Weyl semimetals (WSMs) constitute a 3D phase with linearly dispersing Weyl excitations at low energy, which lead to unusual electrodynamic responses and open Fermi arcs on boundaries. We derive a simple criterion to identify and characterize WSMs in an interacting setting using the exact electronic Green’s function at zero frequency, which defines a topological Bloch Hamiltonian. We apply this criterion by numerically analyzing, via cluster and other methods, interacting lattice models with and without time-reversal symmetry. We identify various mechanisms for how interactions move and renormalize Weyl fermions. Our methods remain valid in the presence of long-ranged Coulomb repulsion. Finally, we introduce a WSM-like phase for which our criterion breaks down due to fractionalization: the charge-carrying Weyl quasiparticles are orthogonal to the electron.

We study the diffusive motion of particles among fixed spherical crowders. The diffusers interact with the crowders through a combination of a hard-core repulsion and a short-range attraction. The long-time effective diffusion coefficient of the diffusers is found to depend nonmonotonically on the strength of their attraction to the crowders. That is, for a given concentration of crowders, a weak attraction to the crowders enhances diffusion. We show that this counterintuitive fact can be understood in terms of the mesoscopic excess chemical potential landscape experienced by the diffuser. The roughness of this excess chemical potential landscape quantitatively captures the nonmonotonic dependence of the diffusion rate on the strength of crowder-diffuser attraction; thus, it is a purely static predictor of dynamic behavior. The mesoscopic view given here provides a unified explanation for enhanced diffusion effects that have been found in various systems of technological and biological interest.

The understanding of disorder effects on crystallization is of fundamental and technological importance. It is well established by both theory and experiment that particle-size polydispersity hinders crystallization for isotropically interacting particles. Here, we address the effects of patch variability in a model for tetrahedral colloids, where polydispersity is introduced independently on the size, position, and strength of the attractive patches. Our simulations indicate that, unlike particle-size polydispersity, angular polydispersity has a minor impact on the crystallization properties of tetrahedral colloidal particles. Particles with angular polydispersity well within current experimental possibilities fully retain their crystallization properties, a result which should encourage the realization of colloidal crystals in experiment.

We study the ground-state entanglement entropy of a finite subsystem of size $L$ of an infinite system of noninteracting fermions scattered by a potential of finite range $a$. We derive a general relation between the scattering matrix and the overlap matrix and use it to prove that for a one-dimensional symmetric potential the von Neumann entropy, the Rényi entropies, and the full counting statistics are robust against potential scattering, provided that $L/a\gg 1$. The results of numerical calculations support the validity of this conclusion for a generic potential.

We discuss energy barriers and their relationship to self-correcting quantum memories. We introduce the solid code, a 3D version of Kitaev’s surface code, and then combine several solid codes using a technique called welding. The resulting code is a $[[O(L^3),1,O(L^{4/3})]]$ stabilizer code with an energy barrier of $O(L^{2/3})$, which is an exponential improvement over the previous highest energy barrier in 3D. No-go results are avoided by breaking microscopic translation invariance.

We present a new technique to measure neutrino masses using their flow field relative to dark matter. Present day streaming motions of neutrinos relative to dark matter and baryons are several hundred $\mathrm{km}/\mathrm{s}$, comparable with their thermal velocity dispersion. This results in a unique dipole anisotropic distortion of the matter-neutrino cross power spectrum, which is observable through the dipole distortion in the cross correlation of different galaxy populations. Such a dipole vanishes if not for this relative velocity and so it is a clean signature for neutrino mass. We estimate the size of this effect and find that current and future galaxy surveys may be sensitive to these signature distortions.

We demonstrate, theoretically and experimentally, that a four-wave mixing parametric interaction is able to arrest the collapse of a two-dimensional multicolor beam in an instantaneous Kerr medium. We consider two weak idlers interacting via a third order nonlinearity with two pump beams and we show that a class of collapse-free quasisolitary solutions can be experimentally observed in a normal dispersion Kerr glass. This observation is sustained by rigorous theoretical analysis demonstrating the stability of the observed self-trapped beams.

We describe the experimental generation and measurement of coherent light that carries orbital angular momentum from a relativistic electron beam radiating at the second harmonic of a helical undulator. The measured helical phase of the light is shown to be in agreement with predictions of the sign and magnitude of the phase singularity and is more than 2 orders of magnitude greater than the incoherent signal. Our setup demonstrates that such optical vortices can be produced in modern free-electron lasers in a simple afterburner arrangement for novel two-mode pump-probe experiments.

A path to a new high performance regime has been discovered in tokamaks that could improve the attractiveness of a fusion reactor. Experiments on DIII-D using a quiescent $H$-mode edge have navigated a valley of improved edge peeling-ballooning stability that opens up with strong plasma shaping at high density, leading to a doubling of the edge pressure over the standard $H$ mode with edge localized modes at these parameters. The thermal energy confinement time increases as a result of both the increased pedestal height and improvements in the core transport and reduced low-$k$ turbulence. Calculations of the pedestal height and width as a function of density using constraints imposed by peeling-ballooning and kinetic-ballooning theory are in quantitative agreement with the measurements.

It is shown that magnetically confined electron-positron plasmas can enjoy remarkable stability properties. Many of the microinstabilities driving turbulence and transport in electron-ion plasmas are absent if the density is so low that the Debye length is significantly larger than the gyroradius. In some magnetic configurations, almost complete linear stability may be attainable in large parts of the parameter space.

We demonstrate that the aberration-corrected scanning transmission electron microscope has a sufficiently small depth of field to observe depth-dependent atomic displacements in a crystal. The depth-dependent displacements associated with the Eshelby twist of dislocations in GaN normal to the foil with a screw component of the Burgers vector are directly imaged. We show that these displacements are observed as a rotation of the lattice between images taken in a focal series. From the sense of the rotation, the sign of the screw component can be determined.

Spin pumping at the ferromagnetic metal (Fe)/normal metal (Au) interface and the subsequent spin transport in $\mathrm{Au}/\mathrm{Pd}$ heterostructures is studied using ferromagnetic resonance. The spin pumping induced damping in the $\mathrm{Fe}/\mathrm{Pd}$ structure is greatly suppressed by the addition of a Au spacer layer in the structure $\mathrm{Fe}/\mathrm{Au}/\mathrm{Pd}$. The rapid decrease in the interface damping with an increasing Au layer thickness does not correspond to an expectation based on a simple spin diffusion theory in the Au layer. It is possible to account for this behavior by introducing a partial reflection of spin current at the $\mathrm{Au}/\mathrm{Pd}$ interface. Furthermore, oscillations in the amplitude of spin pumping damping are observed in the $\mathrm{Fe}/\mathrm{Au}/\mathrm{Pd}$ structure as a function of Au thickness for thicknesses less than half the electron mean free path of bulk Au. This new effect indicates a formation of quantum well states in the accumulated spin density in the Au spacer that affect the time irreversible process of spin pumping.

We investigate the phenomenon of anonymous quantum nonlocality, which refers to the existence of multipartite quantum correlations that are not local in the sense of being Bell-inequality-violating but where the nonlocality is—due to its biseparability with respect to all bipartitions—seemingly nowhere to be found. Such correlations can be produced by the nonlocal collaboration involving definite subset(s) of parties but to an outsider, the identity of these nonlocally correlated parties is completely anonymous. For all $n\ge 3$, we present an example of an $n$-partite quantum correlation exhibiting anonymous nonlocality derived from the $n$-partite Greenberger-Horne-Zeilinger state. An explicit biseparable decomposition of these correlations is provided for any partitioning of the $n$ parties into two groups. Two applications of these anonymous Greenberger-Horne-Zeilinger correlations in the device-independent setting are discussed: multipartite secret sharing between any two groups of parties and bipartite quantum key distribution that is robust against nearly arbitrary leakage of information.

We consider a singlino dark matter (DM) scenario in a singlet extension model of the minimal supersymmetric standard model, which is the so-called the nearly minimal supersymmetric standard model. We find that with high-scale supersymmetry breaking the singlino can obtain a sizable radiative correction to the mass, which opens a window for the DM scenario with resonant annihilation via the exchange of the Higgs boson. We show that the current DM relic abundance and the Higgs boson mass can be explained simultaneously. This scenario can be fully probed by XENON1T.

The first determination of radii of point proton distribution (proton radii) of ${}^{12–17}\mathrm{B}$ from charge-changing cross sections (${\sigma }_{\mathrm{CC}}$) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the ${\sigma }_{\mathrm{CC}}$. The radii show an increase from ${}^{13}\mathrm{B}$ to ${}^{17}\mathrm{B}$ and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in ${}^{17}\mathrm{B}$.

A complete time-resolved x-ray imaging experiment of laser heated solid-density hydrogen clusters is modeled by microscopic particle-in-cell simulations that account self-consistently for the microscopic cluster dynamics and electromagnetic wave evolution. A technique is developed to retrieve the anisotropic nanoplasma expansion from the elastic and inelastic x-ray scattering data. Our method takes advantage of the self-similar evolution of the nanoplasma density and enables us to make movies of ultrafast nanoplasma dynamics from pump-probe x-ray imaging experiments.

A theory of the mode-coupling instability (MCI) in a fluid two-dimensional complex plasma is developed. In analogy to the point-wake model of the wake-mediated interactions commonly used to describe MCI in two-dimensional crystals, the layer-wake model is employed for fluids. It is demonstrated that the wake-induced coupling of wave modes occurs in both crystalline and fluid complex plasmas, but the confinement-density threshold, which determines the MCI onset in crystals, virtually disappears in fluids. The theory shows excellent qualitative agreement with available experiments and provides certain predictions to be verified.

We investigate the effect of interactions on condensate-number fluctuations in Bose-Einstein condensates. For a contact interaction we variationally obtain the equilibrium probability distribution for the number of particles in the condensate. To facilitate comparison with experiment, we also calculate the zero-time delay autocorrelation function $g^{(2)}(0)$ for different strengths of the interaction. Finally, we focus on the case of a condensate of photons and find good agreement with recent experiments.