Interaction between quasiparticles of a different nature, such as magnons and phonons, leads to mixing their properties and forming hybrid quasiparticles—hybrid magnetoelastic bosons, also called magnon polarons—in the areas of intersection of individual spectral branches. In garnet ferrite films, such hybridization results in several new phenomena as the resonant increase in the efficiency of the spin Seebeck effect [1,2] and the spontaneous bottleneck accumulation [3] of the magnetoelastic quasiparticles.<br/>Similar to the Bose-Einstein magnon condensation (BEC) [4], the latter phenomenon occurs at the bottom of the magnon spectrum in yttrium iron garnet films exposed to microwaves. However, unlike the BEC, which is a consequence of the equilibrium Bose statistics, the bottleneck accumulation is determined by changing interparticle interactions. Studying the transport properties of accumulated quasiparticles [5], we found that such accumulation occurs in two frequency-distant groups: quasiphonons and quasimagnons. These quasiparticles propagate in the film plane as spatially localized beams with distinctly different directions and velocities.<br/>The developed theoretical model describes the double accumulation effect. Parametrically pumped magnons scatter through a step-by-step thermalization process towards the lower energy states. At the magnon-phonon hybridization region, the efficiency of nonlinear scattering decreases, and the downward quasiparticle flux slows down. Owing to the bottleneck effect, quasimagnons form a density peak, in which intensity saturates due to their scattering to the lowest branch of the magnon spectrum. The remaining quasimagnons, scattering to phonon states below the magnon spectrum, transform into quasiphonons with vanishing scattering amplitude. These quasiphonons form the second accumulated group.<br/>By considering the 2D magnon-phonon spectrum, we determined the wavevectors and frequencies of each group and concluded about the caustic nature of the quasimagnon beams. Due to nonzero group velocity, the accumulated quasiparticles can be used for data transfer in magnon spintronics.<br/>Funded by the ERC Advanced Grant 694709 SuperMagnonics and by the DFG within TRR173 – 268565370 (project B04).

Double Accumulation and Anisotropic Transport of Magneto-Elastic Bosons in Yttrium Iron Garnet Films

Alzheimer’s disease ranks as the third leading cause of death amongst adults over the age of 60 behind heart disease and cancer. The accumulation of amyloid plaque and neurofibrillary tangles causes the irreversible degradation and destruction of neurons that drastically shrinks brain tissue. Amyloid plaques are due to the buildup of insoluble amyloid beta (Aβ) fibrils formed from self-assembled propagation of peptides. Studies have shown that Aβ can take shape as soluble oligomers or insoluble fibrils with different morphologies. Aβ fibrils attain numerous structures, called polymorphs, both in patients’ brains and in vitro. Prior observations reveal that in agitated solutions the twofold polymorph of Aβ40 fibrils dominates, whereas the threefold polymorph of Aβ40 fibrils preferentially forms in the quiescent solutions. Previous atomic force microscopy (AFM) studies have demonstrated that the twofold symmetric Aβ40 polymorph grows steadily at broad ranges of peptide solution concentrations. It was also established that the fibril growth rate is determined by an activated complex, comprised by a peptide chain partially bound to the fibril tip and folded in a conformation distinct form that in the fibril bulk; the rearrangement of the intermediate configuration of the incoming peptide to the structure in the bulk fibril constitutes the transition state for growth [1]. We employ time-resolved in situ AFM to monitor the growth of seeds nucleated in quiescent solutions that belong to the threefold polymorph. We find that at low peptide concentrations, the fibrils growth bifurcates between two regimes. Growth either completely stalls or it proceeds at a rate, which is reproducible for the chosen solutions concentration. Similar observations of “stop and go” kinetics with other fibril-forming proteins have been attributed to two conformations of the soluble protein chains, growth complement, which supports growth, and growth incompetent, which caps the fibril tips and prevent association of growth competent chains. The recorded consistently steady growth of the two-fold Aβ40 fibrils, however, challenges the presence of growth-incompetent conformations in Aβ40 solutions. We put forth that stalled growth of the three-fold Aβ40 fibrils is due to an activated complex in which the incoming peptide folds into a conformation that cannot transform into the bulk fibril structure. The lifetime of that conformation of the activated complex defines the length of the period of stalled growth of the fibril. Our finding illuminates the complex interplay between fibril structures and the associated transition states during the growth of amyloid β fibrils.

BIFURCATED TRANSITION STATE FOR THE GROWTH OF THE THREEFOLD POLYMORPH OF AMYLOID BETA FIBRILS

It is often thought that cleaving can only be applied to crystalline materials such as silicon and GaAs and that it is an inherently dirty and imprecise process. Dicing by cleaving can be applied to a wide variety of wafer substrates including silicon, sapphire, GaAs, GaN, InP, SiC,  and glass.

Underline digital video library

Double Accumulation and Anisotropic Transport of Magneto-Elastic Bosons in Yttrium Iron Garnet Films

BIFURCATED TRANSITION STATE FOR THE GROWTH OF THE THREEFOLD POLYMORPH OF AMYLOID BETA FIBRILS

Wafer dicing by cleaving: A fast, clean, dry and accurate

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES