The lateral proximity effect and long-range energy-gap gradients in Ta/Al and Nb/Al Josephson junctions

R. den Hartog, Alexandre Avraamovitch Golubov, D. Martin, P. Verhoeve, P.A. Poelaert, A. Peacock, M. Krumrey

    Research output: Contribution to journalArticleAcademicpeer-review

    5 Citations (Scopus)

    Abstract

    We present two independent experiments, each of which suggests that the local energy gap in Ta (and Nb) has a lateral spatial variation on a scale of several μm. The first experiment is a series of current–voltage characterizations of Nb/Al/AlOx and Ta/Al/AlOx Josephson junctions, which reveals a dependence of the measured energy gap on the size of the junction. This implies a geometrical dependence of the energy gap. An extended version of the current theory of the proximity effect could explain this phenomenon when a lateral coherence length is introduced, which is of the order of the bulk coherence length of the materials. The second experiment is a series of coincidence measurements of photon absorption events in a Ta absorber between two Ta/Al junctions. There is a clear distinction in the pulse-height characteristics between events detected in the absorber and the junctions. Interestingly, there are also events indicating the presence of a transition region between the absorber and the junction. Event statistics imply that this region has a size of 6 μm, independent of photon energy, which is quite a bit larger than even the bulk coherence length in Ta. It is argued that an additional effect due to ‘smearing’ by the relaxed quasi-particle cloud must also be present. These effects are interesting and intriguing; not only from a theoretical viewpoint, but also for energy-gap engineering of superconducting materials for practical applications, e.g. in a variety of photon and particle detectors.
    Original languageEnglish
    Pages (from-to)28-32
    Number of pages5
    JournalNuclear instruments & methods in physics research. Section A : Accelerators, spectrometers, detectors and associated equipment
    Volume444
    Issue number1-2
    DOIs
    Publication statusPublished - 7 Apr 2000

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    Josephson junctions
    Energy gap
    absorbers
    gradients
    Photons
    photons
    Particle detectors
    radiation counters
    Experiments
    pulse amplitude
    elementary excitations
    Superconducting materials
    Statistics
    statistics
    engineering
    detectors
    energy

    Keywords

    • Proximity effects
    • Superconducting films
    • Josephson devices
    • Tunneling phenomena
    • IR-58985
    • X- and γ-ray detectors

    Cite this

    @article{5722ac317c4f41a0b7778ee6ee38c45a,
    title = "The lateral proximity effect and long-range energy-gap gradients in Ta/Al and Nb/Al Josephson junctions",
    abstract = "We present two independent experiments, each of which suggests that the local energy gap in Ta (and Nb) has a lateral spatial variation on a scale of several μm. The first experiment is a series of current–voltage characterizations of Nb/Al/AlOx and Ta/Al/AlOx Josephson junctions, which reveals a dependence of the measured energy gap on the size of the junction. This implies a geometrical dependence of the energy gap. An extended version of the current theory of the proximity effect could explain this phenomenon when a lateral coherence length is introduced, which is of the order of the bulk coherence length of the materials. The second experiment is a series of coincidence measurements of photon absorption events in a Ta absorber between two Ta/Al junctions. There is a clear distinction in the pulse-height characteristics between events detected in the absorber and the junctions. Interestingly, there are also events indicating the presence of a transition region between the absorber and the junction. Event statistics imply that this region has a size of 6 μm, independent of photon energy, which is quite a bit larger than even the bulk coherence length in Ta. It is argued that an additional effect due to ‘smearing’ by the relaxed quasi-particle cloud must also be present. These effects are interesting and intriguing; not only from a theoretical viewpoint, but also for energy-gap engineering of superconducting materials for practical applications, e.g. in a variety of photon and particle detectors.",
    keywords = "Proximity effects, Superconducting films, Josephson devices, Tunneling phenomena, IR-58985, X- and γ-ray detectors",
    author = "{den Hartog}, R. and Golubov, {Alexandre Avraamovitch} and D. Martin and P. Verhoeve and P.A. Poelaert and A. Peacock and M. Krumrey",
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    language = "English",
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    The lateral proximity effect and long-range energy-gap gradients in Ta/Al and Nb/Al Josephson junctions. / den Hartog, R.; Golubov, Alexandre Avraamovitch; Martin, D.; Verhoeve, P.; Poelaert, P.A.; Peacock, A.; Krumrey, M.

    In: Nuclear instruments & methods in physics research. Section A : Accelerators, spectrometers, detectors and associated equipment, Vol. 444, No. 1-2, 07.04.2000, p. 28-32.

    Research output: Contribution to journalArticleAcademicpeer-review

    TY - JOUR

    T1 - The lateral proximity effect and long-range energy-gap gradients in Ta/Al and Nb/Al Josephson junctions

    AU - den Hartog, R.

    AU - Golubov, Alexandre Avraamovitch

    AU - Martin, D.

    AU - Verhoeve, P.

    AU - Poelaert, P.A.

    AU - Peacock, A.

    AU - Krumrey, M.

    PY - 2000/4/7

    Y1 - 2000/4/7

    N2 - We present two independent experiments, each of which suggests that the local energy gap in Ta (and Nb) has a lateral spatial variation on a scale of several μm. The first experiment is a series of current–voltage characterizations of Nb/Al/AlOx and Ta/Al/AlOx Josephson junctions, which reveals a dependence of the measured energy gap on the size of the junction. This implies a geometrical dependence of the energy gap. An extended version of the current theory of the proximity effect could explain this phenomenon when a lateral coherence length is introduced, which is of the order of the bulk coherence length of the materials. The second experiment is a series of coincidence measurements of photon absorption events in a Ta absorber between two Ta/Al junctions. There is a clear distinction in the pulse-height characteristics between events detected in the absorber and the junctions. Interestingly, there are also events indicating the presence of a transition region between the absorber and the junction. Event statistics imply that this region has a size of 6 μm, independent of photon energy, which is quite a bit larger than even the bulk coherence length in Ta. It is argued that an additional effect due to ‘smearing’ by the relaxed quasi-particle cloud must also be present. These effects are interesting and intriguing; not only from a theoretical viewpoint, but also for energy-gap engineering of superconducting materials for practical applications, e.g. in a variety of photon and particle detectors.

    AB - We present two independent experiments, each of which suggests that the local energy gap in Ta (and Nb) has a lateral spatial variation on a scale of several μm. The first experiment is a series of current–voltage characterizations of Nb/Al/AlOx and Ta/Al/AlOx Josephson junctions, which reveals a dependence of the measured energy gap on the size of the junction. This implies a geometrical dependence of the energy gap. An extended version of the current theory of the proximity effect could explain this phenomenon when a lateral coherence length is introduced, which is of the order of the bulk coherence length of the materials. The second experiment is a series of coincidence measurements of photon absorption events in a Ta absorber between two Ta/Al junctions. There is a clear distinction in the pulse-height characteristics between events detected in the absorber and the junctions. Interestingly, there are also events indicating the presence of a transition region between the absorber and the junction. Event statistics imply that this region has a size of 6 μm, independent of photon energy, which is quite a bit larger than even the bulk coherence length in Ta. It is argued that an additional effect due to ‘smearing’ by the relaxed quasi-particle cloud must also be present. These effects are interesting and intriguing; not only from a theoretical viewpoint, but also for energy-gap engineering of superconducting materials for practical applications, e.g. in a variety of photon and particle detectors.

    KW - Proximity effects

    KW - Superconducting films

    KW - Josephson devices

    KW - Tunneling phenomena

    KW - IR-58985

    KW - X- and γ-ray detectors

    U2 - 10.1016/S0168-9002(99)01321-2

    DO - 10.1016/S0168-9002(99)01321-2

    M3 - Article

    VL - 444

    SP - 28

    EP - 32

    JO - Nuclear instruments & methods in physics research. Section A : Accelerators, spectrometers, detectors and associated equipment

    JF - Nuclear instruments & methods in physics research. Section A : Accelerators, spectrometers, detectors and associated equipment

    SN - 0168-9002

    IS - 1-2

    ER -