Via Transfer Builds 3D Josephson Junctions with 130 Contact Resistance and Gate-Tunable Supercurrent

Controlling the interface between superconductors and other materials represents a significant challenge in developing advanced quantum technologies, and researchers are continually seeking methods to create high-quality connections. Cequn Li, Le Yi, and Kalana D. Halanayake, along with colleagues from The Pennsylvania State University and the National Institute for Materials Science, now demonstrate a novel approach to building three-dimensional superconducting junctions. The team successfully constructs smooth connections between a superconductor and other materials using a ‘via transfer’ technique, avoiding the damaging effects of conventional fabrication methods. This gentle process yields exceptionally low contact resistance and enables the observation of key superconducting properties, paving the way for the creation of new and more robust superconducting devices and heterostructures.

Time Crystals and Dynamic Atomic Structures

Researchers have created a four-dimensional crystal by manipulating crystal structures to incorporate time as a spatial dimension, designing materials where the atomic arrangement evolves predictably over time. This innovative approach relies on precise control of material composition and growth conditions to induce dynamic changes in the atomic lattice, resulting in a prototype crystal exhibiting unique structural behaviour confirmed by advanced characterisation techniques. The resulting material exhibits time-dependent diffraction patterns, confirming the dynamic evolution of its atomic arrangement, which arises from the designed crystal structure and its inherent temporal dimension, rather than simple thermal fluctuations. This research establishes a new paradigm for materials design, moving beyond static structures to embrace dynamic, time-evolving materials with programmable properties, potentially impacting advanced sensors, adaptive optics, and energy storage devices. This work provides a foundation for future investigations into the fundamental physics of time-dimensional crystals and their potential technological impact, opening possibilities for materials where characteristics can be tuned by controlling the temporal evolution of the structure.

Van der Waals Josephson Junction Fabrication and Characterization

This research details the fabrication and characterization of superconducting Josephson junctions built using graphene and other two-dimensional materials, including hexagonal boron nitride, tungsten ditelluride, and cadmium arsenide, combined with conventional superconductors. The focus is on achieving transparent interfaces between the superconductor and the two-dimensional material to maximize supercurrent and explore novel superconducting phenomena using van der Waals heterostructures. Josephson junctions form when a weak link, such as graphene, connects two superconductors, exhibiting unique quantum phenomena like supercurrent flow and voltage quantization, leveraging the unique electronic properties of two-dimensional materials, including high carrier mobility and tunable bandgaps. These junctions are created by stacking different two-dimensional materials, allowing precise control over the interface and electronic properties. The research explores how superconductivity can be induced in the two-dimensional material through proximity to the superconductor, aiming to create transparent interfaces that minimize electron scattering and maximize supercurrent. Electrical measurements detail the critical current and other supercurrent characteristics, while the use of topological insulators like cadmium arsenide is also explored to enhance superconducting properties.

Smooth Superconductor Contacts to Graphene Demonstrated

Scientists have achieved a novel method for creating superconducting contacts with graphene, utilizing a “via contact” approach that delivers remarkably smooth interfaces and low contact resistance. This gentle, lithography-free technique connects superconductors to delicate materials, opening avenues for advanced heterostructure engineering, resulting in van der Waals-like interfaces with a unit-length contact resistance comparable to conventional deposition techniques. Detailed examination using advanced microscopy confirms the sharp and tightly conforming palladium/graphene interface, with atomic force microscopy revealing a root-mean-square roughness of only 1. 8 Å, demonstrating the smoothness crucial for minimizing interface scattering and maximizing proximity coupling.

This technique was also successfully applied to air-sensitive bismuth selenide, creating smooth, bubble-free stacks. Electrical measurements demonstrate gate-tunable supercurrents and a proximity-induced superconducting gap in the graphene, with analysis revealing a contact resistance comparable to other superconducting contacts on graphene. Furthermore, the niobium nitride/palladium contact dopes the graphene, influencing the carrier density profile and enabling control over the electronic properties of the graphene channel, establishing via contacts as a viable approach for constructing superconducting devices on two-dimensional materials.

Niobium Nitride Graphene Junctions Demonstrate Superconductivity

This work demonstrates a novel method for creating high-quality interfaces between conventional superconductors and two-dimensional materials, achieving van der Waals-like contact between niobium nitride and graphene. By employing a via contact approach, the researchers successfully fabricated low-resistance junctions exhibiting Josephson current and Andreev reflections, confirming the presence of induced superconductivity within the graphene. The team investigated factors influencing the magnitude of the induced superconducting gap, identifying potential limitations stemming from disorder within the niobium nitride films. They propose that employing higher-quality superconducting films could substantially enhance the induced gap and overall superconducting performance of these planar contacts. This via contact method offers a gentle, lithography-free approach suitable for fabricating superconducting heterostructures incorporating air-sensitive or damage-prone materials, paving the way for advanced superconducting devices and fundamental studies of induced superconductivity. Future research directions include utilizing higher-quality superconducting films and optimizing the interface to minimize disorder, potentially leading to significantly enhanced proximity coupling and superconducting performance.