1. Department of Electrical EngineeringStanford University Stanford CA 94305 USA
2. Department of Applied PhysicsStanford University Stanford CA 94305 USA
3. Department of PhysicsFriedrich‐Alexander‐Universität Erlangen‐Nürnberg (FAU) Staudtstrasse 1 Erlangen 91058 Germany
4. Department of Materials Science and EngineeringStanford University Stanford CA 94305 USA