Ungdon Ham

University of California, Irvine, Irvine, California, United States

Are you Ungdon Ham?

Claim your profile

Publications (4)13.42 Total impact

  • Ungdon Ham · W Ho
    [Show abstract] [Hide abstract]
    ABSTRACT: Control of magnetism at the nanoscale is shown by a reversible transfer of an electron to and from a single molecule within the tunable gap of a scanning tunneling microscope. The addition of an electron to magnesium porphine changes the molecule from the diamagnetic state to the paramagnetic state. The existence of the single unpaired electron in the molecule is confirmed by spectroscopy and spatial imaging of the many body Kondo state and inelastic spin excitation between the Zeeman levels at 600 mK and up to 9 Tesla magnetic field. Here, we show that the spin is delocalized in an extended molecular orbital, in contrast to the spatially confined d and f states in atoms and magnetic centers in molecules. Furthermore, by tuning the dimension of the tunneling gap and visualizing the spectroscopic images, the inelastic spin-flip scatterings are shown to underlie the formation of the Kondo state.
    No preview · Article · Feb 2013 · The Journal of Chemical Physics
  • Ungdon Ham · W Ho
    [Show abstract] [Hide abstract]
    ABSTRACT: Spin splitting of individual vibronic states was observed in a single molecule where all the electrons are paired, as well as a molecule with one extra electron injected. This observation was made possible by the use of a scanning tunneling microscope capable of reaching $$\sim${}800\text{ }\text{ }\mathrm{mK}$ in a magnetic field up to 9 T and the sharpness of the vibronic states, $$\sim${}1\text{ }\text{ }\mathrm{meV}$. These conditions also led to the resolution of spectral diffusion caused by minute fluctuations at the probing location of the molecule.
    No preview · Article · Mar 2012 · Physical Review Letters
  • Q Huan · Y Jiang · Y Y Zhang · U Ham · W Ho
    [Show abstract] [Hide abstract]
    ABSTRACT: Selective excitations of specific vibronic modes in position space are realized in single naphthalocyanine molecules adsorbed on an ultrathin alumina film by a scanning tunneling microscope at low temperature. Distinct spatial distributions are imaged for the different vibronic modes, which are in accordance with spectra recorded over different points of the molecule and its orbital structure. These distinct vibronic images, together with the differential conductance images and calculated molecular orbitals, lead to vibrational excitations that are associated with the doubly degenerate lowest unoccupied molecular orbitals (LUMO)--LUMO-α and LUMO-β. These results reveal the presence of different molecular conformations on the surface and the nature of the electron-vibrational coupling.
    No preview · Article · Jul 2011 · The Journal of Chemical Physics
  • Ungdon Ham · Wilson Ho
    [Show abstract] [Hide abstract]
    ABSTRACT: An unpaired spin from a single electron trapped in a molecular orbital in a double barrier scanning tunneling microscope (STM) junction at sub-Kelvin temperature and high magnetic field showed a non-equilibrium transport through a Kondo impurity. Hysteresis and switching in a conductance allows the spin and charge state of the molecule in the junction to be controlled. Mechanically tuning the coupling of the single spin to STM tip showed a gradual change from lowest order spin-flip inelastic tunneling spectroscopy (IETS) to the Kondo resonance. Using the imaging capability of STM, we observed clear sub-molecular node structures of the spin-flip IETS and the Kondo resonance.
    No preview · Article · Mar 2011

Publication Stats

24 Citations
13.42 Total Impact Points


  • 2011-2013
    • University of California, Irvine
      • • Department of Physics and Astronomy
      • • Department of Chemistry
      Irvine, California, United States