In Efimov physics, a three-body parameter (3BP), previously regarded as nonuniversal, uniquely defines bound and scattering properties of three particles. A universal 3BP, however, has been recently shown in experiments and theory in ultracold homonuclear gases. Our present study further predicts a universal 3BP for heteronuclear atomic systems near broad Feshbach resonances and provides physical interpretations for its origin. We show that for a system composed of two light and one heavy atom, the physical origin of the universal 3BP is similar to the homonuclear case, while for systems composed by one light and two heavy atoms, the universality of the 3BP is now mostly controlled by the heavy-heavy interatomic properties. This new universality is explained by the universal properties of the van der Waals interactions in a simple Born-Oppenheimer picture. Finally, we show the numerically determined 3BPs for some combinations of alkali atoms used in ultracold experiments.

This work presents the experimental observation of the nonfactorable near-field spatiotemporal correlation of ultrabroadband twin beams generated by parametric down-conversion, in an interferometric-type experiment using sum frequency generation, where both the temporal and the spatial degrees of freedom of parametric down-conversion light are controlled with high resolution. The revealed correlation is skewed in space-time in accordance with the X structure predicted by the theory.

We experimentally investigate the interplay between spatial shock waves and the degree of disorder during nonlinear optical propagation in a thermal defocusing medium. We characterize the way the shock point is affected by the amount of disorder and scales with wave amplitude. Evidence for the existence of a phase diagram in terms of nonlinearity and amount of randomness is reported. The results are in quantitative agreement with a theoretical approach based on the hydrodynamic approximation.

We study for a dielectric particle the effect of surplus electrons on the anomalous scattering of light arising from the transverse optical phonon resonance in the particle’s dielectric function. Excess electrons affect the polarizability of the particle by their phonon-limited conductivity, either in a surface layer (negative electron affinity) or the conduction band (positive electron affinity). We show that surplus electrons shift an extinction resonance in the infrared. This offers an optical way to measure the charge of the particle and to use it in a plasma as a minimally invasive electric probe.

The estimation of Lyapunov exponents from time series suffers from the appearance of spurious Lyapunov exponents due to the necessary embedding procedure. Separating true from spurious exponents poses a fundamental problem which is not yet solved satisfactorily. We show, in this Letter, analytically and numerically that covariant Lyapunov vectors associated with true exponents lie in the tangent space of the reconstructed attractor. Therefore, we use the angle between the covariant Lyapunov vectors and the tangent space of the reconstructed attractor to identify the true Lyapunov exponents. The usefulness of our method, also for noisy situations, is demonstrated by applications to data from model systems and a NMR laser experiment.

A soft solid is more easily sliced using a combination of normal and shearing deformations rather than diced by squeezing down on it normally with the same knife. To explain why this is so, we experimentally probe the slicing and dicing of a soft agar gel with a wire, and complement this with theory and numerical simulations of cutting of a highly deformable solid. We find that purely normal deformations lead to global deformations of the soft solid, so that the blade has to penetrate deeply into the sample, well beyond the linear regime, to reach the relatively large critical stress to nucleate fracture. In contrast, a slicing motion leads to fracture nucleation with minimal deformation of the bulk and thus a much lower barrier. This transition between global and local deformations in soft solids as a function of the angle of shear explains the mechanics of the paper cut and design of guillotine blades.

We show that the interaction between a surface and a charge packet moving parallel to it can become repulsive above a critical relativistic energy. We find that this is true for a lossless dielectric surface and also for a Drude metallic surface—in apparent contrast with such common notions as image charge. This counterintuitive phenomenon occurs for packets larger in the transverse than in the longitudinal (parallel to the motion) direction. The repulsion does not occur for a point charge that is instead attracted at all energies. In addition to the above attractive or repulsive transverse force, there is a longitudinal decelerating force, which for a dielectric corresponds to the Čerenkov effect. Once again, the behavior of a line packet differs from that of a point charge: for a packet with infinite transverse size, the decelerating field decreases to zero as the relativistic factor $\gamma \to \infty$, whereas, for a point charge, the asymptotic value is finite. These findings have a potential impact not only on fundamental electrodynamics but also on accelerator physics and electron spectroscopy.

We demonstrate that a mm-scale free-electron laser can operate in the x-ray range, in the interaction between a moderately relativistic electron bunch, and a transverse high intensity optical lattice. The corrugated light-induced ponderomotive potential acts simultaneously as a guide and as a low-frequency wiggler, triggering stimulated Raman scattering. The gain law in the small signal regime is derived in a fluid approach, and confirmed from particle-in-cell simulations. We describe the nature of bunching, and discuss the saturation properties. The resulting all-optical Raman x-ray laser opens perspectives for ultracompact coherent light sources up to the hard x-ray range.

It is planned to use external magnetic perturbations at acoustic frequencies at the DIII-D tokamak to attempt to drive geodesic acoustic modes (GAM) to modify the turbulent transport. We show that this might not only be possible—despite the well-known electrostatic nature of the GAMs—but might be a viable and efficient method to generate GAMs in magnetically confined plasmas, by developing an elegant analytic method which allows us to couple numerical dynamic equilibrium calculations with massively parallel non-Boussinesq turbulence code runs and yields practical estimates of the effectivity of the method.

Experimental results showing the agglomeration of large carbonaceous particles in a dusty plasma are reported. Experiments were performed in a capacitively coupled rf argon plasma. Acetylene was injected to produce dust particles. When a sufficient amount of nanoparticles is present in the cathodic sheath, self-excited dust-density waves occur. The latter ones induce the motion of larger clusters, which vertically oscillate with the displacement of wave fronts. In some cases, the relative velocity of large particles was high enough to overcome the Coulomb repulsion forces, and agglomeration can be observed. The mechanisms underlying this process are discussed.

The x-ray intensities made available by x-ray free electron lasers (FEL) open up new x-ray matter interaction channels not accessible with previous sources. We report here on the resonant generation of $K\alpha$ emission, that is to say the production of copious $K\alpha$ radiation by tuning the x-ray FEL pulse to photon energies below that of the $K$ edge of a solid aluminum sample. The sequential absorption of multiple photons in the same atom during the 80 fs pulse, with photons creating $L$-shell holes and then one resonantly exciting a $K$-shell electron into one of these holes, opens up a channel for the $K\alpha$ production, as well as the absorption of further photons. We demonstrate rich spectra of such channels, and investigate the emission produced by tuning the FEL energy to the $K\mathrm{\text{−}}L$ transitions of those highly charged ions that have transition energies below the $K$ edge of the cold material. The spectra are sensitive to x-ray intensity dependent opacity effects, with ions containing $L$-shell holes readily reabsorbing the $K\alpha$ radiation.

Nonradiative carrier recombination is of both applied and fundamental interest. Here a novel algorithm is introduced to calculate such a deep level nonradiative recombination rate using the ab initio density functional theory. This algorithm can calculate the electron-phonon coupling constants all at once. An approximation is presented to calculate the phonon modes for one impurity in a large supercell. The neutral Zn impurity site together with a N vacancy is considered as the carrier-capturing deep impurity level in bulk GaN. Its capture coefficient is calculated as $5.57\times {10}^{-10}{\mathrm{cm}}^3/\mathrm{s}$ at 300 K. We found that there is no apparent onset of such a nonradiative process as a function of temperature.

Dynamical scattering of fast electrons can be inverted by recasting the multislice algorithm as an artificial neural network, enabling the iterative retrieval of the three-dimensional object potential. This allows a nonheuristic treatment of the modulation transfer function of the CCD, partial spatial and temporal coherence, and inelastic scattering through an absorptive potential. Furthermore, prior knowledge about the atomic potential shape and the sparseness and positivity of the object can be used. The method is demonstrated on simulated bright field images recorded at 40 kV.

The energy landscape of $\mathrm{Mg}({\mathrm{BH}}_4{)}_2$ under pressure is explored by ab initio evolutionary calculations. Two new tetragonal structures, with space groups $P\overline{4}$ and $I{4}_1/acd$, are predicted to be lower in enthalpy by 15.4 and $21.2\mathrm{kJ}/\mathrm{mol}$, respectively, than the earlier proposed $P{4}_{2}nm$ phase. We have simulated x-ray diffraction spectra, lattice dynamics, and equations of state of these phases. The density, volume contraction, bulk modulus, and simulated x-ray diffraction patterns of $I{4}_1/acd$ and $P\overline{4}$ structures are in excellent agreement with the experimental results.

We performed combined magnetotransport and cyclotron resonance experiments on two-dimensional electron systems confined in the ${\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}/\mathrm{ZnO}$ heterostructures over a wide range of carrier densities, from 1.9 to $12\times {10}^{11}{\mathrm{cm}}^{-2}$ ($3.5\lesssim r_{\mathrm{s}}\lesssim 10$, where $r_{\mathrm{s}}$ is the Wigner-Seitz radius). As the carrier density was reduced, the transport mass $m_{\mathrm{tr}}^{*}$ was strongly enhanced. In marked contrast, the effective masses determined from the cyclotron resonance $m_{\mathrm{CR}}^{*}$ were found to be independent of the carrier density and as large as the bulk effective mass. The large enhancement of $m_{\mathrm{tr}}^{*}$, which exceeds $m_{\mathrm{CR}}^{*}$ by $\sim 60\%$, at the lowest carrier density with $r_{\mathrm{s}}\sim 10$ is purely attributed to the strong electron correlation.

We use the exact strong-interaction limit of the Hohenberg-Kohn energy density functional to approximate the exchange-correlation energy of the restricted Kohn-Sham scheme. Our approximation corresponds to a highly nonlocal density functional whose functional derivative can be easily constructed, thus transforming exactly, in a physically transparent way, an important part of the electron-electron interaction into an effective local one-body potential. We test our approach on quasi-one-dimensional systems, showing that it captures essential features of strong correlation that restricted Kohn-Sham calculations using the currently available approximations cannot describe.

We present a determinant quantum Monte Carlo study of the competition between instantaneous on-site Coulomb repulsion and retarded phonon-mediated attraction between electrons, as described by the two-dimensional Hubbard-Holstein model. At half filling, we find a strong competition between antiferromagnetism (AFM) and charge-density-wave (CDW) order. We demonstrate that a simple picture of AFM-CDW competition that incorporates the phonon-mediated attraction into an effective-$U$ Hubbard model requires significant refinement. Specifically, retardation effects slow the onset of charge order so that CDW order remains absent even when the effective $U$ is negative. This delay opens a window where neither AFM nor CDW order is well established and where there are signatures of a possible metallic phase.

Spin valves have revolutionized the field of magnetic recording and memory devices. Spin valves are generally realized in thin film heterostructures, where two ferromagnetic (FM) layers are separated by a nonmagnetic conducting layer. Here, we demonstrate spin-valve-like magnetoresistance at room temperature in a bulk ferrimagnetic material that exhibits a magnetic shape memory effect. The origin of this unexpected behavior in ${\mathrm{Mn}}_2\mathrm{NiGa}$ has been investigated by neutron diffraction, magnetization, and ab initio theoretical calculations. The refinement of the neutron diffraction pattern shows the presence of antisite disorder where about 13% of the Ga sites are occupied by Mn atoms. On the basis of the magnetic structure obtained from neutron diffraction and theoretical calculations, we establish that these antisite defects cause the formation of FM nanoclusters with parallel alignment of Mn spin moments in a ${\mathrm{Mn}}_2\mathrm{NiGa}$ bulk lattice that has antiparallel Mn spin moments. The direction of the Mn moments in the soft FM cluster reverses with the external magnetic field. This causes a rotation or tilt in the antiparallel Mn moments at the cluster-lattice interface resulting in the observed asymmetry in magnetoresistance.

We report the magnetothermopower measurements of the nonmetallic topological insulator ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ in magnetic fields up to 35 T. Quantum oscillations arising from surface states are observed in both thermoelectric and conductivity tensors. The inferred surface thermopower has a peak magnitude $\sim 1\mathrm{mV}/\mathrm{K}$ possibly as a result of surface electron and bulk phonon interaction. At the $n=1$ Landau level, we resolve additional quantum oscillations signaling Landau sublevels.

We show that arbitrarily weak interparticle interactions destabilize the surface states of 3D topological superconductors with spin SU(2) invariance (symmetry class CI) in the presence of nonmagnetic disorder. The conduit for the instability is disorder-induced wave function multifractality. We argue that time-reversal symmetry breaks spontaneously at the surface, so that topologically protected states do not exist for this class. The interaction-stabilized surface phase is expected to exhibit ferromagnetic order, or to reside in an insulating plateau of the spin quantum Hall effect.