RESUMO
A combined module that combines a concentrator with planar photovoltaic circuits provides energy conversion of both parts of global terrestrial radiation: direct sunlight by concentrator solar cells and scattered (diffuse) sunlight by planar (non-concentrator) photoconverters. The decrease in Fresnel lens concentrating ability is usually associated with imperfections in the optical refractive surfaces, where some part of the direct light, which arrives normal to the surface of the Fresnel lens and is intended to be concentrated, becomes scattered and directed off the highly efficient concentrator solar cell. The diffuse light flux propagates inside the volume of the combined photovoltaic module. This flux undergoes multiple reflections from the structural elements, is partially absorbed, and ultimately reaches the photoconverters of the planar circuit. Thus, two types of diffuse light impinge the planar circuit: "external" from the atmosphere and "internal" produced by the Fresnel lens from direct light. This Letter proposes a method for determining the diffuse properties of sunlight concentrators such as Fresnel lens.
RESUMO
The recently discovered type-II Weyl points appear at the boundary between electron and hole pockets. Type-II Weyl semimetals that host such points are predicted to exhibit a new type of chiral anomaly and possess thermodynamic properties very different from their type-I counterparts. In this Letter, we describe the prediction of a type-II Weyl semimetal phase in the transition metal diphosphides MoP_{2} and WP_{2}. These materials are characterized by relatively simple band structures with four pairs of type-II Weyl points. Neighboring Weyl points have the same chirality, which makes the predicted topological phase robust with respect to small perturbations of the crystalline lattice. In addition, this peculiar arrangement of the Weyl points results in long topological Fermi arcs, thus making them readily accessible in angle-resolved photoemission spectroscopy.