Does a twisted MoTe2 bilayer superconduct in an unusual way?
Short junctions of twisted bilayer MoTe2 carried supercurrent that survived higher fields and temperatures than the superconducting contacts and was weakest at zero magnetic field, unlike an untwisted control.
Source
Anomalous superconductivity in twisted MoTe<sub>2</sub> nanojunctions
Study at a glance
- Design
- Other — Low-temperature transport and electron-microscopy experiment on Pd7MoTe2/twisted-MoTe2/Pd7MoTe2 junctions, with a natural-bilayer junction as a control
- N
- A handful of devices: twisted-bilayer transport devices D2 and D3, natural-bilayer device D4, a monolayer comparison device, and separate TEM samples
- Population
- Twisted (about 3.7°) and natural bilayer MoTe2 junctions about 100 nm long between superconducting Pd7MoTe2 pads
- Outcome
- Resistance versus temperature, critical current versus magnetic field, critical field, and normal-state resistance
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
The authors grew a superconducting compound, Pd7MoTe2, into encapsulated MoTe2 bilayers by gentle annealing, leaving a narrow junction of MoTe2 (about 100 nm) between two superconducting pads. They confirmed with atomic-resolution electron microscopy that the interface was sharp and the moiré pattern intact. They then measured resistance and critical current versus temperature and perpendicular magnetic field down to millikelvin temperatures, comparing twisted bilayers with an inversion-symmetric natural bilayer made the same way.
What they found
Resistance dropped to zero just below about 1 K and the twisted junction had a critical current of about 42 nA. Superconducting fluctuations in the twisted junction persisted to about 1.2–1.3 K and to fields near 2.2 T, while the Pd7MoTe2 pads lost superconductivity above about 1.2 T. Instead of the usual peak at zero field, the junction's critical current showed a V-shaped minimum at zero field, reproducible across devices and gate voltages. In the natural bilayer control, both anomalies disappeared, pointing to the missing inversion symmetry of the twisted lattice.
The limits
What it doesn't show
The pairing mechanism is not established: the mix of even- and odd-parity pairing is the authors' speculation, not a measurement. The metallic normal-state conduction of these short junctions (MoTe2 should be insulating) is unexplained. Only a few devices were measured, at a single twist angle, and the hoped-for link to fractional Chern insulator states is not yet shown.
Key terms
- Josephson junction
- A weak link between two superconductors through which a supercurrent can flow without voltage, up to a critical current.
- Critical current
- The largest current a superconducting path can carry with zero resistance; above it, a voltage appears.
- Moiré lattice
- A long-wavelength superlattice pattern formed when two atomic layers are stacked with a small twist, which reshapes electronic bands.
- Inversion symmetry
- Symmetry under reflecting every point through a centre; its absence, with strong spin–orbit coupling, allows mixed even- and odd-parity superconducting pairing.
- Proximity effect
- Superconductivity leaking from a superconductor into an adjacent normal material, usually weaker than in the source.
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Quiz yourself
What was the key structural difference between the anomalous and control junctions?
Common questions
Why is a zero-field minimum in critical current surprising?
In an ordinary Josephson junction the supercurrent phases add constructively at zero field, so the critical current peaks there; a minimum implies destructive interference between two channels with a π phase difference.
Why can't the proximity effect explain the results?
Proximity-induced superconductivity should be weaker than in the pads, but the junction survived higher temperatures and fields than the Pd7MoTe2 pads themselves.
What does the natural bilayer control rule out?
It has the same materials, geometry and fabrication but keeps inversion symmetry and shows no anomalies, which argues against artefacts like quasiparticle cooling and points to the twisted lattice's symmetry.
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