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Probing the lattice structure of dynamically compressed and released single crystal iron through the alpha to epsilon phase transition
In this work, experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1 μm thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 100 J, 10 ns duration laser pulse incident on the polyimide ablator was used to shock compress the iron samples to initial stresses greater than 25 GPa, exceeding the ~13 GPa alpha (body-centered-cubic or bcc structure) to epsilon (hexagonal-close-packed or hcp structure) phase transition stress. XRD measurements were performed at various times relative to the shock wave entering the iron sample: early times, <~150 ps while the initial shock waves propagated through the iron; intermediate times, after the iron equilibrated with the ablator and window reaching a plateau stress state (12 or 17 GPa) lasting several nanoseconds; and late times, during uniaxial strain release. The early time measurements show that in <~150 ps, the high-pressure hcp phase is relaxed with a c/a ratio of 1.61, contrary to previous laser shock experiments where a c/a ratio of 1.7 was inferred. In the plateau stress state and partially released states, XRD measurements showed that the hcp structure retained a c/a ratio of 1.61 with no observable changes in the microstructure. Upon stress release at ~1 GPa/ns release rate, the reverse phase transition (hcp to bcc) to the original single crystal orientation (implying a transformation memory effect) was observed to reach completion somewhere between 13 and 11 GPa, indicating little stress hysteresis under rapid uniaxial strain release. A similar memory effect for the reverse hcp to bcc transformation has been previously observed under hydrostatic compression. However, the bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism.
Dual-polarization Dirac cones in a simple 2D square lattice photonic crystal
We report on dual-polarization Dirac cones in a simple square lattice two-dimensional (2D) photonic crystal (PC) based on transmission at accidental degeneracies centered at the k = 0 symmetry ( Γ <#comment/> ) point. Finite difference time domain simulations are used to identify the material and geometric parameters for Dirac-like dispersion. A configuration that produces a Dirac-like point for both transverse electric and transverse magnetic polarizations at the same frequency is presented. The PC dispersion shows the expected threefold degenerate linear branch crossings at the Dirac-like point. Full-field electromagnetic wave simulations exhibit some common behaviors of devices based on Dirac-like dispersion, such as cloaking and waveguiding. The configuration works for a considerable range of the parameter space, and thus is experimentally realizable with a wide range of materials.
The pion-nucleon sigma term from lattice QCD
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Two-phase flow of CO2-brine in a heterogeneous sandstone: Characterization of the rock and comparison of the lattice-Boltzmann, pore-network, and direct numerical simulation methods
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A mechanism for sarcomere breathing: volume change and advective flow within the myofilament lattice
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Physical insights on the low lattice thermal conductivity of AgInSe2
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Lattice Anharmonicity of Stereochemically Active Lone Pairs Controls Thermochromic Band Gap Reduction of PbVO3Cl
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Photocarrier Dynamics in MoTe 2 Nanofilms with 2 H and Distorted 1 T Lattice Structures
Molybdenum telluride (MoTe 2 ), an emerging layered two-dimensional (2D) material, possesses excellent phase-changing properties. Previous studies revealed its reversible transition between 2H and 1T' phases with a transition energy as small as 35 meV. Since 1T'-MoTe 2 is metallic, it can serve as an electrical contact for semiconducting 2H-MoTe 2 -based optoelectronic devices. Here, the photocarrier dynamics in MoTe 2 nanofilms synthesized by a one-step method and with coexisting multiple phases are investigated by transient absorption measurements. Both the energy relaxation time and the recombination lifetime of the excitons are shorter in the 1T'-MoTe 2 compared to its 2H phase. Furthermore, these results provide information on the different photocarrier dynamical properties of these two phases, which is important for future 2D optoelectronic and phase-change electronic devices based on MoTe 2 .
Crystal field-induced lattice expansion upon reversible oxygen uptake/release in YbMn x Fe 2− x O 4
The mechanism for oxygen release and uptake is influenced by crystal field effects in the solid solution YbMn x Fe 2− x O 4 .
Competing higher order topological superconducting phases in triangular lattice magnet-superconductor hybrid systems
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Nonperturbative renormalization of asymmetric staple-shaped operators in twisted mass lattice QCD
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Disassembling 2D van der Waals crystals into macroscopic monolayers and reassembling into artificial lattices
Two-dimensional materials from layered van der Waals (vdW) crystals hold great promise for electronic, optoelectronic, and quantum devices, but technological implementation will be hampered by the lack of high-throughput techniques for exfoliating single-crystal monolayers with sufficient size and high quality. Here, we report a facile method to disassemble vdW single crystals layer by layer into monolayers with near-unity yield and with dimensions limited only by bulk crystal sizes. The macroscopic monolayers are comparable in quality to microscopic monolayers from conventional Scotch tape exfoliation. The monolayers can be assembled into macroscopic artificial structures, including transition metal dichalcogenide multilayers with broken inversion symmetry and substantially enhanced nonlinear optical response. This approach takes us one step closer to mass production of macroscopic monolayers and bulk-like artificial materials with controllable properties.
Electron Accelerator Lattice Design for LHeC with Permanent Magnets
We present a new ’green energy’ approach to the Energy Recovery Linac (ERL) the future Electron Ion Collider at LHeC using single beam line made of very strong focusing combined function permanent magnets and the Fixed Field Alternating Linear Gradient (FFA-LG) principle. We are basing our design on recent very successful commissioning results of the Cornell University and Brookhaven National Laboratory ERL Test Accelerator-CBETA.