Piezoelectric microelectromechanical guided acoustic wave (GAW) sensors are widely used across a range of applications, from inertial sensing to environmental and chemical sensing. These devices typically rely on the resonance frequency of a Lamb mode as readout parameter, making them well suited for detecting parameters of interest (PoIs) that act over their entire vibrating structure. However, this approach is less effective for monitoring localized PoIs. To address this limitation, prior efforts have focused on miniaturizing GAW sensors. While this miniaturization strategy permits us to enhance responsivity to localized PoIs, it also causes a degradation of the limit of detection (LoD). In this paper, we present a GAW sensor for localized PoIs that overcomes the trade-off between responsivity and limit of detection by leveraging topological interface states (ISs). We demonstrate the effectiveness of our approach by sensing the infrared (IR) power emitted by a laser with a 5-$\text{μ}\mathrm{m}$-diameter beam size, focused on the interface at which the IS is transduced. Our results show that harnessing ISs yields significantly higher responsivity to IR power ($R=835\mathrm{Hz}/\text{μ}\mathrm{W}$) and a 2 orders of magnitude better limit of detection (${\mathrm{LoD}}_{\mathrm{tm}}=79\mathrm{fW}/\sqrt{\mathrm{Hz}}$) compared to conventional Lamb modes. Our findings pave the way for deploying GAW sensors in emerging applications that require monitoring localized parameters, such as proteomics, spintronics, mass spectroscopy, and more.

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• Fano resonance
• Piezoelectric devices
• Topological effects in acoustic systems
• Acoustic metamaterials
• Micromechanical devices
• Phononic crystals
• Solid-state detectors
• Topological materials