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The strength of the interactions between electrons in a structure called twisted bilayer graphene has been tuned by adjusting the immediate environment — a major advance for tunable electronic quantum matter.
Electronic materials — materials useful for their electrical properties — have driven progress in condensed-matter physics by revealing that unprecedented quantum states of matter can exist, ranging from superconductors to topological insulators. Fundamentally, the character of an electronic state is determined by the density and interaction strength of electrons. In 2018, as predicted1, a structure known as magic-angle twisted bilayer graphene (MATBG) was found to have a narrow electron energy band in which electronic interactions are particularly important2. MATBG belongs to an exceptional group of material platforms in which the electron density can be tuned in situ to switch between insulating and superconducting states3. Writing in Nature, Stepanov et al.4 and Arora et al.5 report that the electron interaction strength in MATBG can be tuned at a fixed electron density through tailored design of the dielectric (insulating) environment.