Phase coherence length and quantum interference patterns at step edges

Quasiparticle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid

Exploiting inversion symmetry breaking (ISB) in systems with strong spin-orbit coupling promises control of spin through electric fields-crucial to achieve miniaturization in spintronic devices. Delivering on this promise requires a two-dimensional electron gas with a spin precession length shorter than the spin coherence length and a large spin splitting so that spin manipulation can be achieved over length scales of nanometers. Recently, the transition metal oxide terminations of delafossite oxides were found to exhibit a large Rashba spin splitting dominated by ISB. In this limit, the Fermi surface exhibits the same spin texture as for weak ISB, but the orbital texture is completely different, raising questions about the effect on quasiparticle scattering. We demonstrate that the spin-orbital selection rules relevant for conventional Rashba system are obeyed as true spin selection rules in this correlated electron liquid and determine its spin coherence length from quasiparticle interference imaging.

Kondo-free mirages in elliptical quantum corrals

The quantum mirage effect is a fascinating phenomenon in fundamental physics. Landmark experiments on quantum mirages reveal atomic-scale transport of information with potential to remotely probe atoms or molecules with minimal perturbation. Previous experimental investigations are Kondo-effect based; the quantum mirages appear only near the Fermi energy. This strongly limits the exploration of the mechanism and potential application. Here we demonstrate a Kondo-free quantum mirage that operates in a wide energy range beyond Fermi energy. Together with an analytical model, our systematic investigations identify that the quantum mirage is the result of quantum interference of the onsite electronic states with those scattered by the adatom at the focus of elliptical quantum corrals, where two kinds of scattering paths are of critical importance. Moreover, we also demonstrate the manipulation of quantum mirages with pseudo basic logic operations, such as NOT, FANOUT and OR gates.

The quantum mirage effect is a fascinating phenomenon but in general the underlying mechanism is unclear. Here, by building elliptical quantum corrals of adatoms on a metal surface, the authors establish the mechanism of Kondo-free mirages and utilize it to build atomic-scale logic gates.

Probing Dirac fermion dynamics in topological insulator Bi2Se3 films with a scanning tunneling microscope

Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi2Se3 ultrathin films. At the two-dimensional limit, bulk electrons become quantized and the quantization can be controlled by the film thickness at a single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness dependence of the phase relaxation length lϕ and inelastic scattering lifetime τ of topological surface-state electrons. We find that τ exhibits a remarkable (E - EF)(-2) energy dependence and increases with film thickness. We show that the features revealed are typical for electron-electron scattering between surface and bulk states.

Recent ARPES experiments on quasi-1D bulk materials and artificial structures

The spectroscopy of quasi-one-dimensional (1D) systems has been a subject of strong interest since the first experimental observations of unusual line shapes in the early 1990s. Angle-resolved photoemission (ARPES) measurements performed with increasing accuracy have greatly broadened our knowledge of the properties of bulk 1D materials and, more recently, of artificial 1D structures. They have yielded a direct view of 1D bands, of open Fermi surfaces, and of characteristic instabilities. They have also provided unique microscopic evidence for the non-conventional, non-Fermi-liquid, behavior predicted by theory, and for strong and singular interactions. Here we briefly review some of the remarkable experimental results obtained in the last decade.

Role of elastic scattering in electron dynamics at ordered alkali overlayers on Cu(111)

Scanning tunneling spectroscopy of p(2 x 2) Cs and Na ordered overlayers on Cu(111) reveals similar line widths of quasi-two-dimensional quantum well states despite largely different binding energies. Detailed calculations show that 50% of the line widths are due to electron-phonon scattering while inelastic electron-electron scattering is negligible. The mechanism of enhanced elastic scattering due to Brillouin zone backfolding contributes the remaining width.

Lifetimes of stark-shifted image states

The inelastic lifetimes of electrons in image-potential states at Cu(100) that are Stark shifted by the electrostatic tip-sample interaction in the scanning tunneling microscope are calculated using the many-body GW approximation. The results demonstrate that in typical tunneling conditions the image state lifetimes are significantly reduced from their field-free values. The Stark shift to higher energies increases the number of inelastic scattering channels that are available for decay, with field-induced changes in the image state wave function increasing the efficiency of the inelastic scattering through greater overlap with final state wave functions.