Figure 4 (IMAGE) The University of Hong Kong Caption Dr BinBin CHEN and Dr Zi Yang MENG from the Department of Physics, HKU Credit The University of Hong Kong Usage Restrictions This work is licensed for non-commercial, non-exclusive, one-time usage with attribution to the copyright holder. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.