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The spin Seebeck effect is a novel indirect thermoelectric conversion phenomenon, in which magnetic materials play an important role, that is distinct from the traditional direct thermoelectric conversion method. In this paper, we studied the spin Seebeck effect driven by thermal flux in two-dimensional ferromagnets and derived the spin-dependent Seebeck coefficient and the spin Seebeck coefficient contributed by conduction electrons in a ferromagnet based on the non-equilibrium linear irreversible thermodynamics and the Boltzmann linear theory. The spin Seebeck coefficients of six two-dimensional ferromagnetic materials (including manganese halides and transition metal chalcogenides) were numerically calculated. A largest spin Seebeck coefficient is found for MnCl 3 to be 1600 μ V/K in the range of temperature from 50 to 120 K, which is even larger than that of known CrI 3 and CrGeTe 3. The present study on the heat flow-spin current transport properties of ferromagnets could have great significance for the thermoelectric applications in spintronics. [ABSTRACT FROM AUTHOR]

The observation of negative longitudinal magnetoresistivity (NLMR) in Weyl semimetals has gained strong support in recent experiments. It is believed that charged impurities play an important role in the measurement of NLMR. We thus employ a screened Coulomb disorder to model charged impurities and derive a general screening length depending on the magnetic field, chemical potential and temperature. We study the magneto-transport in a two-node Weyl semimetal in which the intra-valley scattering and the inter-valley scattering can be explored simultaneously. We also calculate the effect of the misalignment of the external electric field and the magnetic field on the longitudinal and transverse magnetoconductivities, recovering the experimental observations. We show that the former (latter) is suppressed (enhanced) sensitively with the density of the impurity. This feature makes it hard to observe the NLMR in experiments in the heavy doping case. These results may be exploited to explain the sample-dependent observation of NLMR and deepen our understanding of magneto-transport in Weyl semimetals. [ABSTRACT FROM AUTHOR]

We study a versatile structurally favorable periodic sp2-bonded carbon atomic planar sheet with C4v symmetry by means of the first-principles calculations. This carbon allotrope is composed of carbon octagons and squares with two bond lengths and is thus dubbed as octagraphene. It is a semimetal with the Fermi surface consisting of one hole and one electron pocket, whose low-energy physics can be well described by a tight-binding model of π-electrons. Its Young's modulus, breaking strength, and Poisson's ratio are obtained to be 306 N/m, 34.4 N/m, and 0.13, respectively, which are close to those of graphene. The novel sawtooth and armchair carbon nanotubes as well as unconventional fullerenes can also be constructed from octagraphene. It is found that the Ti-absorbed octagraphene can be allowed for hydrogen storage with capacity around 7.76 wt. %. [ABSTRACT FROM AUTHOR]

Deals with the strategies used in teaching physics in various junior middle schools in China. Observations on the teaching methods of physics teachers in China; Significance of cognitive internalization in teaching physics; Reasons for the differences in the teaching methods.