Local Current Distribution and "Hot Spots" in the Integer Quantum Hall Regime

In a recent experiment, the local current distribution of a two-dimensional electron gas in the quantum Hall regime was probed by measuring the variation of the conductance due to local gating. The main experimental finding was the existence of "hot spots", i.e. regions with high degree of sensitivity to local gating, whose density increases as one approaches the quantum Hall transition. However, the direct connection between these "hot spots" and regions of high current flow is not clear. Here, based on a recent model for the quantum Hall transition consisting of a mixture of perfect and quantum links, the relation between the "hot spots" and the current distribution in the sample has been investigated. The model reproduces the observed dependence of the number and sizes of "hot spots" on the filling factor. It is further demonstrated that these "hot spots" are not located in regions where most of the current flows, but rather, in places where the currents flow both when injected from the left or from the right. A quantitative measure, the harmonic mean of these currents is introduced and correlates very well with the "hot spots" positions

Supplementary Material for the Article “Using Chatbots for Literature Searches and Scholarly Writing: Is the Integrity of the Scientific Discourse in Jeopardy?”

Supplementing our paper “Using Chatbots for Literature Searches and Scholarly Writing: Is the Integrity of the Scientific Discourse in Jeopardy?”, we present complete transcripts of two conversations with ChatGPT that corroborate the assertions in the paper

Using Generative AI for Literature Searches and Scholarly Writing: Is the Integrity of the Scientific Discourse in Jeopardy?

Ever since the public release of ChatGPT in November 2022, serious concerns have been raised about the impact and potentially dire consequences of the increasingly widespread use of generative AI tools for purposes of scientific writing and publishing. We document the ongoing discussion in the science community with a review of news articles, editorials, and position statements by major scientific publishers; discuss the potential pitfalls of using generative AI tools such as ChatGPT as aids in scholarly writing; furnish evidence for the proposition that AI-induced contamination of the scientific literature is not only a threat, but already a reality; and call upon leaders in our field to develop policies and guidelines to stem the spread of such contamination. Closing on a positive note, we provide a brief overview of potentially useful capabilities and sensible applications of ChatGPT and similar AI tools for purposes of scholarly writing.Comment: This article, an expanded version of an open letter sent to the leadership of SIAM, AMS, and NSF-MPS on June 1, 2023, is accepted for publication in the Notices of the AMS. Supplementary material, including a comprehensive bibliography, is available at https://scholar.smu.edu/hum_sci_mathematics_research/

Magic numbers in polymer phase separation -- the importance of being rigid

Cells possess non-membrane-bound bodies, many of which are now understood as phase-separated condensates. One class of such condensates is composed of two polymer species, where each consists of repeated binding sites that interact in a one-to-one fashion with the binding sites of the other polymer. Previous biologically-motivated modeling of such a two-component system surprisingly revealed that phase separation is suppressed for certain combinations of numbers of binding sites. This phenomenon, dubbed the "magic-number effect", occurs if the two polymers can form fully-bonded small oligomers by virtue of the number of binding sites in one polymer being an integer multiple of the number of binding sites of the other. Here we use lattice-model simulations and analytical calculations to show that this magic-number effect can be greatly enhanced if one of the polymer species has a rigid shape that allows for multiple distinct bonding conformations. Moreover, if one species is rigid, the effect is robust over a much greater range of relative concentrations of the two species. Our findings advance our understanding of the fundamental physics of two-component polymer-based phase-separation and suggest implications for biological and synthetic systems.Comment: 8 pages + 15 pages S

1/f noise in a dilute GaAs two-dimensional hole system in the insulating phase

We have measured the resistance and the 1/f resistance noise of a two-dimensional low density hole system in a high mobility GaAs quantum well at low temperature. At densities lower than the metal-insulator transition one, the temperature dependence of the resistance is either power-like or simply activated. The noise decreases when the temperature or the density increase. These results contradict the standard description of independent particles in the strong localization regime. On the contrary, they agree with the percolation picture suggested by higher density results. The physical nature of the system could be a mixture of a conducting and an insulating phase. We compare our results with those of composite thin films.Comment: 4 pages, 3 figures; to appear in Physica E (EP2DS-16 proceedings

A New Spin-Orbit Induced Universality Class in the Quantum Hall Regime ?

Using heuristic arguments and numerical simulations it is argued that the critical exponent $\nu$ describing the localization length divergence at the quantum Hall transition is modified in the presence of spin-orbit scattering with short range correlations. The exponent is very close to $\nu=4/3$, the percolation correlation length exponent, the prediction of a semi-classical argument. In addition, a region of weakly localized regime, where the localization length is exponentially large, is conjectured.Comment: 4 two-column pages including 4 eps figure