1. Materials Department, University of California, Santa Barbara, California 93106, USA
2. Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA
3. Physics Department, University of California, Santa Barbara, California 93106, USA
4. MAX IV Laboratory, Lund University, Lund 221 00, Sweden
5. Department of Physics and NanoLund, Lund University, Lund 221 00, Sweden