Twisted Electron Research Articles

Laser-assisted (e,2e) study with twisted electron beam on H-atom

We study the laser-assisted twisted electron beam impact ionization of the hydrogen atom in coplanar asymmetric geometry. We develop the theoretical model in the first Born approximation. In the presence of the laser field, we treat the incident and scattered electrons as Volkov waves; the ejected electron, moving in the combined field of the laser and residual ion H+ , as a Coulomb–Volkov wave function. In this communication, we compare the angular profile of triple differential cross-section (TDCS) for laser-assisted twisted electron beam incidence with the plane-wave, laser-assisted plane wave, and field-free twisted electron beam for (e,2e) processes for different orbital angular momentum (OAM) number (ml ) values. We analyze the effect of impact-parameter b of twisted electron beam and the laser parameters on the angular distribution of the TDCS. We study the (TDCS)av for the macroscopic target to examine the effect of opening angle θ p of the twisted electron beam on the angular profile of TDCS. We also observe the influence of coherent superposition of two Bessel states on the angular profile of TDCS. Our results clearly show the effects of laser parameters (electric field ɛ and number of photon exchanged (l)) and twisted electron beam parameters (OAM number (ml ) and opening angle (θ p )) on the angular distribution of TDCS.

Bessel beam double ionisation (e, 3e) of Helium atoms

We present the results of previous plane wave and current twisted wave electron double ionisation (e, 3e) near the threshold energy using the second Born approximation to calculate the fully differential cross section (FDCS)T-SBA and also calculate the fully differential cross section for plane wave using the second Born approximation (SBA) and including post-collision interactions (FDCS) PW+PCI of the He atom. We investigate the effect of different “m” parameters on orbital angular momentum (OAM) using the second Born approximation for both twisted and plane waves incident and scattered electrons. We compare our theoretical twisted wave results with experimental non-twisted results (i.e., plane wave); we found that the theoretical twisted wave results are in good agreement with experimental non-twisted (i.e., plane wave) results of He atoms.

Noise self-canceling picoscale twisted interferometer.

We show a noise self-canceling real-time picometer scale interferometer by exploiting the unique spiral phase structure of twisted light. We use a single cylindrical interference-lens to implement the twisted interferometer and perform simultaneous measurement on N phase-orthogonal single-pixel intensity pairs chosen on the petal of the daisy-flower-like interference pattern. A cancellation of various noises by three orders of magnitude was achieved in our setup compared with a conventional single-pixel detection, enabling a sub-100 picometer resolution in measuring a non-repetitive intracavity dynamic event in real-time. Furthermore, the noise cancellation capability of the twisted interferometer scales up statistically for higher radial and azimuthal quantum numbers of the twisted light. The proposed scheme could find applications in precision metrology and in developing analogous ideas for twisted acoustic beam, electron beams, and matter waves.

Conservation laws for electron vortices in strong-field ionisation

We investigate twisted electrons with a well-defined orbital angular momentum, which have been ionised via a strong laser field. By formulating a new variant of the well-known strong field approximation, we are able to derive conservation laws for the angular momenta of twisted electrons in the cases of linear and circularly polarised fields. In the case of linear fields, we demonstrate that the orbital angular momentum of the twisted electron is determined by the magnetic quantum number of the initial bound state. The condition for the circular field can be related to the famous ATI peaks, and provides a new interpretation for this fundamental feature of photoelectron spectra. We find the length of the circular pulse to be a vital factor in this selection rule and, employing an effective frequency, we show that the photoelectron OAM emission spectra are sensitive to the parity of the number of laser cycles. This work provides the basic theoretical framework with which to understand the OAM of a photoelectron undergoing strong field ionisation.Graphic

Detection of magnetic impurities using electron vortex beams

Electron vortex beams generated by a transmission electron microscope (TEM) are employed to study magnetic properties of an impurity often embedded in materials. Compared to the optical wave, a higher spatial resolving power of electron waves enables the detection of impurities on the nanoscale. Here, we investigate theoretically the interaction of the twisted electrons and the magnetic impurity in which the magnetic dipole moment is taken as a demonstration element. In addition to the usual optical phase, the inhomogeneous vector potential generated by the magnetic dipole moment makes an additional contribution to the intrinsic orbital angular momentum of the twisted electrons, resulting in a dipole-dependent Gouy phase shift. By interfering the outgoing twisted electron beam with a reference cylindrical wave, one can determine the magnitude and orientation of the magnetic dipole directly via the rotational and deformed interference pattern. Furthermore, the pattern is shown to be sensitive to the width of the beam in the focal plane, which provides an effective way to reveal the influence of impurities on the twisted electrons more intuitively and distinctly. The obtained results demonstrate the usefulness of the twisted electron beams for probing the nanoscale magnetism of impurity by TEM, while the proposed model provides the conceptual basis for future developments of the TEM method.

General quantum-mechanical solution for twisted electrons in a uniform magnetic field

A theory of twisted (and other structured) paraxial electrons in a uniform magnetic field is developed. The obtained general quantum-mechanical solution of the relativistic paraxial equation contains the commonly accepted result as a specific case of unstructured electron waves. In the weak-field limit, our solution (unlike the existing theory) is consistent with the well-known equation for free twisted electron beams. The observable effect of a different behavior of relativistic Laguerre-Gauss beams with opposite directions of the orbital angular momentum penetrating from the free space into a magnetic field is predicted. Distinguishing features of the quantization of the velocity and the effective mass of structured electrons in the uniform magnetic field are analyzed.

Breathing mode of relativistic twisted electron beams under periodic magnetic field

Transmission electron microscopy typically works with relativistic electron beams of energy 200–300 keV whose wavelength is on the picometer scale. Here, we study theoretically the relativistic dynamics of twisted Dirac-electron beams driven by a time-oscillating magnetic field. The spatial density distribution and the spinor wave-functions of twisted electron beams at each instant time t are obtained. It is demonstrated that the spatial density distribution of electrons can be changed periodically by the external field, whose change is very similar to the “Breathing”. Correspondingly, the azimuthal component of the current changes periodically with the magnetic field. The central “spot size” of spatial distribution of is directly related to the magnitude of the magnetic field. Our results suggest that twisted electron beams are promising for testing the magnitude and frequency of ac magnetic fields created by microsources.

Comment on “Relativistic Quantum Dynamics of Twisted Electron Beams in Arbitrary Electric and Magnetic Fields”

Comment on “Relativistic Quantum Dynamics of Twisted Electron Beams in Arbitrary Electric and Magnetic Fields”

Siberian Snake-Like Behavior for an Orbital Polarization of a Beam of Twisted (Vortex) Electrons

The orbital polarization of twisted electrons carrying an intrinsic orbital angular momentum is not influenced by field perturbations in arbitrary magnetic fields. This property means an existence of the Siberian snake-like behavior for an orbital polarization of a beam of twisted electrons in cyclotrons with the main magnetic field and magnetic focusing. As a result, the acceleration of twisted electron beams in cyclotrons necessary for their applications in high-energy-physics experiments considerably simplifies.

Electric Quadrupole Moment and the Tensor Magnetic Polarizability of Twisted Electrons and a Potential for their Measurements.

For a twisted (vortex) Dirac particle in nonuniform electric and magnetic fields, the relativistic Foldy-Wouthuysen Hamiltonian is derived including high order terms describing new effects. The result obtained shows for the first time that a twisted spin-1/2 particle possesses a tensor magnetic polarizability and a measurable (spectroscopic) electric quadrupole moment. We have calculated the former parameter and have evaluated the latter one for a twisted electron. The tensor magnetic polarizability of the twisted electron can be measured in a magnetic storage ring because a beam with an initial orbital tensor polarization acquires a horizontal orbital vector polarization. The electric quadrupole moment is rather large and strongly influences the dynamics of the intrinsic orbital angular momentum (OAM). Three different methods of its measurements, freezing the intrinsic orbital angular momentum and two resonance methods, are proposed. The existence of the quadrupole moment of twisted electrons can lead to practical applications.

Relativistic Quantum Dynamics of Twisted Electron Beams in Arbitrary Electric and Magnetic Fields.

Relativistic quantum dynamics of twisted (vortex) Dirac particles in arbitrary electric and magnetic fields are constructed for the first time. This allows us to change the controversial contemporary situation when the nonrelativistic approximation is used for relativistic twisted electrons. The relativistic Hamiltonian and equations of motion in the Foldy-Wouthuysen representation are derived. A critical experiment for a verification of the results obtained is proposed. The new important effect of a radiative orbital polarization of a twisted electron beam in a magnetic field resulting in a nonzero average projection of the intrinsic orbital angular momentum on the field direction is predicted.

Highly efficient non-doped OLEDs using aggregation-induced delayed fluorescence materials based on 10-phenyl-10H-phenothiazine 5,5-dioxide derivatives

A highly twisted electron acceptor 10-phenyl-10H-phenothiazine 5,5-dioxide was designed for construction of AIDF material PXZ2PTO. The non-doped devices realized EQEmax of 16.4%, exhibiting similar efficiency to doped devices.

Manipulating Twisted Electron Beams.

A theoretical description of twisted (vortex) electrons interacting with electric and magnetic fields is presented, based on Lorentz transformations. The general dynamical equations of motion of a twisted electron with an intrinsic orbital angular momentum in an external field are derived. Methods for the extraction of an electron vortex beam with a given orbital polarization and for the manipulation of such a beam are developed.

Multifunctional triphenylamine polymers synthesized via direct (hetero) arylation polymerization

ABSTRACTThe design rules for creating multifunctional organic electronic materials are currently limited. By copolymerizing twisted triphenylamine (TPA) and electron rich dioxythiophene (XDOT) monomers via Direct (Hetero) Arylation Polymerization (DHAP), a set of polymers are obtained that perform as yellow to transmissive electrochromic (EC) films with up to 45% contrast, as well as in electroluminescent (EL) applications, achieving a luminance of ∼450 cd/m2 in yellow‐green polymer light‐emitting diodes (PLEDs). In addition, polymerizing TPA with a donor‐acceptor‐donor monomer results in a low‐bandgap polymer that achieves power conversion efficiencies up to 2.5% when blended with PC71BM in conventional organic photovoltaic (OPV) devices. Incorporation of TPA units into the polymer backbone largely breaks any aggregation and ordering in the solid‐state, leading to highly soluble materials that form smooth, reproducible thin films. The TPA unit also serves to break conjugation throughout the polymer backbone, providing precise control over optical and electronic properties through choice of comonomer. These results suggest that TPA copolymers can be useful for achieving multi‐functionality without sacrificing facile solution processability, making them promising candidates for multifunctional devices like dual EC/EL displays. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 147–153

Observation of nanoscale magnetic fields using twisted electron beams

Electron waves give an unprecedented enhancement to the field of microscopy by providing higher resolving power compared to their optical counterpart. Further information about a specimen, such as electric and magnetic features, can be revealed in electron microscopy because electrons possess both a magnetic moment and charge. In-plane magnetic structures in materials can be studied experimentally using the effect of the Lorentz force. On the other hand, full mapping of the magnetic field has hitherto remained challenging. Here we measure a nanoscale out-of-plane magnetic field by interfering a highly twisted electron vortex beam with a reference wave. We implement a recently developed holographic technique to manipulate the electron wavefunction, which gives free electrons an additional unbounded quantized magnetic moment along their propagation direction. Our finding demonstrates that full reconstruction of all three components of nanoscale magnetic fields is possible without tilting the specimen.

A thiazoloquinoxaline based “turn-on” chemodosimeter for detection of copper ions

A novel phenothiazine-thiazoloquinoxaline based sensor which acts as a fluorescence “turn-on” copper chemodosimeter was developed. Excitation of the dye, (E)-10-butyl-3-(2-(thiazolo[4,5-b]quinoxalin-2-yl)vinyl)-10H-phenothiazine [PTQ] results in twisted intramolecular charge transfer (TICT) and electron transfer in the excited state which causes the quenching of fluorescence. On addition of copper to a solution of PTQ in acetonitrile, PTQ undergoes oxidation to PTQO (corresponding sulphoxide) leading to the quenching of charge transfer attributing to the enhancement of fluorescence. The detection limit of the chemodosimeter was observed to be in the range of 10−7 M.

Radiative recombination of twisted electrons with bare nuclei: Going beyond the Born approximation

We present a fully relativistic investigation of the radiative recombination of a twisted electron with a bare heavy nucleus. The twisted electron is described by the wave function which accounts for the interaction with the nucleus in all orders in $\alpha Z$. We use this wave function to derive the probability of the radiative recombination with a single ion being shifted from the twisted electron propagation direction. We also consider more realistic experimental scenarios where the target is either localized (mesoscopic) or infinitely wide (macroscopic). The situation when the incident electron is a coherent superposition of two vortex states is considered as well. For the nonrelativistic case we present analytical expressions which support our numerical calculations. We study in details the influence of the electron twistedness on the polarization and angular distribution of the emitted photon. It is found that these properties of the outgoing photon might be very sensitive to the total angular momentum and kinematic properties of twisted beams. Therefore, the recombination of the twisted electrons can serve as a valuable tool for atomic investigations as well as for the diagnostics of the vortex electron beams.

Quantum calculation of the Vavilov-Cherenkov radiation by twisted electrons

We present the detailed quantum electrodynamical description of Vavilov-Cherenkov radiation emitted by a relativistic twisted electron in the transparent medium. Simple expressions for the spectral and spectral-angular distributions as well as for the polarization properties of the emitted radiation are obtained. Unlike the plane-wave case, the twisted electron produces radiation within the annular angular region, with enhancement towards its boundaries. Additionally, the emitted photons can have linear polarization not only in the scattering plane but also in the orthogonal direction. We find that the Vavilov-Cherenkov radiation emitted by an electron in a superposition of two vortex states exhibits a strong azimuthal asymmetry. Thus, the Vavilov-Cherenkov radiation offers itself as a convenient diagnostic tool of such electrons and complements the traditional microscopic imaging.

Scattering of wave packets on atoms in the Born approximation

Laser photons carrying non-zero orbital angular momentum are known and exploited during the last twenty years. Recently it has been demonstrated experimentally that such (twisted) electrons can be produced and even focused to a subnanometer scale. Thus, twisted electrons emerge as a new tool in atomic physics. The state of a twisted electron can be considered as a specific wave packet of plane waves. In the present paper-I we consider elastic scattering of the wave packets of fast non-relativistic particles on a potential field. We obtain simple and convenient formulae for a number of events in such a scattering. The equations derived represent, in fact, generalization of the well-known Born approximation for the case when finite sizes and inhomogeneity of the initial packet should be taken into account. To illustrate the obtained results, we consider two simple models corresponding to scattering of a Gaussian wave packet on the Gaussian potential and on the hydrogen atom. The scattering of twisted electrons on atoms will be considered in the next paper-II.

Nonfullerene Polymer Solar Cells with 8.5% Efficiency Enabled by a New Highly Twisted Electron Acceptor Dimer.

Fullerene-free and processing additive-free 8.5% efficient polymer solar cells are achieved by using a new 3,4-ethylenedioxythiophene-linked arylene diimide dimer with a 76° twist angle. The devices combine high (78-83%) external quantum efficiency with high (0.91-0.95 V) photovoltages and thus have relatively low optical bandgap energy loss.