Terahertz time-domain spectroscopy of single-atom defects

As device features approach the atomic limit, next generation experimental techniques must characterize them on both their intrinsic length and time scales. The THz range of the electromagnetic spectrum hosts material excitations that are critical for nanotechnology, including the collective motion of charges, ions, and spins. These excitations are often studied with far-field terahertz time-domain spectroscopy, which directly measures the oscillating electric field of a terahertz pulse and relates it to key material processes through the light-matter interaction. Here we show how lightwave-driven microscopy can be used as a platform for atomic-scale terahertz time-domain spectroscopy. As a demonstration, we first apply our new technique to silicon-vacancy centers at the surface of GaAs and discover a single-atom resonator with features reminiscent of the technologically important DX center. Next, we investigate van der Waals materials with atomic-scale terahertz time-domain spectroscopy and demonstrate how atomic defects may be distinguished from the pristine surface by their characteristic vibrational fingerprint.