Propagation properties of electromagnetic waves in an optical medium are mainly determined by the contour of equal-frequency states in \({\boldsymbol{k}}\)-space. In photonic Weyl media, the topological surface waves lead to a unique open arc of the equal-frequency contour, called the Fermi arc. However, for most realistic Weyl systems, the shape of Fermi arcs is fixed due to the constant impedance of the surrounding medium, making it difficult to manipulate the surface wave. Here we demonstrate that by adjusting the thickness of the air layer sandwiched between two photonic Weyl media, the shape of the Fermi arc can be continuously changed from convex to concave. Moreover, we show that the concave Fermi-arc waves can be used to achieve topologically protected electromagnetic pulling forces over a broad range of angles in the air layer. Our finding offers a generally applicable strategy to shape the Fermi arc in photonic Weyl media.

电磁波在光学介质中的传播特性主要由\({\boldsymbol{k}}\)空间中等频态的轮廓决定。在光子外尔介质中，拓扑表面波导致等频轮廓的独特开放弧，称为费米弧。然而，对于大多数现实的Weyl系统，由于周围介质的阻抗恒定，费米弧的形状是固定的，这使得表面波难以操纵。在这里，我们证明，通过调整夹在两个光子外尔介质之间的空气层的厚度，费米弧的形状可以连续地从凸面变为凹面。此外，我们还表明，凹费米弧波可用于在空气层中的大角度范围内实现拓扑保护的电磁拉力。我们的发现提供了一种普遍适用的策略来塑造光子外尔介质中的费米弧。