Association of social jetlag and eating patterns with sleep quality and daytime sleepiness in Japanese high school students.

A high prevalence of excessive daytime sleepiness and poor sleep quality has been reported in adolescents, but the effects of social jetlag on sleep quality and daytime sleepiness are unclear. Therefore, we assessed the association of sleep and eating patterns with daytime sleepiness and sleep quality among a total of 756 Japanese high school students. Participants completed the Pittsburgh Sleep Quality Index to evaluate sleep quality, the Pediatric Daytime Sleepiness Scale to evaluate daytime sleepiness, and an 8-day sleep diary. Data on average sleep duration, social jetlag, midsleep on free days sleep corrected, and the differences in the first and last meal timing between school days and non-school days were obtained from participants' sleep diaries. The results reveal that social jetlag is associated with differences in the first meal timing between school days and non-school days, and that social jetlag of more than 2 hr is associated with extremely poor sleep quality and excessive daytime sleepiness in Japanese high school students. Our findings suggest that reducing social jetlag to within a 2-hr window is important to prevent poor sleep quality and excessive daytime sleepiness for this population.

Challenges for Pulsed Laser Deposition of FeSe Thin Films.

Anti-PbO-type FeSe shows an advantageous dependence of its superconducting properties with mechanical strain, which could be utilized as future sensor functionality. Although superconducting FeSe thin films can be grown by various methods, ultrathin films needed in potential sensor applications were only achieved on a few occasions. In pulsed laser deposition, the main challenges can be attributed to such factors as controlling film stoichiometry (i.e., volatile elements during the growth), nucleation, and bonding to the substrate (i.e., film/substrate interface control) and preventing the deterioration of superconducting properties (i.e., by surface oxidization). In the present study, we address various technical issues in thin film growth of FeSe by pulsed laser deposition, which pose constraints in engineering and reduce the application potential for FeSe thin films in sensor devices. The results indicate the need for sophisticated engineering protocols that include interface control and surface protection from chemical deterioration. This work provides important actual limitations for pulsed laser deposition (PLD) of FeSe thin films with the thicknesses below 30 nm.

Chemical Composition Control at the Substrate Interface as the Key for FeSe Thin-Film Growth.

The strong fascination exerted by the binary compound of FeSe demands reliable engineering protocols and more effective approaches toward inducing superconductivity in FeSe thin films. Our study addresses the peculiarities in pulsed laser deposition that determine FeSe thin-film growth and focuses on the film/substrate interface, which has only been considered hypothetically in the past literature. The FeSe/MgO interface has been assumed (1) to be clean and (2) to obey lattice-matching epitaxy. Our studies reveal that both assumptions are misleading and demonstrate the tendency for domain-matching epitaxial growth, which accompanies the problem of chemical heterogeneity. We propose that homogenization of the film/substrate interface by an Fe buffer can improve the control of stoichiometry and nanostrain in a way that favors superconductivity even in ultrathin FeSe films. We will also show that on a chemically homogenized FeSe/Fe interface, the control of film texture with preparation conditions is still possible.

Natural van der Waals heterostructural single crystals with both magnetic and topological properties.

Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4) m (Bi2Te3) n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.