Structural arrays with nanoscale spacing arise in many device concepts. Carbon nanotube transistors are an extreme example, where a practical technology will require arrays of parallel nanotubes with spacing of order 10 nm or less. We show that with decreasing pitch there is a first-order transition, from a robust structure in which the metal wets the substrate between tubes, to a poorly wetting structure in which the metal rides atop the nanotube array without touching the substrate. The latter is analogous to the superhydrophobic “lotus leaf effect.” There is a sharp minimum in the delamination energy of metal contacts at the transition pitch. We discuss implications for contact resistance and possible mitigation strategies.

The vortex-lattice melting transition of a limited number of vortices confined in mesoscopic square superconductors was studied by $c$-axis resistance measurements using stacks of intrinsic Josephson junctions in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+y}$. In contrast to the melting transition in bulk crystals, we have first found a clear oscillatory behavior in the field dependence of the melting temperature in small samples of $5–10\mu m$ square. The periods of the oscillations roughly obey the regularity of the matching conditions of square vortex lattices surrounded by a square boundary and the melting temperatures are enhanced around the vortex number of $i^2$ (where $i$ is an integer). The results suggest that a confinement effect by the square boundary stabilizes square lattice structures which are realized around $i^2$ vortex number even in competition with the favorable Abrikosov triangular lattice in the bulk.

The phenomenon of magnetization plateaus in antiferromagnets under a magnetic field has always been an important topic in magnetism. We propose to probe the elusive physics of plateaus in 2D by considering a hole-doped antiferromagnet and studying the signatures of magnetization plateaus in terms of the properties of holes, coupled to an effective gauge field generated by the spin sector. The latter mediates interaction between the holes, found to be algebraically decaying and long ranged with both Coulombic and dipolar forms outside the plateau and short ranged (local) inside the plateau. The resulting hole spectral weight is significantly broadened off plateau, while it remains sharply peaked on plateau. We also extend the result obtained for a 1D system where finite hole doping gives rise to a shift in the magnetization value of the plateaus.

The circular polarization (CP) that the photoluminescence inherits from the excitation source in $n$ monolayers of transition-metal dichalcogenides ${(M{X}_2)}_n$ has been previously explained as a special feature of odd values of $n$, where the inversion symmetry is absent. This “valley polarization” effect results from the fact that, in the absence of inversion symmetry, charge carriers in different band valleys could be selectively excited by different circular polarized light. Although several experiments observed CP in centrosymmetric $M{X}_2$ systems, e.g., for bilayer $M{X}_2$, they were dismissed as being due to some extrinsic sample irregularities. Here we show that also for $n=\text{even}$, where inversion symmetry is present and valley polarization physics is strictly absent, such intrinsic selectivity in CP is to be expected on the basis of fundamental spin-orbit physics. First-principles calculations of CP predict significant polarization for $n=2$ bilayers: from 69% in ${\mathrm{MoS}}_2$ to 93% in ${\mathrm{WS}}_2$. This realization could broaden the range of materials to be considered as CP sources.

We propose a simple framework to understand commonly observed crisis waves in macroeconomic agent-based models, which is also relevant to a variety of other physical or biological situations where synchronization occurs. We compute exactly the phase diagram of the model and the location of the synchronization transition in parameter space. Many modifications and extensions can be studied, confirming that the synchronization transition is extremely robust against various sources of noise or imperfections.

Common tools for obtaining physical density matrices in experimental quantum state tomography are shown here to cause systematic errors. For example, using maximum likelihood or least squares optimization to obtain physical estimates for the quantum state, we observe a systematic underestimation of the fidelity and an overestimation of entanglement. Such strongly biased estimates can be avoided using linear evaluation of the data or by linearizing measurement operators yielding reliable and computational simple error bounds.

We observe the emergence of a disorder-induced insulating state in a strongly interacting atomic Fermi gas trapped in an optical lattice. This closed quantum system, free of a thermal reservoir, realizes the disordered Fermi-Hubbard model, which is a minimal model for strongly correlated electronic solids. We observe disorder-induced localization of a metallic state through measurements of mass transport. By varying the lattice potential depth, we detect interaction-driven delocalization of the disordered insulating state. We also measure localization that persists as the temperature of the gas is raised. These behaviors are consistent with many-body localization, which is a novel paradigm for understanding localization in interacting quantum systems at nonzero temperature.

Imprinting of laser nonuniformity is a limiting factor in direct-drive inertial confinement fusion experiments, particularly when available laser smoothing is limited. A thin ($\sim 400\AA$) high-$Z$ metal coating is found to substantially suppress laser imprint for planar targets driven by pulse shapes and intensities relevant to implosions on the National Ignition Facility while retaining low adiabat target acceleration. A hybrid of indirect and direct drive, this configuration results in initial ablation by x rays from the heated high-$Z$ layer, creating a large standoff for perturbation smoothing.

Turbulence and dynamo induced by the magnetorotational instability (MRI) are analyzed using quasilinear statistical simulation methods. It is found that homogenous turbulence is unstable to a large-scale dynamo instability, which saturates to an inhomogenous equilibrium with a strong dependence on the magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the dependence of the angular momentum transport on Pm in the quasilinear model is qualitatively similar to that of nonlinear MRI turbulence. This demonstrates the importance of the large-scale dynamo and suggests how dramatically simplified models may be used to gain insight into the astrophysically relevant regimes of very low or high Pm.

We study domain-wall (DW) motion induced by spin waves (magnons) in the presence of the Dzyaloshinskii-Moriya interaction (DMI). The DMI exerts a torque on the DW when spin waves pass through the DW, and this torque represents a linear momentum exchange between the spin wave and the DW. Unlike angular momentum exchange between the DW and spin waves, linear momentum exchange leads to a rotation of the DW plane rather than a linear motion. In the presence of an effective easy plane anisotropy, this DMI induced linear momentum transfer mechanism is significantly more efficient than angular momentum transfer in moving the DW.

We predict streaming current inversion with multivalent counterions in hydrodynamically driven polymer translocation events from a correlation-corrected charge transport theory including charge fluctuations around mean-field electrostatics. In the presence of multivalent counterions, electrostatic many-body effects result in the reversal of the DNA charge. The attraction of anions to the charge-inverted DNA molecule reverses the sign of the ionic current through the pore. Our theory allows for a comprehensive understanding of the complex features of the resulting streaming currents. The underlying mechanism is an efficient way to detect DNA charge reversal in pressure-driven translocation experiments with multivalent cations.

We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most important properties of Bloch vectors. Our representation, based on covariant matrices introduced by Weinberg in the context of quantum field theory, allows for a simple parametrization of coherent spin states, and a straightforward transformation of density matrices under local unitary and partial tracing operations. It enables us to provide a criterion for anticoherence, relevant in a broader context such as quantum polarization of light.

We present a measurement of the asymmetry $A_{CP}$ between same-sign inclusive dilepton samples ${\ell }^{+}{\ell }^{+}$ and ${\ell }^{-}{\ell }^{-}$ ($\ell =e$, $\mu$) from semileptonic $B$ decays in $\mathrm{\Upsilon }(4S)\to B\overline{B}$ events, using the complete data set recorded by the BABAR experiment near the $\mathrm{\Upsilon }(4S)$ resonance, corresponding to $471\times 10^6$ $B\overline{B}$ pairs. The asymmetry $A_{CP}$ allows comparison between the mixing probabilities $\mathcal{P}({\overline{B}}^0\to B^0)$ and $\mathcal{P}(B^0\to {\overline{B}}^0)$, and therefore probes $CP$ and $T$ violation. The result, $A_{CP}=[-3.9\pm 3.5(\text{stat})\pm 1.9(\text{syst})]\times 10^{-3}$, is consistent with the standard model expectation.

We argue that the proton multiplicities measured in Roman pot detectors at an electron ion collider can be used to determine centrality classes in incoherent diffractive scattering. Incoherent diffraction probes the fluctuations in the interaction strengths of multiparton Fock states in the nuclear wave functions. In particular, the saturation scale that characterizes this multiparton dynamics is significantly larger in central events relative to minimum bias events. As an application, we study the centrality dependence of incoherent diffractive vector meson production. We identify an observable which is simultaneously very sensitive to centrality triggered parton fluctuations and insensitive to details of the model.

The magnetic moment of a single impurity atom in a finite free electron gas is studied in a combined x-ray magnetic circular dichroism spectroscopy, charge transfer multiplet calculation, and density functional theory study of size-selected free chromium-doped gold clusters. The observed size dependence of the local magnetic moment can be understood as a transition from a local moment to a mixed valence regime. This shows that the Anderson impurity model essentially describes finite systems even though the discrete density of states introduces a significant deviation from a bulk metal, and the free electron gas is only formed by less than 10 electrons. Electronic shell closure in the gold host minimizes the interaction of localized impurity states with the confined free electron gas and preserves the magnetic moment of $5{\mu }_{\mathrm{B}}$ fully in ${\mathrm{CrAu}}_2^{+}$ and almost fully in ${\mathrm{CrAu}}_6^{+}$. Even for open-shell species, large local moments are observed that scale with the energy gap of the gold cluster. This indicates that an energy gap in the free electron gas stabilizes the local magnetic moment of the impurity atom.