Single-Molecule Continuous-Wave Terahertz Rectification Spectroscopy and Microscopy

We report rectification spectroscopy (RS) for single molecules performed with continuous-wave terahertz (CW THz) radiation at the tunneling junction of a scanning tunneling microscope (STM) at 8 K. CW THz-RS serves as a new technique in single-molecule vibrational and magnetic excitation spectroscopy besides inelastic electron tunneling spectroscopy (IETS). By quantitatively studying IETS and THz RS, we show that CW THz induces a sinusoidal bias modulation with amplitude linearly dependent on the THz far-field amplitude. Such THz-induced bias modulation amplitude appears to be sensitive to the THz beam alignment but insensitive to variation in the tunneling gap far smaller than the THz wavelength.

Automated summary

We demonstrate rectification spectroscopy (RS) for single molecules using continuous-wave terahertz (CW THz) radiation at the tunneling junction of a scanning tunneling microscope (STM) at 8 K. CW THz-RS offers a new technique for studying single-molecule vibrational and magnetic excitation spectroscopy, alongside inelastic electron tunneling spectroscopy (IETS). By comparing IETS and THz RS, we find that CW THz induces a sinusoidal bias modulation with an amplitude that is linearly dependent on the THz far-field amplitude. This THz-induced bias modulation amplitude appears to be sensitive to the alignment of the THz beam but insensitive to changes in the tunneling gap smaller than the THz wavelength.