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TIME-RESOLVED STM: STM in the constant current mode provides black and white contour plots of the surface while the addition of spectroscopic information provides an equivalent of color. Our objective is to turn the STM into a high speed camera and provide information about dynamic electronic processes on surfaces. Magnetization dynamics occur through thermal activation, spin tunneling and spin precession 1,2,3. The characteristic time scales range from eternity (stable magnetization) down to a few hundred picoseconds. Access to such fast behaviour with the STM migth appears hopeless when the intrinsic STM dynamic bandwidth is limited to a few tens of kHz due to the high gain of the tunneling current amplifier. Nevertheless, Freeman et. al. from the University of Alberta have developed an experimental scheme based on a pump-probe approach and demonstrated a stunning 25 ps time resolution in the junction mixing mode 4 . They were using a room temperature air STM, photo-gated pulse generators and micron sized samples made by lithography. While the time resolution was remarkable, they failed to impress the community by lack of atomic resolution, the real benchmark of STM. We are currently improving the technique on a home-built STM with atomically clean graphite samples and fully tunable high speed pulse generators. Preliminary results open the doors to dynamic spectroscopy and are highly promising for future adaptation of monitoring the dynamics of single molecular magnets. |
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[1]Will Spin-Relaxation Times in Molecular Magnets Permit Quantum Information Processing?. [2]Non-equilibrium magnetization dynamics in the Fe8 single-molecule magnet induced by high-intensity microwave radiation. [3]Quantum oscillations in a molecular magnet. [4]Ultrafast time resolution in scanning tunneling microscopy. |
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