Since the discovery of magic-angle twisted bilayer graphene [1], research on moiré materials has rapidly expanded. Superconductivity in twisted bilayer transition metal dichalcogenides such as twisted WSe₂ has also been realized [2,3]. While extensive studies have been conducted on the mechanism of superconductivity in these systems, the determination of pairing symmetry remains an open question.

To address this issue, we propose to take advantage of surface acoustic waves (SAWs) [4]. SAWs are elastic waves that propagate along the surface of a material, inducing spatio-temporally periodic strain in the crystal lattice. The strain effect induced by SAWs is known to be incorporated into the Hamiltonian as a pseudo gauge field, giving rise to a response analogous to nonlinear optical response, namely the acoustogalvanic effect (AGE) [5]. While AGE has been studied in the normal state, in this study, we extend AGE to superconductors. Unlike optical responses, superconducting acoustogalvanic effect (SAGE) allows us to probe the quantum geometry of the Bogoliubov quasiparticles. Moreover, since the frequency range of SAW lies in the GHz regime, which is much lower than that of optical excitations, it enables the investigation of low-energy physics. Since this energy scale is comparable to the superconducting gap of low-transition-temperature superconductors, SAGE is expected to serve as a probe for observing the superconducting gap structures.

In this presentation, we demonstrate that SAGE can directly observe the quantum geometry of the Bogoliubov quasiparticles and access pairing symmetry and apply this approach to twisted WSe₂ [6].

[1] Y. Cao, et al., Nature 556, 43 (2018).
[2] Y. Xia, et al., Nature 637, 833 (2025).
[3] Y. Guo, et al., Nature 637, 839 (2025).
[4] X. Nie, et al., Nanoscale Horizons 8(2), 158 (2023).
[5] P. O. Shkhachov and H. Rostami, Phys. Rev. Lett. 124, 126602 (2020).
[6] T. Matsumoto, et al., arXiv: 2505.21436.