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.
A research team led by Professors Le Duc Anh and Masaaki Tanaka at the University of Tokyo 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.
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.
Direct laser writing of high-resolution superconducting β-Sn nanopatterns with arbitrary geometries in a topological α-Sn thin film.
Figure 1: Nanopatterning of superconducting β-Sn with arbitrary shapes in a topological semimetal α-Sn thin film by laser irradiation. Focused-laser “writing” locally converts a 40‑nm topological α‑Sn film on InSb (001) into atomically flat superconducting β‑Sn, enabling mask-free, non-destructive fabrication of arbitrary α‑Sn/β‑Sn in-plane nanostructures. Here, α-Sn is a topological Dirac semimetal with a diamond-type crystal structure that can be epitaxially grown on an InSb (001) substrate, while β‑Sn is a superconducting metal with a tetragonal crystal structure. Right panel shows an example of arbitrarily designed β-Sn pattern (white color) in an α-Sn (gray color) film.
Figure 2: Atomic-scale flattening of laser-induced β‑Sn and the superconducting diode effect in β‑Sn nanowires. (a) Laser-induced β‑Sn is atomically smoother than focused-ion-beam (FIB)-made β‑Sn, forming a clean α‑Sn/β‑Sn interface. (b) In an α‑Sn/β‑Sn nanowire device, a superconducting diode effect appears and is observable even at zero magnetic field. The critical current and rectification ratio η depends on the angle θ between the current and applied magnetic field. η reaches ~ 10.8% at θ = 45◦, 135◦, 225◦, and 315◦.
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
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