Interaction potentials used in particle simulations are typically written as a sum of terms which depend on just a few relative particle positions. Traditional simulation methods move all particles at each time step, and may thus spend a lot of time updating interparticle forces. In this Letter we introduce adaptively restrained particle simulations (ARPS) to speed up particle simulations by adaptively switching on and off positional degrees of freedom, while letting momenta evolve. We illustrate ARPS on several numerical experiments, including (a) a collision cascade example that demonstrates how ARPS make it possible to smoothly trade between precision and speed and (b) a polymer-in-solvent study that shows how one may efficiently determine static equilibrium properties with ARPS.

We use the classical correlation between a quantum system being measured and its measurement apparatus to analyze the amount of information being retrieved in a quantum measurement process. Accounting for decoherence of the apparatus, we show that these correlations may have a sudden transition from a decay regime to a constant level. This transition characterizes a nonasymptotic emergence of the pointer basis, while the system apparatus can still be quantum correlated. We provide a formalization of the concept of emergence of a pointer basis in an apparatus subject to decoherence. This contrast of the pointer basis emergence to the quantum to classical transition is demonstrated in an experiment with polarization entangled photon pairs.

Numerical simulations show that, at the onset of Anderson localization, the momentum distribution of a coherent wave packet launched inside a random potential exhibits, in the forward direction, a novel interference peak that complements the coherent backscattering peak. An explanation of this phenomenon in terms of maximally crossed diagrams predicts that the signal emerges around the localization time and grows on the scale of the Heisenberg time associated with the localization volume. Together, coherent back and forward scattering provide evidence for the occurrence of Anderson localization.

We present the first direct measurement of the top-quark mass using $t\overline{t}$ events decaying in the hadronic $\tau +\mathrm{\text{jets}}$ decay channel. Using data corresponding to an integrated luminosity of $2.2{\mathrm{fb}}^{-1}$ collected by the CDF II detector in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ at the Fermilab Tevatron, we measure the $t\overline{t}$ cross section, ${\sigma }_{t\overline{t}}$, and the top-quark mass, $M_{\mathrm{top}}$. We extract $M_{\mathrm{top}}$ from a likelihood based on per-event probabilities calculated with leading-order signal and background matrix elements. We measure ${\sigma }_{t\overline{t}}=8.8\pm 3.3(\mathrm{stat})\pm 2.2(\mathrm{syst})\mathrm{pb}$ and $M_{\mathrm{top}}=172.7\pm 9.3(\mathrm{stat})\pm 3.7(\mathrm{syst})\mathrm{GeV}/c^2$.

Expansion dynamics at the yoctosecond time scale affect the evolution of the quark gluon plasma (QGP) created in heavy ion collisions. We show how these dynamics are accessible through Hanbury Brown–Twiss (HBT) intensity interferometry of direct photons emitted from the interior of the QGP. A detector placed close to the beam axis is particularly sensitive to early polar momentum anisotropies of the QGP. Observing a modification of the HBT signal at the proposed FoCal detector of the LHC ALICE experiment would allow us to measure the isotropization time of the plasma and could provide first experimental evidence for photon double pulses at the yoctosecond time scale.

A laser can be understood as a thermodynamic engine converting heat to a coherent single mode field close to Carnot efficiency. To achieve lasing, spectral shaping of the excitation light is used to generate a higher effective temperature on the pump than on the gain transition. Here, using a toy model of a quantum well structure with two suitably designed tunnel-coupled wells kept at different temperatures, we predict that lasing can also occur on an actual spatial temperature gradient between the pump and gain regions. Gain and narrow band laser emission require a sufficiently large temperature gradient and resonator quality. Lasing appears concurrent with amplified heat flow between the reservoirs and points to a new form of stimulated solid state cooling. In addition, such a mechanism could reduce intrinsic heating and thus extend the operating regime of quantum cascade lasers by substituting phonon emission driven injection by a phonon absorption step.

We demonstrate both theoretically and experimentally nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of previously found accelerating beams. We show that such beams bend into large angles along circular, elliptical, or parabolic trajectories but still retain nondiffracting and self-healing capabilities. The circular nonparaxial accelerating beams can be considered as a special case of the Mathieu accelerating beams, while an Airy beam is only a special case of the Weber beams at the paraxial limit. Not only do generalized nonparaxial accelerating beams open up many possibilities of beam engineering for applications, but the fundamental concept developed here can be applied to other linear wave systems in nature, ranging from electromagnetic and elastic waves to matter waves.

Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle (embrittlement) transitions, is not yet available. Here, we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free-boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elastoplastic crack tip instability for sufficiently relaxed glasses, resulting in a marked drop in the toughness, which we interpret as annealing-induced embrittlement transition similar to experimental observations.

Hall magnetohydrodynamics (MHD) is investigated through three-dimensional direct numerical simulations. We show that the Hall effect induces a spontaneous chiral symmetry breaking of the turbulent dynamics. The normalized magnetic polarization is introduced to separate the right- ($R$) and left-handed ($L$) fluctuations. A classical $k^{-7/3}$ spectrum is found at small scales for $R$ magnetic fluctuations which corresponds to the electron MHD prediction. A spectrum compatible with $k^{-11/3}$ is obtained at large-scales for the $L$ magnetic fluctuations; we call this regime the ion MHD. These results are explained heuristically by rewriting the Hall MHD equations in a succinct vortex dynamical form. Applications to solar wind turbulence are discussed.

Whether the static microstructural order information is strongly correlated with the subsequent structural rearrangement (SR) and their predicting power for SR are investigated experimentally in the quenched dusty plasma liquid with microheterogeneities. The poor local structural order is found to be a good alarm to identify the soft spot and predict the short term SR. For the site with good structural order, the persistent time for sustaining the structural memory until SR has a large mean value but a broad distribution. The deviation of the local structural order from that averaged over nearest neighbors serves as a good second alarm to further sort out the short time SR sites. It has the similar sorting power to that using the temporal fluctuation of the local structural order over a small time interval.

We show how an order-disorder phase transition in a two-dimensional system can discontinuously alter the shape and size of stress-stabilized self-assembled nanostructures. Low energy electron microscopy was used to study the dealloying of the Cu(111)-$\sqrt{3}\times \sqrt{3}\mathrm{\text{−}}R30°\mathrm{\text{−}}\mathrm{Bi}$ surface alloy. The gradual expulsion of embedded bismuth from the alloy with increasing temperature induces a hard-hexagon-type order-disorder transition in the surface alloy. Our low energy electron microscopy results demonstrate how the loss of long-range order induces enormous changes in the domain patterns that the alloy forms with a Bi overlayer phase. We propose that the occurrence of phase transitions in one of the two surface phases that constitute a self-assembled domain pattern, provides a general, largely unexplored, mechanism that can be used to influence the morphological details of two-dimensional nanostructures.

We performed ab initio calculations of the elastic constants of five flexible metal-organic frameworks (MOFs): MIL-53(Al), MIL-53(Ga), MIL-47, and the square and lozenge structures of DMOF-1. Tensorial analysis of the elastic constants reveals a highly anisotropic elastic behavior, some deformation directions exhibiting very low Young’s modulus and shear modulus. This anisotropy can reach a $400:1$ ratio between the most rigid and weakest directions, in stark contrast to the case of nonflexible MOFs such as MOF-5 and ZIF-8. In addition, we show that flexible MOFs can display extremely large negative linear compressibility. These results uncover the microscopic roots of stimuli-induced structural transitions in flexible MOFs, by linking the local elastic behavior of the material and its multistability.

Mode Grüneisen parameters were estimated for $\alpha \mathrm{\text{−}}{\mathrm{ZrW}}_2{\mathrm{O}}_8$ zone-center modes by means of density functional theory calculations and the temperature dependence of the coefficient of thermal expansion was obtained according to the Debye-Einstein model of the quasiharmonic approximation. The lowest energy optic modes were identified at 45 and $46{\mathrm{cm}}^{-1}$, and were shown to be the main modes responsible for negative thermal expansion at low temperature. Experimental evidence of the lowest energy, triply degenerated infrared active optic mode, was also found in the far infrared spectrum of $\alpha \mathrm{\text{−}}{\mathrm{ZrW}}_2{\mathrm{O}}_8$. Upon increasing temperature, other optic modes with $\mathrm{E}<25\mathrm{meV}$ (particularly at 96, 100, 133, 161, and $164{\mathrm{cm}}^{-1}$) also contribute significantly to the coefficient of thermal expansion near room temperature. An analysis was made of selected zone-center modes in light of previously proposed models for explaining negative thermal expansion in open framework materials.

We have studied the interplay between phase separation and crystallization in a colloid-polymer mixture along one kinetic pathway in samples which exhibit three-phase equilibrium coexistence. In analogy with atomic systems, the range of the effective attractive interaction between colloids is sufficiently long to allow for a stable liquid phase. By direct imaging in microgravity on the International Space Station, we observe a unique structure, a “crystal gel,” that occurs when gas-liquid phase separation arrests due to crystallites within the liquid domain spanning the cell. From the initial onset of spinodal decomposition until arrest caused by this structure, the kinetics of phase separation remain largely unaffected by the formation of the third phase. This dynamic arrest appears to result from the stiffness of the crystalline strands exceeding the liquid-gas interfacial tension.

We present evidence for a deep connection between the zero-temperature coarsening of both the two-dimensional time-dependent Ginzburg-Landau equation and the kinetic Ising model with critical continuum percolation. In addition to reaching the ground state, the time-dependent Ginzburg-Landau equation and kinetic Ising model can fall into a variety of topologically distinct metastable stripe states. The probability to reach a stripe state that winds $a$ times horizontally and $b$ times vertically on a square lattice with periodic boundary conditions equals the corresponding exactly solved critical percolation crossing probability ${\mathcal{P}}_{a,b}$ for a spanning path with winding numbers $a$ and $b$.

Atomic force microscopy (AFM) imaging of isolated submicron dodecyltrichlorosilane coated silica spheres, immobilized at the liquid polystyrene- (PS-) air interface at the PS glass transition temperature, $T_g$, allows for determination of the contact angle $\theta$ versus particle radius $R$. At $T_g$, all $\theta$ versus $R$ measurements are well described by the modified Young’s equation for a line tension $\tau =0.93\mathrm{nN}$. The AFM measurements are also consistent with a minimum contact angle ${\theta }_{\min }$ and minimum radius $R_{\min }$, below which single isolated silica spheres cannot exist at the PS-air interface.

Physically adsorbed ${\mathrm{H}}_2$, HD, and ${\mathrm{D}}_2$ desorbs via the low-energy ${}^2\Sigma _u^{+}$ electron scattering resonance with characteristic electron energy dependent cross sections as we show by desorption and electron energy-loss measurements. Only ${\mathrm{H}}_2$ and HD desorb, for energetic reasons, via excitation of the $j=0\to 2$ rotational mode and its subsequent decay into free translational motion, while all three isotopes desorb by direct transitions to unbound continuum states, with a probability close to unity and an unexpectedly weak mass dependence $\sim m^{-1/2}$.

We consider a model for the two-dimensional electron gas formed at the interface of oxide heterostructures, which includes a Rashba spin-orbit coupling proportional to the electric field perpendicular to the interface. Based on the standard mechanism of polarity catastrophe, we assume that the electric field has a contribution proportional to the electron density. Under these simple and general assumptions, we show that a phase separation instability (signaled by a negative compressibility) occurs for realistic values of the spin-orbit coupling and of the electronic band-structure parameters. This provides an intrinsic mechanism for the inhomogeneous phases observed at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ or ${\mathrm{LaTiO}}_3/{\mathrm{SrTiO}}_3$ interfaces.

In graphene, the valleys represent spinlike quantities and can act as a physical resource in valley-based electronics to produce novel quantum computation schemes. Here we demonstrate a direct route to tune and read the valley quantum states of disordered graphene by measuring the mesoscopic conductance fluctuations. We show that the conductance fluctuations in graphene at low temperatures are reduced by a factor of 4 when valley triplet states are gapped in the presence of short-range potential scatterers at high carrier densities. We also show that this implies a gate tunable universal symmetry class that outlines a fundamental feature arising from graphene’s unique crystal structure.

We present experimental evidence of a transverse thermopower, or planar Nernst effect, in ferromagnetic metal thin films driven by thermal gradients applied in the plane of the films. Samples of 20 nm thick Ni and ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ were deposited on 500 nm thick suspended Si-N thermal isolation platforms with integrated platinum strips designed originally to allow measurement of thermally generated spin currents (the spin Seebeck effect). The low thermal conductivity of the thin supporting Si-N structure results in an essentially 2D geometry that approaches the zero substrate limit, dramatically reducing the contribution of thermal gradients perpendicular to the sample plane typically found in similar experiments on bulk substrates. The voltage on the platinum strips generated transverse to the applied thermal gradient ($V_T$) is linear with increasing $△T$ and exhibits a sign reversal on hot and cold sides of the sample. However, $V_T$ is always even in applied magnetic field and shows a $\sin \theta \cos \theta$ angular dependence, both key indicators of the planar Nernst effect. Within the 5 nV estimated error of our experiment there is no evidence of a signal from the spin Seebeck effect, which would have $\cos \theta$ angular dependence, suggesting a reduced spin Seebeck coefficient in a planar, entirely thin-film geometry.