RESUMEN
In this paper, the crystal geometry, electronic structure, lattice vibration, Infrared and Raman spectra of ternary layered borides M3AlB2 (M = Ti, Zr, Hf, Ta) are studied by using first principles calculation method based on the density functional theory. The electronic structure of M3AlB2 indicates that they are all electrical conductors, and the d orbitals of Ti, Zr, Hf, and Ta occupy most of the bottom of the conduction band and most of the top of the valence band. Al and B have lower contributions near their Fermi level. The lightweight and stronger chemical bonds of atom B are important factors that correspond to higher levels of peak positions in the Infrared and Raman spectra. However, the vibration frequencies, phonon density of states, and peak positions of Infrared and Raman spectra are significantly lower because of heavier masses and weaker chemical bonds for M and Al atoms. And, there are 6 Infrared active modes A2u and E1u, and 7 Raman active modes, namely A1g, E2g, and E1g corresponding to different vibration frequencies in M3AlB2. Furthermore, the Infrared and Raman spectra of M3AlB2 were obtained respectively, which intuitively provided a reliable Infrared and Raman vibration position and intensity theoretical basis for the experimental study.
RESUMEN
A new tactic that using Ag nanorice trimer as surface-enhanced hyper Raman scattering substrate is proposed for realizing maximum signal enhancement. In this paper, we numerically simulate and theoretically analyze the optical properties of the nanorice trimer consisting of two short nanorices and a long nanorice. The Ag nanorice trimer can excite Fano resonance at optical frequencies based on the strong interaction between the bright and the dark mode. The bright mode is attributed to the first longitudinal resonance of the short nanorice pair, while the dark mode originates from the third longitudinal mode resonance of the long nanorice. The electric field distributions demonstrate that the two resonances with the largest field strength correspond to the first-order resonance of the long nanorice and the Fano resonance of the trimer, respectively. Two plasmon resonances with maximum electromagnetic field enhancements and same spatial hot spot regions can match spectrally with the pump and second-order Stokes beams of hyper Raman scattering, respectively, through reasonable design of the trimer structure parameters. The estimated enhancement factor of surface-enhanced hyper Raman scattering can achieve as high as 5.32 × 1013.
RESUMEN
This work presents a compact LiNbO3 (lithium niobate, LN) electro-optic (EO) Q-switch with a lower driving voltage than the conventional LN Q-switches. By using non-direct cuts of a certain crystallographic orientation, a LN crystal is used both as a quarter-wave plate (QWP) and a pockels cell in a laser cavity. Through theoretical calculations and experiments, we have determined the optimized crystal orientations with low quarter-wave voltages (QWV). A set of compact LN EO Q-switches were prepared and used successfully in the pulse-on mode in a Nd:YAG laser. The Q-switched laser outputs are comparable to those obtained by using a conventional Z-cut LN Q-switch with a QWP. The QWV of the Q-switch with the optimized crystal orientation is 600V lower than that of the Z-cut LN Q-switch.
RESUMEN
We have investigated the magnetism and magnetocaloric effect of TlCo2-x Ni x S2 (0 [Formula: see text] x [Formula: see text] 0.05). TlCo2S2 and TlCo1.97Ni0.03S2 are ferromagnetically ordered below 153 K and 142 K with saturated moment 0.82 [Formula: see text] [Formula: see text]/Co and 0.80 [Formula: see text] [Formula: see text]/Co, respectively, while TlCo1.95Ni0.05S2 shows ferromagnetic transition at 132 K. The magnetism displays slightly itinerant character, as inferred from the Rhodes-Wohlfarth ratio. An unusual historical dependence of magnetization in TlCo1.95Ni0.05S2 is consistently observed by scanning both the temperature and magnetic field. The isothermal magnetic entropy change ([Formula: see text] S [Formula: see text]) of TlCo2S2 and TlCo1.95Ni0.05S2 are calculated by Maxwell relation and a temperature averaged entropy change is adopted to estimate the figure of merit for the compounds.
RESUMEN
Based on the effective spin-ladder model, we study the properties of quantum dissonance (Q) between two edge spins in chiral graphene nanoribbons (CGNRs) thermalized with a reservoir at temperature T, and discuss the influences of relative location between two edge spins, ribbon width, temperature, and on-site Coulomb repulsion (U) on Q. The results show that Q is widely present in Wannier edge states. For intra-edge coupled spin pairs, quantum entanglement (E) is zero, but there still exists considerable value of Q. Interestingly, Q always keeps a constant for entangled edge spin pairs. Considering the thermal effect, it shows that Q always decays with the increasing temperature T, and the decay rate is very sensitive to the intensity of U. Compared Q with E and total quantum correlation (quantum discord, denoted by D), we conjecture that the quantum correlations for a bipartite Wannier edge state in CGNRs satisfy the relation Q ⩽ D-E.
