Researchers explore dielectric control of superconductivity in twisted bilayer graphene

In the study, the team fabricated twisted bilayer graphene devices and positioned them a few nanometers above a bulk strontium titanate (SrTiO₃) substrate, a synthetic perovskite often referred to as a man‑made “diamond” because of its robustness and very large, tunable dielectric constant. By increasing this dielectric constant in situ, they steadily suppressed both the height and the width of the superconducting dome in magic‑angle devices and, upon further tuning, extinguished superconductivity altogether across the entire dome. At larger twist angles, where devices on standard SiO₂ substrates typically do not superconduct, the SrTiO₃ environment enabled a superconducting “pocket” even in regimes where correlated insulating states were absent, underscoring how delicately the phase diagram depends on dielectric screening.

Researchers from Ohio State University, Imdea Nanoscience and the National Institute for Materials Science in Tsukuba have demonstrated that superconductivity in twisted bilayer graphene (tBLG) can be tuned – and even completely switched off – by engineering its dielectric environment. Their work reveals that, unlike in conventional phonon-mediated superconductors, the pairing mechanism in this moiré system is strongly controlled by electronic interactions that are highly sensitive to nearby materials.In the study, the team fabricated twisted bilayer graphene devices and positioned them a few nanometers above a bulk strontium titanate (SrTiO₃) substrate, a synthetic perovskite often referred to as a man‑made “diamond” because of its robustness and very large, tunable dielectric constant. By increasing this dielectric constant in situ, they steadily suppressed both the height and the width of the superconducting dome in magic‑angle devices and, upon further tuning, extinguished superconductivity altogether across the entire dome. At larger twist angles, where devices on standard SiO₂ substrates typically do not superconduct, the SrTiO₃ environment enabled a superconducting “pocket” even in regimes where correlated insulating states were absent, underscoring how delicately the phase diagram depends on dielectric screening.

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