The helical edge state of a quantum spin-Hall insulator can carry a supercurrent in equilibrium between two superconducting electrodes (separation $L$, coherence length $\xi$). We calculate the maximum (critical) current $I_c$ that can flow without dissipation along a single edge, going beyond the short-junction restriction $L\ll \xi$ of earlier work, and find a dependence on the fermion parity of the ground state when $L$ becomes larger than $\xi$. Fermion-parity conservation doubles the critical current in the low-temperature, long-junction limit, while for a short junction $I_c$ is the same with or without parity constraints. This provides a phase-insensitive, dc signature of the $4\pi$-periodic Josephson effect.

We have performed inelastic neutron scattering measurements on the single-layer cuprate ${\mathrm{Bi}}_{2+x}{\mathrm{Sr}}_{2-x}{\mathrm{CuO}}_{6+y}$ (Bi2201) with $x=0.2$, 0.3, 0.4, and 0.5, a doping range that spans the spin-glass to superconducting phase boundary. The doping evolution of low energy spin fluctuations ($\lesssim 11\mathrm{meV}$) was found to be characterized by a change in the incommensurate modulation wave vector from the tetragonal [110] to [100]/[010] directions, while maintaining a linear relation between the incommensurability and the hole concentration, $\delta \approx p$. In the superconducting regime, the spectral weight is strongly suppressed below $\sim 4\mathrm{meV}$. Similarities and differences in the spin correlations between Bi2201 and the prototypical single-layer system ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ are discussed.

In the tetragonal heavy fermion system ${\mathrm{CeCoIn}}_5$ the unconventional superconducting state is probed by means of muon spin rotation. The pressure dependence (0–1 GPa) of the basal-plane magnetic penetration depth (${\lambda }_a$), the penetration depth anisotropy ($\gamma ={\lambda }_c/{\lambda }_a$) and the temperature dependence of $1/{\lambda }_i^2$ ($i=a$, $c$) were studied in single crystals. A strong decrease of ${\lambda }_a$ with pressure was observed, while $\gamma$ and ${\lambda }_i^2(0)/{\lambda }_i^2(T)$ are pressure independent. A linear relationship between $1/{\lambda }_a^2(270\mathrm{mK})$ and $T_c$ was also found. The large decrease of ${\lambda }_a$ with pressure is the signature of an increase of the number of superconducting quasiparticles by a factor of about 2.

We present measurements of the magnetic susceptibility $\chi$ and the magnetization $M$ of single crystals of metallic ${\mathrm{Yb}}_2{\mathrm{Pt}}_2\mathrm{Pb}$, where localized Yb moments lie on the dimerized and frustrated Shastry-Sutherland lattice (SSL). Strong magnetic frustration is found in this quasi-two-dimensional system, which orders antiferromagnetically at $T_N=2.02\mathrm{K}$ from a paramagnetic liquid of Yb dimers, having a gap $\Delta =4.6\mathrm{K}$ between the singlet ground state and the triplet excited states. Magnetic fields suppress the antiferromagnetic (AF) order, which vanishes at a 1.23 $T$ quantum critical point. The spin gap $\Delta$ persists to 1.5 $T$, indicating that dimer singlets survive the collapse of the $B=0$ AF state. Quantized steps are observed in $M(B)$ within the AF state, a signature of SSL systems. Our results show that ${\mathrm{Yb}}_2{\mathrm{Pt}}_2\mathrm{Pb}$ is unique, both as a metallic SSL system that is close to an AF quantum critical point, and as a heavy fermion compound where quantum frustration plays a decisive role.

We introduce a Bayesian inference approach to analyze magnetic resonance data of granular solids. To characterize structure using magnetic resonance, it is usual to acquire data in $k$ space which are then Fourier transformed to obtain an image. An alternative approach, adopted here, is to utilize the Rayleigh distribution observed in the signal intensity for a given $k$ when a random selection of grains is measured in $k$ space, to define a likelihood function for Bayesian analysis. This Bayesian likelihood function is used to noninvasively characterize grains within a porous medium on length scales below the practical resolution of magnetic resonance imaging. A pore size distribution is then calculated from the measured grain size distribution using a Monte Carlo approach. We demonstrate this general technique with specific examples of water-saturated rock cores.

Transcriptional networks across all domains of life feature a wide range of regulatory architectures. Theoretical models now make clear predictions about how key parameters describing those architectures modulate gene expression, and the ability to construct genetic circuits with tunable parameters enables precise tests of such models. We dissect gene regulation through DNA looping by tuning network parameters such as repressor copy number, DNA binding strengths, and loop length in both thermodynamic models and experiments. Our results help clarify the short-length mechanical properties of DNA.

Red blood cells (RBCs) are known to form aggregates in the form of rouleaux due to the presence of plasma proteins under physiological conditions. The formation of rouleaux can also be induced in vitro by the addition of macromolecules to the RBC suspension. Current data on the adhesion strength between red blood cells in their natural discocyte shapes mostly originate from indirect measurements such as flow chamber experiments, but data is lacking at the single cell level. Here, we present measurements on the dextran-induced aggregation of red blood cells using atomic force microscopy-based single cell force spectroscopy. The effects of dextran concentration and molecular weight on the interaction energy of adhering RBCs were determined. The results on adhesion energy are in excellent agreement with a model based on the depletion effect and previous experimental studies. Furthermore, our method allowed to determine the adhesion force, a quantity that is needed in theoretical investigations on blood flow.

We present an integrated theory and simulation study of polydisperse polymer grafted nanoparticles in a polymer matrix to demonstrate the effect of polydispersity in graft length on the potential of mean force between the grafted nanoparticles. In dense polymer solutions, increasing polydispersity in graft length reduces the strength of repulsion at contact and weakens the attractive well at intermediate interparticle distances, completely eliminating the latter at high polydispersity index. The reduction in contact repulsion is attributable to polydispersity relieving monomer crowding near the particle surface, especially at high grafting densities. The elimination of the midrange attractive well is attributable to the longer grafts in the polydisperse graft length distribution that introduce longer range steric repulsion and alter the wetting of the grafted layer by matrix chains. Dispersion of the grafted particles is stabilized by increased penetration or wetting of the polydisperse grafted layer by the matrix chains. This work demonstrates that at high grafting densities, polydispersity in graft length can be used to stabilize dispersions of grafted nanoparticles in a polymer matrix at conditions where monodisperse grafts would cause aggregation.

We describe experiments that probe the evolution of shear jammed states, occurring for packing fractions ${\varphi }_S\le \varphi \le {\varphi }_J$, for frictional granular disks, where above ${\varphi }_J$ there are no stress-free static states. We use a novel shear apparatus that avoids the formation of inhomogeneities known as shear bands. This fixed $\varphi$ system exhibits coupling between the shear strain, $\gamma$, and the pressure, $P$, which we characterize by the “Reynolds pressure” and a “Reynolds coefficient,” $R(\varphi )=({\partial }^{2}P/\partial {\gamma }^2)/2$. $R$ depends only on $\varphi$ and diverges as $R\sim ({\varphi }_c-\varphi {)}^{\alpha }$, where ${\varphi }_c\simeq {\varphi }_J$ and $\alpha \simeq -3.3$. Under cyclic shear, this system evolves logarithmically slowly towards limit cycle dynamics, which we characterize in terms of pressure relaxation at cycle $n\mathrm{\text{:}}\Delta P\simeq -\beta \ln (n/n_0)$. $\beta$ depends only on the shear cycle amplitude, suggesting an activated process where $\beta$ plays a temperaturelike role.

We investigate the effect of bilayer melting transition on thermodynamics and dynamics of interfacial water using molecular dynamics simulation with the two-phase thermodynamic model. We show that the diffusivity of interface water depicts a dynamic crossover at the chain melting transition following an Arrhenius behavior until the transition temperature. The corresponding change in the diffusion coefficient from the bulk to the interface water is comparable with experimental observations found recently for water near 1,2-dipalmitoyl-$sn$-glycero-3-phosphocholine (DPPC) vesicles [Phys. Chem. Chem. Phys. 13, 7732 (2011)]. The entropy and potential energy of interfacial water show distinct changes at the bilayer melting transition, indicating a strong correlation in the thermodynamic state of water and the accompanying first-order phase transition of the bilayer membrane.

The nonlinear rheology of a soft glassy material is captured by its constitutive relation, shear stress versus shear rate, which is most generally obtained by sweeping up or down the shear rate over a finite temporal window. For a huge amount of complex fluids, the up and down sweeps do not superimpose and define a rheological hysteresis loop. By means of extensive rheometry coupled to time-resolved velocimetry, we unravel the local scenario involved in rheological hysteresis for various types of well-studied soft materials. We introduce two observables that quantify the hysteresis in macroscopic rheology and local velocimetry, respectively, as a function of the sweep rate $\delta t^{-1}$. Strikingly, both observables present a robust maximum with $\delta t$, which defines a single material-dependent time scale that grows continuously from vanishingly small values in simple yield stress fluids to large values for strongly time-dependent materials. In line with recent theoretical arguments, these experimental results hint at a universal time scale-based framework for soft glassy materials, where inhomogeneous flows characterized by shear bands and/or pluglike flow play a central role.

The scale invariance of natural images suggests an analogy to the statistical mechanics of physical systems at a critical point. Here we examine the distribution of pixels in small image patches and show how to construct the corresponding thermodynamics. We find evidence for criticality in a diverging specific heat, which corresponds to large fluctuations in how “surprising” we find individual images, and in the quantitative form of the entropy vs energy. We identify special image configurations as local energy minima and show that average patches within each basin are interpretable as lines and edges in all orientations.

We use a self-consistent strong-coupling expansion for the self-energy (perturbation theory in the hopping) to describe the nonequilibrium dynamics of strongly correlated lattice fermions. We study the three-dimensional homogeneous Fermi-Hubbard model driven by an external electric field showing that the damping of the ensuing Bloch oscillations depends on the direction of the field and that for a broad range of field strengths a long-lived transient prethermalized state emerges. This long-lived transient regime implies that thermal equilibrium may be out of reach of the time scales accessible in present cold atom experiments but shows that an interesting new quasiuniversal transient state exists in nonequilibrium governed by a thermalized kinetic energy but not a thermalized potential energy. In addition, when the field strength is equal in magnitude to the interaction between atoms, the system undergoes a rapid thermalization, characterized by a different quasiuniversal behavior of the current and spectral function for different values of the hopping.

The composite character of two-fermion bosons manifests itself in the interference of many composites as a deviation from the ideal bosonic behavior. A state of many composite bosons can be represented as a superposition of different numbers of perfect bosons and fermions, which allows us to provide the full Hong–Ou–Mandel-like counting statistics of interfering composites. Our theory quantitatively relates the deviation from the ideal bosonic interference pattern to the entanglement of the fermions within a single composite boson.

The impact of coherent light propagation on the excitation and fluorescence of thorium nuclei in a crystal lattice environment is investigated theoretically. We find that in the forward direction, the fluorescence signal exhibits characteristic intensity modulations dominated by a sped-up initial decay signal that is orders of magnitude faster. This feature can be exploited for the optical determination of the isomeric transition energy. In order to obtain a unmistakable signature of the isomeric nuclear fluorescence, we put forward a novel scheme for the direct measurement of the transition energy via electromagnetically modified nuclear forward scattering involving two fields that couple to three nuclear states.

The accurate characterization of eigenmodes and eigenfrequencies of two-dimensional ion crystals provides the foundation for the use of such structures for quantum simulation purposes. We present a combined experimental and theoretical study of two-dimensional ion crystals. We demonstrate that standard pseudopotential theory accurately predicts the positions of the ions and the location of structural transitions between different crystal configurations. However, pseudopotential theory is insufficient to determine eigenfrequencies of the two-dimensional ion crystals accurately but shows significant deviations from the experimental data obtained from resolved sideband spectroscopy. Agreement at the level of $2.5\times {10}^{-3}$ is found with the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and the effect is understood from the dynamics of two-dimensional ion crystals in the Paul trap. The results represent initial steps towards an exploitation of these structures for quantum simulation schemes.

Based on transformation optics, we introduce a magnetic shell with which one can harvest magnetic energy and distribute it as desired in space with unprecedented efficiency at an arbitrary scale. It allows a very large concentration of magnetic energy in a free space region, which can be used for increasing the sensitivity of magnetic sensors, and the transfer of magnetic energy from a source to a given distant point separated by empty space, with possible applications in wireless transmission of energy.

We study the permeability of quasi-two-dimensional porous structures of randomly placed overlapping monodisperse circular and elliptical grains. Measurements in microfluidic devices and lattice Boltzmann simulations demonstrate that the permeability is determined by the Euler characteristic of the conducting phase. We obtain an expression for the permeability that is independent of the percolation threshold and shows agreement with experimental and simulated data over a wide range of porosities. Our approach suggests that the permeability explicitly depends on the overlapping probability of grains rather than their shape.

The Fermi-degenerate plasma conditions created in liquid deuterium by a laser-ablation—driven shock wave were probed with noncollective, spectrally resolved, inelastic x-ray Thomson scattering employing Cl ${\mathrm{Ly}}_{\alpha }$ line emission at 2.96 keV. These first x-ray Thomson scattering measurements of the microscopic properties of shocked deuterium show an inferred spatially averaged electron temperature of $8\pm 5\mathrm{eV}$, an electron density of $2.2(\pm 0.5)\times {10}^{23}{\mathrm{cm}}^{-3}$, and an ionization of 0.8 ($-0.25$, $+0.15$). Two-dimensional hydrodynamic simulations using equation-of-state models suited for the extreme parameters occurring in inertial confinement fusion research and planetary interiors are consistent with the experimental results.

The dissipation mechanism in collisionless magnetic reconnection in a quasisteady period is investigated for the antiparallel field configuration. A three-dimensional simulation in a fully kinetic system reveals that a current-aligned electromagnetic mode produces turbulent electron flow that facilitates the transport of the momentum responsible for the current density. It is found that the electromagnetic turbulence is drastically enhanced by plasmoid formations and has a significant impact on the dissipation at the magnetic $x$-line. The linear analyses confirm that the mode survives in the real ion-to-electron mass ratio, which assures the importance of the turbulence in collisionless reconnection.