M. Wierzbicki

Thermoelectric effects in silicene nanoribbons

Transport and thermoelectric coefficients (including also spin thermopower) of silicene nanoribbons with zigzag edges are investigated by {\it ab-initio} numerical methods. Local spin density of such nanoribbons reveals edge magnetism. Like in graphene, one finds antiferromagnetic and ferromagnetic ordering, with spin polarization at one edge antiparallel or parallel to that at the other edge, respectively. Thermoelectric properties, especially the Seebeck coefficient, significantly depend on the electronic band structure and are enhanced when the Fermi level is in the energy gap. However, these thermoelectric properties are significantly reduced when the phonon contribution to the heat conductance is included. This phonon contribution has been calculated numerically by two different methods. Transition from antiferromagnetic to ferromagnetic states leads to a large magnetoresistance as well as to a considerable magnetothermopower. Thermoelectric parameters in the antiparallel configuration, when spin polarization in the left part of the nanoribbon is opposite to that in the right part, are also analyzed.

Light propagation in an antiferromagnetic spiral

The rotation of the polarization ellipse of a light wave transmitted through a magnetic MnSe layer, exhibiting an antiferromagnetic helical spin structure, was determined for the case of natural gyrotropy. It was shown that the magnitude of the rotation angle is strongly enhanced in comparison with the case of free gyrotropy.

Enhanced thermoelectric efficiency in ferromagnetic silicene nanoribbons terminated with hydrogen atoms

Using ab initio methods we calculate thermoelectric and spin thermoelectric properties of silicene nanoribbons with bare, mono-hydrogenated and di-hydrogenated edges. Asymmetric structures, in which one edge is either bare or di-hydrogenated while the other edge is mono-hydrogenated (0H-1H and 2H-1H nanoribbons), have a ferromagnetic ground state and display remarkable conventional and spin thermoelectric properties. Strong enhancement of the thermoelectric efficiency, both conventional and spin ones, results from a very specific band structure of such nanoribbons, where one spin channel is blocked due to an energy gap while the other spin channel is highly conductive. In turn, 0H-2H and 2H-2H nanoribbons (with one edge being either bare or di-hydrogenated and the other edge being di-hydrogenated) are antiferromagnetic in the ground state. Accordingly, the corresponding spin channels are equivalent, and only conventional thermoelectric effects can occur in these nanoribbons.

Zigzag nanoribbons of two-dimensional silicene-like crystals: magnetic, topological and thermoelectric properties

The effects of electron-electron and spin-orbit interactions on the ground-state magnetic configuration and on the corresponding thermoelectric and spin thermoelectric properties in zigzag nanoribbons of two-dimensional hexagonal crystals are analysed theoretically. The thermoelectric properties of quasi-stable magnetic states are also considered. Of particular interest is the influence of Coulomb and spin-orbit interactions on the topological edge states and on the transition between the topological insulator and conventional gap insulator states. It is shown that the interplay of both interactions also has a significant impact on the transport and thermoelectric characteristics of the nanoribbons. The spin-orbit interaction also determines the in-plane magnetic easy axis. The thermoelectric properties of nanoribbons with in-plane magnetic moments are compared to those of nanoribbons with edge magnetic moments oriented perpendicularly to their plane. Nanoribbons with ferromagnetic alignment of the edge moments are shown to reveal spin thermoelectricity in addition to the conventional one.

Unique magnetic and thermoelectric properties of chemically functionalized narrow carbon polymers

We analyze magnetic, transport and thermoelectric properties of narrow carbon polymers, which are chemically functionalized with nitroxide groups. Numerical calculations of the electronic band structure and the corresponding transmission function are based on density functional theory. Transport and thermoelectric parameters are calculated in the linear response regime, with particular interest in charge and spin thermopowers (charge and spin Seebeck effects). Such nanoribbons are shown to have thermoelectric properties described by large thermoelectric efficiency, which makes these materials promising from the application point of view.

Nonlinear refractive index measurement with temporal phase reconstruction

Knowing the value of nonlinear index of refraction is crucial for understanding how phase modulation affects intense ultra-short pulses propagating through a given material. Measurement of Kerr constant forces building of stand-alone and often complicated setups. Most popular one — Z-scan — requires excellent beam quality, perfect beam alignment and entails separate two-photon absorption measurements [1]. On the other hand, frequency-resolved optical gating (FROG) setups are nowadays a common equipment of ultra-fast laboratories where the complete ultra-short pulse characterization is an ever-growing need.

Nonlinear refractive index measurement by temporal phase reconstruction

Knowing the value of nonlinear index of refraction is crucial for understanding how phase modulation affects intense ultra-short pulses propagating through a given material. Measurement of Kerr constant forces building of stand-alone and often complicated setups. Most popular one — Z-scan — requires excellent beam quality, perfect beam alignment and entails separate two-photon absorption measurements [1]. On the other hand, frequency-resolved optical gating (FROG) setups are nowadays a common equipment of ultra-fast laboratories where the complete ultra-short pulse characterization is an ever-growing need.

Spatially modulated optical tensors in magnetic superlattices

Abstract The spatial modulation of the third-rank optical tensor in superlattices with a ferromagnetic helix as in Dy/Y is calculated. It is shown that a light wave transmitted through a thin layer of such a helical superlattice in a Fabry–Perot cavity exhibits the intensity type optical bistability which is enhanced in comparison with that appearing in a magnetic medium with spatially uniform spin order.