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1. Marginal metallic state at a fractional filling of ’8/5’ and ’4/3’ of Landau levels in the GaAs/AlGaAs 2D electron system

   https://doi.org/10.1038/s41598-021-94563-0  

   Mani, R. G. ; Wijewardena, U. K. ; Nanayakkara, T. R. ; Kriisa, Annika ; Reichl, C. ; Wegscheider, W. ( December 2021 , Scientific Reports)

   null (Ed.)

   Abstract A metallic state with a vanishing activation gap, at a filling factor $$\nu = 8/5$$ ν = 8 / 5 in the untilted specimen with $$n= 2 \times 10^{11} cm^{-2}$$ n = 2 × 10 11 c m - 2 , and at $$\nu = 4/3$$ ν = 4 / 3 at $$n=1.2 \times 10^{11} cm^{-2}$$ n = 1.2 × 10 11 c m - 2 under a $$\theta = 66^{0}$$ θ = 66 0 tilted magnetic field, 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 $$\nu =8/5$$ ν = 8 / 5 , and at $$\nu =4/3$$ ν = 4 / 3 under tilt as mentioned above, over the interval $$1 \le \nu \le 2$$ 1 ≤ ν ≤ 2 , that also includes the $$\nu = 3/2$$ ν = 3 / 2 state, which appears perceptibly gapped in the first instance. 

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2. Two-dimensional finite quantum Hall clusters of electrons with anisotropic features

   https://doi.org/10.1038/s41598-022-06093-y  

   Ciftja, Orion ( December 2022 , Scientific Reports)

   Abstract Low-dimensional nano and two-dimensional materials are of great interest to many disciplines and may have a lot of applications in fields such as electronics, optoelectronics, and photonics. One can create quantum Hall phases by applying a strong magnetic field perpendicular to a two-dimensional electron system. One characterizes the nature of the system by looking at magneto-transport data. There have been a few quantum phases seen in past experiments on GaAs/AlGaAs heterostructures that manifest anisotropic magnetoresistance, typically, in high Landau levels. In this work, we model the source of anisotropy as originating from an internal anisotropic interaction between electrons. We use this framework to study the possible anisotropic behavior of finite clusters of electrons at filling factor 1/6 of the lowest Landau level. 

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3. Self-heating of cryogenic high electron-mobility transistor amplifiers and the limits of microwave noise performance

   https://doi.org/10.1063/5.0103156  

   Ardizzi, Anthony J. ; Choi, Alexander Y. ; Gabritchidze, Bekari ; Kooi, Jacob ; Cleary, Kieran A. ; Readhead, Anthony C. ; Minnich, Austin J. ( August 2022 , Journal of Applied Physics)

   The fundamental limits of the microwave noise performance of high electron-mobility transistors (HEMTs) are of scientific and practical interest for applications in radio astronomy and quantum computing. Self-heating at cryogenic temperatures has been reported to be a limiting mechanism for the noise, but cryogenic cooling strategies to mitigate it, for instance, using liquid cryogens, have not been evaluated. Here, we report microwave noise measurements of a packaged two-stage amplifier with GaAs metamorphic HEMTs immersed in normal and superfluid [Formula: see text]He baths and in vacuum from 1.6 to 80 K. We find that these liquid cryogens are unable to mitigate the thermal noise associated with self-heating. Considering this finding, we examine the implications for the lower bounds of cryogenic noise performance in HEMTs. Our analysis supports the general design principle for cryogenic HEMTs of maximizing gain at the lowest possible power. 

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4. Decay of the coronal magnetic field can release sufficient energy to power a solar flare

   https://doi.org/10.1126/science.aax6874  

   Fleishman, Gregory D. ; Gary, Dale E. ; Chen, Bin ; Kuroda, Natsuha ; Yu, Sijie ; Nita, Gelu M. ( January 2020 , Science)

   Solar flares are powered by a rapid release of energy in the solar corona, thought to be produced by the decay of the coronal magnetic field strength. Direct quantitative measurements of the evolving magnetic field strength are required to test this. We report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field. The field decays at a rate of~5 Gauss per second for 2 minutes, as measured within a flare subvolume of ~10²⁸cubic centimeters. This fast rate of decay implies a sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. The decrease in stored magnetic energy is enough to power the solar flare, including the associated eruption, particle acceleration, and plasma heating.

    

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5. Radiation-induced magnetoresistance oscillations in monolayer and bilayer graphene

   https://doi.org/10.1038/s41598-019-43866-4  

   Mani, R. G. ; Kriisa, A. ; Munasinghe, R. ( May 2019 , Scientific Reports)

   We examine the characteristics of the microwave/mm-wave/terahertz radiation-induced magnetoresistance oscillations in monolayer and bilayer graphene and report that the oscillation frequency of the radiation-induced magnetoresistance oscillations in the massless, linearly dispersed monolayer graphene system should depend strongly both on the Fermi energy, and the radiation frequency, unlike in the case of the massive, parabolic, GaAs/AlGaAs 2D electron system, where the radiation-induced magnetoresistance oscillation frequency depends mainly on the radiation frequency. This possible dependence of the magnetoresistance oscillation frequency on the Fermi level at a fixed radiation frequency also suggests a sensitivity to the gate voltage in gated graphene, which suggests anin-situtunable photo-excitation response in monolayer graphene that could be useful for sensing applications. In sharp contrast to monolayer graphene, bilayer graphene is expected to show radiation-induced magnetoresistance oscillations more similar to the results observed in the GaAs/AlGaAs 2D system. Such expectations for the radiation-induced magnetoresistance oscillations are presented here to guide future experimental studies in both of these modern atomic layer material systems.

    

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