We derive a thermodynamic identity that allows one to infer the change in the number of screening ions that are associated with a charged macromolecule as the macromolecule is continuously stretched. Applying this identity to force-extension data on both single-stranded and double-stranded DNA, we find that the number of polymer-associated ions depends nontrivially on both the bulk salt concentration and the bare rigidity of the polymer, with single-stranded DNA exhibiting a relatively large decrease in ion excess upon stretching. We rationalize these observations using simple models for polyelectrolyte extension.

We propose a form of parallel computing on classical computers that is based on matrix product states. The virtual parallelization is accomplished by representing bits with matrices and by evolving these matrices from an initial product state that encodes multiple inputs. Matrix evolution follows from the sequential application of gates, as in a logical circuit. The action by classical probabilistic one-bit and deterministic two-bit gates such as NAND are implemented in terms of matrix operations and, as opposed to quantum computing, it is possible to copy bits. We present a way to explore this method of computation to solve search problems and count the number of solutions. We argue that if the classical computational cost of testing solutions (witnesses) requires less than $O(n^2)$ local two-bit gates acting on $n$ bits, the search problem can be fully solved in subexponential time. Therefore, for this restricted type of search problem, the virtual parallelization scheme is faster than Grover’s quantum algorithm.

This Letter presents a search for pair production of heavy down-type quarks decaying via $b^{\prime }\to Wt$ in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel, as $b^{\prime }{\overline{b}}^{\prime }\to W^{-}t{W}^{+}\overline{t}\to b\overline{b}{W}^{+}{W}^{-}{W}^{+}{W}^{-}\to l^{\pm }\nu b\overline{b}q\overline{q}q\overline{q}q\overline{q}$. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum $W$ bosons. In data corresponding to an integrated luminosity of $1.04{\mathrm{fb}}^{-1}$ from $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.

We present precision Penning trap mass measurements of neutron-rich calcium and potassium isotopes in the vicinity of neutron number $N=32$. Using the TITAN system, the mass of ${}^{51}\mathrm{K}$ was measured for the first time, and the precision of the ${}^{51,52}\mathrm{Ca}$ mass values were improved significantly. The new mass values show a dramatic increase of the binding energy compared to those reported in the atomic mass evaluation. In particular, ${}^{52}\mathrm{Ca}$ is more bound by 1.74 MeV, and the behavior with neutron number deviates substantially from the tabulated values. An increased binding was predicted recently based on calculations that include three-nucleon (3N) forces. We present a comparison to improved calculations, which agree remarkably with the evolution of masses with neutron number, making neutron-rich calcium isotopes an exciting region to probe 3N forces.

Recently, several femtosecond-laser techniques have demonstrated molecular excitation to high rotational states with a preferred sense of rotation. We consider collisional relaxation in a dense gas of such unidirectionally rotating molecules, and suggest that due to angular momentum conservation, collisions lead to the generation of macroscopic vortex gas flows. This argument is supported using the Direct Simulation Monte Carlo method, followed by a computational gas-dynamic analysis.

We show that complex $\mathcal{P}\mathcal{T}$-symmetric photonic lattices can lead to a new class of self-imaging Talbot effects. For this to occur, we find that the input field pattern has to respect specific periodicities dictated by the symmetries of the system. While at the spontaneous $\mathcal{P}\mathcal{T}$-symmetry breaking point the image revivals occur at Talbot lengths governed by the characteristics of the passive lattice, at the exact phase it depends on the gain and loss parameter, thus allowing one to control the imaging process.

Active control of the spatial pump profile is proposed to exercise control over random laser emission. We demonstrate numerically the selection of any desired lasing mode from the emission spectrum. An iterative optimization method is employed, first in the regime of strong scattering where modes are spatially localized and can be easily selected using local pumping. Remarkably, this method works efficiently even in the weakly scattering regime, where strong spatial overlap of the modes precludes spatial selectivity. A complex optimized pump profile is found, which selects the desired lasing mode at the expense of others, thus demonstrating the potential of pump shaping for robust and controllable single mode operation of a random laser.

Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying $n=1$ nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge $T_e$ and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.

We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, ${}^2\mathrm{H}$ nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.

Using numerical simulations, we study the gravity driven flow of jammed soft disks in confined channels. We demonstrate that confinement results in increasing the yield threshold for the Poiseuille flow, in contrast to the planar Couette flow. By solving a nonlocal flow model for such systems, we show that this effect is due to the correlated dynamics responsible for flow, coupled with the stress heterogeneity imposed for the Poiseuille flow. We also observe that with increasing confinement, the cooperative nature of the flow results in increasing intermittent behavior. Our studies indicate that such features are generic properties of a wide variety of jammed materials.

Further insight into the dissociative adsorption of ${\mathrm{NH}}_3$ on Si(001) has been obtained using a combined computational and experimental approach. A novel route leading to the dissociation of the chemisorbed ${\mathrm{NH}}_3$ is proposed, based on H-bonding interactions between the gas phase and the chemisorbed ${\mathrm{NH}}_3$ molecules. Our model, complemented by synchrotron radiation photoelectron spectroscopy measurements, demonstrates that the low temperature dissociation of molecular chemisorbed ${\mathrm{NH}}_3$ is driven by the continuous flux of ammonia molecules from the gas phase.

We develop a Green’s function approach to quasiparticle excitations of open-shell systems within the $GW$ approximation. It is shown that accurate calculations of the characteristic multiplet structure require a precise knowledge of the self-energy and, in particular, its poles. We achieve this by constructing the self-energy from appropriately chosen mean-field theories on a fine frequency grid. We apply our method to a two-site Hubbard model, several molecules, and the negatively charged nitrogen-vacancy defect in diamond and obtain good agreement with experiment and other high-level theories.

We propose a promising electron entanglement detector consisting of two quantum spin Hall systems weakly coupled to a superconductor. The detection of electron spins along various polarization directions, which is a prerequisite for testing Bell’s inequality on solid state spins, can be achieved in an all-electrical-controlled manner utilizing the helical edge states. It is found that the violation of Bell’s inequality exists in a large range of the tunneling parameters, which can be realized in mercury telluride quantum wells.

By relativistic first-principles photoemission calculations for the topological insulator ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, we study how the spin texture of the Dirac state manifests itself in circular dichroism. On one hand, there are significant modifications of the initial state’s spin texture, which are explained by final-state effects and the symmetry of the photoemission setup. On the other hand, a highly symmetric setup allows us to draw conclusions about the detailed Dirac state’s spin texture. Our study supports that circular dichroism in angular distribution successfully complements spin- and angle-resolved photoelectron spectroscopy from topological insulators.

We report a comprehensive angle-resolved photoemission spectroscopy study of the tridimensional electronic bands in the recently discovered Fe selenide superconductor $(\mathrm{Tl},\mathrm{Rb}{)}_y{\mathrm{Fe}}_{2-x}{\mathrm{Se}}_2$ ($T_c=32\mathrm{K}$). We determined the orbital characters and the $k_z$ dependence of the low energy electronic structure by tuning the polarization and the energy of the incident photons. We observed a small 3D electron Fermi surface pocket near the Brillouin zone center and a 2D like electron Fermi surface pocket near the zone boundary. The photon energy dependence, the polarization analysis and the local-density approximation calculations suggest a significant contribution from the Se $4p_z$ and Fe $3d_{xy}$ orbitals to the small electron pocket. We argue that the emergence of Se $4p_z$ states might be the cause of the different magnetic properties between Fe chalcogenides and Fe pnictides.

An effective Hamiltonian is developed to investigate the magnetic cycloid of the ${\mathrm{BiFeO}}_3$ (BFO) multiferroic. This approach reproduces many complex features of this cycloid, such as its plane of rotation containing the polarization and the newly discovered spin density waves resulting from the canting of magnetic dipoles out of this cycloidal plane. It also suggests that the energetic origin of the cycloid can be thought of in terms of the converse spin-current model, and reveals the mechanisms responsible for the spin density waves. Finally, this atomistic scheme resolves an ongoing controversy about the cycloid anharmonicity, and revisits a recent misconception about the relationship between out-of-plane spin-density waves and the weak magnetization associated with the spin-canted structure of BFO.

Magnetic susceptibility, NMR, muon spin relaxation, and inelastic neutron scattering measurements show that kapellasite, ${\mathrm{Cu}}_3\mathrm{Zn}(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$, a geometrically frustrated spin-$1/2$ kagome antiferromagnet polymorphic with herbertsmithite, is a gapless spin liquid showing unusual dynamic short-range correlations of noncoplanar cuboc2 type which persist down to 20 mK. The Hamiltonian is determined from a fit of a high-temperature series expansion to bulk susceptibility data and possesses competing exchange interactions. The magnetic specific heat calculated from these exchange couplings is in good agreement with experiment. The temperature dependence of the magnetic structure factor and the muon relaxation rate are calculated in a Schwinger-boson approach and compared to experimental results.

We have investigated the low-energy dynamics of the triangular lattice of Skyrmions in a helimagnetic insulator ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ in terms of microwave response. We have observed two elementary excitations of the Skyrmion with different polarization characteristics: the counterclockwise circulating mode at 1 GHz with the magnetic field polarization parallel to the Skyrmion plane and the breathing mode at 1.5 GHz with a perpendicular magnetic field polarization. These modes reflect the topological nature of Skyrmions and may play a central role in the Skyrmion dynamics.

Spontaneous symmetry breaking plays a fundamental role in many areas of condensed matter and particle physics. A fundamental problem in ecology is the elucidation of the mechanisms responsible for biodiversity and stability. Neutral theory, which makes the simplifying assumption that all individuals (such as trees in a tropical forest)—regardless of the species they belong to—have the same prospect of reproduction, death, etc., yields gross patterns that are in accord with empirical data. We explore the possibility of birth and death rates that depend on the population density of species, treating the dynamics in a species-symmetric manner. We demonstrate that dynamical evolution can lead to a stationary state characterized simultaneously by both biodiversity and spontaneously broken neutral symmetry.

Anchoring of spiral and scroll waves in excitable media has attracted considerable interest in the context of cardiac arrhythmias. Here, by bombarding inclusions with drifting spiral and scroll waves, we explore the forces exerted by inclusions onto an approaching spiral and derive the equations of motion governing spiral dynamics in the vicinity of inclusion. We demonstrate that these forces nonmonotonically depend on distance and can lead to complex behavior: (a) anchoring to small but circumnavigating larger inclusions; (b) chirality-dependent anchoring.