Magnetic sensing and control using single-atom spin resonance in an STM*

We combine the atomic resolution of a low-temperature scanning tunneling microscope (STM) with the high energy resolution of electron spin resonance (ESR), to employ individual atoms on a surface as local magnetic sensors [1]. The STM tip drives spin resonance by means of the large electric field available in the tunnel junction, and senses the spin by means of magnetoresistance, using a spin-polarized STM tip. Magnetic dipolar coupling between iron atoms placed a few nanometers apart on a thin MgO film yields a precise measure of the magnetic moment the iron atoms [2], which are then used to sense other atoms, such as the bistable magnetic bits formed by individual holmium atoms [3]. ESR of titanium and copper atoms [4, 5] reveals spin-1/2 behavior, in contrast to the high spin and large magnetic anisotropy of iron. Assembled arrays of spin-1/2 atoms show Heisenberg coupling that results in highly entangled magnetic states. ESR reveals hyperfine coupling [6] that allows electrically driven hyperpolarization of the nucleus [5]. Pulsed ESR allows coherent manipulation of atomic spins in order to observe Rabi oscillations and spin echoes [7]. Recent measurements using thicker insulating films suggest a route to longer coherence times. The combination of STM with ESR thus provides a versatile tool for exploring nano-scale quantum magnetism.

[1] Baumann et al., Science 350, 417 (2015).
[2] Choi et al., Nat. Nanotechnol. 12, 420 (2017).
[3] Natterer et al., Nature 543, 226 (2017).
[4] Yang et al., Phys. Rev. Lett. 119, 227206 (2017).
[5] Yang et al., Nat. Nanotechnol. 13, 1120 (2018).
[6] Willke et al., Science 362, 336 (2018).
[7] Yang et al., Science 366, 509 (2019).