The specific kind of diffusion stimulated (rather than suppressed) by the external magnetic field, which was predicted for the first time by Schmelcher and Cederbaum in 1992, is considered here for the case of high-angular-momentum (i.e., approximately “circular”) Rydberg atoms. The coefficient of such diffusion was calculated by a purely analytical approach and was found to be very relevant to the experiments on antihydrogen formation.

We demonstrate that the vibrational nuclear motion of singly ionized argon dimers can be controlled with two ultrashort laser pulses of different wavelengths. In particular, we observe a striking “gap” in the pump-probe-delay-dependent kinetic-energy release spectrum only if the probe-pulse wavelength exceeds the pump-pulse wavelength. This “frustrated dissociation effect” is reproduced by our two-state quantum mechanical model, validating its interpretation as a pump-pulse-initiated population transfer between dipole-coupled Born-Oppenheimer electronic states of the dissociating $\mathrm{Ar}_2{}^{+}$ molecular ion. Our numerical results also reproduce the measured collapse and fractional revival of the oscillating $\mathrm{Ar}_2{}^{+}$ nuclear wave packet, and, for single-pulse dissociation, the decrease of the kinetic-energy release with increasing laser wavelength.

The Cooper minimum (CM) has been studied using high harmonic generation solely in atoms. Here, we present detailed experimental and theoretical studies on the CM in molecules probed by high harmonic generation using a range of near-infrared light pulses from $\lambda =1.3$ to $1.8\mu \mathrm{m}$. We demonstrate the CM to occur in ${\mathrm{CS}}_2$ and ${\mathrm{CCl}}_4$ at $\sim 42$ and $\sim 40\mathrm{eV}$, respectively, by comparing the high harmonic spectra with the known partial photoionization cross sections of different molecular orbitals, confirmed by theoretical calculations of harmonic spectra. We use CM to probe electron localization in Cl-containing molecules (${\mathrm{CCl}}_4$, ${\mathrm{CH}}_2{\mathrm{Cl}}_2$, and trans-${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{Cl}}_2$) and show that the position of the minimum is influenced by the molecular environment.

Experimental evidence is presented for a scale-free transition from an unordered to an ordered state in a 2D complex plasma that differs from the KTHNY theory of phase transitions in 2D systems. The transition is characterized by the formation and growth of ordered domains. A fractal relationship is found between the domain areas and domain boundary lengths, which can be explained by a recent theoretical model. The experimental findings are supported by a molecular dynamics simulation of a 2D particle system.

We study the influence of particle shape on growth processes at the edges of evaporating drops. Aqueous suspensions of colloidal particles evaporate on glass slides, and convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow inhomogeneously from the edge in two dimensions, and the deposition front, or growth line, varies spatiotemporally. Measurements of the fluctuations of the deposition front during evaporation enable us to identify distinct growth processes that depend strongly on particle shape. Sphere deposition exhibits a classic Poisson-like growth process; deposition of slightly anisotropic particles, however, belongs to the Kardar-Parisi-Zhang universality class, and deposition of highly anisotropic ellipsoids appears to belong to a third universality class, characterized by Kardar-Parisi-Zhang fluctuations in the presence of quenched disorder.

Combining aberration corrected high resolution transmission electron microscopy and density functional theory calculations we propose an explanation of the antisurfactant effect of Si in GaN growth. We identify the atomic structure of a Si delta-doped layer (commonly called ${\mathrm{SiN}}_x$ mask) as a ${\mathrm{SiGaN}}_3$ monolayer that resembles a $\sqrt{3}\times \sqrt{3}R30°$ surface reconstruction containing one Si atom, one Ga atom, and a Ga vacancy ($V_{\mathrm{Ga}}$) in its unit cell. Our density functional theory calculations show that GaN growth on top of this ${\mathrm{SiGaN}}_3$ layer is inhibited by forming an energetically unfavorable electrical dipole moment that increases with layer thickness and that is caused by charge transfer between cation dangling bonds at the surface to $V_{\mathrm{Ga}}$ bound at subsurface sites.

Mass transport in the Pb wetting layer on the Si(111) surface is investigated by observing nonequilibrium coverage profile evolution with low energy electron microscopy and microlow energy electron diffraction. Equilibration of an initial coverage step profile occurs by the exchange of mass between oppositely directed steep coverage gradients that each move with unperturbed shape. The bifurcation of the initial profile, the shape of the profile between the two moving edges, and the time dependence of equilibration are all at odds with expectations for classical diffusion behavior. These observations signal a very unusual coverage dependence of diffusion or may even reveal an exceptional collective superdiffusive mechanism.

We measure the gap density of states and the Fermi level position in thin-film transistors based on pentacene and dinaphtho[2,3-b:$2^{\prime }$,$3^{\prime }$-f]thieno[3,2-b]thiophene (DNTT) films grown on various surfaces using Kelvin probe force microscopy. It is found that the density of states in the gap of pentacene is extremely sensitive to the underlying interface and governs the Fermi level energy in the gap. The density of gap states in pentacene films grown on bare silicon dioxide (${\mathrm{SiO}}_2$) was found to be larger by 1 order of magnitude compared to that in pentacene grown on ${\mathrm{SiO}}_2$ treated with hexamethyldisilazane and larger by 2 orders of magnitude compared to that of pentacene grown on aluminum oxide (${\mathrm{AlO}}_x$) treated with a self-assembled monolayer (SAM) of $n$-tetradecylphosphonic acid (${\mathrm{HC}}_{14}$-PA). When DNTT was grown on ${\mathrm{HC}}_{14}$-PA-SAM-treated ${\mathrm{AlO}}_x$, the gap density of states was even smaller, so that the Fermi level pinning was significantly reduced. The correlation between the measured gap density of states and the transistor performance is demonstrated and discussed.

We investigate the atomic-scale tunneling characteristics of bilayer graphene on silicon carbide using the scanning tunneling microscopy. The high-resolution tunneling spectroscopy reveals an unexpected negative differential resistance (NDR) at the Dirac energy, which spatially varies within the single unit cell of bilayer graphene. The origin of NDR is explained by two near-gap van Hove singularities emerging in the electronic spectrum of bilayer graphene under a transverse electric field, which are strongly localized on two sublattices in different layers. Furthermore, defects near the tunneling contact are found to strongly impact on NDR through the electron interference. Our result provides an atomic-level understanding of quantum tunneling in bilayer graphene, and constitutes a useful step towards graphene-based tunneling devices.

The nature of metallicity and the level of electronic correlations in the antiferromagnetically ordered parent compounds are two important open issues for the iron-based superconductivity. We perform a temperature-dependent angle-resolved photoemission spectroscopy study of ${\mathrm{Fe}}_{1.02}\mathrm{Te}$, the parent compound for iron chalcogenide superconductors. Deep in the antiferromagnetic state, the spectra exhibit a “peak-dip-hump” line shape associated with two clearly separate branches of dispersion, characteristics of polarons seen in manganites and lightly doped cuprates. As temperature increases towards the Néel temperature ($T_N$), we observe a decreasing renormalization of the peak dispersion and a counterintuitive sharpening of the hump linewidth, suggestive of an intimate connection between the weakening electron-phonon ($e$-ph) coupling and antiferromagnetism. Our finding points to the highly correlated nature of the ${\mathrm{Fe}}_{1.02}\mathrm{Te}$ ground state featured by strong interactions among the charge, spin, and lattice and a good metallicity plausibly contributed by the coherent polaron motion.

The tunneling anisotropic magnetoresistance (TAMR) of single Co atoms adsorbed on a double-layer Fe film on W(110) is observed by scanning tunneling spectroscopy. Without applying an external magnetic field the TAMR is found by comparing spectra of atoms that are adsorbed on the domains and domain walls of the Fe film. The TAMR can be as large as 12% and repeatedly changes sign as a function of bias voltage. First-principles calculations show that the hybridization between Co $d$ states of different orbital symmetries depends on the magnetization direction via spin-orbit coupling. This leads to an anisotropy of the density of states and thus induces a TAMR.

Above-band-gap optical excitation produces interdependent structural and electronic responses in a multiferroic ${\mathrm{BiFeO}}_3$ thin film. Time-resolved synchrotron x-ray diffraction shows that photoexcitation can induce a large out-of-plane strain, with magnitudes on the order of half of one percent following pulsed-laser excitation. The strain relaxes with the same nanosecond time dependence as the interband relaxation of excited charge carriers. The magnitude of the strain and its temporal correlation with excited carriers indicate that an electronic mechanism, rather than thermal effects, is responsible for the lattice expansion. The observed strain is consistent with a piezoelectric distortion resulting from partial screening of the depolarization field by charge carriers, an effect linked to the electronic transport of excited carriers. The nonthermal generation of strain via optical pulses promises to extend the manipulation of ferroelectricity in oxide multiferroics to subnanosecond time scales.

Localized wave fronts are a fundamental feature of biological systems from cell biology to ecology. Here, we study a broad class of bistable models subject to self-activation, degradation, and spatially inhomogeneous activating agents. We determine the conditions under which wave-front localization is possible and analyze the stability thereof with respect to extrinsic perturbations and internal noise. It is found that stability is enhanced upon regulating a positional signal and, surprisingly, also for a low degree of binding cooperativity. We further show a contrasting impact of self-activation to the stability of these two sources of destabilization.

A measurement of the $CP$ asymmetry in $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$ decays is presented, based on $1.0{\mathrm{fb}}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011. The measurement is performed in six bins of invariant mass squared of the ${\mu }^{+}{\mu }^{-}$ pair, excluding the $J/\psi$ and $\psi (2S)$ resonance regions. Production and detection asymmetries are removed using the $B^0\to J/\psi K^{*0}$ decay as a control mode. The integrated $CP$ asymmetry is found to be $-0.072\pm 0.040(\mathrm{stat})\pm 0.005(\mathrm{syst})$, consistent with the standard model.

We show how a quantum Ising spin chain in a time-dependent transverse magnetic field can be simulated and experimentally probed in the framework of circuit QED with current technology. The proposed setup provides a new platform for observing the nonequilibrium dynamics of interacting many-body systems. We calculate its spectrum to offer a guideline for its initial experimental characterization. We demonstrate that quench dynamics and the propagation of localized excitations can be observed with the proposed setup and discuss further possible applications and modifications of this circuit QED quantum simulator.

We discuss the fate of chiral symmetry in an extremely strong magnetic field $B$. We investigate not only quark fluctuations but also neutral meson effects. The former enhances the chiral-symmetry breaking at finite $B$ according to the magnetic catalysis, while the latter suppresses the chiral condensate once $B$ exceeds the scale of the hadron structure. Using a chiral model, we demonstrate how neutral mesons are subject to the dimensional reduction and the low dimensionality favors the chiral-symmetric phase. We point out that this effect, the magnetic inhibition, can be a feasible explanation for recent lattice-QCD data indicating the decreasing behavior of the chiral-restoration temperature with increasing $B$.

The ${}^{18}\mathrm{F}(p,\alpha ){}^{15}\mathrm{O}$ reaction rate is crucial for constraining model predictions of the $\gamma$-ray observable radioisotope ${}^{18}\mathrm{F}$ produced in novae. The determination of this rate is challenging due to particular features of the level scheme of the compound nucleus, ${}^{19}\mathrm{Ne}$, which result in interference effects potentially playing a significant role. The dominant uncertainty in this rate arises from interference between $J^{\pi }=3/2^{+}$ states near the proton threshold ($S_p=6.411\mathrm{MeV}$) and a broad $J^{\pi }=3/2^{+}$ state at 665 keV above threshold. This unknown interference term results in up to a factor of 40 uncertainty in the astrophysical $S$-factor at nova temperatures. Here we report a new measurement of states in this energy region using the ${}^{19}\mathrm{F}({}^3\mathrm{He},t){}^{19}\mathrm{Ne}$ reaction. In stark contrast to previous assumptions we find at least 3 resonances between the proton threshold and $E_{cm}=50\mathrm{keV}$, all with different angular distributions. None of these are consistent with $J^{\pi }=3/2^{+}$ angular distributions. We find that the main uncertainty now arises from the unknown proton width of the 48 keV resonance, not from possible interference effects. Hydrodynamic nova model calculations performed indicate that this unknown width affects ${}^{18}\mathrm{F}$ production by at least a factor of two in the model considered.

We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the $N=126$ shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron $1i_{11/2}$ orbital beyond $N=126$ and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single-particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single-particle energies agree with experimental values at the mean-field level.

Neutron matter presents a unique system for chiral effective field theory because all many-body forces among neutrons are predicted to next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$). We present the first complete ${\mathrm{N}}^3\mathrm{LO}$ calculation of the neutron matter energy. This includes the subleading three-nucleon forces for the first time and all leading four-nucleon forces. We find relatively large contributions from ${\mathrm{N}}^3\mathrm{LO}$ three-nucleon forces. Our results provide constraints for neutron-rich matter in astrophysics with controlled theoretical uncertainties.

From the perspective of perturbation theory, we propose a systematic procedure for the evaluation of the derivative discontinuity (DD) of the exchange-correlation energy functional in Kohn-Sham (KS) density functional theory, wherein the exact DD can in principle be obtained by summing up all the perturbation corrections to infinite order. Truncation of the perturbation series at low order yields an efficient scheme for obtaining the approximate DD. While the zeroth-order theory yields a vanishing DD, the first-order correction to the DD can be expressed as an explicit universal functional of the ground-state density and the KS lowest unoccupied molecular orbital density, allowing the direct evaluation of the DD in the standard KS method without extra computational cost. The fundamental gap can be predicted by adding the estimated DD to the KS gap. This scheme is shown to be accurate in the prediction of the fundamental gaps for a wide variety of atoms and molecules.