1. Center for Research on Interface Structures and Phenomena and Department of Applied Physics, Yale University, New Haven, Connecticut 06511, USA
2. Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, Connecticut 06515, USA
3. Department of Physics, The University of Texas at Arlington, Arlington, Texas 76019, USA
4. Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, USA