Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free ${\mathrm{Ba}(\mathrm{Fe}{}_{1-x}\mathrm{Co}{}_x)}_2\mathrm{As}{}_2$ single crystals. The strong enhancement of the Raman response at low temperatures unveils an underlying charge nematic state that extends to superconducting compositions and which has hitherto remained unnoticed. Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematic fluctuations are weakly coupled to the lattice.

We have investigated the structural and electronic properties of phosphorescent planar platinum(II) complexes at the interface of Au(111) with submolecular resolution using combined scanning tunneling microscopy and spectroscopy as well as density functional theory. Our analysis shows that molecule-substrate coupling and lateral intermolecular interactions are weak. While the ligand orbitals remain essentially unchanged upon contact with the substrate, we found modified electronic behavior at the Pt atom due to local hybridization and charge transfer to the substrate. Thus, this novel class of phosphorescent molecules exhibits well-defined and tunable interaction with its local environment.

We study the nonequilibrium dynamics of correlations in quantum lattice models in the presence of long-range interactions decaying asymptotically as a power law. For exponents larger than the lattice dimensionality, a Lieb-Robinson-type bound effectively restricts the spreading of correlations to a causal region, but allows supersonic propagation. We show that this decay is not only sufficient but also necessary. Using tools of quantum metrology, for any exponents smaller than the lattice dimension, we construct Hamiltonians giving rise to quantum channels with capacities not restricted to a causal region. An analytical analysis of long-range Ising models illustrates the disappearance of the causal region and the creation of correlations becoming distance independent. Numerical results obtained using matrix product state methods for the $XXZ$ spin chain reveal the presence of a sound cone for large exponents and supersonic propagation for small ones. In all models we analyzed, the fast spreading of correlations follows a power law, but not the exponential increase of the long-range Lieb-Robinson bound.

Recent molecular dynamics simulations of glass-forming liquids revealed superdiffusive fluctuations associated with the position of a tracer particle (TP) driven by an external force. Such an anomalous response, whose mechanism remains elusive, has been observed up to now only in systems close to their glass transition, suggesting that this could be one of its hallmarks. Here, we show that the presence of superdiffusion is in actual fact much more general, provided that the system is crowded and geometrically confined. We present and solve analytically a minimal model consisting of a driven TP in a dense, crowded medium in which the motion of particles is mediated by the diffusion of packing defects, called vacancies. For such nonglass-forming systems, our analysis predicts a long-lived superdiffusion which ultimately crosses over to giant diffusive behavior. We find that this trait is present in confined geometries, for example long capillaries and stripes, and emerges as a universal response of crowded environments to an external force. These findings are confirmed by numerical simulations of systems as varied as lattice gases, dense liquids, and granular fluids.

Most treatments of large scale anomalies in the microwave sky are a posteriori, with unquantified look-elsewhere effects. We contrast these with physical models of specific inhomogeneities in the early Universe which can generate these apparent anomalies. Physical models predict correlations between candidate anomalies and the corresponding signals in polarization and large scale structure, reducing the impact of cosmic variance. We compute the apparent spatial curvature associated with large-scale inhomogeneities and show that it is typically small, allowing for a self-consistent analysis. As an illustrative example we show that a single large plane wave inhomogeneity can contribute to low-$l$ mode alignment and odd-even asymmetry in the power spectra and the best-fit model accounts for a significant part of the claimed odd-even asymmetry. We argue that this approach can be generalized to provide a more quantitative assessment of potential large scale anomalies in the Universe.

The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of $\sqrt{s}=7\mathrm{TeV}$. By utilizing the very forward TOTEM tracking detectors $T1$ and $T2$, which extend up to $|\eta |=6.5$, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section ${\sigma }_{\mathrm{DD}}=(116\pm 25)\mu \mathrm{b}$ for events where both diffractive systems have $4.7<|\eta {|}_{\min }<6.5$.

Study of ${\beta }^{+}$ decay of the exotic $T_z=-3/2$ nucleus ${}^{55}\mathrm{Cu}$, via delayed $\gamma$ rays, has revealed a strongly isospin mixed doublet (4599–4579 keV) in ${}^{55}\mathrm{Ni}$, which represents the fragmented and previously unknown isobaric analog of the ground state of ${}^{55}\mathrm{Cu}$. The observed small $\log ft$ values to both states in the doublet confirm the superallowed Fermi $\beta$ decay. The near degeneracy of a pair of $3/2^{-}$ levels in ${}^{55}\mathrm{Ni}$ results in the strong isospin mixing. The isospin mixing matrix element between the $T=3/2$ and $T=1/2$ levels is inferred from the experiment to be 9(1) keV, which agrees well with the matrix element of the charge symmetry breaking shell model Hamiltonian of Ormand and Brown. A precise value of the half-life of ${}^{55}\mathrm{Cu}$ at 57(3) ms was also obtained.

We present experimental data that show significant deviations from theoretical predictions for the location of the center of the electron momenta distribution at low values of ellipticity $\epsilon$ of laser light. We show that these deviations are caused by significant Coulomb focusing along the minor axis of polarization, something that is normally neglected in the analysis of electron dynamics, even in cases where the Coulomb correction is otherwise taken into account. By investigating ellipticity-resolved electron momenta distributions in the plane of polarization, we show that Coulomb focusing predominates at lower values of ellipticity of laser light, while Coulomb asymmetry becomes important at higher values, showing that these two complementary phenomena can be used to probe long-range Coulomb interaction at all polarizations of laser light. Our results suggest that both the breakdown of Coulomb focusing and the onset of Coulomb asymmetry are linked to the disappearance of Rydberg states with increasing ellipticity.

Complex revival features of rotational wave packets are obtained from the interplay of a molecular rotational distribution and a measured physical observable. The analysis of the measured temporal behavior can be used to retrieve either one or both quantities. We show here the first observation of high order fractional revival (up to $1/12$ in ${\mathrm{CO}}_2$) using time-of-flight measurements of ion yields leading to the information required for full reconstruction of the rotational wave packet. We further show via an analysis of higher order fractional revivals in high harmonic generation that new information on the participating ionic channels can be clearly identified, showing the general implication of our results.

We investigate the phase winding dynamics of a harmonically trapped two-component BEC subject to inhomogeneous Rabi oscillations between two pseudospin components. While the single-particle dynamics can be explained by mapping the system to a two-component Bose-Hubbard model, nonlinearities due to the interatomic repulsion lead to new effects observed in the experiments: In the presence of a linear magnetic field gradient, a qualitatively stable moving magnetic order that is similar to antiferromagnetic order is observed after critical winding is achieved. We also demonstrate how the phase winding can be used to generate copious dark-bright solitons in a two-component BEC, opening the door for new experimental studies of these nonlinear features.

Electron magnetohydrodynamic turbulence is investigated under the presence of a relatively strong external magnetic field $b_0{\mathbf{e}}_{\parallel }$ and through three-dimensional direct numerical simulations. Our study reveals the emergence of a $k_{\perp }^{-8/3}$ scaling for the magnetic energy spectrum at scales $k_{\parallel }^D\le k_{\perp }\le k_{\perp }^D$, where $k_{\parallel }^D$ and $k_{\perp }^D$ are, respectively, the typical largest dissipative scales along and transverse to the ${\mathbf{b}}_0$ direction. Unlike standard magnetohydrodynamic, this turbulence regime is characterized by filaments of electric currents parallel to ${\mathbf{b}}_0$. The anomalous scaling is in agreement with a heuristic model in which the transfer in the parallel direction is negligible. Implications for solar wind turbulence are discussed.

Particle transport has been studied in the Tore Supra tokamak by using modulated ion cyclotron resonance heating to generate perturbations of density and temperature. For the first time, a reversal of the particle convective velocity and a strong increase in the turbulent particle flux have been clearly observed. When the mixed critical gradient ${\zeta }_c=R/L_T+4(R/L_n)=22$ is exceeded, the particle flux increases sharply and the convective velocity reverses from inward to outward. These observations are in agreement with quasilinear, gyrokinetic calculations. The critical gradient corresponds to a transition from an instability driven by the ion temperature gradient to the onset of another instability caused by trapped electrons.

We consider the two-dimensional Fermi gas at finite temperature with attractive short-range interactions. Using the virial expansion, which provides a controlled approach at high temperatures, we determine the spectral function and contact for the normal state. Our calculated spectra are in qualitative agreement with recent photoemission measurements [M. Feld et al., Nature (London) 480, 75 (2011).], thus suggesting that the observed pairing gap is a feature of the high-temperature gas rather than being evidence of a pseudogap regime just above the superfluid transition temperature. We further argue that the strong pair correlations result from the fact that the crossover to bosonic dimers occurs at weaker interactions than previously assumed.

Controlling the self-assembly of surface-adsorbed molecules into nanostructures requires understanding physical mechanisms that act across multiple length and time scales. By combining scanning tunneling microscopy with hierarchical ab initio and statistical mechanical modeling of 1,4-substituted benzenediamine (BDA) molecules adsorbed on a gold (111) surface, we demonstrate that apparently simple nanostructures are selected by a subtle competition of thermodynamics and dynamics. Of the collection of possible BDA nanostructures mechanically stabilized by hydrogen bonding, the interplay of intermolecular forces, surface modulation, and assembly dynamics select at low temperature a particular subset: low free energy oriented linear chains of monomers and high free energy branched chains.

We report on three-dimensional (3D) imaging of individual Gd dopant atoms in a thin ($\sim 2.3\mathrm{nm}$) foil of ${\mathrm{SrTiO}}_3$, using quantitative scanning transmission electron microscopy. Uncertainties in the depth positions of individual dopants are less than 1 unit cell. The overall dopant concentration measured from atom column intensities agrees quantitatively with electrical measurements. The method is applied to analyze the 3D arrangement of dopants within small clusters containing 4–5 Gd atoms.

Grazing-incidence Rutherford backscattering and angle-resolved x-ray photoelectron spectrometry are used to determine the ion-concentration profiles near the surface of a solution consisting of a salt (TEABr) in a weakly polar organic liquid (polyethylene glycol) with atomic-layer depth resolution. The predictions of a model, in which ions in solution are repelled from the surface due to a screened Coulomb interaction with their image charge, are in good agreement with measured ion profiles. This contrasts with the behavior of salts in aqueous and highly polar organic solutions.

We develop a theory of interaction effects in graphene superlattices, where tunable superlattice periodicity can be used as a knob to control the gap at the Dirac point. Applied to graphene on hexa-boron-nitride ($G/h$-BN), our theory predicts substantial many-body enhancement of this gap. Tunable by the moiré superlattice periodicity, a few orders of magnitude enhancement is reachable under optimal conditions. The Dirac point gap enhancement can be much larger than that of the minigaps opened by Bragg scattering at principal superlattice harmonics. This naturally explains the conundrum of large Dirac point gaps recently observed in $G/h$-BN heterostructures and their tunability by the $G/h$-BN twist angle.

The experimental observation of the strong Coulombic effect on magneto-oscillations of the photoconductivity of surface electrons in liquid helium is reported. The observed broadening of the oscillations and shifts in positions of conductivity extrema with increasing electron density are in good agreement with the linear transport theory, which takes into account an internal electric field of fluctuational origin. These results provide important evidence for identification of the mechanism of the oscillations and zero-resistance states developed in their minima.

We conduct a detailed structural analysis of the $S=1$ pyrochlore antiferromagnet ${\mathrm{MgV}}_2{\mathrm{O}}_4$, which exhibits an antiferromagnetic ordering marginally at $T_N=40\mathrm{K}$, triggered by a structural transition from cubic to tetragonal symmetry at $T_S=62\mathrm{K}$, using high resolution synchrotron x-ray diffraction and convergent beam electron diffraction. We reveal that the tetragonal phase below $T_S$ has the symmetry of $I{4}_1/a$ and that the distortion pattern of ${\mathrm{VO}}_6$ octahedra is consistent with $A$-type antiferro-orbital ordering with alternating stacking of layers with $yz/xy$ orbital chains and $zx/xy$ orbital chains along the tetragonal $c$ axis. This implies that an anisotropic coupling of V moments produced by the orbital ordering below $T_S$ primarily brings about the antiferromagnetic ordering.

Electron-hole recollisions are induced by resonantly injecting excitons with a near-IR laser at frequency $f_{\mathrm{NIR}}$ into quantum wells driven by a $10\mathrm{kV}/\mathrm{cm}$ field oscillating at $f_{\mathrm{THz}}=0.57\mathrm{THz}$. At $T=12\mathrm{K}$, up to 18 sidebands are observed at frequencies $f_{\text{sideband}}=f_{\mathrm{NIR}}+2n{f}_{\mathrm{THz}}$, with $-8\le 2n\le 28$. Electrons and holes recollide with total kinetic energies up to 57 meV, well above the $E_{\mathrm{LO}}=36\mathrm{meV}$ threshold for longitudinal optical (LO) phonon emission. Sidebands with order up to $2n=22$ persist up to room temperature. A simple model shows that LO phonon scattering suppresses but does not eliminate sidebands associated with kinetic energies above $E_{\mathrm{LO}}$.