Superconductors can carry electrical current with zero resistance, offering an ultra-efficient platform for next-generation electronics and quantum technologies. Meanwhile, “topological” materials, whose electrons behave in unusually robust ways, are promising building blocks for fault-tolerant quantum devices. However, combining the two cleanly is highly challenging; standard nanofabrication methods can roughen or damage delicate crystals, and even tiny imperfections at the interface can degrade performance.
Our group has demonstrated a surprisingly simple solution. They used a focused laser beam as a nanoscale “pen” to locally transform a topological tin film into a superconducting region without physically cutting, etching, or bombarding it. The team worked with α-Sn (alpha-tin), a topological Dirac semimetal thin film epitaxially grown on an InSb substrate; they used localized laser heating to trigger a phase change only where the beam was aimed, converting the α-Sn into β-Sn (beta-tin), a well-known superconducting metal. In other words, they can make superconducting nanostructures of almost any shape directly in a topological thin film. This creates a high-precision α-Sn/β-Sn in-plane heterostructure on a single wafer.
Figure. (a) Schematic image of α-Sn/β-Sn planar nanostructures fabricated by laser irradiation (left panel). Phase transition from topological Dirac semimetal α-Sn to superconducting metal β-Sn induced by local heating by irradiating a laser beam (right panel). (b) Optical microscopy image of a 750 nm-wide β-Sn nanowire (white) embedded in a α-Sn matrix (gray), β-Sn/α-Sn/β-Sn Josephson junction structure with a 500 nm-wide central α-Sn region (gray), and arbitrarily designed β-Sn patterns (white). All these patterns were formed by laser irradiation, demonstrating high flexibility and compatibility with standard nanofabrication techniques. (c) Superconducting diode effect (SDE) in a laser-induced β-Sn nanowire (NW) embedded in α-Sn, where the NW exhibits superconductivity in one current direction and normal-conductivity in the opposite one. The SDE efficiency (η) reaches maximum of 10.8% when magnetic field B is applied in-plane and deviated from the current I by an angle θ = 45°, 135°, 225°, 315°.
This approach is especially attractive for future devices because of its quality and gentleness. Since the method uses heat instead of physically invasive processing, the resulting superconducting β-Sn regions have atomically smooth surfaces and nearly single-crystal quality over large areas. These properties are critical for sensitive superconducting and quantum circuits. This approach is also mask-free and potentially scalable, suggesting a practical, lower-cost path toward manufacturing complex superconducting patterns.
To demonstrate the effectiveness of this “laser writing” technique, the research team fabricated β-Sn nanowires just hundreds of nanometers in width and observed a striking phenomenon: a superconducting diode effect, where the nanowires allow current to flow without any resistance (a superconducting current) in one direction but remain resistive－like normal conductors－in the other. Remarkably, the device exhibited this effect even without an applied magnetic field; the diode device showed superconducting transport with zero resistance in one current direction while showing normal transport with non-zero resistance in the opposite current direction. By adjusting the direction of an applied magnetic field, the team achieved a maximum rectification ratio of 10.8%, demonstrating controllable and directional superconducting behavior in a compact nanostructure.
This work is more than just a clever fabrication trick; it provides a new toolkit for building superconducting quantum devices and quantum circuits that require exceptionally clean and well-defined interfaces. Because the platform uses two phases of the single element (tin) to integrate topological and superconducting functionalities, it provides a direct and customizable approach to exploring topological superconductivity and designing device architectures that were previously difficult to produce without causing damage to the material.
Papers
Journal: Advanced Materials
Title: Non-Destructive Laser Nanopatterning of Superconducting Heterostructures in Topological Sn Thin Films
Authors: Le Duc Anh, Takahiro Saeki, Keita Ishihara, Daiki Nishigaki, Hideki Maki, Masaaki Tanaka
DOI: 10.1002/adma.202512571
