Cubic scandium trifluoride (${\mathrm{ScF}}_3$) has a large negative thermal expansion over a wide range of temperatures. Inelastic neutron scattering experiments were performed to study the temperature dependence of the lattice dynamics of ${\mathrm{ScF}}_3$ from 7 to 750 K. The measured phonon densities of states show a large anharmonic contribution with a thermal stiffening of modes around 25 meV. Phonon calculations with first-principles methods identified the individual modes in the densities of states, and frozen phonon calculations showed that some of the modes with motions of F atoms transverse to their bond direction behave as quantum quartic oscillators. The quartic potential originates from harmonic interatomic forces in the ${\mathrm{DO}}_9$ structure of ${\mathrm{ScF}}_3$, and accounts for phonon stiffening with the temperature and a significant part of the negative thermal expansion.

We present the results of a Coulomb explosion experiment that allows for the imaging of the rovibrational wave function of the metastable ${\mathrm{H}}_2^{-}$ ion. Our measurements confirm the predicted large internuclear separation of 6 a.u., and they show that the ion decays by autodetachment rather than by spontaneous dissociation. Imaging of the resulting ${\mathrm{H}}_2$ products reveals a large angular momentum of $J=25\pm 2$, quantifying the rotation that leads to the metastability of this most fundamental molecular anion.

We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission frequency. The decay rates averaged over all dipole orientations are inhibited by a factor of 10 in the photonic band gap and enhanced up to $2\times$ outside the gap, in agreement with theory. We discuss the effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap.

The flapping of the flag is a classical model problem for the understanding of fluid-structure interaction: How does the flat state lose stability? Why do the nonlinear effects induce hysteretic behavior? We show in this Letter that, in contrast with the commonly studied model, the full three-dimensional flag with gravity has no stationary state whose stability can be formally studied: The waves are oblique and must immediately be of large amplitude. The remarkable structure of these waves results from the interplay of weight, geometry, and aerodynamic forces. This pattern is a key element in the force balance which allows the flag to hold and fly in the wind: Large amplitude oblique waves are responsible for lift.

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following $1s^2\to 1s3p$ excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to $10\%$. We observe the peak intensity to scale as ${\rho }^2$ and the emitted pulse width and delay to scale as ${\rho }^{-1}$, where $\rho$ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75 000 times faster than the spontaneous $1s3p\to 1s2s$ decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.

Glycosphingolipids are involved in the first steps of virus-cell interaction, where they mediate specific recognition of the host cell membrane. We have employed total-internal-reflection fluorescence microscopy to explore the interaction kinetics between individual unlabeled noroviruslike particles, which are attached to a glycosphingolipid-containing lipid bilayer, and fluorescent vesicles containing different types and concentrations of glycosphingolipids. Under association equilibrium, the vesicle-binding rate is found to be kinetically limited, yielding information on the corresponding activation energy. The dissociation kinetics are logarithmic over a wide range of time. The latter is explained by the vesicle-size-related distribution of the dissociation activation energy. The biological, pharmaceutical, and diagnostic relevance of the study is briefly discussed.

We report the results of a search for ${\nu }_e$ appearance in a ${\nu }_{\mu }$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2\times {10}^{20}$ protons on the NuMI target at Fermilab, we find that $2{sin}^2({\theta }_{23}){sin}^2(2{\theta }_{13})<0.12(0.20)$ at 90% confidence level for $\delta =0$ and the normal (inverted) neutrino mass hierarchy, with a best-fit of $2{sin}^2({\theta }_{23}){sin}^2(2{\theta }_{13})={0.041}_{-0.031}^{+0.047}({0.079}_{-0.053}^{+0.071})$. The ${\theta }_{13}=0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.

The OPERA collaboration claims that muon neutrinos with a mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about $7.5\mathrm{km}/\mathrm{s}$ or 25 ppm. However, we show that superluminal neutrinos may lose energy rapidly via the bremsstrahlung of electron-positron pairs ($\nu \to \nu +e^{-}+e^{+}$). For the claimed superluminal velocity and at the stated mean energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. This presents a significant challenge to the superluminal interpretation of the OPERA data. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.

A precision measurement of the $\gamma$ yields following the $\beta$ decay of ${}^{32}\mathrm{Cl}$ has determined its isobaric-analogue branch to be $({22.47}_{-0.18}^{+0.21})\%$. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, ${\delta }_C=5.3(9)\%$, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to $0^{+}\to 0^{+}$ transitions for tests of the standard model.

In chemistry and physics symmetry principles are all important, for example, leading to the selection rules governing optical transitions. We have investigated the influence of the molecular symmetry on the surface potential landscape of molecules in the limit of weak molecule-substrate binding. For this purpose, the induced lateral motion of Cu(II)-tetraazaphthalocyanine molecules, for which four symmetry distinct isomers exist, on NaCl(100) was studied by scanning tunneling microscopy. This nonthermal diffusion induced by inelastic excitations is found to be qualitatively different for all four symmetry distinct isomers, demonstrating that symmetry governs the surface potential landscape.

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

In 3D momentum space, a topological phase boundary separating the Chern insulating layers from normal insulating layers may exist, where the gap must be closed, resulting in a “Chern semimetal” state with topologically unavoidable band crossings at the Fermi level. This state is a condensed-matter realization of Weyl fermions in $(3+1)\mathrm{D}$, and should exhibit remarkable features, such as magnetic monopoles and Fermi arcs. Here we predict, based on first principles calculations, that such a novel quantum state can be realized in a known ferromagnetic compound ${\mathrm{HgCr}}_2{\mathrm{Se}}_4$, with a single pair of Weyl fermions separated in momentum space. The quantum Hall effect without an external magnetic field can be achieved in its quantum-well structure.

We investigate how the orbital magnetic moments of electron and hole states in a carbon nanotube quantum dot depend on the number of carriers on the dot. Low temperature transport measurements are carried out in a setup where the device can be rotated in an applied magnetic field, thus enabling accurate alignment with the nanotube axis. The field dependence of the level structure is measured by excited state spectroscopy and excellent correspondence with a single-particle calculation is found. In agreement with band structure calculations we find a decrease of the orbital magnetic moment with increasing electron or hole occupation of the dot, with a scale given by the band gap of the nanotube.

We investigate the local tunnel magnetoresistance (TMR) effect within a single Co nanoisland using spin-polarized scanning tunneling microscopy. We observe a clear spatial modulation of the TMR ratio with an amplitude of $\sim 20\%$ and a spacing of $\sim 1.3\mathrm{nm}$ between maxima and minima around the Fermi level. This result can be ascribed to a spatially modulated spin polarization within the Co island due to spin-dependent quantum interference. Our combined experimental and theoretical study reveals that spin-dependent electron confinement affects all transport properties such as differential conductance, conductance, and TMR. We demonstrate that the TMR within a nanostructured magnetic tunnel junction can be controlled on a length scale of 1 nm through spin-dependent quantum interference.

The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate. We observe that a stress of 10 kPa is sufficient to drastically reduce growth by inhibition of cell proliferation mainly in the core of the spheroid. We compare the results to a simple numerical model developed to describe the role of mechanics in cancer progression.

Using an original pressure-imposed shear cell, we study the rheology of dense suspensions. We show that they exhibit a viscoplastic behavior similarly to granular media successfully described by a frictional rheology and fully characterized by the evolution of the friction coefficient $\mu$ and the volume fraction $\varphi$ with a dimensionless viscous number $I_v$. Dense suspension and granular media are thus unified under a common framework. These results are shown to be compatible with classical empirical models of suspension rheology and provide a clear determination of constitutive laws close to the jamming transition.

Every de Sitter vacuum can transition to every other de Sitter vacuum despite any obstacle, despite intervening anti–de Sitter sinks, despite not being connected by an instanton. Eternal inflation populates the whole landscape.

Entanglement witnesses such as Bell inequalities are frequently used to prove the nonclassicality of a light source and its suitability for further tasks. By demonstrating Bell inequality violations using classical light in common experimental arrangements, we highlight why strict locality and efficiency conditions are not optional, particularly in security-related scenarios.

We report the observation of a steepening in the cosmic ray energy spectrum of heavy primary particles at about $8\times {10}^{16}\mathrm{eV}$. This structure is also seen in the all-particle energy spectrum, but is less significant. Whereas the “knee” of the cosmic ray spectrum at $3–5\times {10}^{15}\mathrm{eV}$ was assigned to light primary masses by the KASCADE experiment, the new structure found by the KASCADE-Grande experiment is caused by heavy primaries. The result is obtained by independent measurements of the charged particle and muon components of the secondary particles of extensive air showers in the primary energy range of ${10}^{16}$ to ${10}^{18}\mathrm{eV}$. The data are analyzed on a single-event basis taking into account also the correlation of the two observables.

We demonstrate a $16{\mathrm{m}}^2$ helium-neon ring laser gyroscope with sufficient sensitivity and stability to directly detect the Chandler wobble of the rotating Earth. The successful detection of both the Chandler and the annual wobble is verified by comparing the time series of the ring laser measurements against the “C04 series” of Earth rotation data from the International Earth Rotation and Reference System Service.