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arXiv · 2511.03599

Negative Refraction of Terahertz Phonons via Interfacial Momentum Compensation

Hao Chen·Zhong-Ke Ding·Yuan Yao·Chang-Hao Ding·Nannan Luo·Jiang Zeng·Li-Ming Tang·Ke-Qiu Chen
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Abstract

Negative refraction provides a route to steer and focus wave energy flow, but it remains difficult to realize for coherent terahertz (THz) phonons. The difficulty stems from conventional dispersion-based mechanisms, which require strongly anisotropic or negative-curvature dispersions, while the long-wavelength acoustic phonons most favorable for coherent transport are nearly isotropic. Here we overcome this limitation by introducing a momentum compensation mechanism mediated by discrete translational symmetry. Discrete translational symmetry parallel to the interface supplies a compensating tangential momentum, reopening transmitted channels beyond the conventional critical condition and enabling negative refraction when this compensation reverses the tangential component. Mode-resolved calculations for hBN/graphene heterostructures establish this mechanism in laterally stitched in-plane interfaces and show how twisted van der Waals moire superlattices shift the negative-refraction window to lower frequencies. These results identify periodic crystalline interfaces as symmetry-engineered elements for THz phonon momentum conversion and wavefront control.

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Hao Chen, Zhong-Ke Ding, Yuan Yao, Chang-Hao Ding, Nannan Luo, Jiang Zeng, Li-Ming Tang, Ke-Qiu Chen. 2025-11-05. Negative Refraction of Terahertz Phonons via Interfacial Momentum Compensation. https://doi.org/10.1103/n9zv-9kc5

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