Laser-driven scanning tunneling microscope

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Abstract
New modes of operation of a scanning tunneling microscope (STM) with laser radiation coupled into the tip of the tunneling junction are demonstrated. The dc current generated by rectifying the laser light and the difference-frequency signal produced in the STM by two laser beams are used to obtain atomic-resolution surface images of graphite, as well as to control the tip-sample distance. Such a laser-driven STM can generate surface images without external bias voltage and, when the difference-frequency signal is used for the distance control, even without any dc current between the tip and the sample. This mode of operation may also allow insulators to be studied.