This article studies a non-Hermitian Su-Schrieffer-Heeger (SSH) model which has periodically staggered Hermitian and non-Hermitian dimers. The changes in topological phases of the considered chiral symmetric model with respect to the introduced non-Hermiticity are studied where we find that the system supports only complex eigenspectra for all values of u≠0 and it stabilizes only non-trivial insulating phase for higher loss-gain strength. Even if the system acts as a trivial insulator in the Hermitian limit, the increase in loss-gain strength induces phase transition to non-trivial insulating phase through a (gapless) semi-metallic phase. Interesting phenomenon is observed in the case where Hermitian system acts as a non-trivial insulator. In such a situation, the introduced non-Hermiticity neither leaves the non-trivial phase undisturbed nor induces switching to trivial phase. Rather, it shows transition from non-trivial insulating phase to the same where it is mediated by the stabilization of (non-trivial) semi-metallic phase. This unusual transition between the non-trivial insulating phases through non-trivial semi-metallic phase gives rise to a question regarding the topological states of the system under open boundary conditions. So, we analyze the possibility of stable edge states in these two non-trivial insulating phases and check the characteristic difference between them. In addition, we study the nature of topological states in the case of non-trivial gapless (semi-metallic) region.
This paper investigates the Joule-Thomson expansion for a five-dimensional neutral Gauss-Bonnet Anti-de Sitter black hole. Firstly, by taking Van der Waals gas as an example, we induce the definition of the Joule-Thomson coefficient and the inversion phenomena. One can give the T–P graph and the inversion curves. Then, we obtain the thermodynamic properties of the Gauss-Bonnet black hole and use the same way to get the T–P figure, which shows differences from Van der Waals gas and other black holes. To our surprise, we can’t observe its inversion phenomena. Due to this reason, we further studied the vanished inversion region and found that the electric charge plays an important role in this phenomenon. We analogy black hole charged and neutral, which get some interesting consequences. Finally, we make Legendre transition to Smarr relation and investigate whether the electric potential has the same result as the electric charge’s landscape. These results will uncover the inner interaction between the enthalpy and the electric charge during the Joule-Thomson process.
An X-ray point source was used to examine the diffraction behavior of a low-angle twist boundary. It is shown that when radiation is focused inside a crystal, because of the dislocation structure of the defect wall, the vertical divergence can be reduced so much that the size of the focus in this direction is significantly smaller than in the horizontal direction. This circumstance can be used to create X-ray optical elements.
The binding energy of the ground and first excited states of a hydrogen-like impurity electron in monolayer graphene is studied by a variational approach. It is shown that the binding energies of the impurity electron can be tuned by changing the value of the gap and the effective fine structure constant. An analytical expression for the dipole matrix element of the electron transition from the ground to the first excited state of a hydrogen-like impurity in graphene is found.
The structural and reflective properties (total reflectance and scattering) of black silicon layers formed by reactive ion etching have been studied. Reflectance spectra were determined in the visible, near-infrared, and near-ultraviolet wavelength ranges. The influence of etching duration on the optical behavior of black silicon layers is studied and the possibilities of their use in solar cells and photodetectors are discussed.
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