Unconventional refraction and broadband Klein tunneling in T-graphene-like lattice photonic crystals
Phys. Rev. A 114, 023511 – Published 17 August, 2026
DOI: https://doi.org/10.1103/v57h-vwyw
Abstract
Klein tunneling, a counterintuitive phenomenon where relativistic particles transmit through potential barriers with near-unity probability, has sparked extensive attention. In this work we demonstrate the anomalous Klein tunneling in the classical system of photonics in a T-graphene-like photonic crystal (TGPC), which is enabled by the triple-degenerate point (TDP) formed by a pair of Dirac-like linear branches and an additional quadratic branch in the TGPC. Unlike conventional Klein tunneling in Dirac system, the TGPC heterojunction not only exhibits broadband near-unity transmission, but also presents a robust and sharp dip at the TDP. Our theoretical model based on the multiple scattering theory accounts well for the phenomenon. In addition, TGPC exhibits unconventional refraction characteristics, which simultaneously shows positive and negative refraction at the interface with air. These findings enable alternative applications in tunable filtering and tailored optical waveguides and bridging quantum-inspired physics with photonic engineering.
