Josephson Junctions in High-Temperature Superconducting Systems

Josephson junctions in high-temperature superconducting systems unite the phenomena of coherent Cooper-pair tunnelling with the elevated critical temperatures of cuprate and pnictide compounds. These junctions act as nonlinear circuit elements in which supercurrent can flow across a weak link—such as an insulating barrier, grain boundary or nanofabricated channel—without any applied voltage, until a critical current is exceeded. Above this threshold they exhibit voltage oscillations at frequencies proportional to the applied current, enabling applications from sensitive magnetometry to terahertz generation. Advances in thin-film growth, focused ion-beam patterning and bicrystal engineering have enhanced reproducibility, reduced device noise and pushed operating temperatures well above liquid-nitrogen levels. Integration of junctions into superconducting quantum interference devices (SQUIDs), series arrays and mixer circuits has broadened dynamic range, improved flux-noise performance and facilitated heterodyne detection in the microwave and terahertz domains. Despite progress, challenges remain in managing inhomogeneities, optimising junction inductance and controlling nonequilibrium effects at high frequencies. The interplay between material microstructure, device geometry and electromagnetic coupling now lies at the heart of ongoing efforts to harness high-temperature superconducting junctions for next-generation quantum electronics and sensing technologies.

Research from Nature Portfolio

Recent studies have reported sub-nanometre Josephson nano-junctions fabricated by focused helium ion beams on yttrium barium copper oxide films. Devices follow the standard resistively-shunted-junction model with characteristic frequencies approaching 300 gigahertz at low temperature. Investigation of linewidths using detector-response techniques has shown that, between around 20 K and 75 K, the oscillation linewidth is limited predominantly by thermal noise. At lower temperatures and higher irradiation doses shot noise becomes significant as the junction approaches a tunnelling regime. These findings demonstrate that high-temperature nano-junctions can reach the lowest attainable noise levels, underlining their potential for applications in microwave and terahertz circuits.

Josephson Junctions in High-Temperature Superconducting Systems publication trend

The graph below shows the total number of articles in josephson junctions in high-temperature superconducting systems across all publications each year (not limited to Nature Index journals).

Technical terms

Josephson junction: A weak link between two superconductors that permits coherent tunnelling of Cooper pairs, producing supercurrents or voltage oscillations.

Resistively-Shunted-Junction (RSJ) model: A circuit representation that treats a Josephson junction as a superconducting element in parallel with a resistance and capacitance.

Characteristic frequency (fc): The frequency at which the junction’s AC Josephson oscillations occur, governed by the product of critical current and normal resistance.

London penetration depth (λ): The distance over which an external magnetic field decays inside a superconductor, influencing inductance.

Shapiro steps: Constant-voltage plateaux in the current–voltage characteristic of a junction under microwave irradiation.

Kinetic inductance: Inductive effect arising from the inertia of Cooper pairs in a superconductor.

Flux noise: Random fluctuations of magnetic flux coupling into superconducting circuits, limiting sensitivity.

Shot noise: Electronic noise originating from the discreteness of charge carriers during tunnelling.

References

1. Dynamic properties of high-Tc superconducting nano-junctions made with a focused helium ion beam. Scientific Reports (2020).
2. Determining the temperature-dependent London penetration depth in HTS thin films and its effect on SQUID performance. Applied Physics Letters (2021).
3. Noise scaling in SQUID arrays. Superconductor Science and Technology (2024).
4. THz Radiation Measurement with HTSC Josephson Junction Detector Matched to Planar Antenna. Applied Sciences (2020).