Topological Optical Achirality
For arbitrary reciprocal single-mode structures, regardless of their geometric shapes or constituent materials, there must exist incident directions of plane waves for which they are optically achiral.
physics.optics↗
arXiv subjects
Z. Qi
Publications and source records attributed to Z. Qi.
Triaxially strained suspended graphene for large-area pseudo-magnetic fields
Strain-engineered graphene has garnered much attention recently owing to the possibilities of creating substantial energy gaps enabled by pseudo-magnetic fields. While theoretical works proposed the possibility of creating large-area pseudo-magnetic fields by straining monolayer graphene along three crystallographic directions, clear experimental demonstration of such promising devices remains elusive. Herein, we experimentally demonstrate a triaxially strained suspended graphene structure that has the potential to possess large-scale and quasi-uniform pseudo-magnetic fields. Our structure employs uniquely designed metal electrodes that function both as stressors and metal contacts for current injection. Raman characterization and tight-binding simulations suggest the possibility of achieving pseudo-magnetic fields over a micrometer-scale area. Current-voltage measurements confirm an efficient current injection into graphene, showing the potential of our devices for a new class of optoelectronic applications. We also theoretically propose a photonic crystal-based laser structure that obtains strongly localized optical fields overlapping with the spatial area under uniform pseudo-magnetic fields, thus presenting a practical route towards the realization of graphene lasers.
cond-mat.mes-hall↗
Scaling of ac Susceptibility and Nonlinear Response in High-temperature Superconductors
The magnetic ac susceptibility of high-temperature superconductors is shown to obey some scaling relations.We try to ananlyse this behavior within the framework of a common nonlinear response function of mixed state.The derived equations for critical current and ac susceptibility (x(T)) agree with the scaling relations of experimental data.
cond-mat.supr-con↗
Resistive Transition Equation of Mixed State
We present a microscopic derivation of the resistive transition equation for mixed state of superconductors. This form fits the experimental data of MgB2 with parameters in agreement with the prediction of BCS superconductivity. It also fits the experimental data of high quality untwined YBCO single crystal but with parameters somewhat different from the BCS prediction. A discussion in connection with the problem of cuprate superconductivity is given.
cond-mat.supr-con↗
Peak Effect of Jc and Nonlinear E-J Characteristies of High-Tc Superconductors
The critical current density Jc in high-Tc superconductors (HTS) often shows a maximum at field far above the self-field. We study this peak effect(PE) with the nonlinear I-V response of type-II superconductors and find analytical equation of Jc in the dependence of filed and temperature. Theis equation is compared with some experimental data of R-Ba-Cu-O single crystals with fair agreement.
cond-mat.supr-con↗
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal nonlinear response function, we derive a nonliear equation in which the mixed state Hall resistivity can be expressed as an analytical function of magnetic field, temperature and applied current. This equation enables one to compare quantitatively the experimental data with theoretical model. We also find some new scaling relations of the temperature and field dependency of Hall resistivity. The comparison between our theoretical curves and experimental data shows a fair agreement.
cond-mat.supr-con↗