Topological insulators and graphene, the two representative 2D Dirac electron systems, have both been widely studied for spintronics applications. On the one hand, strong spin-orbit coupling in topological insulators makes them obvious spin source candidates. On the other hand, minute spin-orbit coupling in graphene makes it a promising spin transport channel. In this talk, I will first present our work on the charge-spin conversion in topological insulators. Our data demonstrate orders of magnitude improvement over conventional spin-Hall metals . Furthermore, they indicate that the high spin generation efficiency originates from the spin-momentum locking of the topological surface states. In the second part of the talk, I will discuss the charge-spin conversion in graphene, when proximity coupled to a model magnetic insulator EuS. The interfacial exchange coupling produces a substantial Zeeman field (>= 14 T) in graphene, which yields orders-of-magnitude enhancement in spin generation by the Zeeman spin-Hall effect. Furthermore, the strong exchange field lifts the spin degeneracy in the graphene quantum Hall regime, which leads to novel spin-polarized edge transport features, potentially interesting for classical and quantum information processing .
 Luqiao Liu, A. Richardella, Ion Garate, Yu Zhu, N. Samarth, and Ching-Tzu Chen, Physical Review B 91, 235437 (2015).
 Luqiao Liu, Ching-Tzu Chen, and J. Z. Sun, Nature Physics 10, 561--566 (2014).
 Peng Wei, Sunwoo Lee, Florian Lemaitre, Lucas Pinel, Davide Cutaia , Wujoon Cha , Ferhat Katmis, Yu Zhu, Donald Heiman, James Hone, Jagadeesh S. Moodera, and Ching-Tzu Chen, Nature Materials 15, 711 (2016).
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