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We demonstrate that within the model of massless Dirac fermions, graphene has a strong nonlinear optical response in the terahertz regime. It is found that the nonlinear contribution significantly alters both the single frequency and frequency tripled optical response at experimentally relevant field strengths. The optical activity of single layer graphene is significantly enhanced by nonlinear effects, and the frequency tripled response opens the gateway to photonic and optoelectronic device applications.

Schwefelgefüllte Kügelchen: Ein neuartiger Kohlenstoff‐Schwefel‐Nanokomposit enthält Schwefel innerhalb von doppelschaligen, „weichen“ Kohlenstoff‐Hohlkugeln (siehe Bild) mit großer Oberfläche und Porosität. Dieses Material zeigt eine herausragende elektrochemische Leistungsfähigkeit als Kathodenmaterial für Lithium‐Schwefel‐Batterien.

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A fiber-optic temperature sensor based on the interference of selective higher-order modes in circular optical fibers is described. The authors demonstrate that by coupling the LP01 mode in a standard single-mode fiber to the LP0m modes in a multimode fiber, and utilizing the interference of the higher-order modes, a fiber-optic temperature sensor which has an extremely simple structure and is suitable for high-temperature measurements can be constructed. The sensing principle, temperature measurement experiments, and results are presented.

For lignin valorization, simultaneously achieving the efficient cleavage of ether bonds and restraining the condensation of the formed fragments represents a challenge thus far. Herein, we report a two-step oxidation–hydrogenation strategy to achieve this goal. In the oxidation step, the O2/NaNO2/DDQ/NHPI system selectively oxidizes CαH–OH to CαO within the β-O-4 structure. In the subsequent hydrogenation step, the α-O-4 and the preoxidized β-O-4 structures are further hydrogenated over a NiMo sulfide catalyst, leading to the cleavage of Cβ–OPh and Cα–OPh bonds. Besides the transformation of lignin model compounds, the yield of phenolic monomers from birch wood is up to 32% by using this two-step strategy. The preoxidation of CαH–OH to CαO not only weakens the Cβ–OPh ether bond but also avoids the condensation reactions caused by the presence of Cα + from dehydroxylation of CαH–OH. Furthermore, the NiMo sulfide prefers to catalyze the hydrogenative cleavage of the Cβ–OPh bond connecting with a CαO rather than catalyze the hydrogenation of CαO back to the original CαH–OH, which further ensures and utilizes the advantages of preoxidation.

In spite of the extreme complexity and uncountable number of materials and substances that are created in nature, all can be classifi ed quite simply in terms of their conductive behavior into one of three types -insulators, semiconductors and metals -depending on the electronic band structure. It is the electrons carried by the constituent elements and their interactions that determine the structure of a material and its physical properties, such as electrical conductivity, magnetism and superconductivity. Th e degrees of freedom of electrons in a material determine the material's electronic properties. Making use of the spin of electrons adds one more degree of freedom, which can be utilized to design enhanced electronic devices [1]. The materials that enable us to take advantage of the spin of electrons are primarily those that exhibit magnetic properties. Ferromagnetic and antiferromagnetic metals, as well as semiconductors and insulators, are the materials that form the foundations for metallic, semiconducting and insulating spintronics, respectively, and these materials have been under active investigation by many groups around the world [2,3]. Th e performance of spintronic devices is determined by the degree of spin polarization of free electrons within a material. Electrons are partially polarized in classical ferromagnetic metals, such as iron, cobalt and nickel, yet can be fully polarized in half-metals and certain dilute semiconductors.Ferroelectric magnets and multiferroic materials, which exhibit coupling between ferroic order parameters, are candidates for use in insulating spintronics. In these materials, the spin (magnetic) dipole and the electric dipole can be mutually manipulated by electric and magnetic fields [4,5]. Figure 1 summarizes the band structures of these various classes of materials. Metals contain a conduction band that is partially filled, which means that the Fermi level (E f ) penetrates into the conduction band. In contrast, insulators have a band structure in which the conduction and valence bands are separated by a large energy gap (E g ). Semiconductors exhibit a narrow energy gap, while semi-metals have a small energy overlap between the conduction and valence bands. Half-metals are metallic in one spin direction and semiconducting in the other [6,7]. Half-metallic antiferromagnets, a newly theorized system predicted in some alloys, perovskite oxides and dilute magnetic semiconductors, have fully In intrinsic zero-gap materials, the conduction band (CB) and valence band (VB) edges touch at the Fermi level. Graphene is a zero-gap material with linear energy dispersion. The band structure of the spin-gapless semiconductors is spin-dependent.