The recent observation of fully gapped superconductivity in Yb doped ${\mathrm{CeCoIn}}_5$ poses a paradox, for the disappearance of nodes suggests that they are accidental, yet $d$-wave symmetry with protected nodes is well established by experiment. Here, we show that composite pairing provides a natural resolution: in this scenario, Yb doping drives a Lifshitz transition of the nodal Fermi surface, forming a fully gapped $d$-wave molecular superfluid of composite pairs. The $T^4$ dependence of the penetration depth associated with the sound mode of this condensate is in accordance with observation.

The London penetration depth $\lambda (T)$ was measured in single crystals of ${\mathrm{Ce}}_{1-x}{R}_x{\mathrm{CoIn}}_5$, $R=\mathrm{La}$, Nd, and Yb down to $T_{\min }\approx 50\mathrm{mK}$ ($T_c/T_{\min }\sim 50$) using a tunnel-diode resonator. In the cleanest samples $\mathrm{\Delta }\lambda (T)$ is best described by the power law $\mathrm{\Delta }\lambda (T)\propto T^n$, with $n\sim 1$, consistent with the existence of line nodes in the superconducting gap. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of $T_c$; however, the effects on $\mathrm{\Delta }\lambda (T)$ differ. While La and Nd substitution leads to an increase in the exponent $n$ and saturation at $n\sim 2$, as expected for a dirty nodal superconductor, Yb substitution leads to $n>3$, suggesting a change from nodal to nodeless superconductivity. This superconducting gap structure change happens in the same doping range where changes of the Fermi-surface topology were reported, implying that the nodal structure and Fermi-surface topology are closely linked.

We explore the flow of highly shear thinning polymer solutions in straight geometry. The strong variations of the normal forces close to the wall give rise to an elastic instability. We evidence a periodic motion close the onset of the instability, which then evolves towards a turbulentlike flow at higher flow rates. Strikingly, we point out that this instability induces genuine drag reduction due to the homogenization of the viscosity profile by the turbulent flow.

We observe the suppression of inelastic dipolar scattering in ultracold Fermi gases of the highly magnetic atom dysprosium: the more energy that is released, the less frequently these exothermic reactions take place, and only quantum spin statistics can explain this counterintuitive effect. Inelastic dipolar scattering in nonzero magnetic fields leads to heating or to loss of the trapped population, both detrimental to experiments intended to study quantum many-body physics with strongly dipolar gases. Fermi statistics, however, is predicted to lead to a kinematic suppression of these harmful reactions. Indeed, we observe a 120-fold suppression of dipolar relaxation in fermionic versus bosonic Dy, as expected from theory describing universal inelastic dipolar scattering, though never before experimentally confirmed. Similarly, low inelastic cross sections are observed in spin mixtures, also with striking correspondence to predictions. The suppression of relaxation opens the possibility of employing fermionic dipolar species in studies of quantum many-body physics involving, e.g., synthetic gauge fields and pairing.

Nanostructures are commonly used for developing superhydrophobic surfaces. However, available wetting theoretical models ignore the effect of vacuum photon-mode alteration on van der Waals forces and thus on hydrophobicity. Using first-principles calculations, we show that superhydrophibicity of nanostructured surfaces is dramatically enhanced by vacuum photon-mode tuning. As a case study, wetting contact angles of a water droplet above a polyethylene nanostructured surface are obtained from the interaction potential energy calculated as a function of the droplet-surface separation distance. This new approach could pave the way for the design of novel superhydrophobic coatings.

Anomalous reduction of the fusion yields by 50% and anomalous scaling of the burn-averaged ion temperatures with the ion-species fraction has been observed for the first time in $\mathrm{D}{}^3\mathrm{He}$-filled shock-driven inertial confinement fusion implosions. Two ion kinetic mechanisms are used to explain the anomalous observations: thermal decoupling of the D and ${}^3\mathrm{He}$ populations and diffusive species separation. The observed insensitivity of ion temperature to a varying deuterium fraction is shown to be a signature of ion thermal decoupling in shock-heated plasmas. The burn-averaged deuterium fraction calculated from the experimental data demonstrates a reduction in the average core deuterium density, as predicted by simulations that use a diffusion model. Accounting for each of these effects in simulations reproduces the observed yield trends.

We examine correlations of transverse particle displacements and their relationship to the shear modulus of a glass and the viscosity of a fluid. To this end we use computer simulations to calculate a correlation function of the displacements, $S_4(q;t)$, which is similar to functions used to study heterogeneous dynamics in glass-forming fluids. We show that in the glass the shear modulus can be obtained from the long-time, small-$q$ limit of $S_4(q;t)$. By using scaling arguments, we argue that a four-point correlation length ${\xi }_4(t)$ grows linearly in time in a glass and grows as $\sqrt{t}$ at long times in a fluid, and we verify these results by analyzing $S_4(q;t)$ obtained from simulations. For a viscoelastic fluid, the simulation results suggest that the crossover to the long-time $\sqrt{t}$ growth of ${\xi }_4(t)$ occurs at a characteristic decay time of the shear stress autocorrelation function. Using this observation, we show that the amplitude of the long-time $\sqrt{t}$ growth is proportional to $\sqrt{\eta }$ where $\eta$ is the viscosity of the fluid.

We show that the excitonic coupling in molecular crystals undergoes a very large fluctuation at room temperature as a result of the combined thermal motions of the nuclei. This observation dramatically affects the description of exciton transport in organic crystals and any other phenomenon (like singlet fission or exciton dissociation) that originates from an exciton in a molecular crystal or thin film. This unexpected result is due to the predominance of the short-range excitonic coupling mechanisms (exchange, overlap, and charge-transfer mediated) over the Coulombic excitonic coupling for molecules in van der Waals contact. To quantify this effect we develop a procedure to evaluate accurately the short-range excitonic coupling (via a diabatization scheme) along a molecular dynamics trajectory of the representative molecular crystals of anthracene and tetracene.

We show, by molecular simulation, that for a range of standard, coarse-grained, nematic liquid crystal models, the director bend fluctuation is a propagating mode. This is in contrast to the generally accepted picture of nematic hydrodynamics, in which all the director modes (splay, twist, bend, and combinations thereof) are overdamped. By considering the various physical parameters that enter the equations of nematodynamics, we propose an explanation of this effect and conclude that propagating bend fluctuations may be observable in some experimental systems.

Reconstructing complex networks from measurable data is a fundamental problem for understanding and controlling collective dynamics of complex networked systems. However, a significant challenge arises when we attempt to decode structural information hidden in limited amounts of data accompanied by noise and in the presence of inaccessible nodes. Here, we develop a general framework for robust reconstruction of complex networks from sparse and noisy data. Specifically, we decompose the task of reconstructing the whole network into recovering local structures centered at each node. Thus, the natural sparsity of complex networks ensures a conversion from the local structure reconstruction into a sparse signal reconstruction problem that can be addressed by using the lasso, a convex optimization method. We apply our method to evolutionary games, transportation, and communication processes taking place in a variety of model and real complex networks, finding that universal high reconstruction accuracy can be achieved from sparse data in spite of noise in time series and missing data of partial nodes. Our approach opens new routes to the network reconstruction problem and has potential applications in a wide range of fields.

In the standard diffusive picture for transport of cosmic rays (CRs), a gradient in the CR density induces a typically small, dipolar anisotropy in their arrival directions. This is being widely advertised as a tool for finding nearby sources. However, the predicted dipole amplitude at TeV and PeV energies exceeds the measured one by almost 2 orders of magnitude. Here, we critically examine the validity of this prediction, which is based on averaging over an ensemble of turbulent magnetic fields. We focus on (1) the deviations of the dipole in a particular random realization from the ensemble average, and (2) the possibility of a misalignment between the regular magnetic field and the CR gradient. We find that if the field direction and the gradient direction are close to $\sim 90°$, the dipole amplitude is considerably suppressed and can be reconciled with observations, which sheds light on a long-standing problem. Furthermore, we show that the dipole direction in general does not coincide with the gradient direction, thus hampering the search for nearby sources.

A fluid in equilibrium in a finite volume $V$ with particle number $N$ at a density $\rho =N/V$ exceeding the onset density ${\rho }_f$ of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

We present a wide class of partially integrable lattice models with two-spin interactions which generalize the Kitaev honeycomb model. These models have a conserved quantity associated with each plaquette, conserved large loop operators on the torus, and topological degeneracy. We introduce a “slave-genon” approach which generalizes the Majorana fermion approach in the Kitaev model. The Hilbert space of our spin model can be embedded in an enlarged Hilbert space of non-Abelian twist defects, referred to as genons. In the enlarged Hilbert space, the spin model is exactly reformulated as a model of non-Abelian genons coupled to a discrete gauge field. We discuss in detail a particular $Z_3$ generalization, and we show that in a certain limit the model is analytically tractable and produces a non-Abelian topological phase with chiral parafermion edge states.