Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene oleh Jiachen Yu, Benjamin A. Foutty, Yves H. Kwan, Mark E. Barber, Kenji Watanabe, Takashi Taniguchi, Zhi-Xun Shen, Siddharth A. Parameswaran, Benjamin E. Feldman