A metallic state with a vanishing activation gap, at a filling factor 8/5 in the untilted specimen with n = 2 × 10^11cm^(−2) , and at filling factor 4/3 at n = 1.2 × 10^11cm^(−2) a t a tilt angle of 66 degrees between the magnetic field and the plane of the specimen, is examined through a microwave photo-excited transport study of the GaAs/AlGaAs 2 dimensional electron system (2DES). The results presented here suggest, remarkably, that at the possible degeneracy point of states with different spin polarization, where the 8/5 or 4/3 FQHE vanish, there occurs a peculiar marginal metallic state that differs qualitatively from a quantum Hall insulating state and the usual quantum Hall metallic state. Such a marginal metallic state occurs most prominently at filling factor of 8/5 , and at filling factor of 4/3 under tilt as mentioned above, between span between filling factors 1 and 2, that also includes the 3/2 state, which appears perceptibly gapped in the first instance.
Biography of the Speaker :
Prof. Ramesh Mani is an Indian-born American physicist who obtained his BS, MS, and Ph.D. at the University of Maryland, College Park, MD in the USA. After the time at the University of Maryland, he worked as a scientist at the Max-Planck-Institute for Solid State Physics in Stuttgart, Germany. He returned to the USA with a position at the University of California at Santa Barbara (UCSB), Cali fornia. After a brief stay at UCSB, he moved to Harvard University as a senior research associate in Dean Venky Narayanamurti's group. In 2006, he moved to Georgia State University where he is now Professor of Physics & Astronomy. At Georgia State University, he has set up a large laboratory for materials preparation, device fabrication by lithography, and low temperature, high magnetic field magneto-transport studies of low dimensional systems based on GaAs/AlGaAs heterostructures, graphene, and other modern atomic layer 2D systems.