Although the cardinal attribute of turbulence is the velocity fluctuations, these fluctuations have been ignored in theories of the frictional drag of turbulent flows. Our goal is to test a new theory that links the frictional drag to the spectral exponent $\alpha$, a property of the velocity fluctuations in a flow. We use a soap-film channel wherein for the first time the value of $\alpha$ can be switched between 3 and $5/3$, the two theoretically possible values in soap-film flows. To induce turbulence with $\alpha =5/3$, we make one of the edges of the soap-film channel serrated. Remarkably, the new theory of the frictional drag holds in both soap-film flows (for either value of the spectral exponent $\alpha$) and ordinary pipe flows (where $\alpha =5/3$), even though these types of flow are governed by different equations.

Electron vortices are shown to possess electric and magnetic fields by virtue of their quantized orbital angular momentum and their charge and current density sources. The spatial distributions of these fields are determined for a Bessel electron vortex. It is shown how these fields lead naturally to interactions involving coupling to the spin magnetic moment and spin-orbit interactions which are absent for ordinary electron beams. The orders of magnitude of the effects are estimated here for ȧngström scale electron vortices generated within a typical electron microscope.

We report the first measurements of x-ray single-pulse duration and two-pulse separation at the Linac Coherent Light Source using a cross-correlation technique involving x rays and electrons. An emittance-spoiling foil is adopted as a very simple and effective method to control the output x-ray pulse. A minimum pulse duration of about 3 fs full width at half maximum has been measured together with a controllable pulse separation (delay) between two pulses. This technique provides critical temporal diagnostics for x-ray experiments such as x-ray pump-probe studies.

We determine the deformation energetics and energy density of twisted carbon nanotubes and nanotube ropes that effectively constitute a torsional spring. Using ab initio and parametrized density functional calculations, we identify structural changes in these systems and determine their elastic limits. The deformation energy of twisted nanotube ropes contains contributions associated not only with twisting but also with stretching, bending, and compression of individual nanotubes. We quantify these energy contributions and show that their relative role changes with the number of nanotubes in the rope.

The variable range hopping theory, as formulated for exponentially localized impurity states, does not necessarily apply in the case of graphene with covalently attached impurities. We analyze the localization of impurity states in graphene using the nearest-neighbor, tight-binding model of an adatom-graphene system with Green’s function perturbation methods. The amplitude of the impurity state wave function is determined to decay as a power law with exponents depending on sublattice, direction, and the impurity species. We revisit the variable range hopping theory in view of this result and find that the conductivity depends as a power law of the temperature with an exponent related to the localization of the wave function. We show that this temperature dependence is in agreement with available experimental results.

The spectrum of electron-phonon complexes in monolayer graphene is investigated in the presence of a perpendicular quantizing magnetic field. Despite the small electron-phonon coupling, usual perturbation theory is inapplicable for the calculation of the scattering amplitude near the threshold of optical phonon emission. Our findings, beyond perturbation theory, show that the true spectrum near the phonon-emission threshold is completely governed by new branches, corresponding to bound states of an electron and an optical phonon with a binding energy of the order of $\alpha {\omega }_0$, where $\alpha$ is the electron-phonon coupling and ${\omega }_0$ the phonon energy.

This contribution presents a study of the atomic and electronic structure of the $(\sqrt{5}\times \sqrt{5})R26.6°$ surface reconstruction on ${\mathrm{BaTiO}}_3$ (001) formed by annealing in ultrahigh vacuum at 1300 K. Through density functional theory calculations in concert with thermodynamic analysis, we assess the stability of several ${\mathrm{BaTiO}}_3$ surface reconstructions and construct a phase diagram as a function of the chemical potential of the constituent elements. Using both experimental scanning tunneling microscopy (STM) and scanning tunneling spectroscopy measurements, we were able to further narrow down the candidate structures, and conclude that the surface is either ${\mathrm{TiO}}_2\mathrm{\text{−}}{\mathrm{Ti}}_{3/5}$, ${\mathrm{TiO}}_2\mathrm{\text{−}}{\mathrm{Ti}}_{4/5}$, or some combination, where Ti adatoms occupy hollow sites of the ${\mathrm{TiO}}_2$ surface. Density functional theory indicates that the defect states close to the valence band are from Ti adatom $3d$ orbitals ($\approx 1.4\mathrm{eV}$ below the conduction band edge) in agreement with scanning tunneling spectroscopy measurements showing defect states $1.56\pm 0.11\mathrm{eV}$ below the conduction band minimum ($1.03\pm 0.09\mathrm{eV}$ below the Fermi level). STM measurements show electronic contrast between empty and filled states’ images. The calculated local density of states at the surface shows that Ti $3d$ states below and above the Fermi level explain the difference in electronic contrast in the experimental STM images by the presence of electronically distinctive arrangements of Ti adatoms. This work provides an interesting contrast with the related oxide ${\mathrm{SrTiO}}_3$, for which the (001) surface $(\sqrt{5}\times \sqrt{5})R26.6°$ reconstruction is reported to be the ${\mathrm{TiO}}_2$ surface with Sr adatoms.

We report the observation of weak magnetism in superlattices of ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ using $\beta$-detected nuclear magnetic resonance. The spin lattice relaxation rate of ${}^8\mathrm{Li}$ in superlattices with a spacer layers of 8 and 6 unit cells of ${\mathrm{LaAlO}}_3$ exhibits a strong peak near $\sim 35\mathrm{K}$, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of $\sim 4–6$ unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments ($\sim 0.002{\mu }_B$) in the two samples with a larger ${\mathrm{LaAlO}}_3$ spacer thickness.

When a nematic liquid crystal is confined in a porous medium with strong anchoring conditions, topological defects, called disclinations, are stably formed with numerous possible configurations. Since the energy barriers between them are large enough, the system shows multistability. Our lattice Boltzmann simulations demonstrate dynamic couplings between the multistable defect pattern and the flow in a regular porous matrix. At sufficiently low flow speed, the topological defects are pinned at the quiescent positions. As the flow speed is increased, the defects show cyclic motions and nonlinear rheological properties, which depend on whether or not they are topologically constrained in the porous networks. In addition, we discover that the defect pattern can be controlled by controlling the flow. Thus, the flow path is recorded in the porous channels owing to the multistability of the defect patterns.

Using field-theoretic techniques, we study the solvation of salt ions in liquid mixtures, accounting for the permanent and induced dipole moments, as well as the molecular volume of the species. With no adjustable parameters, we predict solvation energies in both single-component liquids and binary liquid mixtures that are in excellent agreement with experimental data. Our study shows that the solvation energy of an ion is largely determined by the local response of the permanent and induced dipoles, as well as the local solvent composition in the case of mixtures, and does not simply correlate with the bulk dielectric constant. In particular, we show that, in a binary mixture, it is possible for the component with the lower bulk dielectric constant but larger molecular polarizability to be enriched near the ion.

Contextuality is a natural generalization of nonlocality which does not need composite systems or spacelike separation and offers a wider spectrum of interesting phenomena. Most notably, in quantum mechanics there exist scenarios where the contextual behavior is independent of the quantum state. We show that the quest for an optimal inequality separating quantum from classical noncontextual correlations in a state-independent manner admits an exact solution, as it can be formulated as a linear program. We introduce the noncontextuality polytope as a generalization of the locality polytope and apply our method to identify two different tight optimal inequalities for the most fundamental quantum scenario with state-independent contextuality.

The analytic structure of the nonperturbative gluon propagator contains information on the absence of gluons from the physical spectrum of the theory. We study this structure from numerical solutions in the complex momentum plane of the gluon and ghost Dyson-Schwinger equations in Landau gauge Yang-Mills theory. The resulting ghost and gluon propagators are analytic apart from a distinct cut structure on the real, timelike momentum axis. The propagator violates the Osterwalder-Schrader positivity condition, confirming the absence of gluons from the asymptotic spectrum of the theory.

The first measurement of neutron emission in electromagnetic dissociation of ${}^{208}\mathrm{Pb}$ nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ with neutron emission are ${\sigma }_{\mathrm{singleEMD}}=187.4\pm 0.2(\mathrm{stat}{)}_{-11.2}^{+13.2}(\mathrm{syst})\mathrm{b}$ and ${\sigma }_{\mathrm{mutualEMD}}=5.7\pm 0.1(\mathrm{stat})\pm 0.4(\mathrm{syst})\mathrm{b}$, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.

We present, and derive analytic expressions for, a fundamental limit to the sympathetic cooling of ions in radio-frequency traps using cold atoms. The limit arises from the work done by the trap electric field during a long-range ion-atom collision and applies even to cooling by a zero-temperature atomic gas in a perfectly compensated trap. We conclude that in current experimental implementations, this collisional heating prevents access to the regimes of single-partial-wave atom-ion interaction or quantized ion motion. We determine conditions on the atom-ion mass ratio and on the trap parameters for reaching the $s$-wave collision regime and the trap ground state.

We report the generation of spin squeezing and entanglement in a magnetically sensitive atomic ensemble, and entanglement-enhanced field measurements with this system. A maximal $m_f=\pm 1$ Raman coherence is prepared in an ensemble of $8.5\times {10}^5$ laser-cooled ${}^{87}\mathrm{Rb}$ atoms in the $f=1$ hyperfine ground state, and the collective spin is squeezed by synthesized optical quantum nondemolition measurement. This prepares a state with large spin alignment and noise below the projection-noise level in a mixed alignment-orientation variable. 3.2 dB of noise reduction is observed and 2.0 dB of squeezing by the Wineland criterion, implying both entanglement and metrological advantage. Enhanced sensitivity is demonstrated in field measurements using alignment-to-orientation conversion.

Complex dielectric media often appear opaque because light traveling through them is scattered multiple times. Although the light scattering is a random process, different paths through the medium can be correlated encoding information about the medium. Here, we present spectroscopic measurements of nonuniversal intensity correlations that emerge when embedding quantum emitters inside a disordered photonic crystal that is found to Anderson-localize light. The emitters probe in situ the microscopic details of the medium, and imprint such near-field properties onto the far-field correlations. Our findings provide new ways of enhancing light-matter interaction for quantum electrodynamics and energy harvesting, and may find applications in subwavelength diffuse-wave spectroscopy for biophotonics.

The aim of this letter is to assess existing theories for Rayleigh–Taylor small turbulent scales. For this purpose, we propose to adapt the Monin-Yaglom relation to the Rayleigh–Taylor turbulence context. A special emphasis is put on the inhomogeneity of the flow and on the effect of buoyancy forces. This relation is then used to show that, among existing theories, the standard Kolmogorov–Obukhov theory should apply to Rayleigh–Taylor turbulence in the limit of a large Reynolds number, large times, and small scales.

An intense beam of high energy electrons may create extremely high pressures in solid density materials. An analytical model of ablation pressure formation and shock wave propagation driven by an energetic electron beam is developed and confirmed with numerical simulations. In application to the shock-ignition approach in inertial confinement fusion, the energy transfer by fast electrons may be a dominant mechanism of creation of the igniting shock wave. An electron beam with an energy of 30 keV and energy flux $2–5\mathrm{PW}/{\mathrm{cm}}^2$ can create a pressure amplitude more than 300 Mbar for a duration of 200–300 ps in a precompressed solid material.

We present a theoretical study of the impact of spin fluctuations on electronic properties when these fluctuations are soft and strong, as in low-doped cuprates. We show that they play a triple role: they mediate $d$ pairing, destroy the coherence of antinodal electrons, and create a spin density wave pseudogap. The competition between these effects is responsible for numerous electron anomalies close to those observed experimentally in the low-doping superconducting state.

This Letter demonstrates the possibility of generating coherent population trapping in ${\mathrm{C}}_{60}$. Similar to a three-level $\Lambda$ system, ${\mathrm{C}}_{60}$ has a forbidden transition between the highest occupied molecular orbital (HOMO) ($|a⟩$) and the lowest unoccupied molecular orbital (LUMO) ($|c⟩$), but a dipole-allowed transition between HOMO and $\mathrm{LUMO}+1$ ($|b⟩$) and between $|b⟩$ and $|c⟩$. We employ two cw laser fields, one coupling and one probe. The strong coupling field is switched on first to resonantly excite the transition between $|b⟩$ and $|c⟩$. After a delay, the probe is switched on; the coherent interaction between the coupling and probe fields traps the population in $|a⟩$ and $|c⟩$. This forms a partially dark state in ${\mathrm{C}}_{60}$, analogous to that in atomic vapors. Turning off the coupling field restores ${\mathrm{C}}_{60}$’s absorption. Pulsed lasers work as well. We use two pulses to steer the system into a dark state; when we send in a cw probe field, the electric polarization of ${\mathrm{C}}_{60}$ plunges by five times, in comparison with the noncontrol case. This should be detectable experimentally.