A 2009 paper from Eva Andrei’s group reports values for this quantity at which the induced Van Hove singularities approximate the Fermi energy. A 2011 paper from Bistritzer and MacDonald theorizes several small values of this quantity at which Dirac-point band velocity vanishes, the largest of which was achieved experimentally by Pablo Jarillo-Herrero’s group in 2018. Non-zero values of this quantity characterize TBG, which features (*) Moiré (10[1])(“m’wah-RAY”) patterns. Unconventional superconductivity in a certain superlattice arises at “magic” values of this quantity, like 1.05 of a common unit. Graphene bilayers are often used to study the effect of this quantity on electrical properties in twistronics. For 10 points, name this quantity that measures the relative orientation of two parallel layers. ■END■