Higher-order exceptional points (EPs), which appear as multifold degeneracies in the spectra of non-Hermitian systems, are garnering extensive attention in various multidisciplinary fields. However, constructing higher-order EPs still remains a challenge due to the strict requirement of the system symmetries. Here we demonstrate that higher-order EPs can be judiciously fabricated in parity–time (PT)-symmetric staggered rhombic lattices by introducing not only on-site gain/loss but also non-Hermitian couplings. Zero-energy flatbands persist and symmetry-protected third-order EPs (EP3s) arise in these systems owing to the non-Hermitian chiral/sublattice symmetry, but distinct phase transitions and propagation dynamics occur. Specifically, the EP3 arises at the Brillouin zone (BZ) boundary in the presence of on-site gain/loss. The single-site excitations display an exponential power increase in the PT-broken phase. Meanwhile, a nearly flatband sustains when a small lattice perturbation is applied. For the lattices with non-Hermitian couplings, however, the EP3 appears at the BZ center. Quite remarkably, our analysis unveils a dynamical delocalization-localization transition for the excitation of the dispersive bands and a quartic power increase beyond the EP3. Our scheme provides a new platform toward the investigation of the higher-order EPs and can be further extended to the study of topological phase transitions or nonlinear processes associated with higher-order EPs.

An internal photoemission-based silicon photodetector detects light below the silicon bandgap at room temperature and can exhibit spectrally broad behavior, making it potentially suited to meet the need for a near-infrared pure Si photodetector. In this work, the implementation of a thin Au insertion layer into an ITO/n-Si Schottky photodetector can profoundly affect the barrier height and significantly improve the device performance. By fabricating a nanoscale thin Au layer and an ITO electrode on a silicon substrate, we achieve a well-behaved ITO/Au/n-Si Schottky diode with a record dark current density of 3.7×10-7A/cm2 at -1V and a high rectification ratio of 1.5×108 at ±1V. Furthermore, the responsivity has been obviously improved without sacrificing the dark current performance of the device by decreasing the Au thickness. Such a silicon-based photodetector with an enhanced performance could be a promising strategy for the realization of a monolithic integrated pure silicon photodetector in optical communication.