[1
]Center
for Nanochemistry, Beijing National Laboratory for Molecular Sciences
(BNLMS),
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871,
China
[2
]Department
of Physics, University of Texas at Austin, Austin, Texas 78712, United
States
[3
]Physical
Sciences and Engineering Division, King Abdullah University of Science and
Technology, Thuwal 23955-6900, Saudi Arabia
[4
]Department
of Physics, Durham University, Durham DH1 3LE, United Kingdom