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Generating and manipulating valley polarization in a controlled method is significant. The inherently broken centrosymmetry of the buckled honeycomb structures gives it both ferroelectricity and valley degree of freedom, which provides an opportunity to realize electrically controlled valley polarization. In the first step, we explored the origin of buckling. The hexagonal structure is polar due to buckling of the surface, but the degree of buckling and the energy barrier to switching electric polarization are determined not solely by the chemical composition. We combined the electronegativity difference, bond length and the distribution of charge density to describe quantificationally the polarity of chemical bonds. It shows the characteristics of relatively long bond-length but relatively small electronegativity-difference. For exploring the ferroelectricity of buckling structures and the behavior of ferroelectric (FE) control of the valley degree of freedom, the [Formula: see text]-GaP is used as a model system to elucidate the strain effect on FE behavior and the magnetic proximity effect on the polarization and switching of valley. We found that the spontaneous polarization is positively correlated with the electronegativity difference within a certain range, and the compression strain can effectively manipulate spontaneous polarization and switch barrier. A combination of the magnetic proximity effect and the inversion of electric polarization can generate and switch valley polarization effectively.

We compare the thermal conductance of SH mode and mixing mode of acoustic phonons in a double T-shaped quantum waveguide at low enough temperatures by using the scattering-matrix method, and analyze the influence from mode conversion. Our results show that the small changes of the geometric parameters can induce different variation on the thermal conductivity, where the effect of the stub height of SH wave is the strongest. Moreover, the mode conversion plays an important role on the thermal conductivity, especially at the higher temperatures, and the coupling effect between two stubs at mixing mode is larger than that at single SH mode.

Using the first-principles calculations, the holes-induced [Formula: see text] magnetism associated with oxygen vacancy [Formula: see text] in [Formula: see text] and [Formula: see text] has been investigated. To obtain holes, the divalent calcium and tetravalent IVB-group ions are replaced respectively by the monovalent alkali, IB-group and trivalent III-group ions. It is found that the [Formula: see text] can enhance the magnetic moment of few acceptors-doped [Formula: see text], whereas it enhances the magnetic moment in most acceptor-doped [Formula: see text] except for La doping. Mainly, it is because the [Formula: see text] gives rise to no gap-states in [Formula: see text] but generates gap-states in [Formula: see text]. Based on the similar effect of [Formula: see text] on the band structure in [Formula: see text] or in [Formula: see text] (X = Ca, Sr, Ba), we suggest that there exists a similar effect of [Formula: see text] on [Formula: see text] magnetism in acceptor-doped alkaline titanium (zirconium) perovskites.

It is difficult to tune the magnetic properties of oxide diluted magnetic semiconductors because of the origin of ferromagnetism (FM) under different versions. Using first-principles band-structure calculations, we find that the surface oxygen dangling bonds and Indium vacancy may be responsible for the unexpected ferromagnetism in undoped In 2 O 3 quantum dots (QDs). The surface oxygen dangling bonds produce a magnetic moment of 6 μB, which primarily distribute on the surface oxygen atoms and an Indium vacancy ( V In ) produce a magnetic moment of 3 μB, which primarily distribute on the six O nearest neighbors of the vacancy center. The origin of the collective magnetic moments are the holes which introduced by the surface oxygen dangling bonds and Indium vacancy.

Using a first-principle band-structure method and a special quasirandom structure (SQS) approach, we present state-of-the-art HSE06 functional calculations for demonstrating the possibility of ternary PbxZn1-xTe alloys to be bipolar-doping materials. The results show that the bowing parameters and the band gaps of these alloys sensitively depend on the composition x. Due to the full overlapping and delocalization, the coupling between Pb outermost p orbits and Zn 4s orbits become very strong, thus resulting in a significant downshift of conduction band edge with the increase of Pb concentration x. When the concentration x reaches 0.25, it is demonstrated that the Pb0.25Zn0.75Te alloy has a substantial decrease in the conduction band edge, while leaving the valence band edge almost unchanged compared to that of binary ZnTe, thus improving the possibility for ambipolar-doping. Meanwhile, the spectral response of this alloy (Eg = 1.38 eV) is very consistent with the solar spectrum. We expect that our results will be helpful for the applications of optoelectronic devices.