1. Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA.
2. Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA.
3. California NanoSystems Institute, University of California, Santa Barbara, CA 93106, USA.
4. Materials Department, University of California, Santa Barbara, CA 93106, USA.
5. Eindhoven University of Technology, 5600 MB Eindhoven, Netherlands.
6. Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France.