Quantum tunneling driven giant electric field gradients in plasmonic cavities
Phys. Rev. B 113, 235108 – Published 4 June, 2026
DOI: https://doi.org/10.1103/97tl-qn11
Abstract
Quantum tunneling suppresses extreme nanofocusing in plasmonic cavities while significantly enhancing the electric field gradient. This study employs a plasmonic cavity to drive multipolar Raman scattering of asymmetric thiobenzonitrile, directly observing this phenomenon via the quadrupole-to-dipole Raman intensity ratio. The quantum-corrected model shows that at the subnanometer gap, quantum tunneling simultaneously quenches the electric field enhancement (manifested as a decrease in dipole Raman intensity) and amplifies the electric field gradient effect (resulting in a continuous rise in quadrupole Raman intensity). Experimentally, the introduction of thiobenzonitrile molecules lowers the potential barrier height, enabling quantum tunneling to occur at a larger gap size. This leads to the quadrupole Raman intensity surpassing the dipole Raman intensity (with an enhancement exceeding three orders of magnitude). This work provides new strategies for molecular detection and spectroscopic selection rule manipulation in surface/tip-enhanced Raman spectroscopy and opens avenues for exploring quantum interactions within plasmonic cavities.
