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Methylammonium lead iodide perovskite (MAPbI3) exhibits long charge carrier lifetimes that are linked to its high efficiency in solar cells. Yet, the mechanisms governing these unusual carrier dynamics are not completely understood. A leading hypothesis-disproved in this work-is that a large, static bulk Rashba effect slows down carrier recombination. Here, using second harmonic generation rotational anisotropy measurements on MAPbI3 crystals, we demonstrate that the bulk structure of tetragonal MAPbI3 is centrosymmetric with I4/mcm space group. Our calculations show that a significant Rashba splitting in the bandstructure requires a non-centrosymmetric lead iodide framework, and that incorrect structural relaxations are responsible for the previously predicted large Rashba effect. The small Rashba splitting allows us to compute effective masses in excellent agreement with experiment. Our findings rule out the presence of a large static Rashba effect in bulk MAPbI3, and our measurements find no evidence of dynamic Rashba effects.

The Coriolis force is a significant source of systematic phase errors and dephasing in atom interferometry and is often compensated by counter-rotating the interferometry laser beam against Earth's rotation. We present a novel method for performing Coriolis force compensation for long-baseline atom interferometry, which mitigates atom-beam misalignment due to beam rotation, an effect which is magnified by the long lever arm of the baseline length. The method involves adjustment of the angle of the interferometer beam prior to a magnifying telescope, enabling the beam to pivot around a tunable position along the interferometer baseline. By tuning the initial atom kinematics and adjusting the angle with which the interferometer beam pivots about this point, we can ensure that the atoms align with the center of the beam during the atom optics laser pulses. This approach will be used in the MAGIS-100 atom interferometer and could also be applied to other long-baseline atom interferometers. An additional challenge associated with long baseline interferometry is that since long-baseline atom interferometers are often located outside of typical laboratory environments, facilities constraints may require lasers to be housed in a climate-controlled room a significant distance away from the main experiment. Nonlinear effects in optical fibers restrict the use of fiber-based transport of the high-power interferometry beam from the laser room to the experiment. We present the design of and prototype data from a laser transport system for MAGIS-100 that maintains robustness against alignment drifts despite the absence of a long fiber. [ABSTRACT FROM AUTHOR]

Background: Engineering students like any other students face several stressors in their lives, which make them vulnerable to depression. Depression may affect students' academic performance. Aim: The present study aims to estimate the prevalence and associated risk factors of depression among engineering students. Material and Methods: A cross-sectional study was conducted in December 2016 among 110 randomly selected students from an engineering college in a rural area of Pune district, India. PHQ-9 questionnaire was used. Univariate and multivariable ordinal logistic regression was used to quantify association. Results: Of a total of 110 students, 71.8% were males, while 28.2% were females. The mean age was 20.7 years. 29.1% had no depression, 48.2% had mild depression, and 22.7% had moderate depression. Univariate analysis found four variables significantly associated with a greater risk of depression: parental stress, sibling stress, economic stress, and interpersonal conflict. In the adjusted (multivariable) ordinal logistic regression analysis controlling for all independent variables, only lack of economic support and interpersonal conflicts retained their statistical significance. Conclusion: The prevalence of depression in engineering students is high and strongly associated with the presence of economic and personal stress. Screening for depression and giving them care and support is of paramount importance. [ABSTRACT FROM AUTHOR]

We present a laser system for performing single-photon atom interferometry on the 698 nm clock transition in ultracold strontium. We coherently combine the power of two titanium:sapphire lasers and demonstrate chirps of 200 MHz in 2.5 ms while phase-locked to an optical reference. Moreover, we demonstrate a novel, to the best of our knowledge, scheme to deliver 4 W pulsed beams to the atoms via a mode-cleaning optical fiber using active noise cancellation.