Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 28: Poster Session - Scanning Probe techniques: Method Development
O 28.11: Poster
Monday, March 16, 2020, 18:15–20:00, P1A
Control of broadband THz near fields in an STM junction — •Natalia Martín Sabanés1,2, Sarojini Mahajan1, Martin Wolf1, and Melanie Müller1 — 1Fritz Haber Institute, Berlin, Germany — 2Freie Universität Berlin, Berlin, Germany
In THz-gated Scanning Tunneling Microscopy (THz-STM),[1] the electric field of a single-cycle THz pulse acts as a transient bias modulating the STM-junction, enabling control of the tunneling current on femtosecond time scales. Optimal operation of a THz-STM requires exact knowledge and precise control of the THz near field waveform. In this regard, we demonstrate THz near field sampling via THz-induced modulation of ultrafast photocurrents in a metal-metal junction,[2] and characterize in detail the coupling of broadband (1-30 THz) single-cycle THz pulses generated from a spintronic emitter to the STM tip. Specifically, we show that employing NIR laser pulses with a curved wavefront for THz generation allows for precise control of the phase, amplitude and bandwidth of the THz near field. Depending on the excitation conditions, THz near fields with frequencies up to 10 THz and peak voltages of several volts (up to 4 V) can be achieved at 1 MHz repetition rate. We further discuss the influence of non-instantaneous effects such as THz-streaking, space charge dynamics and hot carriers in the metals on the bandwidth and shape of the measured near field waveforms, and define operation regimes for reliable near field characterization. References: [1] Cocker T., el at, Nature 539, 263-267 (2016); [2] Yoshida S., et al, ACS Phot. 6, 1356-1364 (2019)