1. Department
of Physics, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
2. Department of Micro- and Nanoelectronical Systems, Institute of Micro-
and Nanoelectronics, Technical University Ilmenau, PF 10 05 65, 98684 Ilmenau, Germany
3. Department of Physics, Quantum Nanoelectronics Laboratory, University of California, Berkeley, California 94709, United States