The stability of prototypical defect morphologies in thin films of symmetric diblock copolymers on chemically patterned substrates is investigated by self-consistent field theory. The excess free energy of defects and barriers of defect-removal mechanisms are obtained by computing the minimum free-energy path. Distinct defect-removal mechanisms are illustrated demonstrating that (i) defects will become unstable at a characteristic value of incompatibility $\chi N_{*}$ above the order-disorder transition and (ii) the kinetics is accelerated at weak segregation. Numerical findings are placed in the context of physical mechanisms, and implications for directed self-assembly are discussed.

Spatially entangled twin photons provide both promising resources for modern quantum information protocols, because of the high dimensionality of transverse entanglement, and a test of the Einstein-Podolsky-Rosen paradox in its original form of position versus impulsion. Usually, photons in temporal coincidence are selected and their positions recorded, resulting in a priori assumptions on their spatiotemporal behavior. In this Letter, we record, on two separate electron-multiplying charge coupled devices cameras, twin images of the entire flux of spontaneous down-conversion. This ensures a strict equivalence between the subsystems corresponding to the detection of either position (image or near-field plane) or momentum (Fourier or far-field plane). We report the highest degree of paradox ever reported and show that this degree corresponds to the number of independent degrees of freedom, or resolution cells, of the images.

We investigate the relation between the incompatibility of quantum measurements and quantum nonlocality. We show that a set of measurements is not jointly measurable (i.e., incompatible) if and only if it can be used for demonstrating Einstein-Podolsky-Rosen steering, a form of quantum nonlocality. Moreover, we discuss the connection between Bell nonlocality and joint measurability, and give evidence that both notions are inequivalent. Specifically, we exhibit a set of incompatible quantum measurements and show that it does not violate a large class of Bell inequalities. This suggests the existence of incompatible quantum measurements which are Bell local, similarly to certain entangled states which admit a local hidden variable model.

The fact that not all measurements can be carried out simultaneously is a peculiar feature of quantum mechanics and is responsible for many key phenomena in the theory, such as complementarity or uncertainty relations. For the special case of projective measurements, quantum behavior can be characterized by the commutator but for generalized measurements it is not easy to decide whether two measurements can still be understood in classical terms or whether the already show quantum features. We prove that a set of generalized measurements which does not satisfy the notion of joint measurability is nonclassical, as it can be used for the task of quantum steering. This shows that the notion of joint measurability is, among several definitions, the proper one to characterize quantum behavior. Moreover, the equivalence allows one to derive novel steering inequalities from known results on joint measurability and new criteria for joint measurability from known results on the steerability of states.

We construct a model of inflation based on a low-energy effective theory of spontaneously broken global scale invariance. This provides a shift symmetry that protects the inflaton potential from quantum corrections. Since the underlying scale invariance is noncompact, arbitrarily large inflaton field displacements are readily allowed in the low-energy effective theory. A weak breaking of scale invariance by almost marginal operators provides a nontrivial inflaton minimum, which sets and stabilizes the final low-energy value of the Planck scale. The underlying scale invariance ensures that the slow-roll approximation remains valid over large inflaton displacements, and yields a scale invariant spectrum of perturbations, as required by the cosmic microwave background observations.

We describe a method based on precision magnetometry that can extend the search for axion-mediated spin-dependent forces by several orders of magnitude. By combining techniques used in nuclear magnetic resonance and short-distance tests of gravity, our approach can substantially improve upon current experimental limits set by astrophysics, and probe deep into the theoretically interesting regime for the Peccei-Quinn (PQ) axion. Our method is sensitive to PQ axion decay constants between ${10}^9$ and ${10}^{12}\mathrm{GeV}$ or axion masses between ${10}^{-6}$ and ${10}^{-3}\mathrm{eV}$, independent of the cosmic axion abundance.

An ab initio based framework for quantitatively assessing the phonon contribution due to magnon-phonon interactions and lattice expansion is developed. The theoretical results for bcc Fe are in very good agreement with high-quality phonon frequency measurements. For some phonon branches, the magnon-phonon interaction is an order of magnitude larger than the phonon shift due to lattice expansion, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature. The framework closes the previous simulation gap between the ferro- and paramagnetic limits.

Strain is a leading candidate for controlling magnetoelectric coupling in multiferroics. Here, we use x-ray diffraction to study the coupling between magnetic order and structural distortion in epitaxial films of the orthorhombic ($o$-) perovskite ${\mathrm{LuMnO}}_3$. An antiferromagnetic spin canting in the $E$-type magnetic structure is shown to be related to the ferroelectrically induced structural distortion and to a change in the magnetic propagation vector. By comparing films of different orientations and thicknesses, these quantities are found to be controlled by $b$-axis strain. It is shown that compressive strain destabilizes the commensurate $E$-type structure and reduces its accompanying ferroelectric distortion.

Ponderomotive electron acceleration is demonstrated in a semiconductor-loaded nanoplasmonic waveguide. Photogenerated free carriers are accelerated by the tightly confined nanoplasmonic fields and reach energies exceeding the threshold for impact ionization. Broadband ($375\mathrm{nm}\le \lambda \le 650\mathrm{nm}$) white light emission is observed from the nanoplasmonic waveguides. Exponential growth of visible light emission confirms the exponential growth of the electron population, demonstrating the presence of an optical-field-driven electron avalanche. Electron sweeping dynamics are visualized using pump-probe measurements, and a sweeping time of $1.98\pm 0.40\mathrm{ps}$ is measured. These findings offer a means to harness the potential of the emerging field of ultrafast nonlinear nanoplasmonics.

Nucleosomes provide the basic unit of compaction in eukaryotic genomes, and the mechanisms that dictate their position at specific locations along a DNA sequence are of central importance to genetics. In this Letter, we employ molecular models of DNA and proteins to elucidate various aspects of nucleosome positioning. In particular, we show how DNA’s histone affinity is encoded in its sequence-dependent shape, including subtle deviations from the ideal straight B-DNA form and local variations of minor groove width. By relying on high-precision simulations of the free energy of nucleosome complexes, we also demonstrate that, depending on DNA’s intrinsic curvature, histone binding can be dominated by bending interactions or electrostatic interactions. More generally, the results presented here explain how sequence, manifested as the shape of the DNA molecule, dominates molecular recognition in the problem of nucleosome positioning.

We present neutron scattering data on the structure and dynamics of melts from polyethylene oxide rings with molecular weights up to ten times the entanglement mass of the linear counterpart. The data reveal a very compact conformation displaying a structure approaching a mass fractal, as hypothesized by recent simulation work. The dynamics is characterized by a fast Rouse relaxation of subunits (loops) and a slower dynamics displaying a lattice animal-like loop displacement. The loop size is an intrinsic property of the ring architecture and is independent of molecular weight. This is the first experimental observation of the space-time evolution of segmental motion in ring polymers illustrating the dynamic consequences of their topology that is unique among all polymeric systems of any other known architecture.

We investigate the relevant spectroscopic properties of the 795 nm ${}^3{\mathrm{H}}_6\leftrightarrow {}^3{\mathrm{H}}_4$ transition in 1% ${\mathrm{Tm}}^{3+}:{\mathrm{Y}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ at temperatures as low as 1.2 K for optical quantum memories based on persistent spectral tailoring of narrow absorption features. Our measurements reveal that this transition has uniform coherence properties over a 56 GHz bandwidth, and a simple hyperfine structure split by $\pm 44\mathrm{MHz}/\mathrm{T}$ with lifetimes of up to hours. Furthermore, we find a ${{}^3\mathrm{F}}_4$ population lifetime of 64 ms—one of the longest lifetimes observed for an electronic level in a solid—and an exceptionally long coherence lifetime of $490\mu \mathrm{s}$—the longest ever observed for optical transitions of ${\mathrm{Tm}}^{3+}$ ions in a crystal. Our results suggest that this material allows realizing broadband quantum memories that enable spectrally multiplexed quantum repeaters.

We show that a scalar and a fermion charged under a global $U(1)$ symmetry can not only explain the existence and abundance of dark matter (DM) and dark radiation (DR), but can also imbue DM with improved scattering properties at galactic scales, while remaining consistent with all other observations. Delayed DM-DR kinetic decoupling eases the missing satellites problem, while scalar-mediated self-interactions of DM ease the cusp versus core and too big to fail problems. In this scenario, DM is expected to be pseudo-Dirac and have a mass $100\mathrm{keV}\lesssim m_{\chi }\lesssim 10\mathrm{GeV}$. The predicted DR may be measurable using the primordial elemental abundances from big bang nucleosynthesis, and using the cosmic microwave background.

An experimental method for the verification of the individually different energy dependencies of $L_1-$, $L_2-$, and $L_3-$ subshell photoionization cross sections is described. The results obtained for Pd and Mo are well in line with theory regarding both energy dependency and absolute values, and confirm the theoretically calculated cross sections by Scofield from the early 1970 s and, partially, more recent data by Trzhaskovskaya, Nefedov, and Yarzhemsky. The data also demonstrate the questionability of quantitative x-ray spectroscopical results based on the widely used fixed jump ratio approximated cross sections with energy independent ratios. The experiments are carried out by employing the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin; the obtained fluorescent intensities are thereby calibrated at an absolute level in reference to the International System of Units. Experimentally determined fixed fluorescence line ratios for each subshell are used for a reliable deconvolution of overlapping fluorescence lines. The relevant fundamental parameters of Mo and Pd are also determined experimentally in order to calculate the subshell photoionization cross sections independently of any database.

We report ${}^{95}\mathrm{Zr}$ and ${}^{57}\mathrm{Co}$ radiotracer diffusivities and viscosity data in the equilibrium liquid state of a bulk metallic glass forming ${\mathrm{Zr}}_{46.75}{\mathrm{Ti}}_{8.25}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ melt (Vitreloy 4) far above the liquidus temperature $T_l$ that are not affected by convection, as evidenced via quasielastic neutron scattering. Zr diffusion is strongly decoupled from diffusion of the smaller components by more than a factor of 4 at $T_l$, although it obeys the Stokes-Einstein equation. The results suggest that, in the present Zr-based metallic glass forming systems, diffusion and viscous flow start to develop solidlike, i.e., energy-landscape-controlled, features already in the stable liquid state more than 300 K above the mode coupling temperature $T_c$.

The formation of heavy-fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid ${}^3\mathrm{He}$ that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth $\mathrm{\Lambda }$ quite different from that in BCS theory. Using Leggett’s theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of $\mathrm{\Lambda }$ in high quality samples both Landau parameters $F_0^s$ and $F_1^s$; this has never been accomplished before. A modification of the temperature dependence of the electronic specific heat $C_{\mathrm{el}}$, related to that of $\mathrm{\Lambda }$, is also expected. We have carefully determined the magnitude and temperature dependence of $\mathrm{\Lambda }$ in ${\mathrm{CeCoIn}}_5$ by muon spin relaxation rate measurements to obtain $F_0^s=36\pm 1$ and $F_1^s=1.2\pm 0.3$, and we find a consistent change in the temperature dependence of $C_{\mathrm{el}}$. This, the first determination of $F_1^s$ with a value $\ll F_0^s$ in a heavy-fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.

We argue that superconductivity in the coexistence region with spin-density-wave (SDW) order in weakly doped Fe pnictides erdiffers qualitatively from the ordinary $s^{+-}$ state outside the coexistence region as it develops an additional gap component which is a mixture of intrapocket singlet ($s^{++}$) and interpocket spin-triplet pairings (the $t$ state). The coupling constant for the $t$ channel is proportional to the SDW order and involves interactions that do not contribute to superconductivity outside of the SDW region. We argue that the $s^{+-}$- and $t$-type superconducting orders coexist at low temperatures, and the relative phase between the two is, in general, different from 0 or $\pi$, manifesting explicitly the breaking of the time-reversal symmetry promoted by long-range SDW order. We argue that time reversal may get broken even before true superconductivity develops.

The observed dependence of spin relaxation on the identity of the donor atom in $n$-type silicon has remained without explanation for decades and poses a long-standing open question with important consequences for modern spintronics. Taking into account the multivalley nature of the conduction band in silicon and germanium, we show that the spin-flip amplitude is dominated by short-range scattering off the central-cell potential of impurities after which the electron is transferred to a valley on a different axis in $k$ space. Through symmetry arguments, we show that this spin-flip process can strongly affect the spin relaxation in all multivalley materials in which time-reversal cannot connect distinct valleys. From the physical insights gained from the theory, we provide guidelines to significantly enhance the spin lifetime in semiconductor spintronics devices.