Using the susceptible-infected-susceptible model on unweighted and weighted networks, we consider the disease localization phenomenon. In contrast to the well-recognized point of view that diseases infect a finite fraction of vertices right above the epidemic threshold, we show that diseases can be localized on a finite number of vertices, where hubs and edges with large weights are centers of localization. Our results follow from the analysis of standard models of networks and empirical data for real-world networks.

We show that the orthogonality catastrophe can dramatically affect the probability with which an ultralow energy atom or ion will stick to a surface. We predict new energy-dependent scaling laws for the sticking probability in this low-energy regime. We provide numerical results of this theory for the case of ultracold electrons sticking to the surface of highly porous silicon and show that the sticking probability can differ substantially from that calculated with perturbation theory. We then generalize our results for finite surface temperatures and find surprisingly that the sticking probability can change sharply, vanishing below a critical incident energy that varies with the surface temperature. We describe in detail this superreflective surface phase for ultralow energy matter waves where the reflection coefficient is strictly equal to one.

We find novel phase transitions and critical phenomena that occur only outside the linear-response regime of current-driven nonequilibrium states. We consider the strongly interacting $(3+1)$-dimensional $\mathcal{N}=4$ large-$N_c$ $SU(N_c)$ supersymmetric Yang-Mills theory with a single flavor of fundamental $\mathcal{N}=2$ hypermultiplet as a microscopic theory. We compute its nonlinear nonballistic quark-charge conductivity by using the AdS/CFT correspondence. We find that the system exhibits a novel nonequilibrium first-order phase transition where the conductivity jumps and the sign of the differential conductivity flips at finite current density. A nonequilibrium critical point is discovered at the end point of the first-order regime. We propose a nonequilibrium steady-state analogue of thermodynamic potential in terms of the gravity-dual theory in order to define the transition point. Nonequilibrium analogues of critical exponents are proposed as well. The critical behavior of the conductivity is numerically confirmed on the basis of these proposals. The present work provides a new example of nonequilibrium phase transitions and nonequilibrium critical points.

We study the dynamics of a colloidal fluid including inertia and hydrodynamic interactions, two effects which strongly influence the nonequilibrium properties of the system. We derive a general dynamical density functional theory which shows very good agreement with full Langevin dynamics. In suitable limits, we recover existing dynamical density functional theories and a Navier-Stokes-like equation with additional nonlocal terms.

We investigate the possibility of constraining primordial non-Gaussianity using the 3D bispectrum of the Lyman (Ly)-$\alpha$ forest. The strength of the quadratic non-Gaussian correction to an otherwise Gaussian primordial gravitational field is assumed to be dictated by a single parameter $f_{\mathrm{NL}}$. We present the first prediction for bounds on $f_{\mathrm{NL}}$ using Ly-$\alpha$ flux spectra along multiple lines of sight. The 3D Ly-$\alpha$ transmitted flux field is modeled as a biased tracer of the underlying matter distribution sampled along 1D skewers corresponding to quasar sight lines. The precision to which $f_{\mathrm{NL}}$ can be constrained depends on the survey volume, pixel noise, and aliasing noise (arising from discrete sampling of the density field). We consider various combinations of these factors to predict bounds on $f_{\mathrm{NL}}$. We find that in an idealized situation of full sky survey and negligible Poisson noise one may constrain $f_{\mathrm{NL}}\sim 23$ in the equilateral limit. Assuming a Ly-$\alpha$ survey covering large parts of the sky ($k_{\min }=8\times {10}^{-4}{\mathrm{Mpc}}^{-1}$) and with a quasar density of $\overline{n}=5\times {10}^{-3}{\mathrm{Mpc}}^{-2}$, it is possible to constrain $f_{\mathrm{NL}}\sim 100$ for equilateral configurations. The possibility of measuring $f_{\mathrm{NL}}$ at a precision comparable to large scale structure studies maybe useful for joint constraining of inflationary scenarios using different data sets.

We use data from the Wilkinson Microwave Anisotropy probe temperature maps to constrain a scale-dependent generalization of the popular “local” model for primordial non-Gaussianity. In the model where the parameter $f_{\mathrm{NL}}$ is allowed to run with scale $k$, $f_{\mathrm{NL}}(k)=f_{\mathrm{NL}}^{*}(k/k_{\mathrm{piv}}{)}^{n_{f_{\mathrm{NL}}}}$, we constrain the running to be $n_{f_{\mathrm{NL}}}={0.30}_{-1.2}^{+1.9}$ at 95% confidence, marginalized over the amplitude $f_{\mathrm{NL}}^{*}$. The constraints depend somewhat on the prior probabilities assigned to the two parameters. In the near future, constraints from a combination of Planck and large-scale structure surveys are expected to improve this limit by about an order of magnitude and usefully constrain classes of inflationary models.

The effects of energy loss in cold nuclear matter on $J/\psi$ suppression in $p\mathrm{\text{−}}A$ collisions are studied. A simple model based on first principles and depending on a single free parameter is able to reproduce $J/\psi$ suppression data at large $x_F$ and at various center-of-mass energies. These results strongly support energy loss as a dominant effect in quarkonium suppression. They also give some hint on its hadroproduction mechanism suggesting color neutralization to happen on long time scales. Predictions for $J/\psi$ and ${\rm Y}$ suppression in $p$-Pb collisions at the LHC are made.

Naphthalene molecules are fixed in space by a laser field and rotated, in 2° steps, over 180°. For each orientation, they are ionized by an intense, circularly polarized femtosecond laser pulse, and the 2D projection of the photoelectron momentum distribution is recorded. The molecular-frame 3D momentum distribution is obtained by tomographic reconstruction from all 90 projections. It reveals an anisotropic electron distribution, angularly shifted in the polarization plane, that is not accessible by the 2D momentum images. Our theoretical analysis shows that the magnitude of the angular shift is very sensitive to the exact form of the laser-modified molecular potential.

We report on three-body recombination of a single trapped ${\mathrm{Rb}}^{+}$ ion and two neutral Rb atoms in an ultracold atom cloud. We observe that the corresponding rate coefficient $K_3$ depends on collision energy and is about a factor of 1000 larger than for three colliding neutral Rb atoms. In the three-body recombination process large energies up to several 0.1 eV are released leading to an ejection of the ion from the atom cloud. It is sympathetically recooled back into the cloud via elastic binary collisions with cold atoms. Further, we find that the final ionic product of the three-body processes is again an atomic ${\mathrm{Rb}}^{+}$ ion suggesting that the ion merely acts as a catalyzer, possibly in the formation of deeply bound ${\mathrm{Rb}}_2$ molecules.

Quantum imaging promises increased imaging performance over classical protocols. However, there are a number of aspects of quantum imaging that are not well understood. In particular, it has been unknown so far how to compare classical and quantum imaging procedures. Here, we consider classical and quantum imaging in a single theoretical framework and present general fundamental limits on the resolution and the deposition rate for classical and quantum imaging. The resolution can be estimated from the image itself. We present a utility function that allows us to compare imaging protocols in a wide range of applications.

The dependence of the ion-temperature-gradient scale length on the hydrogen isotope mass was examined in conventional $H$-mode plasmas in JT-60U tokamak. While identical profiles for density and temperature were obtained for hydrogen and deuterium plasmas, the ion conductive heat flux necessary for hydrogen to sustain the same ion temperature profile was two times that required for deuterium, resulting in a clearly higher ion heat diffusivity for hydrogen at the same ion-temperature-gradient scale length. On the other hand, the ion-temperature-gradient scale length for deuterium is less than that for hydrogen at a given ion heat diffusivity.

We report that a series of lanthanide-based bulk metallic glasses show a pressure-induced polyamorphic phase transition observed by in situ angle-dispersive x-ray diffraction under high pressures. The transition started from a low-density state at lower pressures, and went through continuous densification ending with a high-density state at higher pressures. We demonstrate that, under high pressure, this new type of polyamorphism in densely packed metallic glasses is inherited from its lanthanide-solvent constituent and related to the electronic structure of $4f$ electrons. The found electronic structure inheritance could provide the guidance for designing new metallic glasses with unique functional physical properties.

The requirement that packings of frictionless hard spheres, arguably the simplest structural glass, cannot be compressed by rearranging their network of contacts is shown to yield a new constraint on their microscopic structure. This constraint takes the form a bound between the distribution of contact forces $P(f)$ and the pair distribution function $g(r)$: if $P(f)\sim f^{\theta }$ and $g(r)\sim (r-{\sigma }_0{)}^{-\gamma }$, where ${\sigma }_0$ is the particle diameter, one finds that $\gamma \ge 1/(2+\theta )$. This bound plays a role similar to those found in some glassy materials with long-range interactions, such as the Coulomb gap in Anderson insulators or the distribution of local fields in mean-field spin glasses. There are grounds to believe that this bound is saturated, yielding a mechanism to explain the avalanches of rearrangements with power-law statistics that govern plastic flow in packings.

We have investigated anharmonic behavior of Pd by applying systematic nanoscale tensile testing to near defect-free nanowhiskers offering a large range of elastic strain. We measured size-dependent deviations from bulk elastic behavior in nanowhiskers with diameters as small as $\sim 30\mathrm{nm}$. In addition to size-dependent variations in Young’s modulus in the small strain limit, we measured nonlinear elasticity at strains above $\sim 1\%$. Both phenomena are attributed to higher-order elasticity in the bulklike core upon being biased from its equilibrium configuration due to the role of surface stresses in small volumes. Quantification of the size-dependent second- and third-order elastic moduli allows for calculation of intrinsic material nonlinearity parameters, e.g., $\delta$. Comparison of the size-independent values of $\delta$ in our nanowhiskers with studies on bulk fcc metals lends further insight into the role of length scales on both elastic and plastic mechanical behavior.

We experimentally demonstrate a sigmoidal variation of the composition profile across semiconductor heterointerfaces. The wide range of material systems (III-arsenides, III-antimonides, III–V quaternary compounds, III-nitrides) exhibiting such a profile suggests a universal behavior. We show that sigmoidal profiles emerge from a simple model of cooperative growth mediated by two-dimensional island formation, wherein cooperative effects are described by a specific functional dependence of the sticking coefficient on the surface coverage. Experimental results confirm that, except in the very early stages, island growth prevails over nucleation as the mechanism governing the interface development and ultimately determines the sigmoidal shape of the chemical profile in these two-dimensional-grown layers. In agreement with our experimental findings, the model also predicts a minimum value of the interfacial width, with the minimum attainable value depending on the chemical identity of the species.

Using a combination of quantum Monte Carlo simulations, functional renormalization group calculations and mean-field theory, we study the Hubbard model on the Bernal-stacked honeycomb bilayer at half-filling as a model system for bilayer graphene. The free bands consisting of two Fermi points with quadratic dispersions lead to a finite density of states at the Fermi level, which triggers an antiferromagnetic instability that spontaneously breaks sublattice and spin rotational symmetry once local Coulomb repulsions are introduced. Our results reveal an inhomogeneous participation of the spin moments in the ordered ground state, with enhanced moments at the threefold coordinated sites. Furthermore, we find the antiferromagnetic ground state to be robust with respect to enhanced interlayer couplings and extended Coulomb interactions.

We show that a topological phase supporting Majorana fermions can form in a two-dimensional electron gas (2DEG) adjacent to an interdigitated superconductor-ferromagnet structure. An advantage of this setup is that the 2DEG can induce the required Zeeman splitting and superconductivity from a single interface, allowing one to utilize a wide class of 2DEGs including the surface states of bulk InAs. We demonstrate that the interdigitated device supports a robust topological phase when the finger spacing $\lambda$ is smaller than half of the Fermi wavelength ${\lambda }_F$. In this regime, the electrons effectively see a “smeared” Zeeman splitting and pairing field despite the interdigitation. The topological phase survives even in the opposite limit $\lambda >{\lambda }_F/2$, although with a reduced bulk gap. We describe how to electrically generate a vortex in this setup to trap a Majorana mode, and predict an anomalous Fraunhofer pattern that provides a sharp signature of chiral Majorana edge states.

We study the Mott transition in a frustrated Hubbard model with next-nearest neighbor hopping at half-filling. The interplay between interaction, dimensionality, and geometric frustration closes the one-dimensional Mott gap and gives rise to a metallic phase with Fermi surface pockets. We argue that they emerge as a consequence of remnant one-dimensional umklapp scattering at the momenta with vanishing interchain hopping matrix elements. In this pseudogap phase, enhanced $d$-wave pairing correlations are driven by antiferromagnetic fluctuations. Within the adopted cluster dynamical mean-field theory on the $8\times 2$ cluster and down to our lowest temperatures, the transition from one to two dimensions is continuous.

We measured a change in the current transport of an antenna-coupled, multigate, $\mathrm{GaAs}/\mathrm{AlGaAs}$ field-effect transistor when terahertz electromagnetic waves irradiated the transistor and attribute the change to bolometric heating of the electrons in the two dimensional electron channel. The observed terahertz absorption spectrum indicates coherence between plasmons excited under adjacent biased device gates. The experimental results agree quantitatively with a theoretical model we developed that is based on a generalized plasmonic transmission line formalism and describes an evolution of the plasmonic spectrum with increasing electron density modulation from homogeneous to the crystal limit. These results demonstrate an electronically induced and dynamically tunable plasmonic band structure.

$ABC$-stacked trilayer graphene’s chiral band structure results in three ($n=0$, 1, 2) Landau level orbitals with zero kinetic energy. This unique feature has important consequences on the interaction-driven states of the 12-fold degenerate (including spin and valley) $N=0$ Landau level. In particular, at many filling factors ${\nu }_T=\pm 5$, $\pm 4$, $\pm 2$, $\pm 1$ a quantum phase transition from a quantum Hall liquid state to a triangular charge-density wave occurs as a function of the single particle-induced Landau level orbital splitting ${\Delta }_{\mathrm{LL}}$. Experimental signatures of this phase transition are also discussed.