Localized structures such as turbulent stripes and turbulent spots are typical features of transitional wall-bounded flows in the subcritical regime. Based on an assumption for scale separation between large and small scales, we show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of the turbulence patch generates a large-scale flow with a nonzero spanwise component. Advection of the small-scale turbulent fluctuations (streaks) by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other subcritical flows such as plane Poiseuille flow or Taylor-Couette flow.

When submitted to large stresses at high temperature, usual crystals may irreversibly deform. This phenomenon is known as plasticity and it is due to the motion of crystal defects such as dislocations. We have discovered that, in the absence of impurities and in the zero temperature limit, helium 4 crystals present a giant plasticity that is anisotropic and reversible. Direct measurements on oriented single crystals show that their resistance to shear nearly vanishes in one particular direction because dislocations glide freely parallel to the basal planes of the hexagonal structure. This plasticity disappears as soon as traces of helium 3 impurities bind to the dislocations or if their motion is damped by collisions with thermal phonons.

An unexpected insensitivity of the Fermi surface to impurity scattering is found in Ru substituted ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ from first-principles theory, offering a natural explanation of the unusual resilience of transport and superconductivity to a high level of disordered substitution in this material. This robustness is shown to originate from a coherent interference of correlated on-site and intersite impurity scattering, similar in spirit to the microscopic mechanism of superdiffusion in one dimension. Our result also demonstrates a strong substitution dependence of the Fermi surface and carrier concentration and provides a resolution to current discrepancies in recent photoelectron spectroscopy. These effects offer a natural explanation of the diminishing long-range magnetic, orbital, and superconducting orders with high substitution.

Our measurements of the low frequency ac conductivity in strongly disordered two-dimensional films near the magnetic-field-tuned superconductor-to-insulator transition show a sudden drop in the phase stiffness of superconducting order with either increased temperature or magnetic field. Surprisingly, for two different material systems, the abrupt drop in the superfluid density in a magnetic field has the same universal value as that expected for a Berezinskii-Kosterlitz-Thouless transition in a zero magnetic field. The characteristic temperature at which phase stiffness is suddenly lost can be tuned to zero at a critical magnetic field, following a power-law behavior with a critical exponent consistent with that obtained in previous dc transport studies on the dissipative side of the transition.

We show the existence of a stable algebraic spin liquid (ASL) phase in a Hubbard model defined on a honeycomb lattice with spin-dependent hopping that breaks time-reversal symmetry. The effective spin model is the Kitaev model for large on-site repulsion. The gaplessness of the emergent Majorana fermions is protected by the time-reversal invariance of this model. We prove that the effective spin model is time-reversal invariant in the entire Mott phase, thus ensuring the stability of the ASL. The model can be physically realized in cold atom systems, and we propose experimental signals of the ASL.

The optical properties of a ${\mathrm{GaTa}}_4{\mathrm{Se}}_8$ single crystal are investigated under high pressure. At ambient pressure, the optical conductivity exhibits a charge gap of $\approx 0.12\mathrm{eV}$ and a broad midinfrared band at $\approx 0.55\mathrm{eV}$. As pressure is increased, the low energy spectral weight is strongly enhanced and the optical gap is rapidly filled, pointing to an insulator to metal transition around 6 GPa. The overall evolution of the optical conductivity demonstrates that ${\mathrm{GaTa}}_4{\mathrm{Se}}_8$ is a Mott insulator which undergoes a bandwidth-controlled Mott metal-insulator transition under pressure, in remarkably good agreement with theory. With the use of our optical data and ab initio band structure calculations, our results were successfully compared to the ($U/D$, $T/D$) phase diagram predicted by dynamical mean field theory for strongly correlated systems.

An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.

We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-$Q$ optical cavity mode. Large optomechanical factors are reported ($\sim \mathrm{THz}/\mathrm{nm}$ range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range $\mu \mathrm{W}–\mathrm{mW}$, opening the way for the demonstration of phonon “lasing” by parametric instability in these devices.

Theoretical calculations of thermal spin transitions in nanoscale clusters on a surface are presented. The mechanisms for magnetization reversal are identified and the activation energy and pre-exponential factor for the rate are evaluated using a recently developed harmonic transition state theory and a Heisenberg-type Hamiltonian. A maximum is found in the pre-exponential factor as a function of cluster size corresponding to a crossover from a uniform rotation mechanism to temporary domain wall formation. As the islands grow, the energy barrier increases up to a limit where the domain wall is fully established. For larger islands, the minimum energy path becomes flat resulting in a significant recrossing correction to the transition state theory estimate of the rate. The parameters of the Hamiltonian are chosen to mimic Fe clusters on a W(110) surface, a system that has previously been studied extensively in the laboratory and the calculated results are found to be in close agreement with the reported measurements.

The simple interpretation of Pierre Auger Observatory ultrahigh energy cosmic rays (UHECRs) penetration depth measurements suggests a transition at the energy range $1.1–35\times {10}^{18}\mathrm{eV}$ from protons to heavier nuclei. A detailed comparison of this data with air shower simulations reveals strong restrictions on the amount of light nuclei (protons and He) in the observed flux. We find a robust upper bound on the observed proton fraction of the UHECR flux and we rule out a composition dominated by protons and He. Acceleration and propagation effects lead to an observed composition that is different from the one at the source. Using a simple toy model that takes into account these effects, we show that the observations require an extreme metallicity at the sources with metals to protons mass ratio of $1:1$, a ratio that is larger by a factor of a hundred than the solar abundance. This composition imposes an almost impossible constraint on all current astrophysical models for UHECR accelerators. This m4ay provide a first hint toward new physics that emerges at $\sim 100\mathrm{TeV}$ and leads to a larger proton cross section at these energies.

Stable topological defects of light (pseudo)scalar fields can contribute to the Universe’s dark energy and dark matter. Currently, the combination of gravitational and cosmological constraints provides the best limits on such a possibility. We take an example of domain walls generated by an axionlike field with a coupling to the spins of standard-model particles and show that, if the galactic environment contains a network of such walls, terrestrial experiments aimed at the detection of wall-crossing events are realistic. In particular, a geographically separated but time-synchronized network of sensitive atomic magnetometers can detect a wall crossing and probe a range of model parameters currently unconstrained by astrophysical observations and gravitational experiments.

Based on $106\times {10}^6\psi (3686)$ events collected with the BESIII detector at the BEPCII facility, a partial wave analysis of $\psi (3686)\to p\overline{p}{\pi }^0$ is performed. The branching fraction of this channel has been determined to be $B\mathbf{(}\psi (3686)\to p\overline{p}{\pi }^0\mathbf{)}=(1.65\pm 0.03\pm 0.15)\times {10}^{-4}$. In this decay, 7 $N^{*}$ intermediate resonances are observed. Among these, two new resonances, $N(2300)$ and $N(2570)$ are significant, one $1/2^{+}$ resonance with a mass of ${2300}_{-30-0}^{+40+109}\mathrm{MeV}/c^2$ and width of ${340}_{-30-58}^{+30+110}\mathrm{MeV}/c^2$, and one $5/2^{-}$ resonance with a mass of ${2570}_{-10-10}^{+19+34}\mathrm{MeV}/c^2$ and width of ${250}_{-24-21}^{+14+69}\mathrm{MeV}/c^2$. For the remaining 5 $N^{*}$ intermediate resonances [$N(1440)$, $N(1520)$, $N(1535)$, $N(1650)$ and $N(1720)$], the analysis yields mass and width values that are consistent with those from established resonances.

The electromagnetic structure of the lightest hadrons, proton, pion, and kaon is studied by high-precision measurements of their form factors for the highest timelike momentum transfers of $|Q^2|=s=14.2$ and $17.4{\mathrm{GeV}}^2$. Data taken with the CLEO-c detector at $\sqrt{s}=3.772$ and 4.170 GeV, with integrated luminosities of 805 and $586{\mathrm{pb}}^{-1}$, respectively, have been used to study $e^{+}{e}^{-}$ annihilations into ${\pi }^{+}{\pi }^{-}$, $K^{+}{K}^{-}$, and $p\overline{p}$. The dimensional counting rule prediction that at large $Q^2$ the quantity $Q^{2}F(Q^2)$ for pseudoscalar mesons is nearly constant, and should vary only weakly as the strong coupling constant ${\alpha }_S(Q^2)$ is confirmed for both pions and kaons. However, the measurements are in strong quantitative disagreement with the predictions of the existing quantum chromodynamics-based models. For protons, it is found that the timelike form factors continue to remain nearly twice as large as the corresponding spacelike form factors measured in electron elastic scattering, in significant violation of the expectation of their equality at large $Q^2$. Further, in contrast to pions and kaons, a significant difference is observed between the values of the corresponding quantity $|Q^4|G_M(|Q^2|)/{\mu }_p$ for protons at $|Q^2|=14.2$ and $17.4{\mathrm{GeV}}^2$. The results suggest the constancy of $|Q^2|G_M(|Q^2|)/{\mu }_p$, instead, at these large $|Q^2|$.

Evidence is presented for the associated production of a single top quark and $W$ boson in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of $4.9{\mathrm{fb}}^{-1}$. The measurement is performed using events with two leptons and a jet originated from a $b$ quark. A multivariate analysis based on kinematic properties is utilized to separate the $t\overline{t}$ background from the signal. The observed signal has a significance of $4.0\sigma$ and corresponds to a cross section of ${16}_{-4}^{+5}\mathrm{pb}$, in agreement with the standard model expectation of $15.6\pm {0.4}_{-1.2}^{+1.0}\mathrm{pb}$.

The neutron-rich unbound ${}^7\mathrm{He}$ nucleus has been the subject of many experimental investigations. While the ground-state $3/2^{-}$ resonance is well established, there is a controversy concerning the excited $1/2^{-}$ resonance reported in some experiments as low lying and narrow ($E_R\sim 1\mathrm{MeV}$, $\Gamma \le 1\mathrm{MeV}$) while in others as very broad and located at a higher energy. This issue cannot be addressed by ab initio theoretical calculations based on traditional bound-state methods. We introduce a new unified approach to nuclear bound and continuum states based on the coupling of the no-core shell model, a bound-state technique, with the no-core shell model combined with the resonating-group method, a nuclear scattering technique. Our calculations describe the ground-state resonance in agreement with experiment and, at the same time, predict a broad $1/2^{-}$ resonance above 2 MeV.

We investigate the time-dependent evolution of a nonstationary three-body Coulomb system at energies just below the threshold for three-body breakup. Experimentally, short-pulse lasers excite two electrons in Ba to radially localized Rydberg wave packets with well-defined energy and angular momentum. Time-dependent interactions between the two electrons are probed using half-cycle electric field pulses. The measurements indicate that substantial energy exchange between the two electrons is nearly immediate upon the launch of the second wave packet. Fully quantum and classical calculations support this observation, predicting extremely rapid autoionization under the experimental conditions. The calculations also show very fast angular momentum exchange and sensitivity to the relative binding energies of the two electrons.

We present a method for producing a single circularly polarized attosecond pulse by an intense few cycle elliptically polarized laser pulse combined with a terahertz field from numerical solutions of the time-dependent Schrödinger equation for the molecular ion ${\mathrm{H}}_2^{+}$. It is found that in the presence of a 62.5 THz ($\lambda =4800\mathrm{nm}$) field at an intensity of $\sim {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, a single circularly polarized 114 as pulse can be generated by an elliptical polarized laser pulse at a wavelength of 400 nm with an ellipticity of $ϵ=0.59$. The efficiency of circular polarization attosecond pulse generation is interpreted based on a classical model of single electron recollision with the parent ion.

In strong-field ionization (SFI) of polyatomic molecules, the participation of multiple electronic ionization channels is emerging as a key aspect. In the molecular frame, each channel is expected to show a characteristic dependence of the SFI yield on the polarization direction of the ionizing field. We apply a new angle- and channel-resolved SFI technique to the polyatomic molecule 1,3-butadiene and compare these molecular-frame measurements with two leading theoretical models.

We investigate the dependence of solar wind fluctuations measured by the Wind spacecraft on scale and on the degree of alignment between oppositely directed Elsasser fields. This alignment controls the strength of the nonlinear interactions and, therefore, the turbulence. We find that at scales larger than the outer scale of the turbulence the Elsasser fluctuations become on average more antialigned as the outer scale is approached from above. Conditioning structure functions using the alignment angle reveals turbulent scaling of unaligned fluctuations at scales previously believed to lie outside the turbulent cascade in the “$1/f$ range.” We argue that the $1/f$ range contains a mixture of a noninteracting antialigned population of Alfvén waves and magnetic force-free structures plus a subdominant population of unaligned cascading turbulent fluctuations.

This Letter shows the first results from the solar wind monitor onboard the Spektr-R spacecraft which measures plasma moments with a time resolution of 31 ms. This high-time resolution allows us to make direct observations of solar wind turbulence below ion kinetic length scales. We present examples of the frequency spectra of the density, velocity, and thermal velocity. Our study reveals that although these parameters exhibit the same behavior at the magnetohydrodynamic scale, their spectra are remarkably different at the kinetic scale.