Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study

The first principles calculations based on density functional theory(DFT) are employed to investigate the mechanical properties and electronic structure of N and Ta doped Ti C. The result shows that the co-doping of nitrogen and tantalum dilates the lattice constant and improves the stability of Ti C. Nitrogen and tantalum can significantly enhance the elastic constants and elastic moduli of Ti C. The results of B/G and C12-C44 indicate tantalum can markedly increase the ductility of Ti C. The electronic structure is calculated to describe the bonding characteristic, which revealed the strong hybridization between C-p and Ta-d and between N-p and Ti-d. The hardnessis is estimated by a semiempirical model that is based on the Mulliken overlap population and bond length. While the weakest bond takes determinative role of the hardness of materials, the addition of Ta sharply reduces the hardness of Ti C.

Distinguishing high-harmonic generation from surface and bulk states in topological insulator Bi_(2)Se_(3)

We demonstrated a scheme to differentiate the high-harmonic generation[HHG)originating from the surface states and bulk states of the topological insulator Bi_(2)Se_(3).By adopting two-color mid-infrared laser fields on Bi_(2)Se_(3),we found that the nonlinear response sensitively depends on the relative phase of the driving fields.The even harmonics arise from the surface states with a clear signature,whose modulation period equals the cycle of the second-harmonic generation[SHG]field.We reveal that the weak SHG perturbs the nontrivial dipole phase of the electron-hole pair in surface states,and thus leads to the modulation of HHG.It provides a means to manipulate the ultrafast dynamics in surface states through adopting a weak perturbing laser field.