RESUMO
Electrons in two-dimensional crystals with a honeycomb lattice structure possess a valley degree of freedom (DOF) in addition to charge and spin. These systems are predicted to exhibit an anomalous Hall effect whose sign depends on the valley index. Here, we report the observation of this so-called valley Hall effect (VHE). Monolayer MoS2 transistors are illuminated with circularly polarized light, which preferentially excites electrons into a specific valley, causing a finite anomalous Hall voltage whose sign is controlled by the helicity of the light. No anomalous Hall effect is observed in bilayer devices, which have crystal inversion symmetry. Our observation of the VHE opens up new possibilities for using the valley DOF as an information carrier in next-generation electronics and optoelectronics.
RESUMO
Previous research regarding the effects of positive life events on physical health has been inconclusive. We tested the hypothesis that positive life events have a detrimental effect on health only among people with negative self-views. This prediction derives from an identity disruption model of stress, which holds that an accumulation of life events that are inconsistent with the self-concept leads to physical illness. To test the hypothesis, we conducted two prospective studies in which positive life events and self-esteem were used to predict the development of illness over time. In accordance with predictions, both studies showed that desirable life changes were associated with increases in illness only among subjects with low self-esteem; among subjects with high self-esteem, positive life events were linked to better health. Implications for understanding the manner in which life events affect health are considered.