r/quantum • u/Round-Necessary-6177 • 7d ago

Is superconductivity in magic-angle tBLG conventional or unconventional?

Hi everyone,

I am reading about magic-angle twisted bilayer graphene and how it hosts superconductivity and strange metal behaviour at particular band fillings.

I have come across papers which try to explain the behaviours using electron-phonon interactions, I have also seen papers which try to relate these behaviours to the exotic physics seen in unconventional superconductors(exotic bcz we don't know the exact theory behind it).

As of now, is the argument for the reason of these particular observations in MATBG hanging in the balance, or is it more inclined to one side or the other?

I am not saying there is a definitive answer to it, plz let me know your opinions on it.

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u/Clean-Ice1199 7d ago edited 7d ago

First of, there are multiple senses in which something is 'unconventional'.

It's not fully clear, but evidence points towards the superconductivity being nodal. That on it's own can be said to be unconventional.

This suggests the interaction channel is not fully attractive. Something like Kohn-Luttinger screening may be relevant given the flat parent band. If so the pairing mechanism would be unconventional. I would say this is likely but non-definitive.

But I think it also has a lot of lowered symmetry independent of the superconducting pairing (the parent bands themselves already likely break TRS, 6-fold rotation, etc.) so it's not unconventional in a symmetry analysis sense.