9 research outputs found
Gate-tunable negative differential conductance in hybrid semiconductor-superconductor devices
Negative differential conductance (NDC) manifests as a significant
characteristic of various underlying physics and transport processes in hybrid
superconducting devices. In this work, we report the observation of
gate-tunable NDC outside the superconducting energy gap on two types of hybrid
semiconductor-superconductor devices, i.e., normal metal-superconducting
nanowire-normal metal and normal metal-superconducting nanowire-superconductor
devices. Specifically, we study the dependence of the NDCs on back-gate voltage
and magnetic field. When the back-gate voltage decreases, these NDCs weaken and
evolve into positive differential conductance dips; and meanwhile they move
away from the superconducting gap towards high bias voltage, and disappear
eventually. In addition, with the increase of magnetic field, the NDCs/dips
follow the evolution of the superconducting gap, and disappear when the gap
closes. We interpret these observations and reach a good agreement by combining
the Blonder-Tinkham-Klapwijk (BTK) model and the critical supercurrent effect
in the nanowire, which we call the BTK-supercurrent model. Our results provide
an in-depth understanding of the tunneling transport in hybrid
semiconductor-superconductor devices.Comment: 15+6 pages, 4+6 figure
Inverse design for material anisotropy and its application for a compact X-cut TFLN on-chip wavelength demultiplexer
Inverse design focuses on identifying photonic structures to optimize the performance of photonic devices. Conventional scalar-based inverse design approaches are insufficient to design photonic devices of anisotropic materials such as lithium niobate (LN). To the best of our knowledge, this work proposes for the first time the inverse design method for anisotropic materials to optimize the structure of anisotropic-material based photonics devices. Specifically, the orientation dependent properties of anisotropic materials are included in the adjoint method, which provides a more precise prediction of light propagation within such materials. The proposed method is used to design ultra-compact wavelength division demultiplexers in the X-cut thin-film lithium niobate (TFLN) platform. By benchmarking the device performances of our method with those of classical scalar-based inverse design, we demonstrate that this method properly addresses the critical issue of material anisotropy in the X-cut TFLN platform. This proposed method fills the gap of inverse design of anisotropic materials based photonic devices, which finds prominent applications in TFLN platforms and other anisotropic-material based photonic integration platforms