Ballistic superconductivity and tunable π–junctions in InSb quantum wells

Abstract

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.

Quantum transport in high-quality shallow InSb quantum wells

“…With increasing B, the integer filling factor sequence changes from even to even and odd numbers. The magnetic field value beyond which the spin-splitting is resolved in the experiment is consistent with the band edge g-factor values determined in similar InSb QWs 25 and the works in InSb nanoconstrictions 8,24,33,34 . A very rough estimate of the band edge g-factor for our device is found in the supplementary material.…”

“…The obtained effective mass is m * ≈ 0.019 m 0 , where m 0 is the electron mass in vacuum. Using the same method, we find that the effective mass is 24 .…”

“…These layered InSb structures have advantages to achieve direct metal/superconductor contacts on them. Nevertheless, the research on InSb quantum wells (QWs) is still lacking due to the difficulties with heterostructure growth, although QWs have significant potential leading to high-quality devices 23,24 . In QW systems, a thin barrier is required to induce superconductivity in the 2DEG through the proximity effect.…”

Strong and tunable spin–orbit interaction in a single crystalline InSb nanosheet

“…However, to build a device in which braiding of topological quantum states, such as Majorana fermions, can be conveniently performed and thus topological quantum computations can be designed and realized, it could be inevitable to move from single-nanowire structures to multiple-nanowire 20,21 and twodimensional (2D) planar quantum structures [22][23][24] . Recently, highquality InSb/InAlSb heterostructured quantum wells 25,26 and freestanding InSb nanosheets [27][28][29][30] have been achieved by epitaxial growth techniques. In comparison with InSb/InAlSb quantum well systems, the free-standing InSb nanosheets have advantages in direct contact by metals, including superconducting materials, in easy transfer to different substrates, and in convenient fabrication of dual-gate structures.…”

Directional electron filtering at a superconductor-semiconductor interface

“…Different arrangements are possible such as planar electrodes on the active surface of the HgTe layer, in which it is assumed that superconductivity is induced by the proximity effect. More recently, mesa structures are used with superconducting contacts made on the sides of the thin HgTe layer [14] (like also used for graphene [15] and, very recently, for InSb quantum wells [16]). In all cases, a characteristic excess current is observed for applied voltages higher than the superconducting energy gap.…”