The goal of this project is to resolve spin dynamics at nanometer length and picosecond time scales. The spin dynamics in single atoms crucially depends on details in the atomic-scale environment. Relaxation times range from the picosecond (ps) to the millisecond (ms) timescale. Our project is devoted to the study of ultrafast spin dynamics in single atoms and specifically designed nanostructures on a monolayer of molybdenum disulfide (MoS2) grown on Au(111). We will build these magnetic nanostructures with desired properties of magneticstability, anisotropy barriers, and magnetic coupling between the individual atoms. We will investigate the interaction of these magnetic structures with the spin-split electronic bands of MoS2. These investigations demand a new experimental set-up, which combines the atomic lateral resolution of a scanning tunneling microscope (STM) with ultrafast time resolution. To achieve this, our first step will be to couple a terahertz (THz) laser system to a low-temperature STM. The coupling of the electric field of the THz pulses into the STM junction will modify the tunneling barrier and, therefore, the measured dc tunneling current. Sub-picosecond time resolution will be achieved by driving the junction with two THz pulses having variable delay.
In a second step, we will use optical pump pulses for creating excited charge carriers in the MoS2 layer and probe their relaxation dynamics with THz pulses. We will explore the effect of magnetic adatoms and magnetic nanostructures on the trapping of charge carriers and change in relaxation properties. Using circularly polarized light, the optical pump-THz probe scheme also opens the perspective to investigate the creation of spinpolarized charge carriers.
Developing and employing the ultra-fast measurements and control of atomic-size objects, we expect to gain a fundamental understanding of the dynamics of spin states in single atoms coupled to a tailored environment.
Moiré structure of MoS2 on Au(111): Local structural and electronic properties
N. Krane, C. Lotze, and K. J. Franke
Surf. Sci. 678, 136 (2018) - DOI: 10.1016/j.susc.2018.03.015
High-resolution vibronic spectra of molecules on molybdenum disulfide allow for rotamer identification
N. Krane, C. Lotze, G. Reecht, L. Zhang, A. L. Briseno, and K. J. Franke
ACS Nano 12, 11698 (2018) - DOI: 10.1021/acsnano.8b07414