Sensing spin systems with Pico-Radian sensitivity

Abstract

Introduction The spin is a fundamental quantum property of matter. Spin states are coupled to the chemical environment and can be coherently manipulated using microwave radiation. Spectroscopic techniques such as electron spin resonance (ESR) and nuclear magnetic resonance have been used to obtain deep insights into spin systems [1,2]. However, conventional techniques typically sense the global response of spin systems and are therefore not suitable for obtaining local information about the specimen.

Objectives This work aims to develop spin-sensitive techniques for transmission electron microscopy (TEM) to study spin systems on the nanoscale.

Materials & methods The magnetic field B0 created at the pole piece of the TEM is utilized for polarizing the spins in the specimen. A custom-built TEM holder with an integrated microresonator allows for coherent manipulation of spin states by the supply of microwaves (excitation field B1), leading to a collective spin precession M in the specimen [3]. The electron probe, positioned in aloof-mode, interacts with the precessing spins, resulting in beam deflections. These deflections can be extracted by acquiring images in momentum space and subsequent image processing. The setup and the basic concept of the experiment is illustrated in Figure 1.

Results Extracting deflections from the modulated electron beam allows for obtaining signals that are similar to absorption and dispersion spectra observed in conventional ESR spectroscopy. The signals vary with the position of the electron probe relative to the specimen, showing the potential of the developed technique for collecting local information about the sample. Moreover, frequency and magnetic field sweeps confirm the expected Zeeman splitting of spin states. The concept is further optimized by incorporating different electron microscopy modes to enhance both sensitivity and spatial resolution.

Conclusion Our study proves the feasibility of performing ESR measurements within a TEM by analyzing spin induced modulations of the electron beam. The developed technique allows us to sense beam deflections with pico-radian sensitivity and can potentially lay the foundation for studying spin system with high sensitivity on the atomic scale.

References [1] Bienfait, A.; et al. Nat. Nanotechnol. 2016, 11, 253. [2] Callaghan, P. T. Principles of Nuclear Magnetic Resonance Microscopy; Clarendon Press: Oxford, 1993. [3] Jaroš, A.; et al. Electron spin resonance spectroscopy in a transmission electron microscope. arXiv Preprint arXiv:2408.16492 (2024).