Fast radiative cooling of anthracene was observed in a compact electrostatic storage ring by probing the evolution of the internal energy distribution of a stored $({\mathrm{C}}_{14}{\mathrm{H}}_{10}{)}^{+}$ molecular ensemble via laser excitation. We have measured the mean radiative decay rate to be about 120 to $250{\mathrm{s}}^{-1}$ for internal energies in the range from 6.6 to 6.8 eV. Such a high decay rate is 2 orders of magnitude larger than the infrared emission cooling rate expected for vibrational transitions. It is attributed to fluorescence from thermally excited electrons. This fast cooling mechanism may have important implications in astrophysics concerning the lifetime and the critical size of polycyclic aromatic hydrocarbons in interstellar conditions.

Exploiting the time-reversal invariance and reciprocal properties of the lossless wave equation enables elegantly simple solutions to complex wave-scattering problems and is embodied in the time-reversal mirror. Here we demonstrate the implementation of an electromagnetic time-reversal mirror in a wave chaotic system containing a discrete nonlinearity. We demonstrate that the time-reversed nonlinear excitations reconstruct exclusively upon the source of the nonlinearity. As an example of its utility, we demonstrate a new form of secure communication and point out other applications.

A new integrable nonlocal nonlinear Schrödinger equation is introduced. It possesses a Lax pair and an infinite number of conservation laws and is $PT$ symmetric. The inverse scattering transform and scattering data with suitable symmetries are discussed. A method to find pure soliton solutions is given. An explicit breathing one soliton solution is found. Key properties are discussed and contrasted with the classical nonlinear Schrödinger equation.

Bearings are mechanical dissipative systems that, when perturbed, relax toward a synchronized (bearing) state. Here we find that bearings can be perceived as physical realizations of complex networks of oscillators with asymmetrically weighted couplings. Accordingly, these networks can exhibit optimal synchronization properties through fine-tuning of the local interaction strength as a function of node degree [Motter, Zhou, and Kurths, Phys. Rev. E 71, 016116 (2005)]. We show that, in analogy, the synchronizability of bearings can be maximized by counterbalancing the number of contacts and the inertia of their constituting rotor disks through the mass-radius relation, $m\sim r^{\alpha }$, with an optimal exponent $\alpha ={\alpha }_{\times }$ which converges to unity for a large number of rotors. Under this condition, and regardless of the presence of a long-tailed distribution of disk radii composing the mechanical system, the average participation per disk is maximized and the energy dissipation rate is homogeneously distributed among elementary rotors.

In compressible turbulence at high Reynolds and Mach numbers, shocklets emerge as a new type of flow structure in addition to intense vortices as in incompressible turbulence. Using numerical simulation of compressible homogeneous isotropic turbulence, we conduct a Lagrangian study to explore the effects of shocklets on the dynamics of passive tracers. We show that shocklets cause very strong intermittency and short correlation time of tracer acceleration. The probability density function of acceleration magnitude exhibits a $-2.5$ power-law scaling in the high compression region. Through a heuristic model, we demonstrate that this scaling is directly related to the statistical behavior of strong negative velocity divergence, i.e., the local compression. Tracers experience intense acceleration near shocklets, and most of them are decelerated, usually with large curvatures in their trajectories.

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the $z$ axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the $z$ axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the $z$ axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

The first experimental evidence of the higher-order harmonic radiation generated by periodically modulated targets (gratings) irradiated by relativistic, ultrashort ($<30\mathrm{fs}$), high intensity [$I{\lambda }^2={10}^{20}(\mathrm{W}/{\mathrm{cm}}^2)\mu {\mathrm{m}}^2$] laser pulse is presented. The interference effects on the grating surface lead to the emission of high harmonics up to 45th order along the target surface when the laser beam is focused onto a grating target close to normal incidence (5°). By means of numerical simulations we demonstrate the possibility of controlling the composition of the higher harmonic spectrum and we prove the influence of the laser pulse parameters in the interaction area (laser focusing and wavefront curvature) on the emission angle of a certain high harmonic order.

We report the first observation of prompt neutral beam-ion losses due to nonresonant scattering induced by toroidal and reversed shear Alfvén eigenmodes in the DIII-D tokamak. The coherent losses are of full energy beam ions expelled from the plasma on their first poloidal orbit. The first-orbit loss mechanism causes enhanced, concentrated losses on the first wall exceeding nominal levels of prompt losses. The loss amplitude scales linearly with the mode amplitude. The data provide a novel and direct measure of the radial excursion or scatter of particles induced by individual modes and may shed light on the mechanism for the scattering of energetic particles in interstellar medium.

Cubic boron nitride is a promising system for photonics and optoelectronics. Determining the inclusion mechanisms for dopants with a large size mismatch, such as luminous rare-earth elements, is prerequisite to understanding their functional properties and to effective doping control. Combining evidence from subangstrom resolution scanning transmission electron microscopy, imaging simulations, and first-principles calculations, we show that cationic ${\mathrm{Ce}}^{3+}$ single dopants are not located at cationic B sites but rather at anionic N sites surrounded by B-site vacancies.

The structure of solid deuterium confined in 9 nm wide tubular silicon nanochannels has been studied by means of elastic neutron scattering techniques. As a result we report the formation of fcc ${\mathrm{D}}_2$ as the stable solid phase in confinement in contrast to the hcp bulk structure. Further, a preferred alignment of ${\mathrm{D}}_2$ nanocrystals with respect to the surrounding crystalline silicon matrix is discussed in terms of heteroepitaxial growth of solid ${\mathrm{D}}_2$ on crystalline pore walls.

This Letter reports elastic-driven internal yielding in strained ductile polymer glasses. After cold drawing of two different polymer glasses to neck at room temperature, we show that the samples display considerable retractive stress when warmed up above the storage temperature but still considerably below their glass transition temperatures. We conclude that the elastic yielding arises from the distortion of backbones leading to intra-segmental tension in the chain network.

We present the first accurate damping profiles acquired in atomic-resolution hydration force spectroscopy, revealing a monotonic damping profile at the nanoscopic tip apex. Atomic resolution is confirmed by the observed inhomogeneity caused by random substitution of Si by Al on the mica surface, and two distinct damping regimes are identified. Damping only appears above our detection limit of $1\mathrm{nNs}/\mathrm{m}$ once the tip interacts with the second hydration layer, and an onset of strong damping above $100\mathrm{nNs}/\mathrm{m}$ appears upon direct interaction with the adsorbed layer and first hydration layer. These results are compared to various simulations to interpret the damping signals and determine the tip-sample distance.

Droplets deform soft substrates near their contact lines. Using confocal microscopy, we measure the deformation of silicone gel substrates due to glycerol and fluorinated-oil droplets for a range of droplet radii and substrate thicknesses. For all droplets, the substrate deformation takes a universal shape close to the contact line that depends on liquid composition, but is independent of droplet size and substrate thickness. This shape is determined by a balance of interfacial tensions at the contact line and provides a novel method for direct determination of the surface stresses of soft substrates. Moreover, we measure the change in contact angle with droplet radius and show that Young’s law fails for small droplets when their radii approach an elastocapillary length scale. For larger droplets the macroscopic contact angle is constant, consistent with Young’s law.

Half-metallic ferromagnetism stands for the technologically sought-after metallicity with 100% spin polarization. Electrical transport should, in principle, sensitively probe half-metallic ferromagnetism, since electron-magnon scattering processes are expected to be absent, with clear-cut consequences for the resistivity and the magnetoresistance. Here we present electrical transport data for single-crystalline ${\mathrm{Co}}_2\mathrm{FeSi}$, a candidate half-metallic ferromagnet Heusler compound. The data reveal a textbooklike exponential suppression of the electron-magnon scattering rate with decreasing temperature which provides strong evidence that this material indeed possesses perfect spin polarization at low temperature. However, the energy scale for thermally activated spin-flip scattering is relatively low (activation gap $\Delta \approx 100\mathrm{K}$) which has decisive influence on the magnetoresistance and the anomalous Hall effect, which exhibit strong qualitative changes when crossing $T\approx 100\mathrm{K}$.

We determine magnetoresistance effects in stable and clean Permalloy nanocontacts of variable cross section, fabricated by UHV deposition and in situ electromigration. To ascertain the magnetoresistance (MR) effects originating from a magnetic domain wall, we measure the resistance values with and without such a wall at zero applied field. In the ballistic transport regime, the MR ratio reaches up to 50% and exhibits a previously unobserved sign change. Our results can be reproduced by recent atomistic calculations for different atomic configurations of the nanocontact, highlighting the importance of the detailed atomic arrangement for the MR effect.

We formulate a dynamical real space renormalization group (RG) approach to describe the time evolution of a random spin-$1/2$ chain, or interacting fermions, initialized in a state with fixed particle positions. Within this approach we identify a many-body localized state of the chain as a dynamical infinite randomness fixed point. Near this fixed point our method becomes asymptotically exact, allowing analytic calculation of time dependent quantities. In particular, we explain the striking universal features in the growth of the entanglement seen in recent numerical simulations: unbounded logarithmic growth delayed by a time inversely proportional to the interaction strength. This is in striking contrast to the much slower entropy growth as $\log \log t$ found for noninteracting fermions with bond disorder. Nonetheless, even the interacting system does not thermalize in the long time limit. We attribute this to an infinite set of approximate integrals of motion revealed in the course of the RG flow, which become asymptotically exact conservation laws at the fixed point. Hence we identify the many-body localized state with an emergent generalized Gibbs ensemble.

Symmetry-protected topological (SPT) states are short-range entangled states with symmetry. Nontrivial SPT states have symmetry-protected gapless edge excitations. In 2 dimension (2D), there are an infinite number of nontrivial SPT phases with $SU(2)$ or $SO(3)$ symmetry. These phases can be described by $SU(2)$ or $SO(3)$ nonlinear-sigma models with a quantized topological $\theta$ term. At an open boundary, the $\theta$ term becomes the Wess-Zumino-Witten term and consequently the boundary excitations are decoupled gapless left movers and right movers. Only the left movers (if $\theta >0$) carry the $SU(2)$ or $SO(3)$ quantum numbers. As a result, the $SU(2)$ SPT phases have a half-integer quantized spin Hall conductance and the $SO(3)$ SPT phases have an even-integer quantized spin Hall conductance. Both the $SU(2)$ and $SO(3)$ SPT phases are symmetric under their $U(1)$ subgroup and can be viewed as $U(1)$ SPT phases with even-integer quantized Hall conductance.

The acute magnetic proximity effects in $\mathrm{Pt}/\mathrm{YIG}$ compromise the suitability of Pt as a spin current detector. We show that $\mathrm{Au}/\mathrm{YIG}$, with no anomalous Hall effect and a negligible magnetoresistance, allows the measurements of the intrinsic spin Seebeck effect with a magnitude much smaller than that in $\mathrm{Pt}/\mathrm{YIG}$. The experiment results are consistent with the spin polarized density functional calculations for Pt with a sizable and Au with a negligible magnetic moment near the interface with YIG.

This Letter provides evidence for intrinsic longitudinal spin Seebeck effects (LSSEs) that are free from the anomalous Nernst effect (ANE) caused by an extrinsic proximity effect. We report the observation of LSSEs in $\mathrm{Au}/{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG) and Pt/Cu/YIG systems, showing that the LSSE appears even when the mechanism of the proximity ANE is clearly removed. In the conventional Pt/YIG structure, furthermore, we separate the LSSE from the ANE by comparing the voltages in different magnetization and temperature-gradient configurations; the ANE contamination was found to be negligibly small even in the Pt/YIG structure.

Given a microscopic lattice Hamiltonian for a topologically ordered phase, we propose a numerical approach to characterize its emergent anyon model and, in a chiral phase, also its gapless edge theory. First, a tensor network representation of a complete, orthonormal set of ground states on a cylinder of infinite length and finite width is obtained through numerical optimization. Each of these ground states is argued to have a different anyonic flux threading through the cylinder. Then a quasiorthogonal basis on the torus is produced by chopping off and reconnecting the tensor network representation on the cylinder. From these two bases, and by using a number of previous results, most notably the recent proposal of Y. Zhang et al. [Phys. Rev. B 85, 235151 (2012)] to extract the modular $U$ and $S$ matrices, we obtain (i) a complete list of anyon types $i$, together with (ii) their quantum dimensions $d_i$ and total quantum dimension $D$, (iii) their fusion rules $N_{ij}{}^k$, (iv) their mutual statistics, as encoded in the off-diagonal entries $S_{ij}$ of $S$, (v) their self-statistics or topological spins ${\theta }_i$, (vi) the topological central charge $c$ of the anyon model, and, in a chiral phase (vii) the low energy spectrum of each sector of the boundary conformal field theory. As a concrete application, we study the hard-core boson Haldane model by using the two-dimensional density matrix renormalization group. A thorough characterization of its universal bulk and edge properties unambiguously shows that it realizes a $\nu =1/2$ bosonic fractional quantum Hall state.