1. Department of Applied Physics, Stanford University, Stanford, California 94305, USA
2. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
3. Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
4. Department of Physics, New York University, New York, New York 10003, USA
5. Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 45555, USA
6. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA