1. Department of Applied Physics and Physico‐informatics Faculty of Science and Technology Keio University Tokyo 108‐8345 Japan
2. Department of Electrical and Computer Engineering Rice University Houston TX 77005 USA
3. Department of Applied Physics Stanford University Stanford CA 94305 USA
4. Department of Physics and Astronomy Rice University Houston TX 77005 USA
5. Department of Materials Science and NanoEngineering Rice University Houston TX 77005 USA