Planar Josephson junctions (JJs) made in semiconductor quantum wells with large spin-orbit coupling are capable of hosting topological superconductivity. Indium antimonide (InSb) two-dimensional electron gases (2DEGs) are particularly suited for this due to their large Landé g-factor and high carrier mobility, however superconducting hybrids in these 2DEGs remain unexplored. Here we create JJs in high quality InSb 2DEGs and provide evidence of ballistic superconductivity over micron-scale lengths. A Zeeman field produces distinct revivals of the supercurrent in the junction, associated with a 0− π transition. We show that these transitions can be controlled by device design, and tuned in-situ using gates. A comparison between experiments and the theory of ballistic π -Josephson junctions gives excellent quantitative agreement. Our results therefore establish InSb quantum wells as a promising new material platform to study the interplay between superconductivity, spin-orbit interaction and magnetism.

Topological superconductivity can be engineered in semiconductors with strong spin–orbit interaction coupled to a superconductor. Experimental advances in this field have often been triggered by the development of new hybrid material systems. Among these, two-dimensional electron gases (2DEGs) are of particular interest due to their inherent design flexibility and scalability. Here, we discuss results on a 2D platform based on a ternary 2DEG (InSbAs) coupled to in situ grown aluminum. The spin–orbit coupling in these 2DEGs can be tuned with the As concentration, reaching values up to 400 meV Å, thus exceeding typical values measured in its binary constituents. In addition to a large Landé g-factor of ∼55 (comparable to that of InSb), we show that the clean superconductor–semiconductor interface leads to a hard induced superconducting gap. Using this new platform, we demonstrate the basic operation of phase-controllable Josephson junctions, superconducting islands, and quasi-1D systems, prototypical device geometries used to study Majorana zero modes.

Indium antimonide (InSb) two-dimensional electron gases (2DEGs) have a unique combination of material properties: high electron mobility, strong spin-orbit interaction, large Landé g-factor, and small effective mass. This makes them an attractive platform to explore a variety of mesoscopic phenomena ranging from spintronics to topological superconductivity. However, there exist limited studies of quantum confined systems in these 2DEGs, often attributed to charge instabilities and gate drifts. We overcome this by removing the δ-doping layer from the heterostructure, and induce carriers electrostatically. This allows us to perform the first detailed study of stable gate-defined quantum dots in InSb 2DEGs. We demonstrate two distinct strategies for carrier confinement and study the charge stability of the dots. The small effective mass results in a relatively large single particle spacing, allowing for the observation of an even-odd variation in the addition energy. By tracking the Coulomb oscillations in a parallel magnetic field we determine the ground state spin configuration and show that the large g-factor (∼30) results in a singlet-triplet transition at magnetic fields as low as 0.3 T.Mesoscopic devices can be made in a two-dimensional electron gas (2DEG) using electrical gates to confine charge carriers, thus reducing the degrees of freedom. The extreme case is the zero-dimensional system, a quantum dot (QD). QDs have been used to explore a wide range of quantum phenomena 1-3 , and are emerging as a platform for quantum computing 4-6 and quantum simulations 7-9 . QDs in materials with strong spin-orbit interaction have important applications in the field of topological superconductivity. They can be used to realize Majorana zero modes in quantum dot chains 10 , and are essential elements for the readout and manipulation of topological qubits 11,12 .InSb is a promising material in this regard, with a high carrier mobility, large g-factor and strong spinorbit interaction [13][14][15][16] . QDs have been extensively studied in InSb nanowires [17][18][19] and, more recently, in InSb nanoflakes 20 . However, despite the clear benefits of scalability offered by InSb 2DEGs, experimental reports of confined systems in these quantum wells are scarce 14,21,22 . Thus far, most studies of InSb 2DEGs have been limited to heterostructures where carriers are generated in the quantum well via remote δ-doping layers. Such doped 2DEGs are known to suffer from charge instability and gate drifts, which are particularly detrimental to the study of nanostructures.Here, we show that removal of doping layers enables the realization of highly stable gate-defined quantum dots in InSb 2DEGs. We study two different QD designs on deep and shallow undoped quantum wells. In all measured devices, the charge stability diagrams show welldefined Coulomb diamonds and excited states. We find that the small effective mass of InSb results in a large separation between single-particle levels, enabling the observation of an even-odd periodicity in ...