The existence of the ${}^7\mathrm{H}$ nuclear system was investigated via a one-proton transfer reaction with a ${}^8\mathrm{He}$ beam at $15.4\mathrm{A}\mathrm{MeV}$ and a ${}^{12}\mathrm{C}$ gas target. The experimental setup was based on the active-target MAYA which allowed a complete reconstruction of the reaction kinematics. The existence of the ${}^7\mathrm{H}$ was confirmed with the identification of seven events where the system was formed with a resonance energy of ${0.57}_{-0.21}^{+0.42}\mathrm{MeV}$ above the ${}^3\mathrm{H}+4n$ threshold and a resonance width of ${0.09}_{-0.06}^{+0.94}\mathrm{MeV}$. This study represents an unambiguous proof of the existence of the most neutron-proton unbalanced system presently found.

We show that while the statistics of static speckle patterns are generic, fluctuations in the change within speckle patterns are greatly enhanced in the localization transition. The probability distributions of the displacement of phase singularities and the standard deviations of the changes of phase and intensity with frequency shift of incident microwave radiation are given in terms of the same expression which describes the probability distribution of total transmission. This function depends only upon a single parameter, the variance of the corresponding variable. The changing statistics in the localization transition reflects the number of underlying electromagnetic modes with which the incident wave interacts.

We report the first direct observation of the strange $b$ baryon ${\Xi }_b^{-}({\overline{\Xi }}_b^{+})$. We reconstruct the decay ${\Xi }_b^{-}\to J/\psi {\Xi }^{-}$, with $J/\psi \to {\mu }^{+}{\mu }^{-}$, and ${\Xi }^{-}\to \Lambda {\pi }^{-}\to p{\pi }^{-}{\pi }^{-}$ in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. Using $1.3{\mathrm{fb}}^{-1}$ of data collected by the D0 detector, we observe $15.2\pm 4.4(\mathrm{stat}{)}_{-0.4}^{+1.9}(\mathrm{syst})$ ${\Xi }_b^{-}$ candidates at a mass of $5.774\pm 0.011(\mathrm{stat})\pm 0.015(\mathrm{syst})\mathrm{GeV}$. The significance of the observed signal is $5.5\sigma$, equivalent to a probability of $3.3\times {10}^{-8}$ of it arising from a background fluctuation. Normalizing to the decay ${\Lambda }_b\to J/\psi \Lambda$, we measure the relative rate $\frac{\sigma ({\Xi }_b^{-})\times \mathcal{B}({\Xi }_b^{-}\to J/\psi {\Xi }^{-})}{\sigma ({\Lambda }_b)\times \mathcal{B}({\Lambda }_b\to J/\psi \Lambda )}=0.28\pm 0.09(\mathrm{stat}{)}_{-0.08}^{+0.09}(\mathrm{syst})$.

Diamonds melt at temperatures above 4000 K. There are no measurements of the steady-state rate of the reverse process, i.e., diamond nucleation from the melt, because experiments are difficult at these extreme temperatures and pressures. Using numerical simulations, we estimate the diamond nucleation rate and find that it increases by many orders of magnitude when the pressure is increased at constant supersaturation. The reason is that by increasing the pressure the local coordination of the liquid changes from threefold to fourfold, and we show that the free-energy cost to create a diamond-liquid interface is lower in the fourfold than in the threefold liquid. We speculate that this mechanism for nucleation control is relevant for crystallization in many network-forming liquids. We conclude that homogeneous diamond nucleation is likely in carbon-rich stars and unlikely in gaseous planets.

We investigated the physical properties of Cr ions in half-metallic ${\mathrm{CrO}}_2$ using ${}^{53}\mathrm{Cr}$ nuclear magnetic resonance (NMR). The ${}^{53}\mathrm{Cr}$ NMR spectra showed two peaks with a similar intensity instead of the single peak anticipated from a uniform single valence ${\mathrm{Cr}}^{+4}$. Both Cr peaks exhibited a strong anisotropy in the hyperfine field and similar values in the enhancement factor and $T_2$ relaxation time. These results suggest the coexistence of two different Cr ions (provisionally, ${\mathrm{Cr}}^{+4\pm 1/3}$) by a self-doping effect, which is a likely origin of the metallic ferromagnetism in ${\mathrm{CrO}}_2$.

In 1867, Lord Kelvin described an experiment in which two streams of water droplets were connected so that each stream amplified the charge on the second stream [W. Thomson, Proc. R. Soc. London 16, 67 (1867).]. We present here a complementary effect in flowing grains that spontaneously separates similar and well-mixed grains into two charged streams of demixed grains. This effect has important consequences for industrial and natural processes.

According to recent simulations, the coalescence of two spinning black holes (BHs) could lead to a BH remnant with recoil speeds of up to thousands of $\mathrm{km}{\mathrm{s}}^{-1}$. Here we examine the circumstances resulting from a gas-rich galaxy merger under which the ejected BH would carry an accretion disk and be observable. As the initial BH binary emits gravitational radiation and its orbit tightens, a hole is opened in the disk which delays the consumption of gas prior to the eventual BH ejection. The punctured disk remains bound to the ejected BH within the region where the gas orbital velocity is larger than the ejection speed. For a $\sim {10}^7{M}_{\odot }$ BH the ejected disk has a characteristic size of tens of thousands of Schwarzschild radii and an accretion lifetime of $\sim {10}^7\mathrm{yr}$. During that time, the ejected BH could traverse a considerable distance and appear as an off-center quasar with a feedback trail along the path it left behind.

We seek the first indications that a nanoelectromechanical system (NEMS) is entering the quantum domain as its mass and temperature are decreased. We find them by studying the transition from classical to quantum behavior of a driven nonlinear Duffing resonator. Numerical solutions of the equations of motion, operating in the bistable regime of the resonator, demonstrate that the quantum Wigner function gradually deviates from the corresponding classical phase-space probability density. These clear differences that develop due to nonlinearity can serve as experimental signatures, in the near future, that NEMS resonators are entering the quantum domain.

We experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field. This optically induced ultrafast magnetization reversal previously believed impossible is the combined result of femtosecond laser heating of the magnetic system to just below the Curie point and circularly polarized light simultaneously acting as a magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.

We have measured the critical atom number in an array of harmonically trapped two-dimensional (2D) Bose gases of rubidium atoms at different temperatures. We found this number to be about 5 times higher than predicted by the semiclassical theory of Bose-Einstein condensation (BEC) in the ideal gas. This demonstrates that the conventional BEC picture is inapplicable in an interacting 2D atomic gas, in sharp contrast to the three-dimensional case. A simple heuristic model based on the Berezinskii-Kosterlitz-Thouless theory of 2D superfluidity and the local density approximation accounts well for our experimental results.

We study the motion of paramagnetic colloidal particles placed above magnetic bubble domains of a uniaxial garnet film and driven through the lattice by external magnetic field modulation. An external tunable precessing field propels the particles either in localized orbits around the bubbles or in superdiffusive or ballistic motion through the bubble array. This motion results from the interplay between the driving rotating signal, the viscous drag force and the periodic magnetic energy landscape. We explain the transition in terms of the incommensurability between the transit frequency of the particle through a unit cell and the modulation frequency. Ballistic motion dynamically breaks the symmetry of the array and the phase locked particles follow one of the six crystal directions.

On the basis of first-principles Monte Carlo simulations we find that the screw dislocation along the hexagonal axis of an hcp ${}^4\mathrm{He}$ crystal features a superfluid (at $T\to 0$) core. This is the first example of a regular quasi-one-dimensional supersolid—the phase featuring both translational and superfluid orders, and one of the cleanest cases of a Luttinger-liquid system. In contrast, the same type of screw dislocation in solid ${\mathrm{H}}_2$ is insulating.

We observe the proliferation of vortices in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional array of Josephson-coupled Bose-Einstein condensates. As long as the Josephson (tunneling) energy $J$ exceeds the thermal energy $T$, the array is vortex free. With decreasing $J/T$, vortices appear in the system in ever greater numbers. We confirm thermal activation as the vortex-formation mechanism and obtain information on the size of bound vortex pairs as $J/T$ is varied.

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, ${\tau }_{\mu }=2.197013(24)\mu \mathrm{s}$, is in excellent agreement with the previous world average. The new world average ${\tau }_{\mu }=2.197019(21)\mu \mathrm{s}$ determines the Fermi constant $G_F=1.166371(6)\times {10}^{-5}{\mathrm{GeV}}^{-2}$ (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling $g_P$.

We study a colloidal suspension confined between two quasiparallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. For higher volume fraction samples (closer to the glass transition), the onset of confinement effects occurs at larger length scales.

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient ($N=Z+2$) nucleus ${}^{110}\mathrm{Xe}$, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited $2^{+}$ and $4^{+}$ level energies as a function of the decreasing neutron number as the $N=50$ major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar $n\mathrm{\text{−}}p$ interactions becoming increasingly important close to the $N=Z$ line.

We report the discovery of superconductivity below 1.65(6) K in Sr-intercalated graphite ${\mathrm{SrC}}_6$, by susceptibility and specific heat ($C_p$) measurements. In comparison with ${\mathrm{CaC}}_6$, we found that the anisotropy of the upper critical fields for ${\mathrm{SrC}}_6$ is much reduced. The $C_p$ anomaly at $T_c$ is smaller than the BCS prediction, indicating an anisotropic superconducting gap for ${\mathrm{SrC}}_6$ similar to ${\mathrm{CaC}}_6$. The significantly lower $T_c$ of ${\mathrm{SrC}}_6$ as compared to ${\mathrm{CaC}}_6$ can be understood in terms of “negative” pressure effects, which decreases the electron-phonon coupling for both in-plane intercalant and the out-of-plane C phonon modes. We observed no superconductivity for ${\mathrm{BaC}}_6$ down to 0.3 K.

We present experiments on a superconductor–normal-metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor; i.e., the heat flux out from the normal-metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system.

Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at $25\pm 5\mathrm{GPa}$. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at $25\pm 5\mathrm{GPa}$. A maximum variation of 0.08 Å is observed at $65\pm 5\mathrm{GPa}$ where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at $25\pm 5\mathrm{GPa}$ to the case of the other halogens.

We study thin self-assembled columns constrained to lie on a curved, rigid substrate. The curvature presents no local obstruction to equally spaced columns in contrast with curved crystals for which the crystalline bonds are frustrated. Instead, the vanishing compressional strain of the columns implies that their normals lie on geodesics which converge (diverge) in regions of positive (negative) Gaussian curvature, in analogy to the focusing of light rays by a lens. We show that the out of plane bending of the cylinders acts as an effective ordering field.