Scanning tunneling spectroscopy

About: Scanning tunneling spectroscopy is a research topic. Over the lifetime, 7886 publications have been published within this topic receiving 213828 citations.

Scanning tunneling microscopy/spectroscopy of vortices in LiFeAs

Abstract: We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully gapped multiband superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasihexagonal vortex lattice at low field contains domain boundaries which consist of alternating vortices with unusual coordination numbers of 5 and 7. With increasing field, the domain boundaries become ill defined, resulting in a uniformly disordered vortex matter. Tunneling spectra taken at the vortex center are characterized by a sharp peak just below the Fermi energy, apparently violating particle-hole symmetry. The image of each vortex shows energy-dependent 4-fold anisotropy which may be associated with the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing temperature and becomes smaller than the coherence length estimated from the upper critical field. This is direct evidence of the Kramer-Pesch effect expected in a clean superconductor.

Stabilization mechanism of edge states in graphene

Abstract: It has been known that edge states of a graphite ribbon are zero-energy, localized eigen-states. We show that next nearest-neighbor hopping process decreases the energy of the edge states at zigzag edge with respect to the Fermi energy. The energy reduction of the edge states is calculated analytically by first-order perturbation theory and numerically. The resultant model is consistent with the peak of recent scanning tunneling spectroscopy measurements.

Single-crystal magnetotunnel junctions

Abstract: We have grownepitaxialsingle-crystal magnetotunnel junctions using Fe(001) substrates, MgO(001) spacers and Fe top electrodes. We have used scanning tunneling microscopy and atomic force microscopy to measure the tunneling characteristics as a function of position and demonstrated that local tunneling can be obtained such that the buried MgO can be characterized with nm resolution. Local I(V) curves revealed that most of the area had intrinsic tunneling properties corresponding to the proper MgO tunneling barrier. A small fraction of the scanned areas showed localized spikes in the tunneling current which are most likely caused by defects in the MgO.

Fowler-nordheim tunneling induced charge transfer plasmons between nearly touching nanoparticles

Abstract: Summary form only given. A plasmon resonant mode is the collective oscillation of free electrons in a structure stimulated by incident light. Reducing the gap between two metal nanoparticles down to atomic dimensions uncovers novel plasmon resonant modes. Of particular interest is a mode known as the charge transfer plasmon (CTP). This mode has been experimentally observed in touching nanoparticles, where charges can shuttle between the nanoparticles via a conductive path. However, the CTP mode for nearly touching nanoparticles has only been predicted theoretically to occur via direct tunneling when the gap is reduced to ~0.4 nm2. Because of challenges in fabricating and characterizing gaps at these dimensions, experiments have been unable to provide evidence for this plasmon mode that is supported by tunneling. In this work, we consider an alternative tunneling process, that is, the well-known Fowler-Nordheim (FN) tunneling that occurs at high electric fields, and apply it for the first time in the theoretical investigation of plasmon resonances between nearly touching nanoparticles. This new approach relaxes the requirements on gap dimensions, and intuitively suggests that with a sufficiently high-intensity irradiation, the CTP can be excited via FN tunneling for a range of subnanometer gaps. For instance, a plasmonic gap field of 1010 V/m (or an incident power of 3×1010 W/cm2) is needed when the gap length is 0.8 nm. The unique feature of FN tunneling induced CTP is the ability to turn on and off the charge transfer by varying the intensity of an external light source, and this could inspire the development of novel quantum devices, such as high speed switches and modulators.

Imaging the surface and the interface atoms of an oxide film on Ag111 by scanning tunneling microscopy: experiment and theory

Abstract: High-resolution images of the vacuum oxide surface atomic structure of Ag111-p(4x4)-O reveal large terraces of a perfect (4x4) reconstruction. Under certain conditions, the surface Ag atoms at the interface between the reconstructed oxide layer and the underlying Ag111 lattice are also imaged, providing the structural registry. Scanning tunneling microscopy simulations reveal a strong sensitivity to structure and comparison with the experimental images, therefore providing an atom-by-atom model for the entire metal-oxide-vacuum structure.