First optical detection of magnetic resonance in a single molecule

magnetic resonance in a single molecule

When excited at high intensity, certain single molecules spend most of their time in their triplet manifold (this process is called optical pumping). The average dwell time in the triplet manifold is different for each of the three spin sublevels, which are split even in zero magnetic field by magnetic spin-spin interaction. An applied microwave can achieve paramagnetic resonance, i.e. change the average population of the sublevels, thereby changing the average fluorescence of the molecule. The magnetic resonance can then be detected optically (hence the acronym Optically Detected Magnetic Resonance, ODMR).

This experiment was performed for the first time in 1993 on a single pentacene molecule in a p-terphenyl crystal, independently by two collaborations: our group with W. E. Moerner (then at IBM) on one hand [1], and J. Wrachtrup and C. von Borczyskowski with the group of M. Orrit (then in Bordeaux) on the other hand [2]. This was the first measurement of the transitions of a single electronic spin. Their homogeneous width arises from hyperfine interactions with protons, providing information about local spin configurations. This work evolved towards the study of the lineshape as a function of the nuclear isotopes in each molecule [3], and of an applied magnetic field effects [4]. It led to the detection of a single nuclear spin (see next item). The magnetic resonance was also detected for a single terrylene molecule via the fluorescence correlation function, which is more sensitive than the average intensity [5].

  1. J. Köhler, J.A.J.M. Disselhorst, M.C.J.M. Donckers, E.J.J. Groenen, J. Schmidt, W.E. Moerner
    “Magnetic resonance of a single molecular spin”
    Nature 363 (1993) 242-244
  2. J. Wrachtrup, C. von Borczyskowski, J. Bernard, M. Orrit, R. Brown
    “Optical detection of magnetic resonance in a single molecule”
    Nature 363 (1993) 244-245
  3. A.C.J. Brouwer, J. Köhler, E.J.J. Groenen, J. Schmidt
    “13C isotope effects for pentacene in p-terphenyl. High resolution spectroscopy and single-spin detection”
    J. Chem. Phys. 105 (1996) 2212-2222
  4. J. Köhler, A.C.J. Brouwer, E.J.J. Groenen, J. Schmidt
    “On the intersystem crossing of pentacene in p-terphenyl”
    Chem. Phys. Lett. 250 (1996) 137-144
  5. A.C.J. Brouwer, E.J.J. Groenen, J. Schmidt
    “Detecting magnetic resonance through quantum jumps of single molecules”
    Phys. Rev. Lett. 80 (1998) 3944-3947

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