Díaz-Núñez Pablo, Lanza Christian, Wang Ziwei, Kravets Vasyl G, Duan Jiahua, Álvarez-Cuervo José, Martín-Luengo Aitana Tarazaga, Grigorenko Alexander N, Yang Qian, Paarmann Alexander, Caldwell Joshua, Alonso-González Pablo, Mishchenko Artem
Department of Physics and Astronomy, University of Manchester, Manchester, UK.
National Graphene Institute, University of Manchester, Manchester, UK.
Sci Adv. 2025 Jul 18;11(29):eadw3452. doi: 10.1126/sciadv.adw3452.
Low-symmetry crystals have emerged as a platform for exploring unique light-matter interactions in the form of hyperbolic shear polaritons. These excitations exhibit unique properties such as frequency-dispersive optical axes and asymmetric light propagation and energy dissipation. However, only non-vdW materials have been demonstrated to support hyperbolic shear polaritons, limiting their exotic properties and potential applications. Here, we introduce shear phenomena in low symmetry crystals by demonstrating elliptical and canalized shear phonon polaritons in gypsum, an exfoliable monoclinic sulphate mineral. Our results unveil a topological transition from hyperbolic shear to elliptical shear polaritons, passing through a canalization regime with strong field confinement. We observe a notable slowdown of group velocity, reaching values as low as 0.0005. These findings expand the application scope of low-symmetry crystals with the benefits that an exfoliable material provides, such as stronger field confinement, tunability, and versatility for its incorporation in complex photonic devices.
低对称晶体已成为探索以双曲线剪切极化激元形式存在的独特光与物质相互作用的平台。这些激发表现出独特的性质，如频率色散光轴、不对称光传播和能量耗散。然而，只有非范德华材料已被证明能支持双曲线剪切极化激元，这限制了它们的奇异性质和潜在应用。在此，我们通过在石膏（一种可剥离的单斜晶系硫酸盐矿物）中展示椭圆和通道化剪切声子极化激元，引入了低对称晶体中的剪切现象。我们的结果揭示了从双曲线剪切到椭圆剪切极化激元的拓扑转变，该转变经过具有强场限制的通道化区域。我们观察到群速度显著减慢，低至0.0005。这些发现扩展了低对称晶体的应用范围，同时具备可剥离材料所提供的优势，如更强的场限制、可调性以及在复杂光子器件中应用的多功能性。
