AI 中文总结
研究在石墨烯/$α$-MoO$_3$/SiC异质结构中实现电可调谐非互易声子-等离子体极化激元，利用石墨烯直流电流诱导波矢依赖多普勒频移打破互易性，实现等频轮廓转变，展现动量依赖非互易性，确立该结构为中红外非互易纳米光子学平台。
AI 中文摘要
实现光学隔离需要打破向前和向后传播光之间的对称性，这在无磁场的纳米尺度上是一个长期挑战。本文从理论上证明了在中红外波段工作的石墨烯/$α$-MoO$_3$/SiC异质结构中存在电可调谐的非互易声子-等离子体极化激元。石墨烯中的直流电流会引起波矢依赖的多普勒频移，从而打破互易性并在混合等离子体-声子传播中产生强烈的方向不对称性。在互易区域，石墨烯等离子体与$α$-MoO$_3$中的双曲声子极化激元之间的杂化，在SiC衬底的进一步作用下，实现了等频轮廓的栅极控制转变。当漂移速度为费米速度的5%时，系统表现出明显的动量依赖非互易性，对比度达到约0.3，而与漂移方向正交的方向由于对称性约束不受影响。实空间计算证实，这种动量空间不对称性转化为方向近场强度调制。这些结果将电流偏置的范德华异质结构确立为中红外波段电可调谐、无磁非互易纳米光子学的平台。
英文摘要
Achieving optical isolation requires breaking symmetry between forward- and backward-propagating light, a long-standing challenge at the nanoscale in the absence of magnetic fields. Here we theoretically demonstrate electrically tunable nonreciprocal phonon-plasmon polaritons in a graphene/$α$-MoO$_3$/SiC heterostructure operating in the mid-infrared. A dc current in graphene induces a wavevector-dependent Doppler shift that breaks reciprocity and generates strong directional asymmetry in hybrid plasmon-phonon propagation. In the reciprocal regime, hybridization between graphene plasmons and hyperbolic phonon polaritons in $α$-MoO$_3$, further shaped by the SiC substrate, enables gate-controlled transitions of isofrequency contours, including canalization along orthogonal crystal axes. At drift velocities of 5% of the Fermi velocity, the system exhibits pronounced momentum-dependent nonreciprocity with contrast reaching $\sim$ 0.3, while directions orthogonal to the drift remain unaffected due to symmetry imposed constraints. Real-space calculations confirm that this momentum-space asymmetry translates into directional near-field intensity modulation. These results establish current-biased van der Waals heterostructures as a platform for electrically tunable, magnet-free nonreciprocal nanophotonics in the mid-infrared.
Comments10 pages, 4 figures
