Magnetoelectric confinement and stabilization of the plasma column in a soft-x-ray ${\mathrm{Ar}}^{+8}$ laser, which is excited by a capillary $Z$ pinch, via the combined magnetic and electric fields of the gliding surface discharge is experimentally demonstrated. Unlike soft-x-ray lasers excited by the conventional capillary $Z$ pinches, the magnetoelectric confinement and stabilization of plasma do provide the laser operation without using any external preionization circuit.

Shock-wave formation is a generic scenario of wave dynamics known in nonlinear acoustics, fluid dynamics, astrophysics, seismology, and detonation physics. Here, we show that, in nonlinear optics, remarkably short, attosecond shock transients can be generated through a strongly coupled spatial and temporal dynamics of ultrashort light pulses, suggesting a pulse self-compression scenario whereby multigigawatt attosecond optical waveforms can be synthesized.

We discover a nonlinear coupling between the hydrophobicity of a charged substrate and electrokinetic pumping in narrow fluidic confinements. Our analyses demonstrate that the effective electrokinetic transport in nanochannels may get massively amplified over a regime of bare surface potentials and may subsequently get attenuated beyond a threshold surface charging condition because of a complex interplay between reduced hydrodynamic resistance on account of the spontaneous inception of a less dense interfacial phase and ionic transport within the electrical double layer. We also show that the essential physics delineated by our mesoscopic model, when expressed in terms of a simple mathematical formula, agrees remarkably with that portrayed by molecular dynamics simulations. The nontrivial characteristics of the initial increment followed by a decrement of the effective zeta potential with a bare surface potential may open up the realm of hitherto-unexplored operating regimes of electrohydrodynamically actuated nanofluidic devices.

We use direct numerical simulation of the Navier-Stokes equations for a two-phase flow (water and air) to study the dynamics of the modulational instability of free surface waves and its contribution to the interaction between the ocean and atmosphere. If the steepness of the initial wave exceeds a threshold value, we observe wave-breaking events and the formation of large-scale dipole structures in the air. Because of the multiple steepening and breaking of the waves under unstable wave packets, a train of dipoles is released in the atmosphere; those dipoles propagate at a height comparable with the wavelength. The amount of energy dissipated by the breaker in water and air is considered, and contrary to expectations, we observe that the energy dissipation in air is greater than that in water. The possible consequences on the wave modeling and on the exchange of aerosols and gases between air and water are discussed.

Quantum transition points in the $J\mathrm{\text{−}}Q$ model—the test bed of the deconfined critical point theory—and the SU(2)-symmetric discrete noncompact $C{P}^1$ representation of the deconfined critical action are directly compared by the flowgram method. We find that the flows of two systems coincide in a broad region of linear system sizes ($10<L<50$ for the $J\mathrm{\text{−}}Q$ model), implying that the deconfined critical point theory correctly captures the mesoscopic physics of competition between the antiferromagnetic and valence-bond orders in quantum spin systems. At larger sizes, however, we observe significant deviations between the two flows which both demonstrate strong violations of scale invariance. This reliably rules out the second-order transition scenario in at least one of the two models and suggests the most likely explanation for the nature of the transition in the $J\mathrm{\text{−}}Q$ model.

We report photoemission experiments revealing the valence electron spectral function of Mn, Fe, Co, and Ni atoms on the Ag (100) surface. The series of spectra shows splittings of higher energy features which decrease with the filling of the $3d$ shell and a highly nonmonotonic evolution of spectral weight near the Fermi edge. First principles calculations demonstrate that two manifestations of Hund’s exchange $J$ are responsible for this evolution. First, there is a monotonic reduction of the effective exchange splittings with increasing filling of the $3d$ shell. Second, the amount of charge fluctuations and, thus, the weight of quasiparticle peaks at the Fermi level varies nonmonotonically through this $3d$ series due to a distinct occupancy dependence of effective charging energies $U_{\mathrm{eff}}$.

Unique from other rare earth dialuminides, ${\mathrm{PrAl}}_2$ undergoes a cubic to tetragonal distortion below $T=30\mathrm{K}$ in a zero magnetic field, but the system recovers its cubic symmetry upon the application of an external magnetic field of 10 kOe via a lifting of the $4f$ crystal field splitting. The nuclear Schottky specific heat in ${\mathrm{PrAl}}_2$ is anomalously high compared to that of pure Pr metal. First principles calculations reveal that the $4f$ crystal field splitting in the tetragonally distorted phase of ${\mathrm{PrAl}}_2$ underpins the observed unusual low temperature phenomena.

We propose that ordinary semiconductors with large spin-orbit coupling, such as GaAs, can host stable, robust, and tunable topological states in the presence of quantum confinement and superimposed potentials with hexagonal symmetry. We show that the electronic gaps which support chiral spin edge states can be as large as the electronic bandwidth in the heterostructure miniband. The existing lithographic technology can produce a topological insulator operating at a temperature of 10–100 K. Improvement of lithographic techniques will open the way to a tunable room temperature topological insulator.

We show that electronic Raman scattering affords a window into the essential properties of the pairing potential $V_{\mathbf{k},{\mathbf{k}}^{\prime }}$ of iron-based superconductors. In ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{Fe}}_2{\mathrm{As}}_2$ we observe band dependent energy gaps along with excitonic Bardasis-Schrieffer modes characterizing, respectively, the dominant and subdominant pairing channel. The $d_{x^2-y^2}$ symmetry of all excitons allows us to identify the subdominant channel to originate from the interaction between the electron bands. Consequently, the dominant channel driving superconductivity results from the interaction between the electron and hole bands and has the full lattice symmetry. The results in ${\mathrm{Rb}}_{0.8}{\mathrm{Fe}}_{1.6}{\mathrm{Se}}_2$ along with earlier ones in $\mathrm{Ba}({\mathrm{Fe}}_{0.939}{\mathrm{Co}}_{0.061}{)}_2{\mathrm{As}}_2$ highlight the influence of the Fermi surface topology on the pairing interactions.

Dynamic dipolar interactions between spin wave eigenmodes of closely spaced nanomagnets determine the collective behavior of magnonic and spintronic metamaterials and devices. However, dynamic dipolar interactions are difficult to quantify since their effects must be disentangled from those of static dipolar interactions and variations in the shape, size, and magnetic properties of the nanomagnets. It is shown that when two imperfect nanoscale magnetic disks with similar but nonidentical modes are brought into close proximity, the effect of the dynamic dipolar interaction can be detected by considering the difference of the phase of precession within the two disks. Measurements show that the interaction is stronger than expected from micromagnetic simulations, highlighting both the need for characterization and control of magnetic properties at the deep nanoscale, and also the potential for improved control of collective magnetic phenomena. Our approach is equally applicable to other physical systems in which dynamic interactions are obscured by inhomogeneous broadening and static interactions.

The structural, electronic, and optical properties of pyrochlore-type ${\mathrm{Pb}}_2{\mathrm{Ir}}_2{\mathrm{O}}_6{\mathrm{O}}_{0.55}^{\prime }$, which is a metal without spatial inversion symmetry at room temperature, were investigated. Structural analysis revealed that the structural distortion relevant to the breakdown of the inversion symmetry is dominated by the $\mathrm{Pb}\mathrm{\text{−}}{\mathrm{O}}^{\prime }$ network but is very small in the Ir-O network. At the same time, gigantic second-harmonic generation signals were observed, which can only occur if the local environment of the Ir $5d$ electrons features broken inversion symmetry. First-principles electronic structure calculations reveal that the underlying mechanism for this phenomenon is the induction of the noncentrosymmetricity in the Ir $5d$ bands by the strong hybridization with ${\mathrm{O}}^{\prime }$ $2p$ orbitals. Our results stimulate theoretical study of inversion-broken iridates, where exotic quantum states such as a topological insulator and Dirac semimetal are anticipated.

First-principles calculations are performed to investigate energetic and atomistic characteristics of ferroelectric domains walls (DWs) of ${\mathrm{BiFeO}}_3$ (BFO) films subject to compressive strain. Significantly lower DW energies than those previously reported, and a different energetic hierarchy between the various DW types, are found for small strains. In all investigated cases (corresponding to ideal angles of 71°, 109°, and 180° formed by the domain polarizations), the DW energy reaches its maximum value for misfit strains that are around the critical strain at which the transition between the $R$-like and $T$-like phases occurs in single-domain BFO. Near these strains, several quantities depend strongly on the type of domain wall; such distinct behavior is associated with an elastic difference and a large out-of-plane polarization at the DW in the 180° case. A further increase of the magnitude of the strain leads to (i) a change of hierarchy of the DW energies, (ii) large out-of-plane polarizations inside each up and down domain, and (iii) novel atomic arrangements at the domain walls. Our study can thus initiate a new research direction, namely strain engineering of domain-wall functionalities.

Quantum confinement can dramatically slow down electron-phonon relaxation in nanoclusters. Known as the phonon bottleneck, the effect remains elusive. Using a state-of-the-art time-domain ab initio approach, we model the observed bottleneck in CdSe quantum dots and show that it occurs under quantum Zeno conditions. Decoherence in the electronic subsystem, induced by elastic electron-phonon scattering, should be significantly faster than inelastic scattering. Achieved with multiphonon relaxation, the phonon bottleneck is broken by Auger processes and structural defects, rationalizing experimental difficulties.

We present a one-loop calculation of the oblique $S$ and $T$ parameters within strongly coupled models of electroweak symmetry breaking with a light Higgs-like boson. We use a general effective Lagrangian, implementing the chiral symmetry breaking $SU(2{)}_L\otimes SU(2{)}_R\to SU(2{)}_{L+R}$ with Goldstone bosons, gauge bosons, the Higgs-like scalar, and one multiplet of vector and axial-vector massive resonance states. Using a dispersive representation and imposing a proper ultraviolet behavior, we obtain $S$ and $T$ at the next-to-leading order in terms of a few resonance parameters. The experimentally allowed range forces the vector and axial-vector states to be heavy, with masses above the TeV scale, and suggests that the Higgs-like scalar should have a $WW$ coupling close to the standard model one. Our conclusions are generic and apply to more specific scenarios such as the minimal $SO(5)/SO(4)$ composite Higgs model.

Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum likelihood method to search for the appearance of tau leptons resulting from the interactions of oscillation-generated tau neutrinos in the detector. Relative to the expectation of unity, the tau normalization is found to be $1.42\pm 0.35(\mathrm{stat}{)}_{-0.12}^{+0.14}(\mathrm{syst})$ excluding the no-tau-appearance hypothesis, for which the normalization would be zero, at the $3.8\sigma$ level. We estimate that $180.1\pm 44.3(\mathrm{stat}{)}_{-15.2}^{+17.8}(\mathrm{syst})$ tau leptons were produced in the 22.5 kton fiducial volume of the detector by tau neutrinos during the 2806 day running period. In future analyses, this large sample of selected tau events will allow the study of charged current tau neutrino interaction physics with oscillation produced tau neutrinos.

Bottom baryons decaying to a $J/\psi$ meson and a hyperon are reconstructed using $1.0{\mathrm{fb}}^{-1}$ of data collected in 2011 with the LHCb detector. Significant ${\Lambda }_b^0\to J/\psi \Lambda$, ${\Xi }_b^{-}\to J/\psi {\Xi }^{-}$ and ${\Omega }_b^{-}\to J/\psi {\Omega }^{-}$ signals are observed and the corresponding masses are measured to be $M({\Lambda }_b^0)=5619.53\pm 0.13(\mathrm{stat}.)\pm 0.45(\mathrm{syst}.)\mathrm{MeV}/c^2$, $M({\Xi }_b^{-})=5795.8\pm 0.9(\mathrm{stat}.)\pm 0.4(\mathrm{syst}.)\mathrm{MeV}/c^2$, $M({\Omega }_b^{-})=6046.0\pm 2.2(\mathrm{stat}.)\pm 0.5(\mathrm{syst}.)\mathrm{MeV}/c^2$, while the differences with respect to the ${\Lambda }_b^0$ mass are $M({\Xi }_b^{-})-M({\Lambda }_b^0)=176.2\pm 0.9(\mathrm{stat}.)\pm 0.1(\mathrm{syst}.)\mathrm{MeV}/c^2$, $M({\Omega }_b^{-})-M({\Lambda }_b^0)=426.4\pm 2.2(\mathrm{stat}.)\pm 0.4(\mathrm{syst}.)\mathrm{MeV}/c^2$. These are the most precise mass measurements of the ${\Lambda }_b^0$, ${\Xi }_b^{-}$ and ${\Omega }_b^{-}$ baryons to date. Averaging the above ${\Lambda }_b^0$ mass measurement with that published by LHCb using $35{\mathrm{pb}}^{-1}$ of data collected in 2010 yields $M({\Lambda }_b^0)=5619.44\pm 0.13(\mathrm{stat}.)\pm 0.38(\mathrm{syst}.)\mathrm{MeV}/c^2$.

Geometric frustration, the inability of an ordered system to find a unique ground state plays a key role in a wide range of systems. We present a new experimental approach to observe large-scale geometric frustration with 1500 negatively coupled lasers arranged in a kagome lattice. We show how dissipation drives the lasers into a phase-locked state that directly maps to the classical $XY$ spin Hamiltonian ground state. In our system, frustration is manifested by the lack of long range phase ordering. Finally, we show how next-nearest-neighbor coupling removes frustration and restores order.

We experimentally surpass the 3 dB limit to steady-state parametric squeezing of a mechanical oscillator. The localization of an atomic force microscope cantilever, achieved by optimal estimation, is enhanced by up to 6.2 dB in one position quadrature when a detuned parametric drive is used. This squeezing is, in principle, limited only by the oscillator $Q$ factor. Used on low temperature, high frequency oscillators, this technique provides a pathway to achieve robust quantum squeezing below the zero-point motion. Broadly, our results demonstrate that control systems engineering can overcome well established limits in applications of nonlinear processes. Conversely, by localizing the mechanical position to better than the measurement precision of our apparatus, they demonstrate the usefulness of mechanical nonlinearities in control applications.

We consider the superradiance of an extended relativistic electron bunch moving over a periodically corrugated surface for the generation of multimegawatt terahertz pulses. To study the above process we have developed a three-dimensional, self-consistent, quasioptical theory of Cherenkov stimulated emission which includes a description of the formation of an evanescent wave over a corrugated surface and its excitation by rf current induced in the electron bunch.

This Letter presents the first numerical verification for the bounce-harmonic (BH) resonance phenomena of the neoclassical transport in a tokamak perturbed by nonaxisymmetric magnetic fields. The BH resonances were predicted by analytic theories of neoclassical toroidal viscosity (NTV), as the parallel and perpendicular drift motions can be resonant and result in a great enhancement of the radial momentum transport. A new drift-kinetic $\delta f$ guiding-center particle code, POCA, clearly verified that the perpendicular drift motions can reduce the transport by phase-mixing, but in the BH resonances the motions can form closed orbits and particles radially drift out fast. The POCA calculations on resulting NTV torque are largely consistent with analytic calculations, and show that the BH resonances can easily dominate the NTV torque when a plasma rotates in the perturbed tokamak and therefore, is a critical physics for predicting the rotation and stability in the International Thermonuclear Experimental Reactor.