We present an experimental study of density and order fluctuations in the vicinity of the solid-liquid-like transition that occurs in a vibrated quasi-two-dimensional granular system. The two-dimensional projected static and dynamic correlation functions are studied. We show that density fluctuations, characterized through the structure factor, increase in size and intensity as the transition is approached, but they do not change significantly at the transition itself. The dense, metastable clusters, which present square symmetry, also increase their local order in the vicinity of the transition. This is characterized through the bond-orientational order parameter $Q_4$, which in Fourier space shows an Ornstein-Zernike-like behavior. Depending on the filling density and vertical height, the transition can be of first- or second-order type. In the latter case, the associated correlation length ${\xi }_4$, the relaxation time ${\tau }_4$, the zero $k$ limit of $Q_4$ fluctuations (static susceptibility), the pair correlation function of $Q_4$, and the amplitude of the order parameter obey critical power laws, with saturations due to finite size effects. Their respective critical exponents are ${\nu }_{\perp }=1$, ${\nu }_{\parallel }=2$, $\gamma =1$, $\eta =0.67$, and $\beta =1/2$, whereas the dynamical critical exponent $z={\nu }_{\parallel }/{\nu }_{\perp }=2$. These results are consistent with model $C$ of dynamical critical phenomena, valid for a nonconserved critical order parameter (bond-orientation order) coupled to a conserved field (density).

Several scenarios exist for the protein crystallization and aggregation in solutions near a metastable fluid-fluid phase separation below the solubility line. Based on computations, it was proposed that the fluid-fluid critical point enhances the crystallization rate by many orders of magnitude, while, based on experiments, it was proposed that the fluid-fluid spinodal controls the crystallization rate. Using molecular dynamic simulations for an isotropic model with sticky interaction, we show that neither of these scenarios adequately describes the crystallization mechanism near a metastable fluid-fluid phase separation. We find that the emergence of the high-density fluid inside the spinodal drastically enhances the crystal nucleation in the subcritical region following Ostwald’s rule of stages.

When are athermal soft-sphere packings jammed? Any experimentally relevant definition must, at the very least, require a jammed packing to resist shear. We demonstrate that widely used (numerical) protocols, in which particles are compressed together, can and do produce packings that are unstable to shear—and that the probability of generating such packings reaches one near jamming. We introduce a new protocol which, by allowing the system to explore different box shapes as it equilibrates, generates truly jammed packings with strictly positive shear moduli $G$. For these packings, the scaling of the average of $G$ is consistent with earlier results, while the probability distribution $P(G)$ exhibits novel and rich scalings.

We present an analysis of finite-size effects in jammed packings of $N$ soft, frictionless spheres at zero temperature. There is a $\frac{1}{N}$ correction to the discrete jump in the contact number at the transition so that jammed packings exist only above isostaticity. As a result, the canonical power-law scalings of the contact number and elastic moduli break down at low pressure. These quantities exhibit scaling collapse with a nontrivial scaling function, demonstrating that the jamming transition can be considered a phase transition. Scaling is achieved as a function of $N$ in both two and three dimensions, indicating an upper critical dimension of 2.

We demonstrate an all-organic, one-dimensional photonic crystal tuned to the regime of strong exciton-photon coupling. The structure consists of a high index of refraction light-absorbing active layer periodically distributed in a low index of refraction nonabsorbing background medium. The strongly coupled state in this structure is shared between multiple active layers separated by distances longer than the wavelength of light in the structure. In order to investigate the potential for long-range energy transfer, photon-mediated exciton hybridization is demonstrated between multiple absorbing species spatially separated in the photonic crystal.

We calculate the Hall transport in a multiband system with a dominant interband interaction between carriers having electron and hole character. We show that this situation gives rise to an unconventional scenario, beyond the Boltzmann theory, where the quasiparticle currents dressed by vertex corrections acquire the character of the majority carriers. This leads to a larger (positive or negative) Hall coefficient than what may be expected on the basis of the carrier balance, with a marked temperature dependence. Our results explain the puzzling measurements in pnictides and provide a more general framework for transport properties in multiband materials.

In free fermion systems with given symmetry and dimension, the possible topological phases are labeled by elements of only three types of Abelian groups, 0, ${\mathbb{Z}}_2$, or $\mathbb{Z}$. For example, noninteracting one-dimensional fermionic superconducting phases with $S_z$ spin rotation and time-reversal symmetries are classified by $\mathbb{Z}$. We show that with weak interactions, this classification reduces to ${\mathbb{Z}}_4$. Using group cohomology, one can additionally show that there are only four distinct phases for such one-dimensional superconductors even with strong interactions. Comparing their projective representations, we find that all these four symmetry-protected topological phases can be realized with free fermions. Further, we show that one-dimensional fermionic superconducting phases with $Z_n$ discrete $S_z$ spin rotation and time-reversal symmetries are classified by ${\mathbb{Z}}_4$ when $n$ is even and ${\mathbb{Z}}_2$ when $n$ is odd; again, all these strongly interacting topological phases can be realized by noninteracting fermions. Our approach can be applied to systems with other symmetries to see which one-dimensional topological phases can be realized with free fermions.

We study quantum transport in Dirac materials with a single fermionic Dirac cone (strong topological insulators and graphene in the absence of intervalley coupling) in the presence of non-Gaussian long-range disorder. We show, by directly calculating numerically the conductance fluctuations, that in the limit of very large system size and disorder strength, quantum transport becomes universal. However, a systematic deviation away from universality is obtained for realistic system parameters. By comparing our results to existing experimental data on $1/f$ noise, we suggest that many of the graphene samples studied to date are in a nonuniversal crossover regime of conductance fluctuations.

Muon spin rotation and relaxation experiments on the centrosymmetric intermetallic superconductor ${\mathrm{LaNiGa}}_2$ are reported. The appearance of spontaneous magnetic fields coincides with the onset of superconductivity, implying that the superconducting state breaks time reversal symmetry, similarly to noncentrosymmetric ${\mathrm{LaNiC}}_2$. Only four triplet states are compatible with this observation, all of which are nonunitary triplets. This suggests that ${\mathrm{LaNiGa}}_2$ is the centrosymmetric analogue of ${\mathrm{LaNiC}}_2$. We argue that these materials are representatives of a new family of paramagnetic nonunitary superconductors.

We demonstrate that local modulations of magnetic couplings have a profound effect on the temperature dependence of the relaxation rate of optical magnons in a wide class of antiferromagnets in which gapped excitations coexist with acoustic spin waves. In a two-dimensional collinear antiferromagnet with an easy-plane anisotropy, the disorder-induced relaxation rate of the gapped mode, ${\Gamma }_{\mathrm{imp}}\approx {\Gamma }_0+A(T\ln T{)}^2$, greatly exceeds the magnon-magnon damping, ${\Gamma }_{\mathrm{m}\mathrm{\text{−}}\mathrm{m}}\approx B{T}^5$, negligible at low temperatures. We measure the lifetime of gapped magnons in a prototype $XY$ antiferromagnet ${\mathrm{BaNi}}_2({\mathrm{PO}}_4{)}_2$ using a high-resolution neutron-resonance spin-echo technique and find experimental data in close accord with the theoretical prediction. Similarly strong effects of disorder in the three-dimensional case and in noncollinear antiferromagnets are discussed.

Although pinning of domain walls in ferromagnets is ubiquitous, the absence of an appropriate characterization tool has limited the ability to correlate the physical and magnetic microstructures of ferromagnetic films with specific pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the simplest possible domain structure in soft ferromagnets, is strongly correlated with surface roughness, and we make a quantitative comparison of the pinning energy and spatial range in films of various thickness. The results demonstrate that thickness fluctuations on the lateral length scale of the vortex core diameter, i.e., an effective roughness at a specific length scale, provides the dominant pinning mechanism. We argue that this mechanism will be important in virtually any soft ferromagnetic film.

We have performed dielectric measurements and neutron diffraction experiments on the delafossite ${\mathrm{AgFeO}}_2$. A ferroelectric polarization $P\simeq 300\mu \mathrm{C}/{\mathrm{m}}^2$ was observed in a powder sample, below 9 K. The neutron diffraction experiment demonstrated successive magnetostructural phase transitions at $T_{\mathrm{N}1}=15\mathrm{K}$ and $T_{\mathrm{N}2}=9\mathrm{K}$. The magnetic structure for $9\mathrm{K}\le T\le 15\mathrm{K}$ is a spin-density wave with a temperature dependent incommensurate modulation $\mathit{k}=(-1,q,\frac{1}{2})$, $q\simeq 0.384$. Below 9 K, the magnetic structure turns into elliptical cycloid with the incommensurate propagation vector $\mathit{k}=(-\frac{1}{2},q,\frac{1}{2})$, $q\simeq 0.2026$ Based on the deduced magnetic point-group symmetry $m{1}^{\prime }$ of the low-temperature polar phase, we conclude that the ferroelectric polarization in ${\mathrm{AgFeO}}_2$ is perpendicular to the monoclinic $b$ axis and is driven by the inverse Dzyaloshinskii-Moriya effect with two orthogonal components ${\mathit{p}}_1\propto {\mathit{r}}_{ij}\times ({\mathit{S}}_i\times {\mathit{S}}_j)$ and ${\mathit{p}}_2\propto {\mathit{S}}_i\times {\mathit{S}}_j$.

We show that the degree of spin polarization of photoelectrons from the surface states of topological insulators is 100% if fully polarized light is used as in typical photoemission measurements, and, hence, can be significantly higher than that of the initial state. Further, the spin orientation of these photoelectrons in general can also be very different from that of the initial surface state and is controlled by the photon polarization. A rich set of predicted phenomena have recently been confirmed by spin- and angle-resolved photoemission experiments.

Scroll rings are three-dimensional excitation waves rotating around one-dimensional filament loops. In experiments with the Belousov-Zhabotinsky reaction we show that the collapse of these loops can be stopped by local pinning to only two unexcitable heterogeneities. The resulting vortices rotate around stationary but curved filaments. The absence of filament motion can be explained by repulsive interaction that counteracts the expected curvature-induced motion. The shape and key dependencies of the stationary filaments are well described by a curvature-flow model with additive interaction velocities that rapidly decrease with filament distance.

Current photon entangling schemes require resources that grow with the photon number. We present a new approach that generates quantum entanglement between many photons, using only a single source of entangled photon pairs. The different spatial modes, one for each photon as required by other schemes, are replaced by different time slots of only two spatial modes. States of any number of photons are generated with the same setup, solving the scalability problem caused by the previous need for extra resources. Consequently, entangled photon states of larger numbers than before are practically realizable.

We describe a scalable experimental protocol for estimating the average error of individual quantum computational gates. This protocol consists of interleaving random Clifford gates between the gate of interest and provides an estimate as well as theoretical bounds for the average error of the gate under test, so long as the average noise variation over all Clifford gates is small. This technique takes into account both state preparation and measurement errors and is scalable in the number of qubits. We apply this protocol to a superconducting qubit system and find a bounded average error of 0.003 [0,0.016] for the single-qubit gates $X_{\pi /2}$ and $Y_{\pi /2}$. These bounded values provide better estimates of the average error than those extracted via quantum process tomography.

On-shell superspace techniques are used to quantify $R$-symmetry violation in type IIB superstring theory amplitudes in a flat background in 10 dimensions. This shows the existence of a particularly simple class of nonvanishing amplitudes in this theory, which violate $R$ symmetry maximally. General properties of the class and some of its extensions are established that at string tree level are shown to determine the first three nontrivial effective field theory contributions to all multiplicity. This leads to a natural conjecture for the exact analytic part of the first two of these.

The data for 9.3 million ${\rm Y}(2S)$ and 20.9 million ${\rm Y}(1S)$ taken with the CLEO III detector have been used to study the radiative population of states identified by their decay into 26 different exclusive hadronic final states. In the ${\rm Y}(2S)$ decays, an enhancement is observed at a $\sim 5\sigma$ level at a mass of $9974.6\pm 2.3(\mathrm{stat})\pm 2.1(\mathrm{syst})\mathrm{MeV}$. It is attributed to ${\eta }_b(2S)$ and corresponds to the ${\rm Y}(2S)$ hyperfine splitting of $48.7\pm 2.3(\mathrm{stat})\pm 2.1(\mathrm{syst})\mathrm{MeV}$. In the ${\rm Y}(1S)$ decays, the identification of ${\eta }_b(1S)$ is confirmed at a $\sim 3\sigma$ level with $M[{\eta }_b(1S)]$ in agreement with its known value.

The production of charm quark jets in association with electroweak gauge bosons at the LHC can be used as a tool to constrain quark parton distribution functions (PDFs). Motivated by recent measurements at the Tevatron and LHC, we calculate cross sections for $W/Z+c$, comparing these to $W/Z+\mathrm{\text{jet}}$, for various PDF sets. The cross-section differences can be understood in terms of the different underlying PDFs, with the strange quark distribution being particularly important for $W+c$ production. We suggest measurements of appropriately defined ratios and comment on how these measurements at the LHC can be used to extract information on the strange and charm content of the proton at high $Q^2$ scales.

We explore one-dimensional samples of ultracold polar molecules with attractive dipole-dipole interactions and show the existence of a repulsive barrier caused by a strong quadrupole interaction between molecules. This barrier can stabilize a gas of ultracold KRb molecules and even lead to long-range wells supporting bound states between the molecules. The properties of these wells can be controlled by external electric fields, allowing the formation of long polymerlike chains of KRb and studies of quantum phase transitions by varying the effective interaction between molecules. We discuss the generalization of those results to other systems.