Unexpectedly Strong Auger Recombination in Halide Perovskites

The emergence of halide perovskites for photovoltaic applications has triggered great interest in these materials for solidâ state light emission. Higher order electronâ hole recombination processes can critically affect the efficiency of such devices. In the present work, the Auger recombination coefficients are computed in the prototypical halide perovskite, CH3NH3PbI3 (MAPbI3), using firstâ principles calculations. It is demonstrated that Auger recombination is responsible for the exceptionally high thirdâ order recombination coefficient observed in experiment. The large Auger coefficient is attributed to a coincidental resonance between the bandgap and interband transitions to a complex of higherâ lying conduction bands. Additionally, it is found that the distortions of PbI6 octahedra contribute significantly to the high Auger coefficient, offering potential avenues for materials design.The unexpectedly high thirdâ order recombination coefficient in halide perovskites is identified to stem from Auger recombination. Firstâ principles calculations show that the large Auger coefficient originates from a coincidental resonance as well as from distortions in the metalâ halide lattice. These insights point to avenues for improved materials design.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146455/1/aenm201801027_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146455/2/aenm201801027.pd

Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of two-dimensional (2D) van der Waals (vdW) materials. Herein, we report the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi$_\mathrm{2}$Te$_\mathrm{3}$, due to the proximity of FePS$_\mathrm{3}$ (an antiferromagnet (AFM), $T_\mathrm{N}$ $\sim$ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi$_{2}$Te$_{3}$ (106 cm$^{-1}$ and 138 cm$^{-1}$) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi$_{2}$Te$_{3}$ couple to phonons of similar frequencies of FePS$_3$ in the AFM phase, has been adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic $T_\mathrm{N}$ of FePS$_3$ from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, our data suggest a double softening of phonon modes of Bi$_\mathrm{2}$Te$_\mathrm{3}$ (at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible probe for delineating the magnetic ordering in bulk and surface of a hybrid topological insulator

Direct observation of altermagnetic band splitting in CrSb thin films

Altermagnetism represents an emergent collinear magnetic phase with compensated order and an unconventional alternating even-parity wave spin order in the non-relativistic band structure. We investigate directly this unconventional band splitting near the Fermi energy through spinintegrated soft X-ray angular resolved photoemission spectroscopy. The experimentally obtained angle-dependent photoemission intensity, acquired from epitaxial thin films of the predicted altermagnet CrSb, demonstrates robust agreement with the corresponding band structure calculations. In particular, we observe the distinctive splitting of an electronic band on a low-symmetry path in the Brilliouin zone that connects two points featuring symmetry-induced degeneracy. The measured large magnitude of the spin splitting of approximately 0.6 eV and the position of the band just below the Fermi energy underscores the signifcance of altermagnets for spintronics based on robust broken time reversal symmetry responses arising from exchange energy scales, akin to ferromagnets, while remaining insensitive to external magnetic fields and possessing THz dynamics, akin to antiferromagnets.Comment: 10 pages, 7 figures (including supplementary information

Knowledge about hepatitis B and hepatitis C virus infection and consequences: a cross-sectional assessment of baseline knowledge among infected patients in West Bengal, India

Abstract Background India has a high burden of disease from hepatitis B virus (HBV), with 3.7 % point-prevalence, as well as from hepatitis C virus (HCV), with 1–1.5 % prevalence. Societal ignorance about HBV and HCV in India limits the potential for prevention and treatment efforts to bring these diseases under control. Since patients’ own knowledge about their health condition may have important health consequences, this study sought to assess knowledge levels among HBV and HCV patients referred to the virology laboratory of the Liver Foundation, West Bengal. Methods Patients who had tested positive for HBsAg or anti-HCV at government specialty clinics were invited to enroll in the study when they presented for follow-up laboratory testing. Study participants completed a survey that contained three multiple-choice questions about viral hepatitis etiology and five multiple-choice questions about the consequences of HBV and HCV infection. Mean knowledge scores for male and female respondents were compared, and comparisons were also made across different places of residence, age groups, education levels and income levels. One-way ANOVA was used to test for significant differences. Results Among 520 study participants, the mean knowledge score was 4.76 on an eight-point scale. Approximately 40 % of the study sample scored less than 4.0. Almost three-quarters of respondents correctly responded to the question, “Which organ of the human body is affected by hepatitis?” while almost two-thirds knew how hepatitis B is transmitted. Regarding consequences of HBV and HCV infection, less than one-third of study participants answered correctly when asked, “What happens when one is infected with hepatitis B or C?” Slightly more than two-thirds of people correctly answered the question about how hepatitis B is prevented. The mean knowledge score varied across age groups (P = 0.0009), education levels (P = 0.0001) and monthly household income levels (P = 0.0001). With higher levels of schooling and higher household income, there were corresponding increases in knowledge scores. Conclusion There is room for improving knowledge of HBV and HCV etiology and consequences among patients as well as healthcare workers in India. More awareness activities should be organized, accompanied by further research to track whether knowledge scores improve over time