Phase study of oscillatory resistances in high mobility GaAs/AlGaAs devices: Indications of a new class of integral quantum Hall effect

A 2-dimensional electron system (2DES) at high magnetic fields, B, and low temperatures, T, exhibits the integral quantum Hall effect (IQHE), which is characterized by plateaus in the Hall resistance Rxy vs. B, at Rxy = h/ie 2 , with i = 1,2,3,... and concurrent vanishing diagonal resistance Rxx as T ! 0 K, in the vicinity of integral filling factors of Landau levels, i.e., � � i.[1, 2, 3] With the increase of the electron mobility, µ, at a given electron density, n, and T, IQHE plateaus typically become narrower as fractional quantum Hall effects (FQHE) appear in the vicinity of � � p/q, at Rxy = h/[(p/q)e 2 ], where p/q denotes mostly odd-denominator rational fractions.[2, 3] Experimental studies of the highest mobility specimens have mostly focused upon FQHE and other novel phases.[2, 3, 4, 5] Meanwhile, the possibility of new variations of IQHE that might appear with the canonical effect in the reduced-disorder specimen, especially at large-�, has been largely unanticipated by experiment. Here, we show that three distinct phase relationships can occur between the oscillatory diagonaland Hall- resistances in the high-mobility specimen at � > 5, and that IQHE can be manifested in two of these variations. The results therefore identify one new class of IQHE, as they provide insight into the origin of oscillatory variations in the Hall effect, and their evolution into plateaus, in the low-B large-� regime of the radiation-induced zero-resistance states in the photoexcited high mobility 2DES.[6, 7, 8] Thus, these experiments also serve to characterize, classify, and clarify the large-� dark properties. The results recall previous suggestions of new phenomena in the � >> 1 limit.[9]