Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:cond-mat/0107478 · Applied Physics Letters

MgB 2 tunnel junctions and 19 K low-noise dc superconducting quantum interference devices

Y. Zhang, D. Kinion, J. Chen, John Clarke, David G. Hinks, George W. Crabtree

Published Dec 10, 2001• 54 citations
arXivHTMLPDF

Abstract

Point contact junctions made from two pieces of MgB2 can be adjusted to exhibit either superconductor-insulator-superconductor (SIS) or superconductor-normal metal–superconductor (SNS) current–voltage characteristics. The SIS characteristics are in good agreement with the standard tunneling model for s-wave superconductors, and yield an energy gap of (2.02±0.08) meV. The SNS characteristics are in good agreement with the predictions of the resistively-shunted junction model. DC superconducting quantum interference devices made from two SNS junctions yield magnetic flux and field noise as low as 4 μΦ0 Hz−1/2 and 35 fT Hz−1/2 at 19 K; Φ0 is the flux quantum.

DOI
10.1063/1.1424465

Related papers

An ultra-low-noise tunnel junction dc SQUID

M. B. Ketchen, Richard F. Voss

The design, fabrication, and noise properties of an ultra-low-noise tunnel junction dc SQUID (superconducting quantum interference device) are presented. The two resistively shunted Pb-alloy tunnel junctions are each 3.6 μm diam. The SQUID has an inductance L of ≈11 pH, a critical current per junction, I0 of ≈100 μA, and a resistance per shunt R of ≈2 Ω. At 2.3 K, eI0R≈kBT, and simple theory predicts that the minimum intrinsic energy sensitivity should be ≈2h. The actual minimum value of the measured high-frequency (70 kHz) flux noise at 4.2 K is φn=1.3×10−7φ0 Hz−1/2. This corresponds to an intrinsic energy sensitivity, φ2n/2L, of 3.2×10−33 J Hz−1 or 5h. Lowering the bath temperature to 1.8 K gave no improvement in performance.

Applied Physics Letters•Nov 15, 1979•61 citations

DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2epitaxial films

Takayoshi Katase, Yoshihiro Ishimaru, Akira Tsukamoto +4 more

DC superconducting quantum interference devices (dc-SQUIDs) were fabricated in Co-doped BaFe 2 As 2 epitaxial films on (La, Sr)(Al, Ta)O 3 bicrystal substrates with 30° misorientation angles. The 18 × 8 µm 2 SQUID loop with an estimated inductance of 13 pH contained two 3 µm wide grain boundary junctions. The voltage–flux characteristics clearly exhibited periodic modulations with Δ V = 1.4 µV at 14 K, while the intrinsic flux noise of dc-SQUIDs was 7.8 × 10 − 5 Φ 0 Hz − 1/2 above 20 Hz. The rather high flux noise is mainly attributed to the small voltage modulation depth which results from the superconductor–normal-metal–superconductor junction nature of the bicrystal grain boundary.

arXiv:1005.2021•Superconductor Science and Technology•Jul 2, 2010•51 citations

Nonlocal superconducting quantum interference device

Taewan Noh, Andrew Kindseth, Venkat Chandrasekhar

Superconducting quantum interference devices (SQUIDs) that incorporate two superconductor/insulator/superconductor (SIS) Josephson junctions in a closed loop form the core of some of the most sensitive detectors of magnetic and electric fields currently available. SQUIDs in these applications are typically operated with a finite voltage which generates microwave radiation through the ac Josephson effect. This radiation may impact the system being measured. We describe here a SQUID in which the Josephson junctions are formed from strips of normal metal (N) in good electrical contact with the superconductor (S). Such SNS SQUIDs can be operated under a finite voltage bias with performance comparable or potentially better than conventional SIS SQUIDs. However, they also permit a mode of operation that is based on the unusual interplay of quasiparticle currents and supercurrents in the normal metal of the Josephson junction. The method allows measurements of the flux dependence of the critical current of the SNS SQUID without applying a finite voltage bias across the SNS junction, enabling sensitive flux detection without generating microwave radiation.

arXiv:2011.06667•Physical review. B./Physical review. B•Aug 4, 2021•12 citations

High-frequency limits of superconducting tunnel junction mixers

Dag Winkler, T. Claeson

We have investigated high-frequency limits of superconducting quasiparticle mixers from experiments on Al/Al-oxide-In/Al (or Ag) tunnel junctions, and from calculations based on Tucker’s quantum theory of mixing (QTM). The small superconducting energy gap of Al enabled us to study mixer performance at around the junction gap frequency, fg =(Δ1+Δ2)/h≊87 GHz, of superconductor-insulator-superconductor (SIS) mixers, and at twice the junction gap frequency for S-I-normal metal (SIN) mixers ( fg =Δ1/h) with available millimeter wave sources. Because of the low transition temperature of Al (Tc ≊1.3 K), a dilution refrigerator was used for providing temperatures below 1 K. The best mixer conversion efficiency was obtained for a low-resistance (∼34 Ω) six-junction array SIS mixer operated at f/fg ≊1 (in this case 73 GHz). The coupled single sideband conversion gain (with no image rejection) was −13.8 dB and the available conversion gain was estimated to −8.4 dB. Complicating nonequilibrium phenomena made it difficult to compare the performance of these relatively high-current-density mixers to the QTM. However, good agreement between calculated and corresponding measured conversion efficiencies and dynamic resistance values was obtained for the low-current-density mixers. Noise due to switching between rf-induced Josephson steps and interference from Josephson mixing could be quenched by a magnetic field. Several high-frequency limits are considered in this paper (such as Josephson switching noise, nonequilibrium phenomena, pair breaking, and energy gap limitations). Our results indicate that submillimeter wave SIS mixer receivers are likely to perform well, at least up to their gap frequencies, i.e., the THz region for large gap superconductors. Our QTM calculations showed that conversion gain larger than unity should be possible up to twice the gap frequency. Above this frequency the conversion loss will increase rapidly.

Journal of Applied Physics•Dec 1, 1987•35 citations

NBN JOSEPHSON AND TUNNEL JUNCTIONS FOR SPACE THZ OBSERVATION AND SIGNAL PROCESSING

Romano Setzu, N. Hadacek, Vincent Larrey +2 more

ABSTRACT: Active superconducting circuits based on picoseconds switching, i.e. THz oscillating, Josephson tunnel junctions are expected to find a large domain of applications in spatial sub-millimeter wave and FIR detectors as well as in satellite based wideband signal and data processors. In the first case SIS (superconductor-insulator-superconductor) tunnel junctions are required, while in the second case SNS (superconductor-normal metal-superconductor) self-shunted junctions are preferred. We present the advantages of the nitride junction technology currently developed at CEA-Grenoble, based on high-performance MTS (medium temperature superconductor) NbN films in both SIS and SNS junctions. In the SIS case the device performances rely on a sputter deposited and post-annealed, only 0.5-0.7 nm thick, dielectric MgO barrier. This leads to junctions with a Josephson critical current in the range of 10-25 kA/cm, and a large superconducting energy gap (> 5 meV) associated with a low sub-gap quasi-particle leakage current. These parameters are suitable for low “noise temperature ” heterodyne mixers, local oscillators, and integrated receivers in the 0.8 to 1.4 THz frequency range. In the SNS case, a new

•Jul 13, 2005•1 citation

Fabrication of Superconducting Quantum Interference Device with Thin-Film Quantum Point Contacts

Hiroya Abe, K. Hamasaki, Takashi Ishiguro

We have fabricated dc-superconducting quantum interference devices (SQUIDs) with all-thin-film point contacts (Nb–Nb nanoconstriction-NbN). The size of the nanoconstriction may be smaller than the superconducting coherence length of bulk Nb. The quasiparticle characteristic of the all-thin-film point contact can be explained using the Blonder, Tinkham and Klapwijk (BTK) quasiparticle current which is applicable to the superconducting quantum point contact. The flux noise of SQUID with 10 pH operated in a flux locked loop is 8 µΦ0/ Hz1/2 at 1 Hz, and 4 µΦ0/ Hz1/2 at frequencies above 10 Hz is limited by the preamplifier.

Japanese Journal of Applied Physics•Dec 1, 1994•2 citations
Point contact junctions made from two pieces of MgB2 can be adjusted to exhibit either superconductor-insulator-superconductor (SIS) or superconductor-normal metal–superconductor (SNS) current–voltage characteristics. The SIS characteristics are in good agreement with the standard tunneling model for s-wave superconductors, and yield an energy gap of (2.02±0.08) meV. The SNS characteristics are in good agreement with the predictions of the resistively-shunted junction model. DC superconducting quantum interference devices made from two SNS junctions yield magnetic flux and field noise as low as 4 μΦ0 Hz−1/2 and 35 fT Hz−1/2 at 19 K; Φ0 is the flux quantum.
The design, fabrication, and noise properties of an ultra-low-noise tunnel junction dc SQUID (superconducting quantum interference device) are presented. The two resistively shunted Pb-alloy tunnel junctions are each 3.6 μm diam. The SQUID has an inductance L of ≈11 pH, a critical current per junction, I0 of ≈100 μA, and a resistance per shunt R of ≈2 Ω. At 2.3 K, eI0R≈kBT, and simple theory predicts that the minimum intrinsic energy sensitivity should be ≈2h. The actual minimum value of the measured high-frequency (70 kHz) flux noise at 4.2 K is φn=1.3×10−7φ0 Hz−1/2. This corresponds to an intrinsic energy sensitivity, φ2n/2L, of 3.2×10−33 J Hz−1 or 5h. Lowering the bath temperature to 1.8 K gave no improvement in performance.
DC superconducting quantum interference devices (dc-SQUIDs) were fabricated in Co-doped BaFe 2 As 2 epitaxial films on (La, Sr)(Al, Ta)O 3 bicrystal substrates with 30° misorientation angles. The 18 × 8 µm 2 SQUID loop with an estimated inductance of 13 pH contained two 3 µm wide grain boundary junctions. The voltage–flux characteristics clearly exhibited periodic modulations with Δ V = 1.4 µV at 14 K, while the intrinsic flux noise of dc-SQUIDs was 7.8 × 10 − 5 Φ 0 Hz − 1/2 above 20 Hz. The rather high flux noise is mainly attributed to the small voltage modulation depth which results from the superconductor–normal-metal–superconductor junction nature of the bicrystal grain boundary.
Superconducting quantum interference devices (SQUIDs) that incorporate two superconductor/insulator/superconductor (SIS) Josephson junctions in a closed loop form the core of some of the most sensitive detectors of magnetic and electric fields currently available. SQUIDs in these applications are typically operated with a finite voltage which generates microwave radiation through the ac Josephson effect. This radiation may impact the system being measured. We describe here a SQUID in which the Josephson junctions are formed from strips of normal metal (N) in good electrical contact with the superconductor (S). Such SNS SQUIDs can be operated under a finite voltage bias with performance comparable or potentially better than conventional SIS SQUIDs. However, they also permit a mode of operation that is based on the unusual interplay of quasiparticle currents and supercurrents in the normal metal of the Josephson junction. The method allows measurements of the flux dependence of the critical current of the SNS SQUID without applying a finite voltage bias across the SNS junction, enabling sensitive flux detection without generating microwave radiation.
We have investigated high-frequency limits of superconducting quasiparticle mixers from experiments on Al/Al-oxide-In/Al (or Ag) tunnel junctions, and from calculations based on Tucker’s quantum theory of mixing (QTM). The small superconducting energy gap of Al enabled us to study mixer performance at around the junction gap frequency, fg =(Δ1+Δ2)/h≊87 GHz, of superconductor-insulator-superconductor (SIS) mixers, and at twice the junction gap frequency for S-I-normal metal (SIN) mixers ( fg =Δ1/h) with available millimeter wave sources. Because of the low transition temperature of Al (Tc ≊1.3 K), a dilution refrigerator was used for providing temperatures below 1 K. The best mixer conversion efficiency was obtained for a low-resistance (∼34 Ω) six-junction array SIS mixer operated at f/fg ≊1 (in this case 73 GHz). The coupled single sideband conversion gain (with no image rejection) was −13.8 dB and the available conversion gain was estimated to −8.4 dB. Complicating nonequilibrium phenomena made it difficult to compare the performance of these relatively high-current-density mixers to the QTM. However, good agreement between calculated and corresponding measured conversion efficiencies and dynamic resistance values was obtained for the low-current-density mixers. Noise due to switching between rf-induced Josephson steps and interference from Josephson mixing could be quenched by a magnetic field. Several high-frequency limits are considered in this paper (such as Josephson switching noise, nonequilibrium phenomena, pair breaking, and energy gap limitations). Our results indicate that submillimeter wave SIS mixer receivers are likely to perform well, at least up to their gap frequencies, i.e., the THz region for large gap superconductors. Our QTM calculations showed that conversion gain larger than unity should be possible up to twice the gap frequency. Above this frequency the conversion loss will increase rapidly.
ABSTRACT: Active superconducting circuits based on picoseconds switching, i.e. THz oscillating, Josephson tunnel junctions are expected to find a large domain of applications in spatial sub-millimeter wave and FIR detectors as well as in satellite based wideband signal and data processors. In the first case SIS (superconductor-insulator-superconductor) tunnel junctions are required, while in the second case SNS (superconductor-normal metal-superconductor) self-shunted junctions are preferred. We present the advantages of the nitride junction technology currently developed at CEA-Grenoble, based on high-performance MTS (medium temperature superconductor) NbN films in both SIS and SNS junctions. In the SIS case the device performances rely on a sputter deposited and post-annealed, only 0.5-0.7 nm thick, dielectric MgO barrier. This leads to junctions with a Josephson critical current in the range of 10-25 kA/cm, and a large superconducting energy gap (> 5 meV) associated with a low sub-gap quasi-particle leakage current. These parameters are suitable for low “noise temperature ” heterodyne mixers, local oscillators, and integrated receivers in the 0.8 to 1.4 THz frequency range. In the SNS case, a new
We have fabricated dc-superconducting quantum interference devices (SQUIDs) with all-thin-film point contacts (Nb–Nb nanoconstriction-NbN). The size of the nanoconstriction may be smaller than the superconducting coherence length of bulk Nb. The quasiparticle characteristic of the all-thin-film point contact can be explained using the Blonder, Tinkham and Klapwijk (BTK) quasiparticle current which is applicable to the superconducting quantum point contact. The flux noise of SQUID with 10 pH operated in a flux locked loop is 8 µΦ0/ Hz1/2 at 1 Hz, and 4 µΦ0/ Hz1/2 at frequencies above 10 Hz is limited by the preamplifier.