NCAFM2023 Programme Booklet

Friday 1200-1220

SINGLE-MOLECULE ELECTRON-SPIN RESONANCE WITH ATOMIC FORCE MICROSCOPY

Lisanne Sellies* , Raffael Spachtholz, Sonja Bleher, Philipp Scheuerer, Jascha Repp*

Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany *Email: lisanne.sellies@ur.de; jascha.repp@ur.de

Recently, we combined the high energy resolution of electron spin resonance (ESR) with the spatial resolution offered by atomic force microscopy (AFM). Our ESR-AFM technique relies on driving electron spin transitions between the non-equilibrium triplet state levels of a single molecule. First, the molecule is brought to its triplet excited state, after which the decay of this state is read-out, using a recently developed electronic pump-probe scheme [1]. Since the three non-degenerate triplet states have typically different lifetimes, the lifetime can be used as a measure for driving resonant transitions between two of these states [2,3]. Therefore, we employ the setup illustrated in Fig. 1A [4]. Individual molecules (here pentacene) are adsorbed on a thick NaCl film deposited on an Au(111) microstrip. This setup allows the application of both voltage pulses (to initialize and read-out the triplet state) as well as an RF magnetic field (to drive ESR transitions). Fig. 1B shows an ESR-AFM signal of pentacene measured with this setup. Upon resonantly driving the transition between two of the triplet states, the triplet lifetime reduces and consequently the measured triplet population after a fixed delay time. The ESR-AFM spectra have a sub-nanoelectronvolt energy resolution. Thereby, molecules only differing in their isotopic configuration can be distinguished. Moreover, due to the minimally invasive nature of the ESR-AFM technique, the electron spins of pentacene can be coherently manipulated over tens of microseconds, likely not limited by the detection method but by the molecular properties [4]. After introducing ESR-AFM, recent results obtained by this technique will be presented.

Fig. 1: A Schematic of the setup, by which we probe the ESR-AFM signal of an individual pentacene molecule. B ESR-AFM spectrum of the T X -T Z transitions of pentacene. A normalized AFM signal was measured (Δf norm ), which can be calibrated against the triplet population. Figure adapted from [4]. References [1] J. Peng, S. Sokolov, D. Hernangómez-Pérez, F. Evers, L. Gross, J. M. Lupton, J. Repp, Science, 2021, 373 , 452. [2] J. Köhler, J. A. Disselhorst, M.C. J. M. Donckers, E. J. Groenen, J. Schmidth, W. E. Moerner, Nature, 1993, 363 , 242. [3] J. Wrachtrup, C. Von Borczyskowski, J. Bernard, M. Orrit, R. Brown, Nature, 1993, 363 , 244. [4] L. Sellies, R. Spachtholz, P. Scheuerer, J. Repp, arXiv, 2022, arXiv:2212.12244.

93