Microwave and terahertz spectroscopy in the scanning tunneling microscope captures dynamics of charges, spins and phonons
Sebastian Loth
University of Stuttgart, Institute for Functional Matter and Quantum Technologies
www.fastatoms.de
The low-energy dynamics of electrons and phonons shape the characteristics and functionality of materials. By combining scanning tunneling microscopy, STM, with ultrafast spectroscopy methods, it has become possible to resolve these dynamics even at atomic dimensions. Two promising methods that drastically boost the time resolution of STM are all-electronic excitation using arbitrary waveform generators and optical excitation by THz light.
We use all-electronic excitation to measure the GHz range stochastic [1] or coherent spin dynamics [2] of magnetic atoms on surfaces up to the speed of the intrinsic electron-spin scattering. This gives detailed insight into to the interaction of quantized spins with the electron bath of the substrate.
THz excitation features a bandwidth exceeding 1 THz, enabling spectroscopy with femtosecond time resolution [3]. We use this method to resolve coherent acoustic phonons on metallic surfaces [4] and collective charge excitations of charge-density waves on layered materials.
In this talk I will introduce recent advances of ultrafast STM-based experiments and discuss how they can be applied to measure the dynamics of fundamental processes in matter at their intrinsic time and length scale.
[1] M. Hänze, G. McMurtrie, S. Baumann, L. Malavolti, S. N. Coppersmith, S. Loth, Science Adv. 7 eabg2616 (2021).
[2] S. Baumann, W. Paul, T. Choi. C. P. Lutz, A. Ardavan, A. J. Heinrich, Science 350 417 (2015).
[3] T. L. Cocker, V. Jelic, M. Gupta, S. J. Molesky, J. A. J. Burgess, G. de Los Reyes, L. V. Titova, Y. Y. Tsui, M. R. Freeman, F. A. Hegmann, Nat. Photon. 7 620 (2013).
[4] S. Sheng, A.C. Oeter, M. Abdo, K. Lichtenberg, M. Hentschel, S. Loth, Phys. Rev. Lett. 129 043001 (2022).
image: S. Sheng, University of Stuttgart