Terahertz light can induce femtosecond force pulses on surfaces when it is focused onto the tip of a scanning tunneling microscope. The force pulses act as a “nano hammer” that launches coherent acoustic phonon wave packets into the material.
Typically, ultrafast lasers are used to excite acoustic phonons in materials by rapid heating of micrometer-sized areas. By contrast, the terahertz-induced phonon excitation uses the Coulomb interaction between tip and material surface. It doesn’t require heating and can be localized to a few nanometers.
Buried interfaces and defects reflect the phonon wave packets, creating a detectable beating of the surface. This enables depth-sensitive phonon nanoscopy akin to sonar on the nanometer scale and highlights the possibility of coherent control of acoustic phonons at the atomic scale.
- Shaoxiang Sheng1
- Anne-Catherine Oeter1
- Mohamad Abdo1,2
- Kurt Lichtenberg1
- Mario Hentschel3
- Sebastian Loth1,2
- 1University of Stuttgart, Institute for Functional Matter and Quantum Technologies, 70569 Stuttgart, Germany
- 2Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
- 3University of Stuttgart, 4th Physics Institute and Research Center SCoPE, 70569 Stuttgart, Germany