Revealing the superconducting limit of ‘magic’ material graphene

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"... Now ... researchers are making headway into understanding how the material achieves this state by identifying its highest achievable superconducting temperature – 60 Kelvin. The finding is mathematically exact, a rare feat in the field, and is spurring new insights into the factors that fundamentally control superconductivity.  ...

In 2023, ... developed a new theoretical formalism to compute the highest possible superconducting transition temperature in any material obtained by stacking and twisting two-dimensional materials. For the current work, they applied it to twisted bilayer graphene. ...

The theoretical framework the team developed can be applied to other materials in the future ..."

From the abstract:

"Few layers of graphene at small twist angles have emerged as a fascinating platform for studying the problem of strong interactions in regimes with a nearly quenched single-particle kinetic energy and nontrivial band topology. Starting from the strong-coupling limit of twisted bilayer graphene with a vanishing single-electron bandwidth and interlayer tunneling between the same sublattice sites, we present an exact analytical theory of the Coulomb interaction-induced low-energy optical spectral weight at all integer fillings. In this limit, while the interaction-induced single-particle dispersion is finite, the optical spectral weight vanishes identically at integer fillings. We study corrections to the optical spectral weight by systematically including the effects of experimentally relevant strain-induced renormalization of the single-electron bandwidth and interlayer tunnelings between the same sublattice sites. Given the relationship between the optical spectral weight and the diamagnetic response that controls superconducting 𝑇𝑐, our results highlight the relative importance of specific parent insulating phases in enhancing the tendency towards superconductivity when doped away from integer fillings."

Revealing the superconducting limit of ‘magic’ material | Cornell Chronicle

Low-Energy Optical Sum Rule in Moiré Graphene (no public access)