We investigate nanopillars in which two thin ferromagnetic particles are separated by a nanometer thin nonmagnetic spacer and can be set into stable spin vortex-pair configurations. We find that the previously unexplored limit of strong vortex core-core coupling can dominate the spin dynamics in the system. We observe experimentally and explain analytically and numerically how the 0.2 GHz gyrational resonance modes of the individual vortices are transformed into a 2 GHz collective rotational resonance mode in the configurations where the two cores form a bound pair.

We use numerical linked-cluster expansions to compute the specific heat $C(T)$ and entropy $S(T)$ of a quantum spin ice Hamiltonian for ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ using anisotropic exchange interactions, recently determined from inelastic neutron scattering measurements, and find good agreement with experimental calorimetric data. This vindicates ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ as a model quantum spin ice. We find that in the perturbative weak quantum regime, such a system has a ferrimagnetic ordered ground state, with two peaks in $C(T)$: a Schottky anomaly signaling the paramagnetic to spin ice crossover, followed at a lower temperature by a sharp peak accompanying a first-order phase transition to the ordered state. We suggest that the two $C(T)$ features observed in ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ are associated with the same physics. Spin excitations in this regime consist of weakly confined spinon-antispinon pairs. We anticipate that the conventional ground state with exotic quantum dynamics will prove a prevalent characteristic of many real quantum spin ice materials.

The spatial fluctuations of the dynamics of a colloidal system composed of nanoparticles are probed by a novel experimental setup, which combines homodyne and heterodyne dynamic light scattering focused onto a micron-sized volume via a microscope objective. The technique is used to measure the four-point susceptibility of an aging colloidal suspension, revealing a breakdown of the Gaussian approximation for the correlation function of the scattered electromagnetic field. The deviation from the Gaussian approximation increases with waiting time as the system evolves toward an arrested phase, signaling the gradual emergence of higher-order nontrivial dynamic correlations.

We resonantly inject spin-polarized field-emitted electrons in thermally switching nanomagnets. A detailed lifetime analysis as a function of the spin-polarized emission current reveals that considerable Joule heating is generated, and spin-transfer torque results in a directed switching. A trend of higher switching efficiency per electron is observed with an increasing emission current, probably due to the excitation of Stoner modes. On a quasistable nanomagnet, a spin-polarized emission current in the low nA regime already triggers magnetization reversal, thereby demonstrating the high impact of hot-electron spins onto atomic-scale magnets.

We derive a hydrodynamic description of metric-free active matter: starting from self-propelled particles aligning with neighbors defined by “topological” rules, not metric zones—a situation advocated recently to be relevant for bird flocks, fish schools, and crowds—we use a kinetic approach to obtain well-controlled nonlinear field equations. We show that the density-independent collision rate per particle characteristic of topological interactions suppresses the linear instability of the homogeneous ordered phase and the nonlinear density segregation generically present near threshold in metric models, in agreement with microscopic simulations.

We introduce a mesoscale simulation method based on multiparticle collision dynamics (MPCD) for the electrohydrodynamics of polyelectrolytes with finite Debye lengths. By applying the Debye-Hückel approximation to assign an effective charge to MPCD particles near charged monomers, our simulations are able to reproduce the rapid rise in the electrophoretic mobility with respect to the degree of polymerization for the shortest polymer lengths followed by a small decrease for longer polymers due to charge condensation. Moreover, these simulations demonstrate the importance of a finite Debye length in accurately determining the mobility of uniformly charged polyelectrolytes and net neutral polyampholytes.

We put under experimental scrutiny the preferential attachment model that is commonly accepted as a generating mechanism of the scale-free complex networks. To this end we chose a citation network of physics papers and traced the citation history of 40 195 papers published in one year. Contrary to common belief, we find that the citation dynamics of the individual papers follows the superlinear preferential attachment, with the exponent $\alpha =1.25–1.3$. Moreover, we show that the citation process cannot be described as a memoryless Markov chain since there is a substantial correlation between the present and recent citation rates of a paper. Based on our findings we construct a stochastic growth model of the citation network, perform numerical simulations based on this model and achieve an excellent agreement with the measured citation distributions.

We describe a new mechanism of tunneling between period-two vibrational states of a weakly nonlinear, parametrically modulated oscillator. The tunneling results from resonant transitions induced by the fast oscillating terms conventionally disregarded in the rotating wave approximation (RWA). The tunneling amplitude displays resonant peaks as a function of the modulation frequency; near the maxima it is exponentially larger than the RWA tunneling amplitude.

A minimal model of a quantum refrigerator, i.e., a periodically phase-flipped two-level system permanently coupled to a finite-capacity bath (cold bath) and an infinite heat dump (hot bath), is introduced and used to investigate the cooling of the cold bath towards absolute zero ($T=0$). Remarkably, the temperature scaling of the cold-bath cooling rate reveals that it does not vanish as $T\to 0$ for certain realistic quantized baths, e.g., phonons in strongly disordered media (fractons) or quantized spin waves in ferromagnets (magnons). This result challenges Nernst’s third-law formulation known as the unattainability principle.

The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady state, leading to universal out-of-equilibrium behavior. This attractive notion has been demonstrated in just a few cases. We demonstrate how holography—a mapping between the quantum critical system and a gravity dual—provides an illuminating perspective and new results. Nontrivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system. We calculate this in a two-dimensional system driven by a strong in-plane electric field and deduce a universal scaling function interpolating between previously established equilibrium and far-from-equilibrium current noise. Since this applies at all fields, out-of-equilibrium experiments no longer require very high fields for comparison with theory.

The recent discovery by the Daya-Bay and RENO experiments, that ${\theta }_{13}$ is nonzero and relatively large, significantly impacts existing experiments and the planning of future facilities. In many scenarios, the nonzero value of ${\theta }_{13}$ implies that ${\theta }_{23}$ is likely to be different from $\pi /4$. Additionally, large detectors will be sensitive to matter effects on the oscillations of atmospheric neutrinos, making it possible to determine the neutrino mass hierarchy and the octant of ${\theta }_{23}$. We show that a 50 kT magnetized liquid argon neutrino detector can ascertain the mass hierarchy with a significance larger than $4\sigma$ with moderate exposure times, and the octant at the level of $2–3\sigma$ with greater exposure.

Only one-third of the nucleons in ${}^{208}\mathrm{Pb}$ occupy the saturation density area. Consequently, nuclear observables related to the average properties of nuclei, such as masses or radii, constrain the equation of state not at the saturation density but rather around the so-called crossing density, localized close to the mean value of the density of nuclei: $\rho \simeq 0.11{\mathrm{fm}}^{-3}$. This provides an explanation for the empirical fact that several equation of state quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative $M$ of the energy per unit of volume at the crossing density is constrained by the giant monopole resonance measurements in an isotopic chain rather than the incompressibility at saturation density. The giant monopole resonance measurements provide $M=1100\pm 70\mathrm{MeV}$ (6% uncertainty), whose extrapolation gives $K_{\infty }=230\pm 40\mathrm{MeV}$ (17% uncertainty).

We measure photoelectron angular distributions of single ionization of krypton and xenon atoms by laser pulses at 1320 nm, $0.2–1.0\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, and observe that the yield of near-zero-momentum electrons in the strong-field tunneling ionization regime is significantly suppressed. Semiclassical simulations indicate that this local ionization suppression effect can be attributed to a fraction of the tunneled electrons that are released in a certain window of the initial field phase and transverse velocity are ejected into Rydberg elliptical orbits with a frequency much smaller than that of the laser; i.e., the corresponding atoms are stabilized. These electrons with high-lying atomic orbits are thus prevented from ionization, resulting in the substantially reduced near-zero-momentum electron yield. The refined transition between the Rydberg states of the stabilized atoms has implication on the THz radiation from gas targets in strong laser fields.

The click statistics from on-off detector systems is quite different from the counting statistics of the more traditional detectors. This necessitates the introduction of new parameters to characterize the nonclassicality of fields from measurements using on-off detectors. To properly replace the Mandel $Q_{\mathrm{M}}$ parameter, we introduce a parameter $Q_{\mathrm{B}}$. A negative value represents a sub-binomial statistics. This is possible only for quantum fields, even for super-Poisson light. It eliminates the problems encountered in discerning nonclassicality using Mandel’s $Q_{\mathrm{M}}$ for on-off data.

Following the first successful high-resolution study of the “perpendicular” band of dimethylsulfoxyde at $324{\mathrm{cm}}^{-1}$, associated with the ${\nu }_{23}$ bending vibration, we discovered a sequence of fourfold degenerate clusters of rotational levels at high angular momenta $J>40$. This unusual system of localized states corresponds to classical rotations about a pair of “tilted” axes, which become stationary at high $J$, after the principal axis of inertia $A$ loses stability and bifurcates for $J\approx 27$.

In this Letter, we report the first experimental realization and investigation of a spin-orbit coupled Fermi gas. Both spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state are observed as hallmarks of spin-orbit coupling in a Fermi gas. The single particle dispersion is mapped out by using momentum-resolved radio-frequency spectroscopy. From momentum distribution and momentum-resolved radio-frequency spectroscopy, we observe the change of fermion population in different helicity branches consistent with a finite temperature calculation, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system.

The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum degenerate matter. We directly reveal the spin-orbit gap via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. We also create a spin-orbit coupled lattice and probe its spinful band structure, which features additional spin gaps and a fully gapped spectrum. In the presence of $s$-wave interactions, such systems should display induced $p$-wave pairing, topological superfluidity, and Majorana edge states.

We derive general analytical expressions relating the equilibrium fluctuations of a grain boundary to key parameters governing its motion coupled to shear deformation. We validate these expressions by molecular dynamics simulations for symmetrical tilt boundaries and demonstrate how they can be used to extract the misorientation dependence of the grain-boundary mobility. The results shed light on fundamental relationships between equilibrium and nonequilibrium grain-boundary properties and provide new means to predict those properties.

Under ion irradiation, all crystalline materials display some degree of dynamic annealing when defects experience evolution after the thermalization of collision cascades. The exact time scales of such defect relaxation processes are, however, unknown even for Si at room temperature. Here, we use a pulsed ion-beam method to measure a characteristic time constant of dominant dynamic annealing processes of about 6 ms in Si bombarded at room temperature with 500 keV Ar ions.

High-resolution x-ray powder-diffraction experiments were performed on europium metal at high pressure up to 50 GPa. At variance with previous reports, the hcp phase of Eu was observed to be stable not only to 18 GPa, but to 31.5 GPa. At 31.5(5) GPa, europium transforms to a phase (Eu-IV) with an incommensurately modulated monoclinic crystal structure with superspace group $C2/c(q_{1}0q_3)00$. This new phase was observed to be stable to $\sim 37.0\mathrm{GPa}$, where another phase transition was observed. Eu-IV is the first phase in the lanthanide elements with an incommensurate crystal structure.