Coherence time characterization method for hard X-ray free-electron lasers
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43 PARTICLE ACCELERATORS↗
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Results for “electronic coherence”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Electronic correlation induced expansion of Fermi pockets in δ-plutonium
Plutonium is a critically important material as the behavior of its 5f electrons stands midway between the metalliclike itinerant character of the light actinides and localized atomic-core-like character of the heavy actinides. The δ phase of plutonium (δ-Pu), whereas still itinerant, has a large coherent Kondo peak and strong electronic correlations coming from its near-localized character. Here, using sophisticated Gutzwiller wave function and dynamical mean-field theory correlated theories, we study the Fermi surface and associated mass renormalizations of δ-Pu together with calculations of the de Haas–van Alphen frequencies. We find a large (~200%) correlation induced volume expansion in both the hole and the electron pockets of the Fermi surface in addition to an intermediate mass enhancement. All of the correlated electron theories predict, approximately, the same hole pocket placement in the Brillouin zone, which is different from that obtained in conventional density-functional band-structure theory, whereas the electron pockets from all theories are in, roughly, the same place.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Sizes of pure and doped helium droplets from single shot x-ray imaging
Advancements in x-ray free-electron lasers on producing ultrashort, ultrabright, and coherent x-ray pulses enable single-shot imaging of fragile nanostructures, such as superfluid helium droplets. Furthermore, this imaging technique gives unique access to the sizes and shapes of individual droplets. In the past, such droplet characteristics have only been indirectly inferred by ensemble averaging techniques. Here, we report on the size distributions of both pure and doped droplets collected from single-shot x-ray imaging and produced from the free-jet expansion of helium through a 5 μm diameter nozzle at 20 bars and nozzle temperatures ranging from 4.2 to 9 K. This work extends the measurement of large helium nanodroplets containing 10 9 –10 11 atoms, which are shown to follow an exponential size distribution. Additionally, we demonstrate that the size distributions of the doped droplets follow those of the pure droplets at the same stagnation condition but with smaller average sizes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Feasibility study consisting of a review of contour generation methods from stereograms
A review of techniques for obtaining contour information from stereo pairs is given. Photogrammetric principles including a description of stereoscopic vision are presented. The use of conventional contour generation methods, such as the photogrammetric plotting technique, electronic correlator, and digital correlator are described. Coherent optical techniques for contour generation are discussed and compared to the electronic correlator. The optical techniques are divided into two categories: (1) image plane operation and (2) frequency plane operation. The description of image plane correlators are further divided into three categories: (1) image to image correlator, (2) interferometric correlator, and (3) positive negative transparencies. The frequency plane correlators are divided into two categories: (1) correlation of Fourier transforms, and (2) filtering techniques.
Kim, C. J.↗
Layer-by-layer disentanglement of Bloch states
Layer-by-layer material engineering has produced interesting quantum phenomena such as interfacial superconductivity and the quantum anomalous Hall effect. However, probing electronic states layer-by-layer remains challenging. This is exemplified by the difficulty in understanding the layer origins of topological electronic states in magnetic topological insulators. In this work, we report a layer-encoded frequency-domain photoemission experiment on the magnetic topological insulator (MnBi 2 Te 4 )(Bi 2 Te 3 ) that characterizes the origins of its electronic states. Infrared laser excitations launch coherent lattice vibrations with the layer index encoded by the vibration frequency. Photoemission spectroscopy then tracks the electron dynamics, where the layer information is carried in the frequency domain. This layer-frequency correspondence reveals wavefunction relocation of the topological surface state from the top magnetic layer into the buried second layer, reconciling the controversy over the vanishing broken-symmetry energy gap in (MnBi 2 Te 4 )(Bi 2 Te 3 ) and its related compounds. The layer-frequency correspondence can be harnessed to disentangle electronic states layer-by-layer in a broad class of van der Waals superlattices.
36 MATERIALS SCIENCE↗
Atomic Resolution Imaging of Light Elements in a Crystalline Environment using Dynamic Hollow-Cone Illumination Transmission Electron Microscopy
Multiple electron scattering and the nonintuitive nature of image formation with coherent radiation complicate the interpretation of conventional transmission electron microscopy images. Precession of the illuminating beam in transmission electron microscopy (TEM) can lead to more robust and interpretable images with some penalty to image contrast, a technique known as dynamic hollow-cone illumination TEM. Here, we demonstrate direct and robust imaging of light and heavy atoms in a crystalline environment with this technique. This method is similar to the annular bright-field technique in scanning transmission electron microscopy, via the principle of reciprocity. Dynamic hollow-cone illumination TEM is challenging in practice due to sensitivity to the misalignment of the precession axis, microscope objective aperture, and crystal zone axis.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A Self Consistent 2D Simulation of Coherent Synchrotron Radiation Effects on Beam Dynamics
An increasing interest in high quality and high current electron beams necessitates a thorough understanding and prediction of coherent synchrotron radiation effects. The self-interaction of charged particles in a beam undergoing synchrotron motion is a physically significant process that is all too often computationally intensive with very little analytical results to rely on for the general case. The coherent spectrum of this interaction is of utmost importance to the design of free electron lasers (FELs) and an accurate assessment is imperative for their design. This work presents a novel implementation to the numerical simulation of charged particle beams. The simulation is a self-consistent approach including the self-fields generated by the beam of which coherent synchrotron radiation effects are of primary interest. A particle-in-cell model is used where a planar beam sampled by point particles is deposited on an encompassing grid at each timestep. The electromagnetic fields are calculated on the grid using the retarded potentials according to causality. The electromagnetic forces from the fields are interpolated on each particle which in turn advance in time. The simulation is benchmarked against well-established results for coherent synchrotron radiation effects. In addition, studies are provided that show the convergence of simulation results for increasing resolution. A study into the transverse beam size effects on beam dynamics is performed as well as a proof of concept where the simulation is used by a genetic algorithm to optimize the design parameters of a beam lattice. The results of these studies in tandem verify the efficacy of the simulation for its practical use in accelerator design or the study of synchrotron radiation effects
Duffin, Dallan [Old Dominion Univ., Norfolk, VA (U↗
Theoretical examination of nuclear spin diffusion in light-induced spin coherences in photosystem I
Microsecond coherence times are predicted in spin dynamics calculations of a donor–acceptor electron spin pair P + A 1A - created upon light excitation of photosystem I (PSI). The effects of nuclear spin diffusion (NSD) due to the anisotropic protein environment on the predicted coherence times T M are studied. Closely positioned pairs and triples of protons located 5–8 Å from the electron spin are shown to largely control T M . Additionally, knowledge of the crystal structure of PSI allows for spin dynamics calculations where specific cofactors and amino acid residues are removed or replaced and the identification of anisotropic environmental features controlling electronic decoherence. Finally, we show that NSD alone cannot explain the >3× shorter experimentally observed coherence times and suggest that methyl groups at key protein sites may explain this discrepancy.
74 ATOMIC AND MOLECULAR PHYSICS↗
Multimode Storage of Quantum Microwave Fields in Electron Spins over 100 ms
In this work, we report long coherence times (up to 300 ms) for near-surface bismuth donor electron spins in silicon coupled to a superconducting microresonator, biased at a clock transition. This enables us to demonstrate the partial absorption of a train of weak microwave fields in the spin ensemble, their storage for 100 ms, and their retrieval, using a Hahn-echo-like protocol. Phase coherence and quantum statistics are preserved in the storage.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Potential Constraints to Neutrino-Nucleus Interactions Based on Electron Scattering Data
A thorough understanding of neutrino-nucleus interactions physics is crucial to achieving precision goals in broader neutrino physics programs. The complexity of nuclei comprising the detectors and limited understanding of their weak response constitutes one of the biggest systematic uncertainties in neutrino experiments - both at intermediate energies affecting the short- and long-baseline neutrino programs as well as at lower energies affecting coherent scattering neutrino programs. While electron and neutrino interactions are different at the primary vertex, many underlying relevant physical processes in the nucleus are the same in both cases, and electron scattering data collected with precisely controlled kinematics, large statistics and high precision allows one to constrain nuclear properties and specific interaction processes. To this end, electron-nucleus scattering experiments provide vital complementary information to test, assess and validate different nuclear models and event generators intended to be used in neutrino experiments. In fact, for many decades, the study of electron scattering off a nucleus has been used as a tool to probe the properties of that nucleus and its electromagnetic response. While previously existing electron scattering data provide important information, new and proposed measurements are tied closely to what is required for the neutrino program in terms of expanding kinematic reach, the addition of relevant nuclei and information on the final states hadronic system.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Is the Orbital-Selective Mott Phase Stable against Interorbital Hopping?
The localization-delocalization transition is at the heart of strong correlation physics. Recently, there is great interest in multiorbital systems where this transition can be restricted to certain orbitals, leading to an orbital-selective Mott phase (OSMP). Theoretically, the OSMP is widely studied for kinetically decoupled orbitals, but the effect of interorbital hopping remains unclear. Here, we show how nonlocal interorbital hopping leads to local hybridization in single-site dynamical mean-field theory (DMFT). Under fairly general circumstances, this implies that, at zero temperature, the OSMP, involving the Mott-insulating state of one orbital, is unstable against interorbital hopping to a different, metallic orbital. We further show that the coherence scale below which all electrons are itinerant is very small and gets exponentially suppressed even if the interorbital hopping is not overly small. Within this framework, the OSMP with interorbital hopping may thus reach down to extremely low temperatures T, but not to T = 0. Accordingly, it is part of a coherence-incoherence crossover and not a quantum critical point. Finally, we present analytical arguments supported by numerical results using the numerical renormalization group as a DMFT impurity solver. We also compare our findings with previous slave-spin studies.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Ligand Control of Ultrafast Hot-Carrier Cooling in CdSe Quantum Dots by a Coherent Nonadiabatic Mechanism
Using the results from global modeling of the broadband two-dimensional electronic spectrum and an analysis of the concurrent damping of excited-state vibronic coherences, we show herein that a coherent nonadiabatic mechanism converts the electronic excitation energy of the X3 (1P 3/2 –1P e ) exciton state to ligand vibrations on the <50 fs time scale in oleate- and hexadecylamine-capped CdSe quantum dots. A comparison of the rates for the two ligands suggests that this process is promoted by mid-frequency vibrations of the ligands due to modulation of their electron-donating tendency. An intramolecular vibrational redistribution process then follows on the ∼200 fs time scale with both ligands, which accompanies thermalization in the band-edge X1 (1S 3/2 –1S e ) state and dephasing of the spectator ligand vibrations. These findings suggest that charge-separated intermediates associated with photoinduced charge transfer or triplet–triplet excitation energy transfer will be produced with retention of phase coherence in the vibrations that modulate the charge-transfer character of surface-bound organic acceptors.
14 SOLAR ENERGY↗
Optical radiation from the Crab pulsar
Possible mechanisms for producing the optical radiation from the Crab pulsar are proposed and discussed. There are severe difficulties in interpreting the radiation as being produced by an incoherent process, whether it be synchrotron radiation, inverse-Compton radiation, or curvature radiation. It is proposed, therefore, that radiation in the optical part of the spectrum is coherent. In the polar cap model, a small bunch of electrons and positrons forms near each primary electron as a result of the pair-production cascade process. Turbulent electric field components associated with large-scale bunching may lead to separation of the electrons and positrons in space and in energy, with the result that coherent radiation may be produced by the electrons, the positrons, or both. Calculations, which involve a number of simplifying assumptions, indicate that the optical radiation from the Crab pulsar can be understood in this way if the mass of the star is approximately 0.3 solar mass. Various consequences of this model, which may be subjected to observational test, are discussed.
Sturrock, P. A.↗
Transient Symmetry Controls Photo Dynamics near Conical Intersections
Excited-state chemistry lacks generalised symmetry rules. With many femtochemistry studies focused on individual cases, it is hard to build up the same level of chemical intuition for excited-states as exists for ground states. Here, we unravel the degrees of freedom involved in ultrafast internal conversion (IC) by mapping the vibrational coherence of the initial wavepacket, and the dependence on molecular symmetry in various cyclic tertiary amines. Molecular symmetry plays an important role in the preservation of vibrational coherence in the transit from one electronic state to another. We show here that it is sufficient for the molecule to simply have the possibility of a more symmetric structure to achieve the preservation of vibrational coherence. It can be transient and still lead to preservation. Furthermore, this finding provides an additional angle on how symmetry influences electronic transitions and an additional piece to the puzzle of establishing symmetry-based selection rules for excited-state processes.
74 ATOMIC AND MOLECULAR PHYSICS↗
Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Synthesis of Narrow SnTe Nanowires Using Alloy Nanoparticles
Topological crystalline insulator tin telluride (SnTe) provides a rich playground to examine interactions of correlated electronic states, such as ferroelectricity, topological surface states, and superconductivity. The study of SnTe nanowires may lead to even richer physics owing to the one-dimensional (1D) confinement effect and an increased contribution from the topological surface states. Thus, for transport measurements, SnTe nanowires must be synthesized with reduced diameters and high crystalline quality to ensure 1D confinement and phase coherence of the topological surface electrons. Here, we report a facile growth method to produce narrow SnTe nanowires with a high yield using alloy nanoparticles as growth catalysts. The average diameter of the SnTe nanowires grown using alloy nanoparticles is 85 nm, nearly a factor of three reduction compared to the average diameter of 240 nm when using gold nanoparticles as growth catalysts. Transport measurements reveal the effect of the nanowire diameter on the residual resistance ratio and magnetoresistance. Particularly, the ferroelectric transition temperature for SnTe evolves systematically with the nanowire diameter. In situ cryogenic cooling of narrow SnTe nanowires in a transmission electron microscope directly reveals the cubic to rhombohedral structural transition, which is associated with the ferroelectric transition. Thus, these narrow SnTe nanowires represent a model system to study electronic states arising from 1D confinement, such as 1D topological superconductivity and potential multiband superconductivity.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electron beam pumped semiconductor laser
Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.
Hug, William F.↗
Revealing the three-dimensional structure of microbunched plasma-wakefield-accelerated electron beams
Abstract Plasma wakefield accelerators use tabletop equipment to produce relativistic femtosecond electron bunches. Optical and X-ray diagnostics have established that their charge concentrates within a micrometre-sized volume, but its sub-micrometre internal distribution, which critically influences gain in free-electron lasers or particle yield in colliders, has proven elusive to characterize. Here, by simultaneously imaging different wavelengths of coherent optical transition radiation that a laser-wakefield-accelerated electron bunch generates when exiting a metal foil, we reveal the structure of the coherently radiating component of bunch charge. The key features of the images are shown to uniquely correlate with how plasma electrons injected into the wake: by a plasma-density discontinuity, by ionizing high- Z gas-target dopants or by uncontrolled laser–plasma dynamics. With additional input from the electron spectra, spatially averaged coherent optical transition radiation spectra and particle-in-cell simulations, we reconstruct coherent three-dimensional charge structures. The results demonstrate an essential metrology for next-generation compact X-ray free-electron lasers driven by plasma-based accelerators.
43 PARTICLE ACCELERATORS↗