Terahertz Vibrational Condensation in Out-of-Equilibrium Nanoscale Reverse Micelles

In situ terahertz absorption spectroscopy was conducted under microwave energy input at 2.45 GHz for nanoscale reverse micelles. We observed a spectral transition at ∼0.32 THz for interfacial water in the reverse micelle. That is, the spectral amplitude is remarkably enhanced, accompanied by spectral narrowing and a shift to lower frequencies above a certain microwave intensity compared to the spectrum in thermal equilibrium. This spectral narrowing reaches the experimental resolution of ∼5 GHz, indicating a coherent vibration lasting for at least ∼200 ps. These features agree with those derived from the terahertz vibrational condensation proposed by Fröhlich. Furthermore, it is considered that this condensation occurs in the heat flow resulting from an inhomogeneous temperature distribution in the sample solution induced by microwave irradiation. Therefore, our findings may have biological implications.