A general new technique to solve the two-center problem with arbitrarily oriented deformed realistic potentials is demonstrated, which is based on the powerful potential separable expansion method. As an example, molecular single-particle spectra for ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}\to {}^{24}\mathrm{Mg}$ are calculated using deformed Woods-Saxon potentials. These clearly show that nonaxial symmetric configurations play a crucial role in molecular resonances observed in reaction processes for this system at low energy.

By using heteroepitaxy on two different GaAs templates, we have investigated the impact of anisotropic strain on the magnetocaloric effect (MCE) of MnAs. The temperature range, spread around room temperature, and the maximal MCE position are markedly different in the two epitaxial systems. Simulated MCE curves, obtained from a model based on the mean-field approximation, are in good agreement with the experimental data, indicating that the entropy variation is magnetic in origin. These results illustrate how strain can be used to tune the MCE in materials with coupled structural and magnetic phase transition and suggest that the MCE of MnAs may find applications in microelectronic circuitry.

One of the most fundamental questions in tribology concerns the area dependence of friction at the nanoscale. Here, experiments are presented where the frictional resistance of nanoparticles is measured by pushing them with the tip of an atomic force microscope. We find two coexisting frictional states: While some particles show finite friction increasing linearly with the interface areas of up to $310000{\mathrm{nm}}^2$, other particles assume a state of frictionless sliding. The results further suggest a link between the degree of surface contamination and the occurrence of this duality.

We report on experimental observation of localized structures in two mutually coupled broad-area semiconductor resonators, one of which acts as a saturable absorber. These structures coexist with a dark homogeneous background and they have the same properties as cavity solitons without requiring the presence of a driving beam into the system. They can be switched individually on and off by means of a local addressing beam.

We experimentally demonstrate increased diffuse transmission of light through strongly scattering materials. Wave front shaping is used to selectively couple light to the open transport eigenchannels, specific solutions of Maxwell’s equations which the sample transmits fully, resulting in an increase of up to 44% in the total angle-integrated transmission compared to the case where plane waves are incident. The results for each of several hundreds of experimental runs are in excellent quantitative agreement with random matrix theory. From our measurements we conclude that with perfectly shaped wave fronts the transmission of a disordered sample tends to a universal value of $2/3$, regardless of the thickness.

The number $N(E)$ of complex zeros of the Riemann zeta function with positive imaginary part less than $E$ is the sum of a “smooth” function $\overline{N}(E)$ and a “fluctuation.” Berry and Keating have shown that the asymptotic expansion of $\overline{N}(E)$ counts states of positive energy less than $E$ in a “regularized” semiclassical model with classical Hamiltonian $H=xp$. For a different regularization, Connes has shown that it counts states “missing” from a continuum. Here we show how the “absorption spectrum” model of Connes emerges as the lowest Landau level limit of a specific quantum-mechanical model for a charged particle on a planar surface in an electric potential and uniform magnetic field. We suggest a role for the higher Landau levels in the fluctuation part of $N(E)$.

The possibility of a magnetic field controlling the chirality of matter has been debated for a long time. Here, we report the successful induction of chirality in the noncentrosymmetric canted antiferromagnet, ${\mathrm{CuB}}_2{\mathrm{O}}_4$, by application of a low intensity static magnetic field. The chirality is reversed by a 90° rotation of the direction of the magnetic field. The induction of chirality by a magnetic field gives rise to a gigantic enhancement of magnetochiral dichroism in this material. The ability to switch handedness in combination with this large magnetochiral optical effect allows us to design new optical devices such as a magnetically controllable isolator.

We report the Autler-Townes doublet demonstrating a novel type of coherent interaction of atoms not with photons but with a periodic crystal field when the atom is in flight through a crystal at high velocity. It was observed by the nonoptical X-VUV (vacuum-ultraviolet) double resonance of three-dimensional resonant coherent excitation with good coherence. The states strongly coupled in the VUV region were probed by the excitation in the x-ray region. The characteristic spectra are well interpreted by an analogy of the dressed atom concept often adopted for the atom-photon interaction.

A novel dimensionless parameter, the particle moment number Pa, was derived using dimensional analysis of the particle-laden Navier-Stokes equations, in order to understand the underlying physics of turbulence modification by particles. A set of 80 previous experimental measurements where the turbulent kinetic energy was modified by particles was examined, and all results could clearly be divided into three groups in Re-Pa mappings. The turbulence attenuation region was observed between the augmentation regions with two critical particle momentum numbers.

We show, experimentally and theoretically, that the application of modest voltages, $U_0=(0.1–1)\mathrm{kV}$, to ${\mathrm{LiNbO}}_3:\mathrm{Fe}$ crystals at sufficiently high temperatures, $T\approx (550–700)°\mathrm{C}$, leads to the formation of ultraslow shock waves (moving discontinuities) of the electron density owing to the removal of electrons from ${\mathrm{Fe}}^{2+}$ centers. Behind the sharp wave front, almost all iron centers are in the ${\mathrm{Fe}}^{3+}$ state, the sample is optically transparent, and its transport properties are strongly modified. The front velocity decreases during the propagation; it is controlled by the electron mobility.

We report measurements of a coherent coupling between surface plasmon polaritons (SPP) and quantum well excitons in a hybrid metal-semiconductor nanostructure. The hybrid structure is designed to optimize the radiative exciton-SPP interaction which is probed by low-temperature, angle-resolved, far-field reflectivity spectroscopy. As a result of the coupling, a significant shift of $\sim 7\mathrm{meV}$ and an increase in broadening by $\sim 4\mathrm{meV}$ of the quantum well exciton resonance are observed. The experiments are corroborated by a phenomenological coupled-oscillator model predicting coupling strengths as large as 50 meV in structures with optimized detunings between the coupled exciton and SPP resonances. Such a strong interaction can, e.g., be used to enhance the luminescence yield of semiconductor quantum structures or to amplify SPP waves.

We derive the consequences of the Myhrer-Thomas explanation of the proton spin problem for the distribution of orbital angular momentum on the valence and sea quarks. After QCD evolution, these results are found to be in very good agreement with both recent lattice QCD calculations and the experimental constraints from Hermes and JLab.

The ternary iron arsenide ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. We have discovered bulk superconductivity at $T_c=38\mathrm{K}$ in $({\mathrm{Ba}}_{1-x}{\mathrm{K}}_x){\mathrm{Fe}}_2{\mathrm{As}}_2$ with $x\approx 0.4$. The parent compound ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ crystallizes in the tetragonal ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type structure, which consists of $(\mathrm{FeAs}{)}^{\delta -}$ iron arsenide layers separated by ${\mathrm{Ba}}^{2+}$ ions. ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ is a poor metal and exhibits a spin density wave anomaly at 140 K. By substituting ${\mathrm{Ba}}^{2+}$ for ${\mathrm{K}}^{+}$ ions we have introduced holes in the $(\mathrm{FeAs}{)}^{-}$ layers, which suppress the anomaly and induce superconductivity. The $T_c$ of 38 K in $({\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}){\mathrm{Fe}}_2{\mathrm{As}}_2$ is the highest in hole doped iron arsenide superconductors so far. Therefore, we were able to expand this class of superconductors by oxygen-free compounds with the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type structure.

New high-$T_c$ Fe-based superconducting compounds, $A{\mathrm{Fe}}_2{\mathrm{As}}_2$ with $A=\mathrm{K}$, Cs, $\mathrm{K}/\mathrm{Sr}$, and $\mathrm{Cs}/\mathrm{Sr}$, were synthesized. The $T_c$ of ${\mathrm{KFe}}_2{\mathrm{As}}_2$ and ${\mathrm{CsFe}}_2{\mathrm{As}}_2$ is 3.8 and 2.6 K, respectively, which rises with partial substitution of Sr for K and Cs and peaks at 37 K for 50%–60% Sr substitution, and the compounds enter a spin-density-wave state with increasing electron number (Sr content). The compounds represent $p$-type analogs of the $n$-doped rare-earth oxypnictide superconductors. Their electronic and structural behavior demonstrate the crucial role of the (${\mathrm{Fe}}_2{\mathrm{As}}_2$) layers in the superconductivity of the Fe-based layered systems, and the special feature of having elemental $A$ layers provides new avenues to superconductivity at higher $T_c$.

We use the Stokes photon of a biphoton pair to set the time origin for electro-optic modulation of the wave function of the anti-Stokes photon thereby allowing arbitrary phase and amplitude modulation. We demonstrate conditional single-photon wave functions composed of several pulses, or instead, having Gaussian or exponential shapes.

Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized $\mathrm{Si}/{\mathrm{Si}}_{0.4}{\mathrm{Ge}}_{0.6}$ superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal.

We report the first observation of the decay $J/\psi \to 3\gamma$. The signal has a statistical significance of $6\sigma$ and corresponds to a branching fraction of $\mathcal{B}(J/\psi \to 3\gamma )=(1.2\pm 0.3\pm 0.2)\times {10}^{-5}$, in which the errors are statistical and systematic, respectively. The measurement uses $\psi (2S)\to {\pi }^{+}{\pi }^{-}J/\psi$ events acquired with the CLEO-$c$ detector operating at the CESR $e^{+}{e}^{-}$ collider.

We show that a system of Josephson junctions coupled via low-resistance tunneling contacts to graphene substrate(s) may effectively operate as a current switching device. The effect is based on the dissipation-driven superconductor-to-insulator quantum phase transition, which happens due to the interplay of the Josephson effect and Coulomb blockade. Coupling to a graphene substrate with gapless excitations further enhances charge fluctuations favoring superconductivity. The effect is shown to scale exponentially with the Fermi energy in graphene, which can be controlled by the gate voltage. We develop a theory that quantitatively describes the quantum phase transition in a two-dimensional Josephson junction array, but it is expected to provide a reliable qualitative description for one-dimensional systems as well.

Direct observation of current-induced propagation of purely transverse magnetic domain walls with spin-polarized scanning electron microscopy is reported in ${\mathrm{Fe}}_{30}{\mathrm{Ni}}_{70}$ nanowires. After propagation, the domain walls keep their transverse nature but switch polarity in some cases. For uniform ${\mathrm{Ni}}_{70}{\mathrm{Fe}}_{30}$ wires, the effect is random and illustrates domain-wall propagation above the Walker threshold. In the case of ${\mathrm{Ni}}_{70}{\mathrm{Fe}}_{30}/\mathrm{Fe}$ wires, the transverse magnetization component in the wall is entirely determined by the polarity of the current pulse, an effect that is not reconciled by present theories even when taking into account the nonuniform Oersted field generated by the current.

Double ionization of helium by electron impact is studied in a kinematical complete experiment in the threshold regime at 5 eV excess energy. As expected the recoil ion carries the full initial projectile momentum and the emitted electrons’ sum momentum in average is zero. The electron emission is revealed to be completely dominated by the symmetric 120° configuration predicted by many threshold theories but never observed experimentally before. Fully differential cross sections show a more complex structure than expected for a pure threshold collision dynamics.