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.

Klein paradox and resonant tunneling in a graphene superlattice

Abstract: This paper studies the transport properties of charge carriers through graphene superlattices consisting of monolayer or bilayer graphene on the basis of the transfer-matrix method. Emphasis is placed on the relationship between the Klein paradox and resonant tunneling in double-barrier junctions. It is shown that normal incidence transmission probabilities for two kinds of graphene structure exhibit different features. Independent of structure parameters, they are always perfectly transmitted in a monolayer graphene structure. In contrast, the transmission resonances occur in a bilayer graphene structure. However, the angularly averaged conductivities for both depend on the thickness and height of the barriers as well as the width and number of the well. That is to say, the angularly averaged conductivities in monolayer and bilayer graphene superlattices can be controlled by changing the structure parameters even if Klein tunneling exists.

Superconductivity at the Two-Dimensional Limit

Abstract: Superconductivity in the extreme two-dimensional limit is studied on ultrathin lead films down to two atomic layers, where only a single channel of quantum well states exists. Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers, where the transition temperature abruptly plunges to a lower value, depending sensitively on the exact atomic structure of the film. Our result shows that Cooper pairs can still form in the last two-dimensional channel of electron states, although their binding is strongly affected by the substrate.

Many-Body Effects in Angle-Resolved Photoemission: Quasiparticle Energy and Lifetime of a Mo(110) Surface State

Abstract: Recent investigations of strongly correlated electron systems have questioned the validity of one of the most fundamental paradigms in solid state physics— Fermi liquid theory. The latter picture is based on the existence of “quasiparticles,” or single-particle-like low energy excitations which obey the exclusion principle and have lifetimes long enough to be considered as particles. Strictly speaking, the quasiparticle concept is restricted to zero temperature and a narrow region around the Fermi level [1], but its usefulness often continues to finite temperatures, and energies away from the Fermi level [2]. Indications for possible non-Fermi-liquid behavior have been found in some organic one-dimensional conductors [3] and in the normal state of high temperature superconductors [4]. A whole variety of experimental techniques have been employed in the search for such behavior, including resistivity measurements [5], infrared spectroscopy [6], scanning tunneling spectroscopy [7], and time-resolved two-photon photoemission [8]. Angle-resolved photoemission spectroscopy (ARPES) has an advantage, in that the energy and lifetime of the photohole are directly observable in the experiment. ARPES in principle measures the quasiparticle spectral function [9]:

On-Surface Synthesis and Characterization of 9-Atom Wide Armchair Graphene Nanoribbons

Abstract: The bottom-up approach to synthesize graphene nanoribbons strives not only to introduce a band gap into the electronic structure of graphene but also to accurately tune its value by designing both the width and edge structure of the ribbons with atomic precision. We report the synthesis of an armchair graphene nanoribbon with a width of nine carbon atoms on Au(111) through surface-assisted aryl–aryl coupling and subsequent cyclodehydrogenation of a properly chosen molecular precursor. By combining high-resolution atomic force microscopy, scanning tunneling microscopy, and Raman spectroscopy, we demonstrate that the atomic structure of the fabricated ribbons is exactly as designed. Angle-resolved photoemission spectroscopy and Fourier-transformed scanning tunneling spectroscopy reveal an electronic band gap of 1.4 eV and effective masses of ≈0.1 me for both electrons and holes, constituting a substantial improvement over previous efforts toward the development of transistor applications. We use ab initio c...

High-resolution molecular orbital imaging using a p-wave STM tip.

Abstract: Individual pentacene and naphthalocyanine molecules adsorbed on a bilayer of NaCl grown on Cu(111) were investigated by means of scanning tunneling microscopy using CO-functionalized tips. The images of the frontier molecular orbitals show an increased lateral resolution compared with those of the bare tip and reflect the modulus squared of the lateral gradient of the wave functions. The contrast is explained by tunneling through the $p$-wave orbitals of the CO molecule. Comparison with calculations using a Tersoff-Hamann approach, including $s$- and $p$-wave tip states, demonstrates the significant contribution of $p$-wave tip states.