Individual low-energy E1 toroidal and compression states in light nuclei: deformation effect, spectroscopy and interpretation

The existence of individual low-energy E1 toroidal and compression states (TS and CS) in 24Mg was predicted recently in the framework of quasiparticle random phase approximation (QRPA) model with Skyrme forces. It was shown that the strong axial deformation of 24Mg is crucial to downshift the toroidal strength to the low-energy region and thus make the TS the lowest E1(K=1) dipole state. In this study, we explain this result by simple mean-field arguments. Comparing TS in two strongly axial nuclei, 24Mg and 20Ne, we show that the lowest TS is not a universal phenomenon but rather a peculiarity of 24Mg. The spectroscopy of TS and CS is analyzed and some additional interpretation of these states is suggested.

Resonant conversion based on GaAs-metal metamaterials within terahertz range

In this paper, by utilizing the variable conductivity with photo-injection in gallium arsenide (GaAs), we have designed an asymmetrical planar terahertz (THz) metamaterial, which is connected with two single-gap split ring resonator (SRR) by GaAs strip and demonstrated the resonant conversion of SRR within the THz range under appropriate optical pumping. As central trailing arm of the structure, GaAs is skillfully inserted between the two cross arms of the THz metamaterial and plays a key role in resonant conversion. Through modulation of its conductivity (σ GaAs ), the variable conductivity of GaAs can make one dual-gap SRR into two connective single-gap SRRs in physical structure, at the same time, the state conversion of two different resonances in the THz metamaterial has been achieved. The simulation results show that the resonant states of THz metamaterial can be switched from one LC and one dipole (state 1) to two LC and one new dipole (state 2) through the intermediate state with the increasing σ GaAs . This structural design provides a new example to apply variable conductivity to achieve state conversion of resonance and can be extended to the additional application in THz devices.