Funding for this research was provided by:
National Science Foundation (DMS-1521965)
U.S. Department of Energy (SC-0016540)
National Natural Science Foundation of China (11401350, 11471196)
National Natural Science Foundation of China (11701562)
Article History
Received: 28 April 2017
Revised: 5 September 2017
Accepted: 3 October 2017
First Online: 24 October 2017