Breaking the Intrinsic Strength-Ductility Tradeoff in Graphene-Metal Composites.

Small carbon materials, such as graphene, offer excellent mechanical strength. Micro/nano carbon materials are often dispersed into a metal matrix to form bulk composites with mechanical enhancement. Despite technical progress, such composites intrinsically suffer from a trade-off condition between strength and ductility because the load transfer path forms between mechanically strong yet chemically inert micro/nano carbon materials or between the carbon-metal interfaces. In other words, conventional carbon and metal composites become stronger with increasing carbon contents, but the weak interfaces also increase, leading to premature failure. In this regard, crucial advances are presented toward breaking the strength-ductility trade-off condition by utilizing Axially bi-Continuous Graphene-Nickel (ACGN) wires. This innovative ACGN achieves excellent combined strength and ductility-the highest among the current Ni-, Al-, and Cu-based carbon-enhanced metal matrix composites. For example, the ultimate strength and failure strain of 25-µm-diameter ACGN wires are improved by 71.76% and 58.24%, compared to their counterparts. The experimental and theoretical analyses indicate that the graphene-nickel interplay via their axially bi-continuous structure is the main underlying mechanism for the superb mechanical behavior. In specific, the continuous graphene, in addition to effective load-sharing, passivates the free surface of fine wire, forming dislocation pileups along the graphene-nickel interface and, therefore, hindering localized necking.

Theory of Two-Dimensional Nonlinear Spectroscopy for the Kitaev Spin Liquid.

Unambiguous identification of fractionalized excitations in quantum spin liquids has been a long-standing issue in correlated topological phases. Conventional spectroscopic probes, such as the dynamical spin structure factor, can only detect composites of fractionalized excitations, leading to a broad continuum in energy. Lacking a clear signature in conventional probes has been the biggest obstacle in the field. In this work, we theoretically investigate what kinds of distinctive signatures of fractionalized excitations can be probed in two-dimensional nonlinear spectroscopy by considering the exactly solvable Kitaev spin liquids. We demonstrate the existence of a number of salient features of the Majorana fermions and fluxes in two-dimensional nonlinear spectroscopy, which provide crucial information about such excitations.

Nonsymmorphic-Symmetry-Protected Topological Magnons in Three-Dimensional Kitaev Materials.

Topological phases in magnetic materials offer novel tunability of topological properties via varying the underlying magnetism. We show that three-dimensional Kitaev materials with nonsymmorphic symmetries can provide a great opportunity for controlling symmetry-protected topological nodal magnons. These materials are originally considered as strong candidates for the Kitaev quantum spin liquid due to the bond-dependent frustrating spin-exchange interactions. As a concrete example, we consider the symmetry and topology of the magnons in the canted zigzag ordered state in the hyperhoneycomb ß-Li_{2}IrO_{3}, which can be obtained by applying a magnetic field in the counter-rotating spiral state at zero field. It is shown that the magnetic glide symmetries and the non-Hermitian nature of the bosonic magnons lead to unique topological protection that is different from the case of their fermionic counterparts. We investigate how such topological magnons can be controlled by changing the symmetry of the underlying spin-exchange interactions.

Fluctuations of red blood cell membranes: The role of the cytoskeleton.

We theoretically investigate the membrane fluctuations of red blood cells with focus laid on the role of the cytoskeleton, viewing the system as a membrane coupled to a sparse spring network. This model is exactly solvable and enables us to examine the coupling strength dependence of the membrane undulation. We find that the coupling modifies the fluctuation spectrum at wavelengths longer than the mesh size of the network, while leaving the fluid-like behavior of the membrane intact at shorter wavelengths. The fluctuation spectra can be markedly different, depending on not only the relative amplitude of the bilayer bending energy with respect to the cytoskeleton deformation energy but also the bilayer-cytoskelton coupling strength.

Optical activity enhanced by strong inter-molecular coupling in planar chiral metamaterials.

The polarization of light can be rotated in materials with an absence of molecular or structural mirror symmetry. While this rotating ability is normally rather weak in naturally occurring chiral materials, artificial chiral metamaterials have demonstrated extraordinary rotational ability by engineering intra-molecular couplings. However, while in general, chiral metamaterials can exhibit strong rotatory power at or around resonances, they convert linearly polarized waves into elliptically polarized ones. Here, we demonstrate that strong inter-molecular coupling through a small gap between adjacent chiral metamolecules can lead to a broadband enhanced rotating ability with pure rotation of linearly polarized electromagnetic waves. Strong inter-molecular coupling leads to nearly identical behaviour in magnitude, but engenders substantial difference in phase between transmitted left and right-handed waves.