About the Authors

Liping Xiong

Affiliation Department of Physics, George Washington University, Washington, D.C., United States of America

Ganhui Lan

glan@gwu.edu

Affiliation Department of Physics, George Washington University, Washington, D.C., United States of America

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: GL. Performed the experiments: LX GL. Analyzed the data: LX GL. Wrote the paper: GL.