Understanding acoustic surface plasmons (ASPs) in the presence of nanosized gratings is necessary for the development of future devices that couple light with ASPs. We show here by experiment and theory that two ASPs exist on Au(788), a vicinal surface with an ordered array of monoatomic steps. The ASPs propagate across the steps as long as their wavelength exceeds the terrace width, thereafter becoming localized. Our investigation identifies, for the first time, ASPs coupled with intersubband transitions involving multiple surface-state subbands.

We present a theory of the anomalous Hall effect (AHE) in a doped Weyl semimetal, or Weyl metal, including both intrinsic and extrinsic (impurity scattering) contributions. We demonstrate that a Weyl metal is distinguished from an ordinary ferromagnetic metal by the absence of the extrinsic and the Fermi surface part of the intrinsic contributions to the AHE, as long as the Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal is thus shown to be a purely intrinsic, universal property, fully determined by the location of the Weyl nodes in the first Brillouin zone.

A cluster state cannot be a unique ground state of a two-body interacting Hamiltonian. Here, we propose the creation of a cluster state of logical qubits encoded in spin-$1/2$ particles by adiabatically weakening two-body interactions. The proposal is valid for any spatial dimensional cluster states. Errors induced by thermal fluctuations and adiabatic evolution within finite time can be eliminated ensuring fault-tolerant quantum computing schemes.

We follow the time evolution of non-Abelian gauge bosons from far-from-equilibrium initial conditions to thermal equilibrium by numerically solving an effective kinetic equation that becomes accurate in the weak coupling limit. We consider isotropic initial conditions that are either highly overoccupied or underoccupied. We find that overoccupied systems thermalize through a self-similar cascade reaching equilibrium in multiples of a thermalization time $t_{\text{eq}}\approx 72./(1+0.12\log {\lambda }^{-1})\times 1/{\lambda }^{2}T$, whereas underoccupied systems undergo a “bottom-up” thermalization in a time $t_{\text{eq}}\approx [34.+21.\log (Q/T)]/(1+0.037\log {\lambda }^{-1})\times {(Q/T)}^{1/2}/{\lambda }^{2}T$, where $Q$ is the characteristic momentum scale of the initial condition. We apply this result to model initial stages of heavy-ion collisions and find rapid thermalization roughly in a time $Q{t}_{\text{eq}}\lesssim 10$ or $t_{\text{eq}}\lesssim 1\mathrm{fm}/c$.

The reduced transition probability $B(E2;0^{+}\to 2^{+})$ has been measured for the neutron-rich nucleus ${}^{74}\mathrm{Ni}$ in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained $B(E2;0^{+}\to 2^{+})=642_{-226}^{+216}{e}^2{\mathrm{fm}}^4$ value defines a trend which is unexpectedly small if referred to ${}^{70}\mathrm{Ni}$ and to a previous indirect determination of the transition strength in ${}^{74}\mathrm{Ni}$. This indicates a reduced polarization of the $Z=28$ core by the valence neutrons. Calculations in the $pfgd$ model space reproduce well the experimental result indicating that the $B(E2)$ strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.

The quasifission mechanism hinders fusion in heavy systems through breakup within zeptoseconds into two fragments with partial mass equilibration. Its dependence on the structure of both the collision partners and the final fragments is a key question. Our original approach is to combine an experimental measurement of the fragments’ mass-angle correlations in ${}^{40}\mathrm{Ca}+{}^{238}\mathrm{U}$ with microscopic quantum calculations. We demonstrate an unexpected interplay between the orientation of the prolate deformed ${}^{238}\mathrm{U}$ with quantum shell effects in the fragments. In particular, calculations show that only collisions with the tip of ${}^{238}\mathrm{U}$ produce quasifission fragments in the magic $Z=82$ region, while collisions with the side are the only ones that may result in fusion.

We report, in theory and experiment, on a new class of optical beams that are radially self-accelerating and nondiffracting. These beams continuously evolve on spiraling trajectories while maintaining their amplitude and phase distribution in their rotating rest frame. We provide a detailed insight into the theoretical origin and characteristics of radial self-acceleration and prove our findings experimentally. As radially self-accelerating beams are nonparaxial and a solution to the full scalar Helmholtz equation, they can be implemented in many linear wave systems beyond optics, from acoustic and elastic waves to surface waves in fluids and soft matter. Our work generalized the study of classical helicon beams to a complete set of solutions for rotating complex fields.

The contribution of small scale turbulent fluctuations to the induction of a mean magnetic field is investigated in our liquid sodium spherical Couette experiment with an imposed magnetic field. An inversion technique is applied to a large number of measurements at $\mathrm{Rm}\approx 100$ to obtain radial profiles of the $\alpha$ and $\beta$ effects and maps of the mean flow. It appears that the small scale turbulent fluctuations can be modeled as a strong contribution to the magnetic diffusivity that is negative in the interior region and positive close to the outer shell. Direct numerical simulations of our experiment support these results. The lowering of the effective magnetic diffusivity by small scale fluctuations implies that turbulence can actually help to achieve self-generation of large scale magnetic fields.

Inelastic light scattering in crystals has historically been treated as a spatially incoherent process, giving rise to incoherent optical radiation. Here we demonstrate that Raman scattering can be spatially coherent, in which case it depends on the dimensionality and symmetry of the scatterer. Using near-field spectroscopy, we measure a correlation length of $\sim 30\mathrm{nm}$ for the optical phonons in graphene, the results varying with vibrational symmetries and spatial confinement of the phonons.

Based on first-principles density functional calculations we propose a novel Al vacancy induced ferromagnetism occurring at the ${\mathrm{LaAlO}}_3$ surface of ${\mathrm{SrTiO}}_3/{\mathrm{LaAlO}}_3$ bilayers. Magnetism at cation vacancies away from the surface is quenched due to charge compensation. Magnetic surface Al vacancies are stabilized due to the built-in electric field inside the ${\mathrm{LaAlO}}_3$ region that raises the energy of the defect level, making charge compensation unfavorable. Surface Al vacancies prefer to form clusters and exhibit two-dimensional ferromagnetic alignment mediated by a long-range magnetic interaction. These results are discussed in light of recent experimental observations.

We show how Raman spectroscopy can serve as a valuable tool for diagnosing quantum spin liquids (QSL). We find that the Raman response of the gapless QSL of the Kitaev-Heisenberg model exhibits signatures of spin fractionalization into Majorana fermions, which give rise to a broad signal reflecting their density of states, and $Z_2$ gauge fluxes, which also contribute a sharp feature. We discuss the current experimental situation and explore more generally the effect of breaking the integrability on response functions of Kitaev spin liquids.

We report on a novel compact laser-driven neutron source with an unprecedented short pulse duration ($<50\mathrm{ps}$) and high peak flux ($>{10}^{18}\mathrm{n}/{\mathrm{cm}}^2/\mathrm{s}$), an order of magnitude higher than any existing source. In our experiments, high-energy electron jets are generated from thin ($<3\mu \mathrm{m}$) plastic targets irradiated by a petawatt laser. These intense electron beams are employed to generate neutrons from a metal converter. Our method opens venues for enhancing neutron radiography contrast and for creating astrophysical conditions of heavy element synthesis in the laboratory.

First-principles prediction of lattice thermal conductivity ${\kappa }_L$ of strongly anharmonic crystals is a long-standing challenge in solid-state physics. Making use of recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics. Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Nonintuitively, high accuracy is achieved when the model is trained on first-principles forces in quasirandom atomic configurations. The method is demonstrated for Si, NaCl, and ${\mathrm{Cu}}_{12}{\mathrm{Sb}}_4{S}_{13}$, an earth-abundant thermoelectric with strong phonon-phonon interactions that limit the room-temperature ${\kappa }_L$ to values near the amorphous limit.

We theoretically study transport in two-dimensional semimetals. Typically, electron and hole puddles emerge in the transport layer of these systems due to smooth fluctuations in the potential. We calculate the electric response of the electron-hole liquid subject to zero and finite perpendicular magnetic fields using an effective medium approximation and a complementary mapping on resistor networks. In the presence of smooth disorder and in the limit of a weak electron-hole recombination rate, we find for small but finite overlap of the electron and hole bands an abrupt upturn in resistivity when lowering the temperature but no divergence at zero temperature. We discuss how this behavior is relevant for several experimental realizations and introduce a simple physical explanation for this effect.

We show that strong $CP$ violation from the QCD axion can be responsible for the matter antimatter asymmetry of the Universe in the context of cold electroweak baryogenesis if the electroweak phase transition is delayed below the GeV scale. This can occur naturally if the Higgs couples to a $\mathcal{O}(100)\mathrm{GeV}$ dilaton, as expected in some models where the Higgs is a pseudo-Nambu-Goldstone boson of a new strongly interacting sector at the TeV scale. The existence of such a second scalar resonance with a mass and properties similar to the Higgs boson will soon be tested at the LHC. In this context, the QCD axion would not only solve the strong $CP$ problem, but also the matter antimatter asymmetry and dark matter.

We present a measurement of the ratio of the ${\overline{B}}_s^0$ meson lifetime, in the flavor-specific decay to $D_s^{+}{\pi }^{-}$, to that of the ${\overline{B}}^0$ meson. The $pp$ collision data used correspond to an integrated luminosity of $1{\mathrm{fb}}^{-1}$, collected with the LHCb detector, at a center-of-mass energy of 7 TeV. Combining our measured value of $1.010\pm 0.010\pm 0.008$ for this ratio with the known ${\overline{B}}^0$ lifetime, we determine the flavor-specific ${\overline{B}}_s^0$ lifetime to be $\tau ({\overline{B}}_s^0)=1.535\pm 0.015\pm 0.014\mathrm{ps}$, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.

An energy-principle-based dispersion relation is derived for the resistive wall mode, which incorporates both the drift kinetic resonance between the mode and energetic particles and the resistive layer physics. The equivalence between the energy-principle approach and the resistive layer matching approach is first demonstrated for the resistive plasma resistive wall mode. As a key new result, it is found that the resistive wall mode, coupled to the favorable average curvature stabilization inside the resistive layer (as well as the toroidal plasma flow), can be substantially more stable than that predicted by drift kinetic theory with fast ion stabilization, but with the ideal fluid assumption. Since the layer stabilization becomes stronger with decreasing plasma resistivity, this regime is favorable for reactor scale, high-temperature fusion devices.

Considerable recent theoretical and experimental effort has been devoted to the study of quantum criticality and novel phases of antiferromagnetic heavy-fermion metals. In particular, quantum phase transitions have been discovered in heavy-fermion compounds with geometrical frustration. These developments have motivated us to study the competition between the Ruderman-Kittel-Kasuya-Yosida and Kondo interactions on the Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as a function of magnetic frustration and Kondo coupling within a slave-fermion approach. Pertinent phases include the valence bond solid and heavy Fermi liquid. In the presence of antiferromagnetic order, our zero-temperature phase diagram is remarkably similar to the global phase diagram proposed earlier based on general grounds. We discuss the implications of our results for the experiments on ${\mathrm{Yb}}_2{\mathrm{Pt}}_2\mathrm{Pb}$ and related compounds.