Scanning Tunneling Microscopy Observation of Phonon Condensate.

Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance.

Imaging the electron-phonon interaction at the atomic scale.

Thin Pb films epitaxially grown on 7×7 reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that λ increases when the electron scattering at the Pb/Si(111) interface is diffuse and decreases when the electron scattering is specular.

Vacuum phonon tunneling.

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

Magic-sized diamond nanocrystals.

The 2D structural transformation of a heavily boron-doped diamond surface has been revealed using scanning tunneling microscopy (STM). We found that at boron densities above the metal-insulator transition the diamond surface is comprised of spatially ordered magic-sized nanocrystals. The development of quantized electron gas inside these nanocrystals is directly confirmed by STM observation of standing electron waves.

Anisotropic charge ordering on the gallium surface.

Low-temperature scanning tunneling microscopy of atomically flat Ga(001) islands revealed the 2D electronic superlattice composed of stripe domains. Tunnel spectroscopy of these surface electrons indicates the formation of a 2D charge-ordered state of Wigner-crystal type driven by competition of short-range and long-range Coulomb energies. At the boundaries of stripe domains the energy spectra exhibit splitting due to charged excitonic states and shift due to charge doping, altogether indicating the self-assembly of 1D hole stripes.