Bloch surface waves mediated enhancement of nonreciprocal thermal radiation for mid-infrared atmospheric windows

Realizing a tunable nonreciprocal thermal emitter (NTE) with strong magnitude in mid-infrared (mid-IR) atmospheric window is a fundamental yet challenging task, particularly overcoming the limitations of external magnetic fields. Here, we present a hybrid thermal emitter design that integrates a Weyl semimetal (WSM) layer with a dielectric multilayer stack engineered to support Bloch surface waves (BSWs). The excitation of BSW modes at the interface leads to enhanced electromagnetic field confinement, significantly increasing absorption within the WSM layer and enabling nonreciprocal thermal emission. By optimizing the geometric parameters, a nonreciprocity ratio exceeding 0.95 can be maintained over a wide range, such as the WSM thickness (t= 0.1–0.5μm) and incident angle (θ= 50°–90°), indicating near-complete suppression of thermal emission in one direction relative to the opposite. To introduce dynamic tunability, a thermally responsive vanadium dioxide (VO2) layer is incorporated, allowing active modulation of the emission profile via its insulator-to-metal phase transition. Importantly, the nonreciprocity changes sign with negative under TM at 11.39μm and positive after the phase change. Our strategy represents a novel approach to directional thermal radiation, merging the advanced control capabilities of BSWs with nonreciprocal properties achieved through WSM. This combination paves the way for enhancing the potential in thermal management system and energy-harvesting technology.