A Stradivarius violin can only be made from wood that grew under special conditions. For a long time, it was believed that graphene for delicate quantum effects also had to be peeled off graphite with tape, and that a crystal grown in a test tube was not up to the task. Now, graphene grown from a gas mixture has begun to sing like a Stradivarius.

Graphene is a layer of carbon atoms just one atom thick. If you stack two such layers with a twist of about 1.1 degrees, the electrons in them start moving in sync, and flat bands emerge where their velocity drops to nearly zero. In these bands, electrons, like cars in a traffic jam, begin to interact with each other, leading to superconductivity. Previously, such bands were only seen in samples peeled by hand, while grown films were considered too dirty.

The scientists grew two graphene crystals from a gas mixture, stacked them with the required twist, and measured the electronic structure. It turned out that the flat bands are present and just as high-quality as in hand-made samples. The largest region with a nearly magic angle measured about 84 square micrometers, which is enough for creating devices. Before this work, it was unknown whether grown graphene could preserve such fragile bands. Now it is clear: it can. One problem remains: the magic-angle region gradually relaxes, but even that is enough for experiments. So the test-tube violin has started to sound, and the next step is to tune it so that the tone is clear in every single copy.