Upgrade of a low-temperature scanning tunneling microscope for electron-spin resonance

Abstract

Electron spin resonance with a scanning tunneling microscope (ESR-STM) combines the high energy resolution of spin resonance spectroscopy with the atomic scale control and spatial resolution of STM. Here we describe the upgrade of a helium-3 STM with a 2D vector-field magnet ($B_z$ = 8.0 T, $B_x$ = 0.8 T) to an ESR-STM. The system is capable of delivering RF power to the tunnel junction at frequencies up to 30 GHz. We demonstrate magnetic field sweep ESR for the model system TiH/MgO/Ag(100) and find a magnetic moment of $(1.004\pm 0.001)$ ${\mu }_B$. Our upgrade enables to toggle between a DC mode, where the STM is operated with the regular control electronics, and an ultrafast-pulsed mode that uses an arbitrary waveform generator for pump-probe spectroscopy or reading of spin-states. Both modes allow for simultaneous radiofrequency excitation, which we add via a resistive pick-off tee to the bias voltage path. The RF cabling from room temperature to the 350 mK stage has an average attenuation of 18 dB between 5 and 25 GHz. The cable segment between the 350 mK stage and the STM tip presently attenuates an additional $34_{-3}^{+5}$ dB from 10 to 26 GHz and $38_{-2}^{+3}$ dB between 20 and 30 GHz. We discuss our transmission losses and indicate ways to reduce this attenuation. We finally demonstrate how to synchronize the arrival times of RF and DC pulses coming from different paths to the STM junction, a prerequisite for future pulsed ESR experiments.

arXiv comment7 figures

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• Electric Control of Spin Transitions at the Atomic Scale
• Single spin resonance driven by electric modulation of the g factor anisotropy
• Development of a Scanning Tunneling Microscope for Variable Temperature Electron Spin Resonance
• Combining Electron Spin Resonance Spectroscopy with Scanning Tunneling Microscopy at High Magnetic Fields
• Optimizing tip-surface interactions in ESR-STM experiments
• Waveform-sequencing for scanning tunneling microscopy based pump-probe spectroscopy and pulsed-ESR
• Frequency-independent voltage amplitude across a tunnel junction
• A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field
• Theory of Electron Spin Resonance Scanning Tunneling Microscopy: The First Decade