We report the existence of a critical ionic conductivity below which oppositely charged drops only partially coalesce. The extent of coalescence between dissimilarly sized water drops in oil can be tuned from complete coalescence at low electric field strengths to complete noncoalescence at high field strengths, thus providing external control over the daughter droplet size. Strikingly, the size and charge of the daughter droplet are both independent of the ionic conductivity. We present evidence suggesting the charge transfer is instead strongly influenced by convection associated with the capillary-driven penetration of a vortex into the larger drop, and we demonstrate that the size of the daughter droplet is consistent with a scaling model based on a balance between capillary-driven inertia and electrostatic repulsion.

Knudsen layer losses of tail fuel ions can significantly reduce the fusion reactivity of multi-keV DT in capsules with small fuel $\rho r$; sizable yield reduction can result for small inertial confinement fusion (ICF) capsules. This effect is most pronounced when the distance from a burning DT gas region to a nonreacting or cold wall is comparable to the mean free path of reacting fuel ions. A simplified asymptotic theory of Knudsen layer tail depletion is presented and a nonlocal reduced fusion reactivity model is obtained. Application of the model in simulations of ICF capsule implosion experiments gives calculated yields and ion temperatures that are in much closer agreement with observations than are the results of “nominal” or mixed simulations omitting the model.

Chemical functionalization of graphene holds promise for various applications ranging from nanoelectronics to catalysis, drug delivery, and nanoassembly. In many applications it is important to be able to transport adsorbates on graphene in real time. We propose to use electromigration to drive the adsorbate transport across the graphene sheet. To assess the efficiency of electromigration, we develop a tight-binding model of electromigration of an adsorbate on graphene and obtain simple analytical expressions for different contributions to the electromigration force. Using experimentally accessible parameters of realistic graphene-based devices as well as electronic structure theory calculations to parametrize the developed model, we argue that electromigration on graphene can be efficient. As an example, we show that the drift velocity of atomic oxygen covalently bound to graphene can reach $\sim 1\mathrm{cm}/\mathrm{s}$.

We introduce a general, efficient method to completely describe the topology of individual grains, bubbles, and cells in three-dimensional polycrystals, foams, and other multicellular microstructures. This approach is applied to a pair of three-dimensional microstructures that are often regarded as close analogues in the literature: one resulting from normal grain growth (mean curvature flow) and another resulting from a random Poisson-Voronoi tessellation of space. Grain growth strongly favors particular grain topologies, compared with the Poisson-Voronoi model. Moreover, the frequencies of highly symmetric grains are orders of magnitude higher in the grain growth microstructure than they are in the Poisson-Voronoi one. Grain topology statistics provide a strong, robust differentiator of different cellular microstructures and provide hints to the processes that drive different classes of microstructure evolution.

In the present Letter, we report on a combined ab initio density functional theory calculation, multislice simulation, and electron holography study, performed on a $\Sigma 9$ grain boundary (GB) in a ${\mathrm{CuGaSe}}_2$ bicrystal, which exhibits a lower symmetry compared with highly symmetric $\Sigma 3$ GBs. We find an electrostatic potential well at the $\Sigma 9$ GB of 0.8 V in depth and 1.3 nm in width, which in comparison with results from $\Sigma 3$ and random GBs exhibits the trend of increasing potential-well depths with lower symmetry. The presence of this potential well at the $\Sigma 9$ GB can be explained conclusively by a reduced density of atoms at the GB. Considering experimental limitations in resolution, we demonstrate quantitative agreement of experiment and theory.

We show that slowly sheared metallic nanocrystals deform via discrete strain bursts (slips), whose size distributions follow power laws with stress-dependent cutoffs. We show for the first time that plasticity reflects tuned criticality, by collapsing the stress-dependent slip-size distributions onto a predicted scaling function. Both power-law exponents and scaling function agree with mean-field theory predictions. Our study of 7 materials and 2 crystal structures, at various deformation rates, stresses, and crystal sizes down to 75 nm, attests to the universal characteristics of plasticity.

$\mathrm{GeTe}/{\mathrm{Sb}}_2{\mathrm{Te}}_3$ superlattice phase-change memory devices demonstrated greatly improved performance over that of ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$, a prototype record media for phase-change random access memory. In this work, we show that this type of $\mathrm{GeTe}/{\mathrm{Sb}}_2{\mathrm{Te}}_3$ superlattice exhibits topological insulating behavior on the basis of ab initio calculations. The analysis of the band structures and parities as well as $Z_2$ topological invariants unravels the topological insulating nature in these artificial materials. Furthermore, the topological insulating character remains in the $\mathrm{GeTe}/{\mathrm{Sb}}_2{\mathrm{Te}}_3$ superlattice under small compressive strains, whereas it is not observed as more ${\mathrm{Sb}}_2{\mathrm{Te}}_3$ building blocks introduced in the superlattice. The present results show that multifunctional data storages may be achieved in the $\mathrm{GeTe}/{\mathrm{Sb}}_2{\mathrm{Te}}_3$ superlattice. Such kinds of artificial materials can be used in phase-change random access memory, spintronics, and quantum computing.

We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics—a large, robust spin splitting and ambipolar conduction—are present in this material.

The relaxation dynamics of an exciton in rubrene was investigated by femtosecond absorption spectroscopy. Exciton relaxation to a self-trapped state occurs via the coherent oscillation with $78{\mathrm{cm}}^{-1}$ due to a coupled mode of molecular deformations with phenyl-side-group motions and molecular displacements. From the temperature dependence of the decay time of excitons, the energy necessary for an exciton to escape from a self-trapped state is evaluated to be $\sim 35\mathrm{meV}$ ($\sim 400\mathrm{K}$). As a result, a self-trapped exciton is stable at low temperatures. At room temperature, excitons can escape from a self-trapped state and, subsequently, they are dissociated to charged species. The exciton dissociation mechanism is discussed on the basis of the results.

Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (${\mathrm{NV}}^0$) and negatively charged (${\mathrm{NV}}^{-}$) states. Luminescence of ${\mathrm{NV}}^{-}$ is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of ${\mathrm{NV}}^0$. The dark state of ${\mathrm{NV}}^{-}$ is identified as ${\mathrm{NV}}^0$. A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to ${\mathrm{NV}}^0$.

It has been predicted theoretically and demonstrated experimentally that a planar slab supporting surface plasmons or surface phonon polaritons can behave as a super lens. However, the resolution is limited by the losses of the slab. In this Letter, we point out that the resolution limit imposed by losses can be overcome by using time-dependent illumination.

Laser-induced condensed phase reactions are often interpreted as nonequilibrium phenomena that go beyond conventional thermodynamics. Here, we show by Langevin dynamics and for the example of femtosecond-laser desorption of hydrogen from a ruthenium surface that light adsorbates thermalize rapidly due to ultrafast energy redistribution after laser excitation. Despite the complex reaction mechanism involving hot electrons in the surface region, all desorption product properties are characterized by equilibrium distributions associated with a single, unique temperature. This represents an example of ultrahot chemistry on the subpicosecond time scale.

There is currently no experimental technique available to probe spatially resolved rotational diffusion of nanoparticles in the vicinity of a wall. We present the first experimental study of rotational diffusion of small spherical colloids, using dynamic evanescent wave scattering. A setup is used where the wave vector components parallel and perpendicular to the wall can be varied independently, and an expression is derived for the first cumulant of the intensity correlation function in VH evanescent wave geometry for optically anisotropic spheres. The experimental results are in agreement with theoretical predictions that take particle-wall hydrodynamic interactions into account.

We show that the influence of thermal noise, simulated by a 2D ferromagnetic Ising spin lattice on a pair of noninteracting, initially entangled qubits, represented by quantum spins, leads to unexpected evolution of quantum correlations. The high temperature noise leads to ultraslow decay of the quantum correlations. Decreasing the noise temperature we observe a decrease of the characteristic decay time scale. When the noise originates from a critical state, a revival of the quantum correlations is observed. This revival becomes oscillatory with a slowly decaying amplitude when the temperature is decreased below the critical region, leading to persistence of the quantum correlations.

A shock-accelerated particle flux $\propto p^{-s}$, where $p$ is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with $s\approx 2.8$ provides an adequate fit to the Fermi Large Area Telescope $\gamma$-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, and Taylor [Phys. Rev. Lett. 108, 051105 (2012)] when fitting the $\gamma$-ray spectra of high-latitude molecular clouds is a consequence of using a cosmic-ray proton flux described by a power law in kinetic energy.

We provide a geometrical argument for the emergence of a Wess-Zumino-Witten (WZW) term in a Fermi surface threaded by a Berry curvature. In the presence of external fields, the gauged WZW term yields a chiral (triangle) anomaly for the fermionic current at the edge of the Fermi surface. The fermion number is conserved, though, since Berry curvatures always occur in pairs with opposite (monopole) charge. The anomalous vector and axial currents for a fermionic fluid at low temperature threaded by pairs of Berry curvatures are discussed. The leading temperature correction to the chiral vortical effect in a slowly rotating Fermi surface threaded by a Berry curvature may be tied to the gravitational anomaly.

We extract ratios of $B\to K^{*}$ form factors at low hadronic recoil from recent data on $B\to K^{*}{\mu }^{+}{\mu }^{-}$ decays in a model independent way. The presented method will improve in the future with further (angular) studies in semileptonic rare $B$ decays and advance our understanding of form factors, which are important inputs in precision tests of the standard model.

The $0_2^{+}$ state in ${}^{34}\mathrm{Si}$ has been populated at the GANIL-LISE3 facility through the $\beta$ decay of a newly discovered $1^{+}$ isomer in ${}^{34}\mathrm{Al}$ of 26(1) ms half-life. The simultaneous detection of $e^{+}{e}^{-}$ pairs allowed the determination of the excitation energy $E(0_2^{+})=2719(3)\mathrm{keV}$ and the half-life $T_{1/2}=19.4(7)\mathrm{ns}$, from which an electric monopole strength of ${\rho }^2(E0)=13.0(0.9)\times {10}^{-3}$ was deduced. The $2_1^{+}$ state is observed to decay both to the $0_1^{+}$ ground state and to the newly observed $0_2^{+}$ state [via a 607(2) keV transition] with a ratio $R(2_1^{+}\to 0_1^{+}/2_1^{+}\to 0_2^{+})=1380(717)$. Gathering all information, a weak mixing with the $0_1^{+}$ and a large deformation parameter of $\beta =0.29(4)$ are found for the $0_2^{+}$ state, in good agreement with shell model calculations using a new sdpf-u-mix interaction allowing $np\mathrm{\text{−}}nh$ excitations across the $N=20$ shell gap.

Amplified spontaneous emission is a common noise source in active optical systems, it is generally seen as being an incoherent process. Here we excite an ensemble of rare earth ion dopants in a solid with a $\pi$ pulse, resulting in amplified spontaneous emission. The application of a second $\pi$ pulse leads to a coherent echo of the amplified spontaneous emission that is correlated in both amplitude and phase. For small optical thicknesses, we see evidence that the amplified spontaneous emission and its echo are entangled.

In this paper we report the first demonstration of “rephased amplified spontaneous emission” (RASE) with photon-counting detection. This protocol provides an all-in-one photon-pair source and quantum-memory that has applications as a quantum repeater node. The RASE protocol is temporally multimode, and in this demonstration the photon echo was generated in a way that is spatially multimode and includes intermediate storage between two potentially long-lived spin states. A correlation between spontaneous emission and its photon echo was observed, using an ensemble of ${\mathrm{Pr}}^{3+}$ ions doped into a ${\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal. Alterations that would allow for the measurement of nonclassical correlations are identified. These should generally apply for future experiments in rare-earth ion crystals, which are promising systems for implementing highly-multiplexed quantum repeater operations.