Displacive ion movements induced by localised surface plasmon resonance

The Jahn–Teller effect, a phase transition phenomenon involving spontaneous breakdown of symmetry in molecules and crystals, causes important physical and chemical changes that impact various fields of science, from the natural photosystem II to superconductors. In this study, we discovered that localised surface plasmon resonance (LSPR) induced the cooperative Jahn–Teller effect in covellite CuS nanocrystals (NCs), causing metastable displacive ion movements. Although light–matter interaction of plasmonic metal NCs has been widely investigated, the scope has been limited to collective mode stimulation. Electron diffraction measurements under photo illumination, ultrafast time-resolved electron diffraction analyses, and theoretical calculations of semiconductive plasmonic CuS NCs showed that metastable displacive ion movements due to the LSPR-induced cooperative Jahn–Teller effect caused a delay in the relaxation of LSPR in the microsecond region. Furthermore, the displacive ion movements caused photo-switching of conductivity in CuS NCs films used in room temperature ranges such as in transparent variable resistance infrared sensors. This study pushes the limits of plasmonics from the increase in tentative collective oscillation to metastable crystal structure manipulation, thereby expanding on Faraday's discovery.