北京师范大学

Using exact quantum Monte Carlo method, we identify the phase diagram of the half filled, the lightly doped and heavily doped graphene, which shows a rather rich physical properties. At half filling, the system is driven to a Mott insulator with antiferromagnetic long range order by increasing interaction, and a transition from a d+id pairing to a p+ip pairing is revealed, depends on the next-nearest hoping and the electronic fillings. We also examine the recent novel electronic states seen in magic-angle graphene superlattices. From the Hubbard model on a double-layer honeycomb lattice with a rotation angle θ=1.08 , we reveal that an antiferromagnetically ordered Mott insulator emerges beyond a critical Uc  at half filling, and with a small doping, the pairing with d+id  symmetry dominates over other pairings at low temperature. The effective d+id  pairing interaction strongly increase as the on-site Coulomb interaction increases, indicating that the superconductivity is driven by electron-electron correlation. Our non-biased numerical results demonstrate that the twisted bilayer graphene share the similar superconducting mechanism of high temperature superconductors, which is a new and idea platform for further investigating the strongly correlated phenomena.

报告人简介：马天星，北京师范大学物理学系教授，博士研究生导师。分别于2000年7月和2005年7月在北京师范大学获得学士和博士学位。2005年8月至2010年6月先后在复旦大学、德国马普所、香港中文大学从事凝聚态物理理论方面的博士后研究。2010年7月至今在北京师范大学物理学系工作。主要从事电子关联体系磁性和超导电性的研究，包括石墨烯、铁基超导体、有阻挫系统等 。

邀请人：杨义峰，9448