Using a 3D spin-dependent optical lattice, we study thermalization and energy exchange between two ultracold Bose gases, one of which is strongly correlated and bound to the lattice and another that is free from the lattice potential. Disruption of interspecies thermalization is revealed through measurements of condensate fraction after the lattice is superimposed on the parabolic confining potential. By selectively heating the lattice-bound species and measuring the rate of heat transfer to the free state, suppression of energy exchange is observed. Comparison with a Fermi’s golden rule prediction confirms that this effect is caused by a dispersion mismatch that reduces the phase space available for elastic collisions. This result has critical implications for methods proposed to cool strongly correlated lattice gases.

A model for a new electron-vortex beam production method is proposed and experimentally demonstrated. The technique calls on the controlled manipulation of the degrees of freedom of the lens aberrations to achieve a helical phase front. These degrees of freedom are accessible by using the corrector lenses of a transmission electron microscope. The vortex beam is produced through a particular alignment of these lenses into a specifically designed astigmatic state and applying an annular aperture in the condenser plane. Experimental results are found to be in good agreement with simulations.

Sputtering yields, enhanced by more than an order of magnitude, have been observed for 80 keV Xe ion irradiation of monocrystalline Au nanorods. Yields are in the range $100–1900\mathrm{atoms}/\mathrm{ion}$ compared with values for a flat surface of $\approx 50$. This enhancement results in part from the proximity of collision cascades and ensuing thermal spikes to the nanorod surfaces. Molecular dynamic modeling reveals that the range of incident angles occurring for irradiation of nanorods and the larger number of atoms in “explosively ejected” atomic clusters make a significant contribution to the enhanced yield.

A new form of ${\mathrm{TiO}}_2$ which is black in color has been shown to exhibit high efficiency for photocatalytic reactions under solar radiation [X. Chen, L. Liu, P. Y. Yu, and S. S. Mao, Science 331, 746 (2011)]. However, the mechanism behind this disorder-engineering process is not fully understood. In this Letter, based on density functional theory, we describe the role of hydrogen in producing lattice disorder in the anatase nanocrystals. We clarify further that the highly localized nature of the midgap states results in spatial separation of photoexcited electrons and holes in black ${\mathrm{TiO}}_2$, and that accounts for its high photocatalytic efficiency.

We report the first use of direct detection for recording electron backscatter diffraction patterns. We demonstrate the following advantages of direct detection: the resolution in the patterns is such that higher order features are visible; patterns can be recorded at beam energies below those at which conventional detectors usefully operate; high precision in cross-correlation based pattern shift measurements needed for high resolution electron backscatter diffraction strain mapping can be obtained. We also show that the physics underlying direct detection is sufficiently well understood at low primary electron energies such that simulated patterns can be generated to verify our experimental data.

Maximum strength sets the limit of a material’s intrinsic resistance to permanent deformation. Its significance, however, lies not in the highest strength value that a solid can possibly achieve, but rather in how this quantity is degraded, from which one could decipher the underlying mechanisms of yielding in a real material. A wide range of maximum strength values have been measured experimentally for metallic glasses. However, the true maximum strength remains unknown to date. Here, using finite deformation theory, we give the first theoretical estimate of the ultimate strength of metallic glasses. Our theoretical results, along with those from experiment and simulation, lead us to several mechanisms of degradation of the theoretical strength that are closely connected to correlated atomic motion with varying characteristic length in real metallic glasses.

We perform ab initio calculations of hydrogen-based tunneling defects in alumina to identify deleterious two-level systems (TLS) in superconducting qubits. The defects analyzed include bulk hydrogenated Al vacancies, bulk hydrogen interstitial defects, and a surface OH rotor. The formation energies of the defects are first computed for an Al- and O-rich environment to give the likelihood of defect occurrence during growth. The potential energy surfaces are then computed and the corresponding dipole moments are evaluated to determine the coupling of the defects to an electric field. Finally, the tunneling energy is computed for the hydrogen defect and the analogous deuterium defect, providing an estimate of the TLS energy and the corresponding frequency for photon absorption. We predict that hydrogenated cation vacancy defects will form a significant density of GHz frequency TLSs in alumina.

Using numerical simulation of a 2D Lennard-Jones system, we study the crossover from shear thinning to Newtonian flow. We find that the short-time elastic response of our system essentially does not change through this crossover, and show that, in the Newtonian regime, thermal activation triggers shear transformations, i.e., local irreversible shear events that produce Eshelby (long-ranged, anisotropic) deformation fields as previously seen in low-$T$ glasses. Quite surprisingly, these Eshelby fields are found to persist much beyond the $\alpha$-relaxation time, and shear thinning to coincide with the emergence of correlations between shear relaxation centers.

Quantum molecular dynamics simulations of $\alpha \mathrm{\text{−}}{\mathrm{Al}}_2{\mathrm{O}}_3(0001)/3\mathrm{C}\mathrm{\text{−}}\mathrm{SiC}(111)$ interfaces reveal profound effects of thermal annealing for producing strong interfaces consisting solely of cation-anion bonds and their consequence on interfacial structures. A Si-terminated SiC surface and ${\mathrm{Al}}_2{\mathrm{O}}_3$ form a stronger interface (Si-interface) with a Si-O bond density of $12.2{\mathrm{nm}}^{-2}$, whereas the C interface has an Al-C bond density of $9.46{\mathrm{nm}}^{-2}$. The interfacial bond strengthening is accompanied by the formation of an ${\mathrm{Al}}_2{\mathrm{O}}_3$ interphase with a thickness of 2–8 Å. Such atomistic understanding may help rational interfacial design of high-temperature ceramic composites for broad applications such as power generation systems.

We investigate the field-tuned quantum phase transition in a 2D low-disorder amorphous ${\mathrm{InO}}_x$ film in the frequency range of 0.05 to 16 GHz employing microwave spectroscopy. In the zero-temperature limit, the ac data are consistent with a scenario where this transition is from a superconductor to a metal instead of a direct transition to an insulator. The intervening metallic phase is unusual with a small but finite resistance that is much smaller than the normal state sheet resistance at the lowest measured temperatures. Moreover, it exhibits a superconducting response on short length and time scales while global superconductivity is destroyed. We present evidence that the true quantum critical point of this 2D superconductor metal transition is located at a field $B_{\mathrm{sm}}$ far below the conventionally defined critical field $B_{\mathrm{cross}}$ where different isotherms of magnetoresistance cross each other. The superfluid stiffness in the low-frequency limit and the superconducting fluctuation frequency from opposite sides of the transition both vanish at $B\approx B_{\mathrm{sm}}$. The lack of evidence for finite-frequency superfluid stiffness surviving $B_{\mathrm{cross}}$ signifies that $B_{\mathrm{cross}}$ is a crossover above which superconducting fluctuations make a vanishing contribution to dc and ac measurements.

Using an optimally coupled nanometer-scale SQUID, we measure the magnetic flux originating from an individual ferromagnetic Ni nanotube attached to a Si cantilever. At the same time, we detect the nanotube’s volume magnetization using torque magnetometry. We observe both the predicted reversible and irreversible reversal processes. A detailed comparison with micromagnetic simulations suggests that vortexlike states are formed in different segments of the individual nanotube. Such stray-field free states are interesting for memory applications and noninvasive sensing.

We study the Skyrmion dynamics in thin films under a temperature gradient. Our numerical simulations show that both single and multiple Skyrmions in a crystal move towards the high temperature region, which is contrary to particle diffusion. Noticing a similar effect in the domain wall motion, we employ a theory based on magnon dynamics to explain this counterintuitive phenomenon. Unlike the temperature driven domain wall motion, the Skyrmion’s topological charge plays an important role, and a transverse Skyrmion motion is observed. Our theory turns out to be in agreement with numerical simulations, both qualitatively and quantitatively. Our calculation indicates that a very promising Skyrmion dynamic phenomenon can be observed in experiments.

The tip of an atomic force microscope is used as a local probe for photoelectrons excited by laser illumination. The tip-sample distance is precisely controlled by the van der Waals force and the pure photoemission current is measured without tunneling current contribution. The nanoscale photoelectron mapping with high current contrast is obtained on a cesium covered Au(111) surface. By sweeping the laser photon energy, the local photoelectron spectra are measured on Cs islands and terraces. The results reveal distinct electronic states and photoemission thresholds for different Cs coverage, providing the photoemission current contrast mechanism. The contrast in photoelectron mapping can be further tuned by the incident laser polarization exploiting the symmetry selection rules in the optical excitation.

We show for the first time that entangled polymeric liquids containing long-chain branching can exhibit strain hardening upon startup shear. As the significant long-chain branching impedes chain disentanglement, Gaussian coils between entanglements can deform to reach the finite extensibility limit where the intrachain retraction force exceeds the value expected from the usual conformational entropy loss evaluated based on Gaussian chain statistics. The phenomenon is expected to lead to further theoretical understanding.

The dynamics of thermally stimulated surface fluctuations of 100 nm thick films of long-branched polymers are measured for the first time. In contrast to comparable films of linear or cyclic chains that show no change in viscosity upon confinement, films of 6-pom, 6-star, and 6-end end-branched stars show viscosities, inferred from x-ray photon correlation spectroscopy, as much as 100 times higher than in the bulk. This difference varies in magnitude with chain architecture. Branching has a profound effect on confinement, even for these unentangled chains.

In this Letter, we show that the electromagnetic duality symmetry, broken in the microscopic Maxwell’s equations by the presence of charges, can be restored for the macroscopic Maxwell’s equations. The restoration of this symmetry is shown to be independent of the geometry of the problem. These results provide a tool for the study of light-matter interactions within the framework of symmetries and conservation laws. We illustrate its use by determining the helicity content of the natural modes of structures possessing spatial inversion symmetries and by elucidating the root causes for some surprising effects in the scattering off magnetic spheres.

We report a diversity of stable gap solitons in a spin-orbit-coupled Bose-Einstein condensate subject to a spatially periodic Zeeman field. It is shown that the solitons can be classified by the main physical symmetries they obey, i.e., symmetries with respect to parity ($P$), time ($T$), and internal degree of freedom, i.e., spin ($C$), inversions. The conventional gap and gap-stripe solitons are obtained in lattices with different parameters. It is shown that solitons of the same type but obeying different symmetries can exist in the same lattice at different spatial locations. $PT$ and $CPT$ symmetric solitons have antiferromagnetic structure and are characterized, respectively, by nonzero and zero total magnetizations.

The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is its questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles $\propto r^{-3/2}$ if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile $\propto r^{-1}$. This way we further show how the formerly known lower Liu limit of the critical Rossby number $\mathrm{Ro}\approx -0.828$ connects naturally with the upper Liu limit $\mathrm{Ro}\approx +4.828$.

The ${}^{146}\mathrm{Sm}/{}^{144}\mathrm{Sm}$ ratio in the early solar system has been constrained by $\mathrm{Nd}/\mathrm{Sm}$ isotope ratios in meteoritic material. Predictions of ${}^{146}\mathrm{Sm}$ and ${}^{144}\mathrm{Sm}$ production in the $\gamma$ process in massive stars are at odds with these constraints, and this is partly due to deficiencies in the prediction of the reaction rates involved. The production ratio depends almost exclusively on the $(\gamma ,n)/(\gamma ,\alpha )$ branching at ${}^{148}\mathrm{Gd}$. A measurement of ${}^{144}\mathrm{Sm}(\alpha ,\gamma ){}^{148}\mathrm{Gd}$ at low energy had discovered considerable discrepancies between cross-section predictions and the data. Although this reaction cross section mainly depends on the optical $\alpha +\mathrm{\text{nucleus}}$ potential, no global optical potential has yet been found that can consistently describe the results of this and similar $\alpha$-induced reactions at the low energies encountered in astrophysical environments. The untypically large deviation in ${}^{144}\mathrm{Sm}(\alpha ,\gamma )$ and the unusual energy dependence can be explained, however, by low-energy Coulomb excitation, which is competing with compound nucleus formation at very low energies. Considering this additional reaction channel, the cross sections can be described with the usual optical potential variations, compatible with findings for ($n$, $\alpha$) reactions in this mass range. Low-energy ($\alpha$, $\gamma$) and ($\alpha$, $n$) data on other nuclei can also be consistently explained in this way. Since Coulomb excitation does not affect $\alpha$ emission, the ${}^{148}\mathrm{Gd}(\gamma ,\alpha )$ rate is much higher than previously assumed. This leads to very small ${}^{146}\mathrm{Sm}/{}^{144}\mathrm{Sm}$ stellar production ratios, in even more pronounced conflict with the meteorite data.

The late stage of an inspiraling neutron-star binary gives rise to strong gravitational wave emission due to its highly dynamic, strong gravity. Moreover, interactions between the stellar magnetospheres can produce considerable electromagnetic radiation. We study this scenario using fully general relativistic, resistive magnetohydrodynamic simulations. We show that these interactions extract kinetic energy from the system, dissipate heat, and power radiative Poynting flux, as well as develop current sheets. Our results indicate that this power can (i) outshine pulsars in binaries, (ii) display a distinctive angular- and time-dependent pattern, and (iii) radiate within large opening angles. These properties suggest that some binary neutron-star mergers are ideal candidates for multimessenger astronomy.