Intramolecular vibronic dynamics in molecular solids: C60

Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.

Tuning fulleride electronic structure and molecular ordering via variable layer index

C60 fullerides are uniquely flexible molecular materials that exhibit a rich variety of behavior, including superconductivity and magnetism in bulk compounds, novel electronic and orientational phases in thin films, and quantum transport in a single-C60 transistor. The complexity of fulleride properties stems from the existence of many competing interactions, such as electron-electron correlations, electron-vibration coupling, and intermolecular hopping. The exact role of each interaction is controversial due to the difficulty of experimentally isolating the effects of a single interaction in the intricate fulleride materials. Here we report a unique level of control of the material properties of KxC60 ultra-thin films through well-controlled atomic layer indexing and accurate doping concentrations. Using STM techniques, we observe a series of electronic and structural phase transitions as the fullerides evolve from two-dimensional monolayers to quasi-threedimensional multilayers in the early stages of layer-by-layer growth. These results demonstrate the systematic evolution of fulleride electronic structure and molecular ordering with variable KxC60 film layer index, and shed new light on creating novel molecular structures and devices.Comment: 16 pages, 4 figures, to appear in Nature Material

Metastable surface phase for NaxC60

NaxC60 thin films with Na concentration

Polarization-dependent angular photoelectron distribution of solid C-60

We present angle- and polarization-dependent photoelectron spectra of solid C-60 recorded over a large range of emission angles. The bands derived from the three highest molecular orbitals are very similar in their angular distribution and show a strong dependence on both light polarization direction and sample orientation. We show that a molecular emission pattern modified by solid-state effects accounts for the observations

Magnetic instability in YBa Cu O \B "lms

Abstract Using a magneto-optic technique we have investigated the magnetic #ux propagation into and out of superconducting thin YBa Cu O \B "lms. After "eld cooling below ¹ , the external magnetic "eld B perpendicular to the "lm is changed which gives rise to shielding currents in the sample. The current distribution is disturbed momentarily by heating with a focused laser pulse near the sample edge. This triggers a magnetic instability, in which a magnetic #ux avalanche starts to propagate