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A quantum state of matter that is forbidden to interact with photons and is therefore undetectable by spectroscopic means is called a dark state. This basic concept can be applied to condensed matter where it suggests that a whole band of quantum states could be undetectable across a full Brillouin zone. Here we report the discovery of such condensed-matter dark states in palladium diselenide as a model system that has two pairs of sublattices in the primitive cell. By using angle-resolved photoemission spectroscopy, we find valence bands that are practically unobservable over the whole Brillouin zone at any photon energy, polarization and scattering plane. Our model shows that two pairs of sublattices located at half-translation positions and related by multiple glide-mirror symmetries make their relative quantum phases polarized into only four kinds, three of which become dark due to double destructive interference. This mechanism is generic to other systems with two pairs of sublattices, and we show how the phenomena observed in cuprates, lead halide perovskites and density wave systems can be resolved by the mechanism of dark states. Our results suggest that the sublattice degree of freedom, which has been overlooked so far, should be considered in the study of correlated phenomena and optoelectronic characteristics.

Recently, LG Display completed the "EX Technology" development and is prioritizing technological innovation. This technology includes deuterium technology and personalization algorithms, which increase screen brightness (luminance) by 30% compared to existing OLEDs while producing more accurate and natural colors. In this paper, we will describe how deuterium technology can improve the lifetime of OLED products and the degradation mechanism of deuterated materials. By replacing the C‐H bond with a C‐D bond, isotope species exhibit electrochemical stability, leading to a longer device lifetime.

Perovskite photovoltaic (PV) cell researches have been extensively conducted due to its unprecedentedly excellent power conversion efficiencies (PCEs), which are reported to be over 23.7% in maximum. Despite the high PCEs, there are several unresolved issues on optimal interface states in the cell and device stabilities. Moreover, beyond the simple PV device issues, extended device or circuit applications have rarely been reported although it seems equally important to fully reveal the self-power energy harvesting functions of the perovskite cells to modern ubiquitous environment. Here, we integrate a realistic self-power circuit utilizing a few nm-thin molybdenum ditelluride (MoTe2) field effect transistors (FETs) as well as perovskite PV cells. The PV cells intrinsically show more than 0.9 V of open circuit voltage (VOC) under artificial sun (AM 1.5) or visible photon illumination, so we thus used a red-light emitting diode (LED) to simply generate ~1 V of photovoltage. Two modes for practical operation were consequently observed from the circuit, depending on the light intensity: self-power current/voltage source mode (high intensity) and photosensor mode (low intensity). We now conclude that our self-power circuit approaches integrating perovskite cells and 2D MoTe2FET could attract much attention for future ubiquitous electronics and energy harvest applications.