Current-Phase-Relation of Two Potentially Topological-Superconductors: WTe2 and Magic-Angle Twisted Graphene

Christian Schönenberger (Unviversity of Basel and YQuantum)

Conference hall, IMDEA Nanociencia

Tuesday, 28 July 2026 10:30

In this talk the current-phase relation (CPR) of two potentially topological superconducting junctions are discussed. Few layer WTe2 has been predicted to be a higher-order topological insulator. We have found that palladium (Pd) bottom contacts result in superconducting contacts. Using cross-sectional TEM we have found that Pd alloys with the WTe2 giving rise to a superconducting material. Single wide junctions of length up to 2 𝜇𝑚 display a supercurrent with a dominant SQUID like pattern in a weak perpendicular magnetic field indicative of edge currents as expected for a topological insulator. We try to deduce the CPR of a single junction be embedding it into an asymmetric SQUID. In some cases, two CPR patterns shifted in phase are simultaneously present. This pattern looks like what one would expect for a topological Josephson junction where parity is not conserved. However, we have found that this multivalued behaviour is due to large spurious inductors in the SQUID loop that most likely originate form the alloyed contacts. The second case is magic angle twisted graphene where correlated insulators and superconductors have been discovered. The interaction driven phases are a result of flat bands that occur in moiré heterostructures at certain (magic) angles.

 

We have studied superconductivity in magic angle twisted trilayer graphene (MATTG) by integrating it as the weak link in a SQUID loop. We study the CPR of MATTG in various configurations by electrostatically tuning the two weak links. We show that superconducting MATTG has a large kinetic inductance up to 150 nH per square which is electrostatically tuneable. We further discuss bounds for the superconducting coherence length, for which we obtain values larger than previously published. The relatively large coherence length is – at first site - at odd with flat bands for which a small Fermi velocity is expected. However, if topology matters, quantum geometry may renormalize the velocity.

 

Meeting chat link

https://nanoscience-imdea.zoom.us/launch/jc/92014514206

https://nanoscience-imdea.zoom.us/j/92014514206?pwd=8KROLxMDcNKb0LhmLirhou7U3R3sUk.1#success

Meeting ID: 920 1451 4206

Passcode: L0NwAV

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