Investigation of relaxation behavior in highly rejuvenated bulk metallic glasses by in-situ synchrotron X-ray scattering
Abstract not provided
Meng, Fanqiang↗
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Neutron Spin–Echo Studies of the Structural Relaxation of Network Liquid ZnCl 2 at the Structure Factor Primary Peak and Prepeak
Using neutron spin-echo spectroscopy, we studied the microscopic structural relaxation of a prototypical network ionic liquid ZnCl 2 at the structure factor primary peak and pre-peak. The results show that the relaxation at the primary peak is faster than the pre-peak and the activation energy is ≈33% higher. Stretched exponential relaxation is observed even at temperatures well above the melting point T m . Surprisingly, the stretching exponent shows a rapid increase upon cooling, especially at the primary peak, where it changes from stretched exponential to simple exponential on approaching T m . Furthermore, these results suggest that the appearance of glassy dynamics typical of the supercooled state even in the equilibrium liquid state of ZnCl 2 as well as the difference of activation energy at the two investigated length scales are related to the formation of network structure on cooling.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Self-Consistent Theory for Structural Relaxation, Dynamic Bond Exchange Times, and the Glass Transition in Polymeric Vitrimers
Here, we formulate a statistical mechanical theory for how dynamic bond exchange influences the activated hopping-driven relaxation of Kuhn segments in dynamically cross-linked networks or vitrimers over a wide range of temperatures and cross-link densities. The key new methodological aspect is to address in a self-consistent manner the dynamic consequences of bond exchange on the Kuhn segmental alpha relaxation, and vice versa. The predicted temperature dependence of the segmental alpha time of vitrimers at high temperatures remains the same as that of permanent networks, but at lower temperatures, a significant acceleration of relaxation occurs due to bond exchanges. From a mechanistic perspective, the vitrimer local cage barrier is very weakly affected by bond exchange, while the collective elastic barrier contribution decreases significantly in the deeply supercooled regime. The vitrimer glass transition temperature is predicted to grow linearly with the square root of the cross-link density, as previously found for permanent networks. Material-specific chemical effects such as cross-linker size relative to that of the normal Kuhn segment or special attraction of a cross-linker with polymers are crudely considered based on model calculations. The theory is quantitatively applied to recent experiments on dry ethylene vitrimers. Good agreements are found including that the bond exchange time follows an Arrhenius law at high enough temperatures but upward non-Arrhenius deviations emerge in the deeply supercooled regime, and a collapsed master curve of the segment alpha time exists over a wide range of cross-link densities and temperatures. Possible extensions to treat dynamic heterogeneity effects and penetrant transport in vitrimers are briefly discussed.
chemical calculations↗
Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films
We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Uranyl Carbonate Complexes in Aqueous Solution and Their Ligand NMR Chemical Shifts and 17 O Quadrupolar Relaxation Studied by ab Initio Molecular Dynamics
Dynamic structural effects, NMR ligand chemical shifts, and 17 O NMR quadrupolar relaxation rates are investigated in the series of complexes UO 2 2+ , UO 2 (CO 3 ) 3 4– , and (UO 2 ) 3 (CO 3 ) 6 6– . Car–Parrinello molecular dynamics (CPMD) is used to simulate the dynamics of the complexes in water. NMR properties are computed on clusters extracted from the CPMD trajectories. In the UO 2 2+ complex, coordination at the uranium center by water molecules causes a decrease of around 300 ppm for the uranyl 17 O chemical shift. The final value of this chemical shift is within 40 ppm of the experimental range. The UO 2 (CO 3 ) 3 4– and (UO 2 ) 3 (CO 3 ) 6 6– complexes show a solvent dependence of the terminal carbonate 17 O and 13 C chemical shifts that is less pronounced than that for the uranyl oxygen atom. Corrections to the chemical shift from hybrid functionals and spin–orbit coupling improve the accuracy of chemical shifts if the sensitivity of the uranyl chemical shift to the uranyl bond length (estimated at 140 ppm per 0.1 Å from trajectory data) is taken into consideration. The experimentally reported trend in the two unique 13 C chemical shifts is correctly reproduced for (UO 2 ) 3 (CO 3 ) 6 6– . NMR relaxation rate data support large 17 O peak widths, but remain below those noted in the experimental literature. Furthermore, comparison of relaxation data for solvent-including versus solvent-free models suggest that carbonate ligand motion overshadows explicit solvent effects.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: enlightenment from high-energy x-ray diffraction
Abstract not provided
Ochoa, D. A.↗
THE ZENER RELAXATION AND A NEW MAGNETIC RELAXATION EFFECT IN FE-RICH FE-AL ALLOYS
Zener relaxation and a new magnetic relaxation effect in fe-rich fe-al alloys
MAGNETIC RELAXATION↗
KINETIC STUDY OF RADIATION-REACTION-LIMITED PARTICLE ACCELERATION DURING THE RELAXATION OF UNSTABLE FORCE-FREE EQUILIBRIA
Many powerful and variable gamma-ray sources, including pulsar wind nebulae, active galactic nuclei and gamma-ray bursts, seem capable of accelerating particles to gamma-ray emitting energies efficiently over very short timescales. These are likely due to the rapid dissipation of electromagnetic energy in a highly magnetized, relativistic plasma. In order to understand the generic features of such processes, we have investigated simple models based on the relaxation of unstable force-free magnetostatic equilibria. In this work, we make the connection between the corresponding plasma dynamics and the expected radiation signal, using 2D particle-in-cell simulations that self-consistently include synchrotron radiation reactions. We focus on the lowest order unstable force-free equilibrium in a 2D periodic box. We find that rapid variability, with modest apparent radiation efficiency as perceived by a fixed observer, can be produced during the evolution of the instability. The “flares” are accompanied by an increased polarization degree in the high energy band, with rapid variation in the polarization angle. Furthermore, the separation between the acceleration sites and the synchrotron radiation sites for the highest energy particles facilitates acceleration beyond the synchrotron radiation reaction limit. We also discuss the dynamical consequences of the radiation reaction, and some astrophysical applications of this model. Our current simulations with numerically tractable parameters are not yet able to reproduce the most dramatic gamma-ray flares, e.g., from the Crab Nebula. Higher magnetization studies are promising and will be carried out in the future.
79 ASTRONOMY AND ASTROPHYSICS↗
Structural relaxation and aging scaling in the Coulomb and Bose glass models
We employ Monte Carlo simulations to study the relaxation properties of the two-dimensional Coulomb glass in disordered semiconductors and the three-dimensional Bose glass in type-II superconductors in the presence of extended linear defects. We investigate the effects of adding non-zero random on-site energies from different distributions on the properties of the correlation-induced Coulomb gap in the density of states (DOS) and on the non-equilibrium aging kinetics highlighted by the density autocorrelation functions. Here, we also probe the sensitivity of the system’s equilibrium and non-equilibrium relaxation properties to instantaneous changes in the density of charge carriers in the Coulomb glass or flux lines in the Bose glass.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Novel Relaxation Time Approximation: A Consistent Calculation of Transport Coefficients with QCD-inspired Relaxation Times
We use a novel formulation of the relaxation time approximation to consistently calculate the bulk and shear viscosity coefficients using QCDinspired energy-dependent relaxation times and phenomenological thermal masses obtained from fits to lattice QCD thermodynamics. The matching conditions are conveniently chosen to simplify the computations.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
T 1 Anisotropy Elucidates Spin Relaxation Mechanisms in an S = 1 Cr(IV) Optically Addressable Molecular Qubit
Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin–lattice relaxation ( T 1 ) even at sub-liquid nitrogen temperatures. Here, we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground state zero-field splitting (ZFS) and assign T 1 anisotropy to specific types of motion in an optically addressable S = 1 Cr(o-tolyl) 4 molecular qubit. The anisotropy displays a distinct sin 2 (2θ) functional form that is not observed in S = 1/2 Cu(acac) 2 or other Cu(II)/V(IV) microwave addressable molecular qubits. The Cr(o-tolyl) 4 T 1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudoacoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.
magnetic properties↗
Correlated charge noise and relaxation errors in superconducting qubits
In This report, the central challenge in building a quantum computer is error correction. Unlike classical bits, which are susceptible to only one type of error, quantum bits (“qubits”) are susceptible to two types of error, corresponding to flips of the qubit state about the X- and Z-directions. While the Heisenberg Uncertainty Principle precludes simultaneous monitoring of X- and Z-flips on a single qubit, it is possible to encode quantum information in large arrays of entangled qubits that enable accurate monitoring of all errors in the system, provided the error rate is low. Another crucial requirement is that errors cannot be correlated. Here, we characterize a superconducting multiqubit circuit and find that charge fluctuations are highly correlated on a length scale over 600 µm; moreover, discrete charge jumps are accompanied by a strong transient suppression of qubit energy relaxation time across the millimeter-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle poisoning associated with absorption of gamma rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Multi-fluid systems—Multi-Beltrami relaxed states and their implications
Not Available
Mahajan, Swadesh M.↗
Effect of the Magnus force on skyrmion relaxation dynamics
We perform systematic Langevin molecular dynamics simulations of interacting skyrmions in thin films. The interplay between the Magnus force, the repulsive skyrmion-skyrmion interaction, and the thermal noise yields different regimes during nonequilibrium relaxation. In the noise-dominated regime, the Magnus force enhances the disordering effects of the thermal noise. In the Magnus-force-dominated regime, theMagnus force cooperates with the skyrmion-skyrmion interaction to yield a dynamic regime with slow decaying correlations. Furthermore, these two regimes are characterized by different values of the aging exponent. In general, the Magnus force accelerates the approach to the steady state.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Searching for new spin-dependent interactions with SmCo 5 spin sources and a spin-exchange-relaxation-free comagnetometer
We propose a novel method to search for possible new macroscale spin- and/or velocity-dependent forces (SVDFs) based on specially designed SmCo 5 spin sources and a spin exchange relaxation-free (SERF) comagnetometer. A simulation shows that, by covering a SmCo 5 permanent magnet with a layer of pure iron, a high net spin density source of about $1×10^{22}/cm^3$ could be obtained. Taking advantages of the high spin density of this iron-shielded SmCo 5 and the high sensitivity of the SERF, the proposed method could set up new limits of greater than 10 orders of magnitude more sensitive than those from previous experiments or proposals in exploring SVDFs in force ranges larger than 1 cm.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗