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Artificial Tribotactic Microscopic Walkers: Walking Based on Friction Gradients
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Microscopic study of the Fulde-Ferrell-Larkin-Ovchinnikov state in an all-organic superconductor.
Quasi-two-dimensional superconductors with a sufficiently weak interlayer coupling allow magnetic flux to penetrate in the form of Josephson vortices for in-plane applied magnetic fields. A consequence is the dominance of the Zeeman interaction over orbital effects. In the clean limit, the normal state is favored over superconductivity for fields greater than the paramagnetic limiting field, unless an intermediate, inhomogeneous state is stabilized. Presented here are nuclear magnetic resonance (NMR) studies of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state for beta ''-(ET)(2)SF5CH2CF2SO3. The uniform superconductivity-FFLO transition is identified at an applied field value of 9.3(0.1) T at low temperature (T = 130 mK), and evidence for a possible second transition between inhomogeneous states at similar to 11 T is presented. The spin polarization distribution inferred from the NMR absorption spectrum compares favorably to a single-Q modulation of the superconducting order parameter.
Gravitational Waves from Rapid Structure Formation on Microscopic Scales before Matter-Radiation Equality
We propose a new scenario for the formation of asteroid-mass primordial black holes (PBHs). Our mechanism is based on the annihilation of the string-wall network associated with thebreaking of a U(1) global symmetry into a discrete ZN symmetry. If the potential hasmultiple local minima (N > 1) the network is stable, and the annihilation is guaranteed by a biasamong the different vacua. The collapse of the string-wall network is accompanied bycatastrogenesis, a large production of pseudo-Goldstone bosons (pGBs) — e.g. axions,ALPs, or majorons — gravitational waves, and PBHs. If pGBs rapidly decay into products thatthermalize, as predicted e.g. in the high-quality QCD axion and heavy majoron models, they do notcontribute to the dark matter population, but we show that PBHs can constitute 100% of the darkmatter. The gravitational wave background produced by catastrogenesis with heavy unstable axions,ALPs, or majorons could be visible in future interferometers.
Microscopic Encoding of Macroscopic Universality: Scaling Properties of Dirac Eigenspectra near QCD Chiral Phase Transition
Not Available
Microscopic Origin of the Entropy of Astrophysical Black Holes
We construct an infinite family of microstates for black holes in Minkowski spacetime which have effective semiclassical descriptions in terms of collapsing dust shells in the black hole interior. Quantum mechanical wormholes cause these states to have exponentially small, but universal, overlaps. We show that these overlaps imply that the microstates span a Hilbert space of log dimension equal to the event horizon area divided by four times the Newton constant, explaining the statistical origin of the Bekenstein-Hawking entropy. Published by the American Physical Society 2024
Microscopic signatures of yielding in concentrated nanoemulsions under large-amplitude oscillatory shear
Here, we report x-ray photon correlation spectroscopy (XPCS) experiments on a series of concentrated oil-in-water nanoemulsions with varying droplet volume fraction subjected to in situ steady-state large-amplitude oscillatory shear (LAOS). The shear strain causes periodic echoes in the x-ray speckle patterns that lead to peaks in the intensity autocorrelation function. Above an onset strain amplitude that depends on nanoemulsion concentration, the peaks become attenuated, signaling spatially heterogeneous, shear-induced droplet dynamics. These dynamics include irreversible re- arrangements among the droplets that occur in some regions of the nanoemulsions during a given shear cycle and residual strain-like displacements in those regions that do not re-arrange. The wave-vector dependence of the peak attenuation indicates a power-law distribution in the size of regions undergoing shear-induced rearrangement that is similar to that observed previously in LAOS-XPCS measurements on concentrated nanocolloidal gels. The values of the onset strains for re-arrangement correlate with the concentration-dependent macroscopic yielding behavior of the nanoemulsions. Specically, they occur below the strains at which the nanoemulsions become effectively uidized and, except for the lowest concentration nanoemulsion in the study, signicantly above the threshold strain for nonlinear rheological response.
Microscopic dynamics of stress relaxation in a nanocolloidal soft glass
Here, we report x-ray photon correlation spectroscopy (XPCS) experiments with in situ rheometry performed on a soft glass composed of a concentrated suspension of charged silica nanoparticles subjected to step strains that induce yielding and flow. The XPCS measurements characterize the particle-scale and mesoscale motions within the glass that underlie the highly protracted decay of the macroscopic stress following the step strains. These dynamics are anisotropic, with slow, convective particle motion along the direction of the preceding shear that persists for surprisingly large times and that is accompanied by intermittent motion in the perpendicular (vorticity) direction. A close correspondence between the convective dynamics and stress relaxation is demonstrated by power-law scaling between the characteristic velocity of the collective particle motion and the rate of stress decay.
Microscopic origin of temperature-dependent magnetism in spin-orbit-coupled transition metal compounds
A few 4 d and 5 d transition metal compounds with various electron fillings were recently found to exhibit magnetic susceptibilities χ and magnetic moments that deviate from the well-established Kotani model. This model has been considered for decades to be the canonical expression for descriing the temperature dependence of magnetism in systems with nonnegligible spin-orbit coupling effects. In this paper, we uncover the origin of such discrepancies and determine the applicability and limitations of the Kotani model by calculating the temperature dependence of the magnetic moments of a series of 4 d (Ru-based) and 5 d (W-based) systems at different electron fillings. For this purpose, we perform exact diagonalization of -derived relativistic multiorbital Hubbard models on finite clusters and compute their magnetic susceptibilities. Comparison with experimentally measured magnetic properties indicates that contributions such as a temperature-independent χ 0 background, crystal field effects, Coulomb and Hund's couplings, and intersite interactions—not included in the Kotani model—are especially crucial for correctly describing the temperature dependence of χ and magnetic moments at various electron fillings in these systems. Based on our results, we propose a generalized approach beyond the Kotani model to accurately describe their magnetism. Published by the American Physical Society 2025
Microscopic Origin of the Entropy of Black Holes in General Relativity
We construct an infinite family of microstates with geometric interiors for eternal black holes in general relativity with a negative cosmological constant in any dimension. Wormholes in the Euclidean path integral for gravity cause these states to have small, but nonzero, quantum mechanical overlaps that have a universal form. The overlaps have a dramatic consequence: The microstates span a Hilbert space of log dimension equal to the Bekenstein-Hawking entropy. The semiclassical microstates we construct contain Einstein-Rosen bridges of arbitrary size behind their horizons. Our results imply that all these bridges can be interpreted as quantum superpositions of wormholes of size at most exponential in the entropy.
Microscopic Real-Space Resistance Mapping Across CdTe Solar Cell Junctions by Scanning Spreading Resistance Microscopy
Abstract not provided
Microscopic Removal Function and the Relationship Between Slurry Particle Size Distribution and Workpiece Roughness During Pad Polishing
Abstract not provided
Patterning corrosion-susceptible metallic alloys for digital image correlation in a scanning electron microscope: Patterning corrosion susceptible alloys for SEM-DIC
Here we investigate the self-assembly of gold nanoparticles on the surface of magnesium functionalized with 3-(aminopropyl)trimethoxysilane or 3-(mercaptopropyl)trimethoxysilane. These nanoparticles served as a speckle pattern for high magnification deformation tracking via digital image correlation combined with scanning electron microscopy. Controlling the pH of the gold nanoparticle suspension to a specific basicity passivated corrosion in magnesium and in three of its alloys to enable proper nanoparticle bonding and self-assembly. Magnesium was used as a model material as it is particularly difficult to modify for self-assembly because of its propensity to quickly form a thick oxide, hydroxide, and carbonate layer in the presence of oxygen, water, and carbon dioxide, respectively. Moreover, it corrodes in acidic and slightly basic solutions, further complicating the self-assembly process. Due to these difficulties, the successful self-assembly of nanoparticles on magnesium has not previously been reported, to the best of the authors' knowledge. This technique is potentially amendable to other corrosion-susceptible materials. Gold nanoparticles were self-assembled in a uniformly dispersed random distribution on pure cast magnesium, cast AM60 (Mg-6Al-0.5Mn), rolled WE43 (Mg-4Y-3Nd/Gd), and extruded ZE20 (Mg-2Zn-0.2Ce).
Commissioning an EUV mask microscope for lithography generations reaching 8 nm
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