Experimental probing of the interplay between ferromagnetism and localisation in (Ga,Mn)As

The question whether the Anderson-Mott localisation enhances or reduces magnetic correlations is central to the physics of magnetic alloys. Particularly intriguing is the case of (Ga,Mn)As and related magnetic semiconductors, for which diverging theoretical scenarios have been proposed. Here, by direct magnetisation measurements we demonstrate how magnetism evolves when the density of carriers mediating the spin-spin coupling is diminished by the gate electric field in metal/insulator/semiconductor structures of (Ga,Mn)As. Our findings show that the channel depletion results in a monotonic decrease of the Curie temperature, with no evidence for the maximum expected within the impurity-band models. We find that the transition from the ferromagnetic to the paramagnetic state proceeds via the emergence of a superparamagnetic-like spin arrangement. This implies that carrier localisation leads to a phase separation into ferromagnetic and nonmagnetic regions, which we attribute to critical fluctuations in the local density of states, specific to the Anderson-Mott quantum transition.Comment: 8 pages, 3 figure

Impact of COVID-19 on antibiotic usage in primary care: a retrospective analysis

Abstract The COVID-19 pandemic has contributed to many changes in the medical practice, including a wider access to tele-consultations. It not only influenced the type of treatment but also shed light on mistakes often made by doctors, such as the abuse of antibiotics. This study aimed to evaluate the antibiotic treatment, and the impact of the COVID-19 pandemic on antibiotic prescribing during a GP’s visit. The retrospective medical history analysis involved data from a first-contact medical center (Pantamed, Olsztyn, Poland), from 1 January 2018 to 31 May 2023. Quantities of prescribed antibiotics were assessed and converted into the so-called active list for a given working day of adult patients (> 18 years of age). Statistical analysis based on collective data was performed. During the COVID-19 pandemic, a decline in the number of medical consultations has been observed, both remotely via tele-medicine and in personal appointments, compared to the data from before the pandemic: n = 95,251 versus n = 79,619. Also, during the COVID-19 pandemic, there was a decrease in the total amount of prescribed antibiotics relative to the data before the pandemic (2.44 vs. 4.54; p > 0.001). The decrease in the quantities of prescribed antibiotics did not depend on the way doctor consultations were provided. The COVID-19 pandemic has contributed to changing the family doctors’ management of respiratory infections. The ability to identify the etiological agent—the SARS-COV2 virus—contributed to the reduction of the antibiotics use