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Ferroelectric materials are an alternative to semiconductor-based photovoltaics and offer the advantage of above bandgap photovoltage generation. However, there are few known compounds, and photovoltaic efficiencies remain low. Here, we report the discovery of a photovoltaic effect in undoped lead magnesium niobate-lead titanate crystal and a significant improvement in the photovoltaic response under suitable electric fields and temperatures. The photovoltaic effect is maximum near the electric-field-driven ferroelectric dipole reorientation, and increases threefold near the Curie temperature (T c ). Moreover, at ferroelectric saturation, the photovoltaic response exhibits clear remanent and transient effects. The transient-remanent combinations together with electric and thermal tuning possibilities indicate photoferroelectric crystals as emerging elements for photovoltaics and optoelectronics, relevant to all-optical information storage and beyond. DOI: 10.1103/PhysRevMaterials.2.012401 Photoferroelectrics are remarkable materials that have great potential for multifunctional applications [1]. These materials that exhibit (multi)ferroic order are particularly interesting, because they offer advanced electric operation that is related to multiple electric polarization switching states [2]. The field was rejuvenated after the discovery of the photovoltaic effect in the multiferroic BiFeO 3 [3,4], resulting in the revival of ferroelectric-based photovoltaic operation and related materials [5][6][7][8]. Based on recent progress in photovoltaic efficiency of Bi 2 FeCrO 6 films [9], ferroelectric (FE) cells might become competitors for conventional photovoltaics in the near future. In this respect, better insight into photoinduced changes of electrical properties over a wide range of temperatures and electric fields would be helpful. Such a study, however, requires high-quality crystals that are free from the surface/interface effects occurring in thin films [10] and the grain size dependence occurring in ceramics [11]. This task is challenging because the total number of currently known photovoltaicferroelectric compounds is well below 20 [5][6][7][8] We also detail the remanent photopolarization properties originating from the photocarrier generation-distribution mechanism, and demonstrate how the photovoltaic response can be tuned by varying the applied electric field and temperature.The crystals had (001) orientation, and were square shaped with edges along the [010] and [100] directions [ Fig. 1(a)]. In-* Corresponding author: kundysATipcms.unistra.fr dependent energy-dispersive x-ray spectroscopy (EDS) analysis confirmed the PMN-32%PT composition of the crystal. The sample's dimensions were 901 μm × 272 μm × 2161 μm, and both electrodes were formed with silver paste covering the edges in the planes parallel to yz [ Fig. 1(a)]. This experimental geometry was chosen to minimize light power loss and to avoid possible extrinsic contributions related to light-assisted charge injection from electrodes. The hyster...

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Achieving optical operation of logic elements, especially those that involve two-dimensional (2D) layers, can begin the long-awaited era of optical computing. However, efficient optical modulation of the electronic properties of 2D materials, including the rewritable memory effect, is currently lacking. Here we report a fully optical control of the conductivity of graphene with write-erase operation yet under ultralow optical fluence. The competition between light-induced charge generation in a ferroelectric-photovoltaic substrate and relaxation processes provides the selective photocarrier-trapping control affecting the doping of the 2D overlayer. These findings open the way to photonic control of 2D devices for all-optical modulators and a variety of all-optical logic circuits, memories, and field-effect transistors.

Magnetic circular x-ray-dichroism measurements at the Co L 2,3 edges of the Co/Pt͑111͒ interface are presented. Ultrathin Co films, deposited and measured at room temperature, order magnetically above a thickness of 1.8 monolayers and show magnetic anisotropy perpendicular to the surface up to coverage of at least 5 monolayers. An enhancement of the orbital magnetic momentum relative to the bulk value of Co metal is observed. A further increase after addition of a thick Pt overlayer reveals the influence of hybridization at the Co/Pt interface. Observations of magnetic surface alloys with perpendicular anisotropy are also reported.

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