Nonreciprocal Metasurfaces through Biasing with Circularly Polarized Waves
Spatiotemporal modulation (STM) has emerged as a promising paradigm for the development of magnetless nonreciprocal devices, but it poses significant practical challenges when sought to be implemented over structures with a large number of modulated components, such as metasurfaces. Here it is shown that this problem may be overcome in metasurfaces biased with circular-polarized waves. In particular, it is shown that this type of biasing can create modulation equivalent to angular-momentum modulation, without any complicated modulation network. Different forms of CP modulation are discussed and shown how they can lead to different nonreciprocal functionalities, including Faraday rotation, nonreciprocal amplification and isolation.
We study in this paper the properties of a two-body random matrix ensemble for distinguishable spins. We require the ensemble to be invariant under the group of local transformations and analyze a parametrization in terms of the group parameters and the remaining parameters associated with the 'entangling' part of the interaction. We then specialize to a spin chain with nearest-neighbour interactions and numerically find a new type of quantum-phase transition related to the strength of a random external field, i.e. the time-reversal-breaking one-body interaction term.