"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures

We show that in dilute metallic p-SiGe heterostructures, magnetic field can cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating states are observed between quantum Hall states with filling factors \nu=1 and 2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The latter are in contradiction with the original global phase diagram for the quantum Hall effect. We suggest that the application of a (perpendicular) magnetic field induces insulating behavior in metallic p-SiGe heterostructures in the same way as in Si MOSFETs. This insulator is then in competition with, and interrupted by, integer quantum Hall states leading to the multiple re-entrant transitions. The phase diagram which accounts for these transition is similar to that previously obtained in Si MOSFETs thus confirming its universal character

Low-field magnetoresistance in GaAs 2D holes

We report low-field magnetotransport data in two-dimensional hole systems in GaAs/AlGaAs heterostructures and quantum wells, in a large density range, $2.5 \times 10^{10} \leq p \leq 4.0 \times 10^{11}$ cm$^{-2}$, with primary focus on samples grown on (311)A GaAs substrates. At high densities, $p \gtrsim 1 \times 10^{11}$ cm$^{-2}$, we observe a remarkably strong positive magnetoresistance. It appears in samples with an anisotropic in-plane mobility and predominantly along the low-mobility direction, and is strongly dependent on the perpendicular electric field and the resulting spin-orbit interaction induced spin-subband population difference. A careful examination of the data reveals that the magnetoresistance must result from a combination of factors including the presence of two spin-subbands, a corrugated quantum well interface which leads to the mobility anisotropy, and possibly weak anti-localization. None of these factors can alone account for the observed positive magnetoresistance. We also present the evolution of the data with density: the magnitude of the positive magnetoresistance decreases with decreasing density until, at the lowest density studied ($p = 2.5 \times 10^{10}$ cm$^{-2}$), it vanishes and is replaced by a weak negative magnetoresistance.Comment: 8 pages, 8 figure

Biocontrol Properties and Functional Characterization of Rice Rhizobacterium Pseudomonas sp. VSMKU4036

A total of 30 fluorescent pseudomonads (FPs) were showed significant antagonistic activity against different fungal phytopathogens with different level of the zone of inhibition (ZOI) for Rhizoctonia solani (5mm-34mm), Macrophomina phaseolina (9mm-37mm), Scleotium rolfsii (4mm-36mm), Helminthusporium solani (5mm-27mm), Fusarium oxysporum (2mm-25mm) and Fusarium oxysporum RACE (4mm-31mm) compared to control. The maximum growth of our selected isolate VSMKU4036 was observed in King’B Broth (KBB), pH 7.0 and at 37°C. The VSMKU4036 isolate has been recognized as Pseudomonas sp, based on the morphological, biological, and different functional characteristics. Antagonistic rhizobacterium Pseudomonas sp VSMKU4036 produced antimicrobial traits, such as plant growth promotion and various functional characters like siderophores, hydrogen cyanide (HCN), phosphate solubilization, indole acetic acid (IAA), biofilms formation, protease, gelatinase, amylase, and pectinase. Our superior biocontrol isolate VSMKU4036 was high resistance to tetracycline, streptomycin and nalidixic acid, however, it was sensitive to ampicillin and rifamycin. Pseudomonas sp VSMKU4036 showed maximum resistance to cadmium, nickel chloride, copper sulphate, magnesium sulphate, zinc chloride and ferric chloride where as highly sensitive to mercuric chloride, and selenium dioxide compared to control