The Joint Condensed Matter Seminar (JCMS) series is organised by KTH Royal Insitute of Technology, Nordita, and Stockholm University.
On Monday, November 10th, 2025 from 11.00 am to 12.00 we will host a seminar by Xinghai Zhang from KTH.
Quantum Criticality and Enhanced Superconductivity in Twisted Multilayer Graphene
Multilayer moiré materials can exhibit topological electronic features yet are inherently quasiperiodic—leading to wave function interference whose Anderson-localizing tendency can be mitigated by topology. While the atomic scale quasiperiodicity is elegantly glossed over in the Bistritzer-MacDonald model of twisted bilayer graphene, twisted multilayer graphene (TMG) are generically quasiperiodic on the moiré scale, due to the incommensurate twist angle mismatch. Here we show that quasiperiodic TMG exhibits normal state quantum criticality and hosts robust superconductivity with rigid phase stiffness, not relying on the fine-tuning to magic angles. The enhanced superconductivity results from wave function criticality in the normal state, which effectively simulates topological superconductor surface states. The interplay of quasiperiodicity and nontrivial topology in TMG make it behave like a critical metal, with fractal wave function statistics at all energies linked to the plateau transition of the integer quantum Hall effect. We show that the criticality and robust superconductivity is further stabilized by increasing interlayer coupling in TMG, which is experimentally accessible by applying pressure.