Plasma carrying a spectrum of counterpropagating field-aligned ion-cyclotron waves can strongly and preferentially heat ions through a stochastic Fermi mechanism. Such a process has been proposed to explain the extreme temperatures, temperature anisotropies, and speeds of ions in the solar corona and solar wind. We quantify how differential flow between ion species results in a Doppler shift in the wave spectrum that can prevent this strong heating. Two critical values of differential flow are derived for strong heating of the core and tail of a given ion distribution function. Our comparison of these predictions to observations from the Wind spacecraft reveals excellent agreement. Solar wind helium that meets the condition for strong core heating is nearly 7 times hotter than hydrogen on average. Ion-cyclotron resonance contributes to heating in the solar wind, and there is a close link between heating, differential flow, and temperature anisotropy.

We prepare arrays of gold nanoparticles that include both noncentrosymmetric particles with a second-order nonlinear optical response (active particles) and centrosymmetric particles with no second-order response (passive particles). The plasmon resonances of the active and passive particles are at distinct wavelengths, yet the passive particles modify the electromagnetic modes of the structure in such a way that second-harmonic generation from the active particles is enhanced. Our results provide a completely new concept for optimizing the nonlinear responses of metamaterials.

We report a new type of standing gravity wave of large amplitude, having alternatively the shape of a star and of a polygon. This wave is observed by means of a laboratory experiment by vertically vibrating a tank. The symmetry of the star (i.e., the number of branches) is independent of the container form and size, and can be changed according to the amplitude and frequency of the vibration. We show that a nonlinear resonant coupling between three gravity waves can be envisaged to trigger the observed symmetry breaking, although more complex interactions certainly take place in the final periodic state.

The third-integer coupling resonance at ${\nu }_x-2{\nu }_z=\ell$, known as the Walkinshaw resonance, is important in high-power accelerators. We find that, when the betatron tunes ramp through a Walkinshaw resonance the fractional emittance growth (FEG) is a universal function of the effective resonance strength: $G_{1,-2,\ell }\sqrt{{ϵ}_{xi}}|\Delta ({\nu }_x-2{\nu }_z)/\Delta n{|}^{-1/2}$, where $G_{1,-2,\ell }$ is the resonance strength; ${ϵ}_{xi}$ and ${ϵ}_{zi}$ are the initial horizontal and vertical emittances, respectively; and $|\Delta ({\nu }_x-2{\nu }_z)/\Delta n|$ is the resonance crossing rate per revolution. At large effective resonance strengths, the FEG reaches an asymptotic maximum value $(\mathrm{FEG}{)}_{\max }\sim 2{ϵ}_{xi}/{ϵ}_{zi}$ for ${ϵ}_{xi}\gg \frac{1}{2}{ϵ}_{zi}$ or ${ϵ}_{zi}/(2{ϵ}_{xi})$ for ${ϵ}_{xi}\ll \frac{1}{2}{ϵ}_{zi}$. There is little emittance exchange at ${ϵ}_{xi}=\frac{1}{2}{ϵ}_{zi}$, which can be used to minimize emittance growth in crossing a Walkinshaw resonance.

A finite-size supercell correction scheme is introduced for the formation energy of charged defects at surfaces and interfaces. The scheme combines classical electrostatics with the dielectric profile and the electrostatic potential extracted from the electronic-structure calculation. Spurious electrostatic interactions are removed while retaining the dielectric and quantum-mechanical features of the system of interest, which may have no interface (bulk), a single interface or surface, or two interfaces. A pertinent extrapolation scheme validates the proposed corrections. Applications to the charged Cl vacancy at the surface of NaCl and to the dangling bond at the Si(100) surface show that the corrected formation energies are largely independent of the supercell dimensions and of the size of the vacuum region.

Diamond anvil cells allow the behavior of materials to be studied at pressures up to hundreds of gigapascals in a small and convenient instrument. However, physical access to the sample is impossible once it is pressurized. We show that optical tweezers can be used to hold and manipulate particles in such a cell, confining micron-sized transparent beads in the focus of a laser beam. Here, we use a modified optical tweezers geometry, allowing us to trap through an objective lens with a higher working distance, overcoming the constraints imposed by the limited angular acceptance of the anvil cell. We demonstrate the effectiveness of the technique by measuring water’s viscosity at pressures of up to 1.3 GPa. In contrast to previous viscosity measurements in anvil cells, our technique measures absolute viscosity and does not require scaling to the accepted value at atmospheric pressure. This method could also measure the frequency dependence of viscosity as well as being sensitive to anisotropy in the medium’s viscosity.

We report the observation of a premelting transition at chemically sharp solid-liquid interfaces using molecular-dynamics simulations. The transition is observed in the solid-Al—liquid-Pb system and involves the formation of a liquid interfacial film of Al with a width that grows logarithmically as the bulk melting temperature is approached from below, consistent with current theories of premelting. The premelting behavior leads to a sharp change in the temperature dependence of the diffusion coefficient in the interfacial region and could have important consequences for phenomena such as particle coalescence and shape equilibration, which are governed by interfacial kinetic processes.

In the prototypical heavy-fermion system ${\mathrm{CeCu}}_{6-x}{\mathrm{Au}}_x$, a magnetic quantum critical point can be tuned by Au concentration $x$, hydrostatic pressure $p$, or magnetic field $B$. A striking equivalence of the tuning behavior with $x$ or $p$ had been found with respect to thermodynamic and transport properties. By means of elastic neutron scattering on single crystalline ${\mathrm{CeCu}}_{5.5}{\mathrm{Au}}_{0.5}$, we demonstrate this $x-p$ equivalence on a microscopic level by showing that the magnetic ordering wave vector ${\mathbf{q}}_m$ can be tuned accordingly. At ambient pressure,${\mathrm{CeCu}}_{5.5}{\mathrm{Au}}_{0.5}$ orders at ${\mathbf{q}}_m\approx (0.5900)$. Upon applying $p=4.1\mathrm{kbar}$, ${\mathbf{q}}_m\approx (0.6100.21)$ is found corresponding to ${\mathrm{CeCu}}_{5.6}{\mathrm{Au}}_{0.4}$ at ambient pressure. The transition seems to occur in a first-order fashion and to be governed by slight changes in the nesting properties of the Fermi surface.

As a minimal fermionic model with kinetic frustration, we study a system of spinless fermions in the lowest band of a triangular lattice with nearest-neighbor repulsion. We find that the combination of interactions and kinetic frustration leads to spontaneous symmetry breaking in various ways. Time-reversal symmetry can be broken by two types of loop current patterns, a chiral one and one that breaks the translational lattice symmetry. Moreover, the translational symmetry can also be broken by a density wave forming a kagome pattern or by a Peierls-type trimerization characterized by enhanced correlations among the sites of certain triangular plaquettes (giving a plaquette-centered density wave). We map out the phase diagram as it results from leading-order Ginzburg-Landau mean-field theory. Several experimental realizations of the type of system under study are possible with ultracold atoms in optical lattices.

Anomalous pressure dependent conductivity is revealed for heteroacene organic field-effect transistors of dinaphtho[2, 3-b:$2^{\prime }$, $3^{\prime }$-f]thieno[3, 2-b]thiophene single crystals in the direction of $a$ and $b$ crystallographic axes. In contrast to the normal characteristics of a monotonic increase in mobility $\mu$ with the application of external hydrostatic pressure $P$ in conductors, we found that the present organic semiconductor devices exhibit nonmonotonic and gigantic pressure dependence including an even negative pressure coefficient $d\mu /dP$. In combination with a structural analysis based on x-ray diffraction experiments under pressure, it is suggested that on-site molecular orientation and displacement peculiar in heteroacene molecules are responsible for the anomalous pressure effect.

We explore the phase diagram of spin-orbit Mott insulators on a honeycomb lattice, within the Kitaev-Heisenberg model extended to its full parameter space. Zigzag-type magnetic order is found to occupy a large part of the phase diagram of the model, and its physical origin is explained as due to interorbital $t_{2g}-e_g$ hopping. The magnetic susceptibility, spin wave spectra, and zigzag order parameter are calculated and compared to the experimental data, obtaining thereby the spin coupling constants in ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ and ${\mathrm{Li}}_2{\mathrm{IrO}}_3$.

A proposed coarse-grained model of nucleic acids demonstrates that average interactions between base dipoles, together with chain connectivity and excluded-volume interactions, are sufficient to form double-helical structures of DNA and RNA molecules. Additionally, local interactions determine helix handedness and direction of strand packing. This result, and earlier research on reduced protein models, suggests that mean-field multipole-multipole interactions are the principal factors responsible for the formation of regular structure of biomolecules.

We introduce the totally asymmetric simple exclusion process with Langmuir kinetics on a network as a microscopic model for active motor protein transport on the cytoskeleton, immersed in the diffusive cytoplasm. We discuss how the interplay between active transport along a network and infinite diffusion in a bulk reservoir leads to a heterogeneous matter distribution on various scales: we find three regimes for steady state transport, corresponding to the scale of the network, of individual segments, or local to sites. At low exchange rates strong density heterogeneities develop between different segments in the network. In this regime one has to consider the topological complexity of the whole network to describe transport. In contrast, at moderate exchange rates the transport through the network decouples, and the physics is determined by single segments and the local topology. At last, for very high exchange rates the homogeneous Langmuir process dominates the stationary state. We introduce effective rate diagrams for the network to identify these different regimes. Based on this method we develop an intuitive but generic picture of how the stationary state of excluded volume processes on complex networks can be understood in terms of the single-segment phase diagram.

Nanoscale imaging of biological specimens in their native condition is of long-standing interest, in particular with direct, high resolution views of internal structures of intact specimens, though as yet progress has been limited. Here we introduce wet coherent x-ray diffraction microscopy capable of imaging fully hydrated and unstained biological specimens. Whole cell morphologies and internal structures better than 25 nm can be clearly visualized without contrast degradation.

The genome of influenza A virus consists of eight separate RNA segments, which are selectively packaged into virions prior to virus budding. The microscopic mechanism of highly selective packaging involves molecular interactions between packaging signals in the genome segments and remains poorly understood. We propose that the condition of proper packaging can be formulated as a large gap between RNA-RNA interaction energies in the viable virion with eight unique segments and in improperly packed assemblages lacking the complete genome. We then demonstrate that selective packaging of eight unique segments into an infective influenza virion can be achieved by self-repulsion of identical segments at the virion assembly stage, rather than by previously hypothesized intricate molecular recognition of particular segments. Using Monte Carlo simulations to maximize the energy gap, without any other assumptions, we generated model eight-segment virions, which all display specific packaging, strong self-repulsion of the segments, and reassortment patterns similar to natural influenza. The model provides a biophysical foundation of influenza genome packaging and reassortment and serves as an important step towards robust sequence-driven prediction of reassortment patterns of the influenza virus.

Large-scale simulations of thermal welding of polymers are performed to investigate the rise of mechanical strength at the polymer-polymer interface with the welding time $t_w$. The welding process is at the core of integrating polymeric elements into devices as well as in the thermal induced healing of polymers, processes that require the development of interfacial strength equal to that of the bulk. Our simulations show that the interfacial strength saturates at the bulk shear strength long before polymers diffuse by their radius of gyration. Along with the strength increase, the dominant failure mode changes from chain pullout at the interface to chain scission as in the bulk. The formation of sufficient entanglements across the interface, which we track using a primitive path analysis, is required to arrest catastrophic chain pullout at the interface. The bulk response is not fully recovered until the density of entanglements at the interface reaches the bulk value. Moreover, the increase of interfacial strength before saturation is proportional to the number of interfacial entanglements between chains from opposite sides.

The counting rule for Nambu-Goldstone modes is discussed using Mori’s projection operator method in nonrelativistic systems at zero and finite temperatures. We show that the number of Nambu-Goldstone modes is equal to the number of broken charges, $Q_a$, minus half the rank of the expectation value of [$Q_a$, $Q_b$].

We report on the monotonic increase and the oscillation of electrical conductance in multiwalled carbon nanotubes with compressive strain. Combined experimental and theoretical analyses confirm that the conductance variation with strain is because of the transition from $s{p}^2$ to $s{p}^3$ configurations that are promoted by the interaction of walls in the nanotubes. The intrawall interaction is the reason for the monotonic increase in the conduction, while the oscillations are attributable to interwall interactions. This explains the observed electromechanical oscillation in multiwalled nanotubes and its absence in single-walled nanotubes, thereby resolving a long-standing debate on the interpretation of these results. Moreover, the current carrying capability of nanotubes can be enhanced significantly by controlling applied strains.

A transverse acoustic wave propagates through supercooled liquids in an anomalous manner: for a macroscopic wave number $k$, the wave propagates long distances, as in elastic solids, whereas it attenuates rapidly for a mesoscopic to microscopic wave number $k$, as in viscous liquids. In this work, we theoretically describe this anomalous wave propagation using the hydrodynamics of the two-mode Maxwell constitutive model, which were determined independently from the mechanical properties under oscillatory shear strains. To ensure that the Maxwell model can be applied down to a microscopic length scale, we extended it to a $k$-dependent equation, taking into account the recently reported $k$ dependences of the shear viscosity and modulus [A. Furukawa and H. Tanaka, Phys. Rev. Lett. 103, 135703 (2009); A. FurukawaH. TanakaPhys. Rev. E 84, 061503 (2011)]. The anomalous wave propagation in supercooled liquids can also be understood in terms of a linear coupling of many independent normal modes, as in amorphous solids.

Realizations of Majorana fermions in solid state materials have attracted great interest recently in connection to topological order and quantum information processing. We propose a novel way to create Majorana fermions in superconductors. We show that an incipient noncollinear magnetic order turns a spin-singlet superconductor with nodes into a topological superconductor with a stable Majorana bound state in the vortex core, at a topologically stable magnetic point defect, and on the edge. We argue that such an exotic non-Abelian phase can be realized in extended $t-J$ models on the triangular and square lattices. It is promising to search for Majorana fermions in correlated electron materials where nodal superconductivity and magnetism are two common caricatures.