splitter

Borzenets, Ivan; Shimazaki, Yuya; Jones, Gareth F.; Craciun, Monica F.; Russo, Saverio; Yamamoto, Yasuhiko; Tarucha, Seigo

doi:10.48550/arxiv.1506.04597

2015

DOI: 10.48550/arxiv.1506.04597

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High Efficiency CVD Graphene-lead (Pb) Cooper Pair Splitter

Ivan Borzenets¹,

Yuya Shimazaki²,

Gareth F. Jones³

et al.

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2016

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“…23 In Pb-based devices large transport gaps have already been demonstrated for carbon nanotubes (CNTs) using tunnel barriers [24][25][26] and allowed the observation of Cooper pair splitting in graphene. 27 Here we present the growth and fabrication of well-defined, reproducible multi-layered Pb-based superconducting contacts to CNTs, which can be easily applied to other materials like graphene or semiconducting nanowires. We demonstrate reproducibly large and clean superconducting transport gaps in CNT QDs with a narrow Pb-based and a normal metal contact.…”

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Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

Gramich

Baumgärtner

Schönenberger

2016

Applied Physics Letters

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We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube (CNT) quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor's finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multilayer contacts, which result in reproducibly large and "clean" superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.Quantum phenomena in nanostructures with a superconductor (S) and a normal metal contact (N) coupled to low-dimensional electron systems like a quantum dot (QD) 1 have recently gained much attention due to potential applications in quantum technology. Especially prominent are transport phenomena at energies below the superconductor's energy gap, ∆, which typically comprise quasi-particle (QP) tunneling and Andreev processes due to Cooper pair transport. These processes result in a large variety of subgap features, for example Majorana Fermions, 2 which might be used for topological quantum computation, 3 Cooper pair splitting 4-8 as a source of entangled electrons, resonant and inelastic Andreev tunneling, 9 or Andreev bound states (ABSs) 10-13which can be implemented as Andreev qubits. 14,15 Recent experiments have highlighted the importance to understand in detail the QP excitations in such structures, which, for example, lead to additional subgap features, 16,17 or to a poisoning of the bound state parity lifetime. 18To identify subgap transport mechanisms, a transport gap much larger than the QD life time, ∆ Γ, is very beneficial -a regime which is not easily achieved in S-QD hybrid devices. In addition, a strong suppression of the QP conductance in the subgap regime is required, which is commonly known as a "clean gap". While the widely used superconductor Al 5-7 has yielded devices with good transport characteristics, long superconducting coherence lengths, ξ 0 , and more recently also clean gaps, 18-20it's small gap renders spectroscopic investigations difficult. S-QD devices based on the large-gap superconductor Nb allowed the observation of several fundamental transport processes 9,13,16,17,21 and new effects due to the large critical field.22 However, Nb has rather short coherence lengths and the devices often exhibit strongly suppressed or "soft" gaps 16,21,22 and complex magnetic field characteristics, 9,22 which make normal state control experiments difficult. In contrast, in the superconductor Pb one finds a large bulk coherence length of ξ 0 ∼ 90 nm, a supercondu...

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confidence: 99%

Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

Gramich

Baumgärtner

Schönenberger

2016

Applied Physics Letters

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High Efficiency CVD Graphene-lead (Pb) Cooper Pair Splitter

Cited by 1 publication

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Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

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