Hard Superconducting Gap in PbTe Nanowires

Abstract

Semiconductor nanowires coupled to a superconductor provide a powerful testbed for quantum device physics such as Majorana zero modes and gate-tunable hybrid qubits. The performance of these quantum devices heavily relies on the quality of the induced superconducting gap. A hard gap, evident as vanishing subgap conductance in tunneling spectroscopy, is both necessary and desired. Previously, a hard gap has been achieved and extensively studied in III-V semiconductor nanowires (InAs and InSb). In this study, we present the observation of a hard superconducting gap in PbTe nanowires coupled to a superconductor Pb. The gap size ($\Delta$) is $\sim$ 1 meV (maximally 1.3 meV in one device). Additionally, subgap Andreev bound states can also be created and controlled through gate tuning. Tuning a device into the open regime can reveal Andreev enhancement of the subgap conductance. These results pave the way for diverse superconducting quantum devices based on PbTe nanowires.

Selective-Area-Grown PbTe-Pb Planar Josephson Junctions for Quantum Devices

“…The size of the gap (Δ) is not accurately known. If we assumed Δ ∼ 1 meV, a value extracted from nanowire devices grown under identical conditions, eI excess R n /Δ can be estimated to be ∼1.344, corresponding to a junction transparency of ∼0.81. , Note that this is a rough estimation due to the uncertainty of Δ: if Δ of 0.815 meV was assumed (see Figure g), the transparency would be ∼0.9. The transparency is gate-dependent; see Figure d for another example with a transparency of ∼0.7.…”

“…Here, we present the PbTe-Pb hybrid as a new planar JJ material platform for exploring topological superconductivity and other potential applications, such as gate tunable qubits. − While the PbTe-Pb hybrid has recently been proposed in its nanowire form as a Majorana candidate with promising experimental progress, − in this paper, we realize its 2DEG version, motivated by the Majorana proposals for topological planar JJs. , Selective area growth (SAG) of PbTe film has been previously achieved on InP, a substrate that is lattice-mismatched with PbTe . In this work, the SAG PbTe film is grown on a lattice-matched substrate to minimize the disorder.…”

“…Figure briefly illustrates the device design, growth procedure, and material analysis. We started with a CdTe/Pb 0.92 Eu 0.08 Te substrate − and covered it with a thin SiN dielectric layer. A Hydrogen SilsesQuioxane (HSQ) shadow wall was fabricated prior to the Pb 0.92 Eu 0.08 Te growth .…”