Superconductivity
Can a superconductor induce pairing in a magnetic topological edge?
Open access · cc by · source: Europe PMC
A narrow superconducting strip on the edge of a quantum anomalous Hall insulator turns incoming electrons into outgoing holes, showing superconducting correlations have leaked into the edge state.
Study at a glance
- Design
- Other — Low-temperature three-terminal transport on V-doped (Bi,Sb)2Te3 Hall bars with Nb finger electrodes of different widths, plus tight-binding transport simulations
- N
- Several devices (A to F) with Nb finger widths from 160 to 520 nm; no single sample count
- Population
- Thin-film quantum anomalous Hall insulator devices contacted by superconducting niobium fingers
- Outcome
- Downstream (nonlocal) resistance versus magnetic field, temperature and finger width
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
For the narrowest finger (160 nm) the downstream resistance was negative below about 1 T, the signature of crossed Andreev reflection, and it turned positive once the niobium stopped superconducting. The Andreev contribution shrank exponentially with finger width, with a characteristic length of about 100 nm, much longer than niobium's own coherence length of about 30 nm, suggesting pairing is induced in the topological film under the finger. Simulations showed that both trivial and topological superconducting scenarios can produce this effect.
Methodology
The team grew thin films of a vanadium-doped topological insulator that shows the quantum anomalous Hall effect without any applied field, and patterned Hall bars with niobium superconducting fingers of different widths touching the chiral edge. They measured the voltage on the edge downstream of the finger while sweeping magnetic field and temperature at dilution-refrigerator temperatures. They also ran tight-binding quantum transport simulations of a proximitized magnetic topological insulator film.
Limitations
The data cannot tell whether the induced superconductivity is topological, so it does not demonstrate Majorana modes. The CAR signal is only about 3% of the ideal maximum, varies with magnetic history, and depends on contact quality and film ageing. The simulations use parameters that are qualitative rather than matched to the devices, and they fail to explain why the signal is always negative in experiment.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Hybrid devices can carry pair correlations into topological films.
Superconductivity can be induced into topological materials: niobium fingers on a quantum anomalous Hall film produced crossed Andreev reflection with a decay length of about 100 nm, and a Nb-contacted BiSbTeSe2 nanowire showed a gate- and field-tunable superconducting diode effect with efficiency up to about 0.3.
Evidence for the claim as stated.
Topological or not? Both hybrid-device studies see signatures compatible with topological superconductivity, but simulations in the QAH study show trivial pairing produces the same crossed Andreev signal, and the nano-SQUID link to Majorana modes is theoretical; neither detects Majoranas.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Topological or not? Both hybrid-device studies see signatures compatible with topological superconductivity, but simulations in the QAH study show trivial pairing produces the same crossed Andreev signal, and the nano-SQUID link to Majorana modes is theoretical; neither detects Majoranas.
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