Tungsten diselenide (WSe2) and related transition metal dichalcogenides exhibit interesting optoelectronic properties owing to their peculiar band structures originating from the valley degree of freedom. Although the optical generation and detection of valley polarization has been demonstrated, it has been difficult to realize active valley-dependent functions suitable for device applications. We report an electrically switchable, circularly polarized light source based on the material's valley degree of freedom. Our WSe2-based ambipolar transistors emit circularly polarized electroluminescence from p-i-n junctions electrostatically formed in transistor channels. This phenomenon can be explained qualitatively by the electron-hole overlap controlled by the in-plane electric field. Our device demonstrates a route to exploit the valley degree of freedom and the possibility to develop a valley-optoelectronics technology.

Liquid/solid interfaces are attracting growing interest not only for applications in catalytic activities and energy storage, but also for their new electronic functions in electric double-layer transistors (EDLTs) exemplified by high-performance organic electronics, field-induced electronic phase transitions, as well as superconductivity in SrTiO(3) (ref. 12). Broadening EDLTs to induce superconductivity within other materials is highly demanded for enriching the materials science of superconductors. However, it is severely hampered by inadequate choice of materials and processing techniques. Here we introduce an easy method using ionic liquids as gate dielectrics, mechanical micro-cleavage techniques for surface preparation, and report the observation of field-induced superconductivity showing a transition temperature T(c)=15.2 K on an atomically flat film of layered nitride compound, ZrNCl. The present result reveals that the EDLT is an extremely versatile tool to induce electronic phase transitions by electrostatic charge accumulation and provides new routes in the search for superconductors beyond those synthesized by traditional chemical methods.

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ImportanceExisting studies concentrate on exploring mid-life to late-life risk factors on racial disparities in cognition. Given the critical role of neurocognitive development in early life, understanding contributions of early-life circumstances has important implications for early-stage interventions.ObjectiveTo evaluate the association between early-life circumstances and racial disparities in cognition, and to determine their overall and respective contributions.Design, Setting, and ParticipantsWe assembled three analytic samples from the Health and Retirement Study (HRS) (1995-2018), a nationally representative longitudinal survey of Americans 50 years or older. 17,092 participants, with 13,907 identifying as non-Hispanic White (White) and 3,185 as non-Hispanic Black (Black), were included in the Core sample. The Trauma and PGS samples respectively included 6,533 participants (5,696 White, 837 Black) and 5,532 participants (4,893 White, 639 Black).Main Outcomes and MeasuresThe main outcomes were cognitive score and cognitive impairment, as assessed by the Telephone Interview for Cognitive Status (TICS). We used the Blinder-Oaxaca Decomposition (BOD) to evaluate disparities in cognitive outcomes between White and Black participants attributable to differences in early-life circumstances.ResultsAmong all White and Black participants at initial survey, their respective average age were 58.1 (95% CI, 58.0-58.3) years and 55.8 (95% CI, 55.5-56.0) years; their respective average cognitive score were 17.3 (95% CI, 17.2-17.3) points and 14.6 (95% CI, 14.4-14.7) points; and their respective proportion with cognitive impairment were 7.2 (95% CI, 6.8-7.6) percentage points (pp) and 22.9 (95% CI, 21.5-24.4) pp. Across three analytic samples, overall differences in early-life circumstances respectively explained 23.5%–40.4% and 33.8%–65.3% of the racial gaps in cognitive score and proportion of cognitive impairment between White and Black participants. Difference in educational attainment contributed the most. In the Trauma sample, for example, years of education explained 3.1 (95% CI, 1.9-4.3) pp or 18.6% of the racial gap in proportion of cognitive impairment using the baseline assessment, and 3.3 (95% CI, 2.0-4.5) pp or 26.9% using the latest assessment. Additional early-life contributors included educational environments (e.g., ownership of books, parental education, time spent with mothers) and socioeconomic status (e.g., financial difficulty). However, childhood trauma and selected genetic factors were not significant contributors.Conclusions and RelevanceLess favorable early-life circumstances are associated with clinically meaningful and statistically significant racial gaps in cognition.Key PointsQuestionsHow much do differences in early-life circumstances explain late-life disparities in cognitive outcomes between non-Hispanic Black (Black) and non-Hispanic White (White) older adults? What are the key early-life contributors to these racial disparities?FindingsEarly-life circumstances contribute substantially to racial disparities in cognitive outcomes over age 50. Educational attainment and early-life educational environment are the most important contributors, even after accounting for a rich set of other early-life socioeconomic, demographic, health, traumatic, and genetic factors.MeaningExposure to less favorable early-life circumstances for Black than White adults was associated with large racial gaps in cognitive outcomes.

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