Electron Interference Phenomena Research Articles

Correlation Between Magnetic Ordering and Crossover from Weak Anti-Localization (WAL) to Weak Localization (WL) in Cobalt- and Manganese-Doped Bi0.94Sb0.06 Topological Insulator Nanoparticles

The discovery of magnetically doped topological insulators (TIs) provides a strong platform for investigating the correlation between long-range ferromagnetic/antiferromagnetic (FM/AFM) ordering and low temperature electron interference phenomena like weak anti-localization (WAL) or weak localization (WL). One such TI material Bi1−xSbx, which has recently been realised as a potential topological material for spintronics, has been studied in the present work. Influence of magnetic doping such as cobalt (Co) and manganese (Mn) in structural, morphological and magneto-transport properties on Bi0.94Sb0.06 nanoparticles has been investigated. The focus was on studying the correlation between magnetic ordering and WAL/WL. In undoped sample for temperatures up to 5K, field dependent magneto resistance (MR) shows a prominent WAL dip around zero field demonstrating the presence of surface states. In both the Co- and Mn-doped samples, the WAL feature is destroyed indicating the absence of time reversal symmetry (TRS) in the system on doping. Interestingly, in the case of 49% manganese (Mn) doping, a clear crossover from WAL to WL has been observed in the MR alongside magnetic ordering and is evident from magnetic force microscopy as well.

Fundamentally fastest optical processes at the surface of a topological insulator

We predict that a single oscillation of a strong optical pulse can significantly populate the surface conduction band of a three-dimensional topological insulator, Bi2Se3. Both linearly- and circularly-polarized pulses generate chiral textures of interference fringes of population in the surface Brillouin zone. These fringes constitute a self-referenced electron hologram carrying information on the topology of the surface Bloch bands, in particular, on the effect of the warping term of the low-energy Hamiltonian. These electron-interference phenomena are in a sharp contrast to graphene where there are no chiral textures for a linearly-polarized pulse and no interference fringes for circularly-polarized pulse. These predicted reciprocal space electron-population textures can be measured experimentally by time resolved angle resolved photoelectron spectroscopy (TR-ARPES) to gain direct access to non-Abelian Berry curvature at topological insulator surfaces.

The AB effect and its expanding applications

Electron interference phenomena are now easily observable with the advent of bright and yet coherent field-emission electron beams. The interaction of electron waves with electromagnetic fields is essentially described by the Aharonov–Bohm (AB) effect. However, the AB effect has long been disputed due to a feature that cannot be understood in terms of classical electrodynamics. This paper describes the experiments that confirmed its existence and discusses its expanding applications to the observation of electromagnetic fields in the microscopic region.

Electron Interference Effects on the Conductance of Doped Carbon Nanotubes

We investigate the effects of impurity scattering on the conductance of metallic carbon nanotubes as a function of the relative separation of the impurities. First, we compute the conductance of a clean (6,6) tube and the effect of model gold contacts on this conductance. Then, we compute the effect of introducing a single, two, and three oxygen atom impurities. We find that the conductance of a single-oxygen-doped (6,6) nanotube decreases by about 30% with respect to that of the perfect nanotube. The presence of a second doping atom induces strong changes of the conductance which, however, depend very strongly on the relative position of the two oxygen atoms. We observe regular oscillations of the conductance that repeat over an O−O distance that corresponds to an integral number of half Fermi wavelengths (mλF/2). These fluctuations reflect strong electron interference phenomena produced by electron scattering from the oxygen defects whose contribution to the resistance of the tube cannot be obtained by simply summing up their individual contributions.

Quantum wells and electron interference phenomena in Al due to subsurface noble gas bubbles.

Scanning tunneling microscopy on Ar ion bombarded and annealed aluminum surfaces shows electron interference between the surface and subsurface bubbles of implanted gas. The depth of the bubbles as determined from the energy dependence of the standing waves indicates a minimum around 6--7 layers on Al(111). The appearance and energy dependence of the interference pattern is in good agreement with scattering theory based on free electrons, and indicates the bubbles have a shape given by the Wulff construction.

Electron Localization and the Aharonov-Bohm Effect in Two-Dimensional Metal Systems

ABSTRACTDuring the last few years, it became clear that electron interference phenomena strongly modify the conductance of disordered systems. In thin metal films, this interference produces an anomalous low temperature magneto-resistance which enables to obtain detailed information about the inelastic, spin-orbit and magnetic scattering mechanisms. In a multiply-connected geometry, the interference leads to magnetoresistance oscillations. In long metal cylinders, only the oscillations which are not destroyed by impurity averaging, can be observed (flux period h/2e). In single loops, the original Aharonov-Bohm oscillations with flux period h/e are also present. A review will be presented of recent experimental results obtained for quasi two-dimensional plane films, cylinders, rings and arrays.

On the statistical aspect of electron interference phenomena

First Page

Recent developments in electron microscopy

The new high resolution electron microscopes have made possible the imaging of molecular lattices directly and of metal lattices by the moiré effects they give when superimposed. Dislocations can be observed both in such patterns and also in thin metal foils, in which their motion can be followed by electron cine-photography. In biology the trend is towards critical examination of the various stages in cutting thin sections - fixation, dehydration, embedding and sectioning - to control artefacts and to improve contrast. For this purpose the use of compounds of heavy elements as "electron stains" is being actively explored. Their value is illustrated by a study of the localization of nucleic acid in the cell nucleus and in sperm. Of two new departures in instrument design the first is the development of scanning electron microscopes: recording the scattered electrons shows the surface relief of solid specimens, recording the emitted characteristic X-rays shows the distribution of a particular element. In the second place, electron interference phenomena have been studied in some detail and the first tentative results obtained with a type of electron interference microscope, which would allow the measurement of inner potential as well as the thickness of very thin films.