Singular robust room-temperature spin response from topological Dirac fermions

Topological insulators are a class of solids in which the nontrivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields which persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, likely of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.Comment: 20 pages, 14 figure

Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3\mathrm{Bi}_2\mathrm{Se}_3

Topological insulators constitute a new and fascinating class of matter with insulating bulk yet metallic surfaces that host highly mobile charge carriers with spin-momentum locking. Remarkably, the direction and magnitude of surface currents can be controlled with tailored light beams, but the underlying mechanisms are not yet well understood. To directly resolve the "birth" of such photocurrents we need to boost the time resolution to the scale of elementary scattering events ($\sim$ 10 fs). Here, we excite and measure photocurrents in the three-dimensional model topological insulator $\mathrm{Bi}_2\mathrm{Se}_3$ with a time resolution as short as 20 fs by sampling the concomitantly emitted broadband THz electromagnetic field from 1 to 40 THz. Remarkably, the ultrafast surface current response is dominated by a charge transfer along the Se-Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to have orders of magnitude smaller magnitude than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are also of direct relevance for optoelectronic devices based on topological-insulator surface currents

Stable topological insulators achieved using high energy electron beams

Topological insulators are transformative quantum solids with immune-to-disorder metallic surface states having Dirac band structure. Ubiquitous charged bulk defects, however, pull the Fermi energy into the bulk bands, denying access to surface charge transport. Here we demonstrate that irradiation with swift ($\sim 2.5$ MeV energy) electron beams allows to compensate these defects, bring the Fermi level back into the bulk gap, and reach the charge neutrality point (CNP). Controlling the beam fluence we tune bulk conductivity from \textit{p}- (hole-like) to \textit{n}-type (electron-like), crossing the Dirac point and back, while preserving the Dirac energy dispersion. The CNP conductance has a two-dimensional (2D) character on the order of ten conductance quanta $G_0 =e^2/h$, and reveals, both in Bi$_2$Te$_3$ and Bi$_2$Se$_3$, the presence of only two quantum channels corresponding to two topological surfaces. The intrinsic quantum transport of the topological states is accessible disregarding the bulk size.Comment: Main manuscript - 12 pages, 4 figures; Supplementary file - 15 pages, 11 figures, 1 Table, 4 Note

Maternal body mass index and external cephalic version success rate — are they related?

Objectives: External cephalic version (ECV) is a useful method helping to reduce the incidence of planned caesarean deliveries for fetal malpresentation. There is an effort to look for the best predictors for a successful ECV, the effect of maternal weight is still unclear. The aim of our study is to determine maternal body mass index (BMI) in association with the ECV success rate and the risk of complications.Material and methods: A retrospective observational cohort study in 981 women after the 36th week of gestation with a fetus in a breech presentation who had undergone an ECV attempt. We evaluated the success rate and complications of ECV in association with BMI categories according to the WHO classification of obesity.Results: ECV was successful in 478 cases (48.7%). In the category of overweight patients (BMI > 25; n = 484), ECV was successful in 51% and unsuccessful in 49% (p = 0.28) of cases. In obese patients (BMI > 30; n = 187), ECV was successful in 44.8% and unsuccessful in 55.2% (p = 0.28) of cases. The effect of BMI on the success rate of ECV for the category of overweight and obesity was not proven by statistical analysis. Serious complications occurred in seven cases in similar numbers in all three subgroups according to BMI.Conclusions: BMI in the categories of overweight and obesity is not a factor influencing the success rate and risk of complications of ECV. These results can be helpful when consulting pregnant women the chance of successful ECV

Stable topological insulators achieved using high energy electron beams

Topological insulators are potentially transformative quantum solids with metallic surface states which have Dirac band structure and are immune to disorder. Ubiquitous charged bulk defects, however, pull the Fermi energy into the bulk bands, denying access to surface charge transport. Here we demonstrate that irradiation with swift (B2.5MeV energy) electron beams allows to compensate these defects, bring the Fermi level back into the bulk gap and reach the charge neutrality point (CNP). Controlling the beam fluence, we tune bulk conductivity from p- (hole-like) to n-type (electron-like), crossing the Dirac point and back, while preserving the Dirac energy dispersion. The CNP conductance has a two-dimensional character on the order of ten conductance quanta and reveals, both in Bi2Te3 and Bi2Se3, the presence of only two quantum channels corresponding to two topological surfaces. The intrinsic quantum transport of the topological states is accessible disregarding the bulk size

COVID-19 Vaccine Acceptance of Pregnant and Lactating Women (PLW) in Czechia: An Analytical Cross-Sectional Study

Pregnant and lactating women (PLW) represent a particular population subset with increased susceptibility for COVID-19 morbidity and mortality, even though the evidence about the safety and efficacy of COVID-19 vaccines was delayed due to their initial exclusion from development trials. This unclear situation could have led to increased COVID-19 vaccine hesitancy levels among PLW; therefore, this study aimed to evaluate the attitudes of Czech PLW towards COVID-19 vaccines and the determinants of their attitudes. An analytical cross-sectional survey-based study was carried out in the University Hospital Brno (South Moravia, Czechia) between August and October 2021. The study utilised a self-administered questionnaire (SAQ) adapted from previous instruments used for the same purpose. The SAQ included closed-ended items covering demographic characteristics, clinical and obstetric characteristics, attitudes towards COVID-19 vaccination, and potential psychosocial predictors of vaccine acceptance. Out of the 362 included participants, 278 were pregnant (PW) and 84 were lactating women (LW). The overall COVID-19 vaccine acceptance (immediate and delayed) level was substantially high (70.2%), with a significant difference between PW (76.6%) and LW (48.8%). Out of the 70.2% who agreed to receive the vaccine, 3.6% indicated immediate acceptance, and 66.6% indicated delayed acceptance. Only 13.3% of the participants indicated their acceptance of their physician's vaccination recommendation during pregnancy or while lactating, and 62.2% were against it. Our results agreed with the recent studies that revealed that PW tended to have a high level of COVID-19 vaccine acceptance, and they were also inclined to resist professional recommendations because they predominantly preferred to delay their vaccination. The pregnancy trimester, education level, employment status, and previous live births were significant determinants for COVID-19 vaccine acceptance. The most commonly preferred vaccine type was mRNA-based vaccines, followed by viral vector-based and inactivated virus vaccines. The first top priority of PLW was vaccine safety for their children, followed by vaccine safety for the PLW and vaccine effectiveness. Regarding psychosocial predictors, media/social media, trust in the government, the pharmaceutical industry, and healthcare professionals, partners, and a positive risk-benefit ratio were significant promoters for COVID-19 vaccine acceptance. Findings from this study suggest that promotional interventions targeting PLW should use web platforms and focus on vaccine safety evidence, the expected benefits of vaccines and potential harms of the infection

Conservative management of complete fetal expulsion into the abdominal cavity after silent uterine rupture - case report

Abstract Background Clinically silent uterine rupture with complete fetal expulsion into the abdominal cavity is an extremely rare complication. Diagnosis can be difficult and the risk to the mother and fetus is high. Conservative management has been described only in a few cases of partial expulsion of the fetus so far. Case presentation We present a case of 43-year-old tercigravida with a history of previous laparotomic myomectomy and subsequent cesarean section. The subsequent pregnancy was complicated by uterine wall loosening and rupture at the site of the previous uterine scar after myomectomy and complete fetal expulsion into the abdominal cavity. The diagnosis was made at 24 + 6 weeks of gestation. Considering the absence of clinical symptomatology and the good condition of the fetus, a conservative approach was chosen with intensive monitoring of the maternal and fetal conditions. The pregnancy ended by elective cesarean section and hysterectomy at 28 + 0 weeks of gestation. The postpartum course was uneventful and the newborn was discharged to home care 63 days after delivery. Conclusions Fetal expulsion into the abdominal cavity after silent uterine rupture of the scarred uterus may be accompanied by minimal symptomatology making early diagnosis difficult. This rare complication must be considered in the differential diagnosis in women after major uterine surgery. In selected cases and under conditions of intensive maternal and fetal monitoring, conservative management may be chosen to reduce the risks associated with prematurity