We perform extensive monomer-resolved computer simulations of suitably designed amphiphilic dendritic macromolecules over a broad range of densities, proving the existence and stability of cluster crystals formed in these systems, as predicted previously on the basis of effective pair potentials [B. M. Mladek et al., Phys. Rev. Lett. 96, 045701 (2006)]. Key properties of these crystals, such as the adjustment of their site occupancy with density and the possibility to heal defects by dendrimer migration, are confirmed on the monomer-resolved picture. At the same time, important differences from the predictions of the pair potential picture, stemming from steric crowding, arise as well, and they place an upper limit in the density for which such crystals can exist.

We have modulated the density of a trapped Bose-Einstein condensate by changing the trap stiffness, thereby modulating the speed of sound. We observe the creation of correlated excitations with equal and opposite momenta, and show that for a well-defined modulation frequency, the frequency of the excitations is half that of the trap modulation frequency.

The suppression of the individual ${\rm Y}(nS)$ states in PbPb collisions with respect to their yields in $pp$ data has been measured. The PbPb and $pp$ data sets used in the analysis correspond to integrated luminosities of $150\mu {\mathrm{b}}^{-1}$ and $230{\mathrm{nb}}^{-1}$, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The ${\rm Y}(nS)$ yields are measured from the dimuon invariant mass spectra. The suppression of the ${\rm Y}(nS)$ yields in PbPb relative to the yields in $pp$, scaled by the number of nucleon-nucleon collisions, $R_{AA}$, is measured as a function of the collision centrality. Integrated over centrality, the $R_{AA}$ values are $0.56\pm 0.08(\mathrm{stat})\pm 0.07(\mathrm{syst})$, $0.12\pm 0.04(\mathrm{stat})\pm 0.02(\mathrm{syst})$, and lower than 0.10 (at 95% confidence level), for the ${\rm Y}(1S)$, ${\rm Y}(2S)$, and ${\rm Y}(3S)$ states, respectively. The results demonstrate the sequential suppression of the ${\rm Y}(nS)$ states in PbPb collisions at LHC energies.

The cooperative motion induced structural evolution of the liquid with microheterogeneity is investigated in quasi-2D dusty plasma liquids, through direct optical visualization. A novel bond-dynamics analysis is used to further classify the robust cooperative 2D clusters into static, rotating, and drifting patches, beyond the earlier findings of the cooperative hopping strings and bands. The relative motion between two adjacent clusters causes the formation of a fractal network with narrow shear strips along the cluster interface. The rotation of the large ordered patch through rupturing into multiple rotating patches followed by the healing process, and the growth to a larger ordered patch by aligning the different lattice orientations of the adjacent ordered domains through patch rupturing, rotation, drifting, and merging are the key processes for the microstructural evolution.

Extending a previously developed two-phase equation of state, we simulate head-on relativistic lead-lead collisions with fluid dynamics, augmented with a finite-range term, and study the effects of the phase structure on the evolution of the baryon density. For collision energies that bring the bulk of the system into the mechanically unstable spinodal region of the phase diagram, the density irregularities are being amplified significantly. The resulting density clumping may be exploited as a signal of the phase transition, possibly through an enhanced production of composite particles.

We experimentally investigate a recently proposed optical excitation scheme V. I. Yudin et al. [Phys. Rev. A 82, 011804(R) (2010)] that is a generalization of Ramsey’s method of separated oscillatory fields and consists of a sequence of three excitation pulses. The pulse sequence is tailored to produce a resonance signal that is immune to the light shift and other shifts of the transition frequency that are correlated with the interaction with the probe field. We investigate the scheme using a single trapped ${}^{171}\mathrm{Yb}^{+}$ ion and excite the highly forbidden ${}^{2}S_{1/2}-{}^{2}F_{7/2}$ electric-octupole transition under conditions where the light shift is much larger than the excitation linewidth, which is in the hertz range. The experiments demonstrate a suppression of the light shift by four orders of magnitude and an immunity against its fluctuations.

The NASA/ESA Cassini probe of Saturn analyzed the molecular composition of plumes emanating from one of its moons, Enceladus, and the upper atmosphere of another, Titan. However, interpretation of this data is complicated by the hypervelocity (HV) flybys of up to $\sim 18\mathrm{km}/\sec$ that cause substantial molecular fragmentation. To interpret this data we use quantum mechanical based reactive force fields to simulate the HV impact of various molecular species and ice clathrates on oxidized titanium surfaces mimicking those in Cassini’s neutral and ion mass spectrometer (INMS). The predicted velocity dependent fragmentation patterns and composition mixing ratios agree with INMS data providing the means for identifying the molecules in the plume. We used our simulations to predict the surface damage from the HV impacts on the INMS interior walls, which we suggest acts as a titanium sublimation pump that could alter the instrument’s readings. These results show how the theory can identify chemical events from hypervelocity impacts in space plumes and atmospheres, providing in turn clues to the internal structure of the corresponding sources (e.g., Enceladus). This may be valuable in steering modifications in future missions.

We investigated the bonding stiffness of individual atoms on substrate surfaces using noncontact atomic force microscopy with frequency modulation. We measured the frequency shift distribution of the (110) plane above buckling-up and buckling-down dimer atoms of the Ge(001)-$c(4\times 2)$ surface using a tungsten-coated atomic force microscopy cantilever. The tip-surface chemical force distribution was reproduced from the frequency shift data using calculations based on Sader’s formula. The total harmonic bonding stiffness between the dimer atoms and the substrate was first discovered by fitting the Morse force to the tip-surface chemical force distribution with consideration of the relaxation in the tip-surface gap. By excluding the contribution exerted by the probe tip, we observed that the harmonic bonding compliance of the buckling-up dimer atom was $4.8\times {10}^{-3}\mathrm{m}/\mathrm{N}$ stiffer than that of the buckling-down dimer atom. This technique for probing the elastic bonding states of individual surface atoms at the atomic scale is unique.

The dynamics of propagating polariton condensates in one-dimensional microcavities is investigated through time resolved experiments. We find a strong increase in the condensate intensity when it travels through the nonresonantly excited area. This amplification is shown to come from bosonic stimulated relaxation of reservoir excitons into the polariton condensate, allowing for the repopulation of the condensate through nonresonant pumping. Thus, we experimentally demonstrate a polariton amplifier with a large band width, opening the way towards the transport of polaritons with high densities over macroscopic distances.

The existence of topological superconductors preserving time-reversal symmetry was recently predicted, and they are expected to provide a solid-state realization of itinerant massless Majorana fermions and a route to topological quantum computation. Their first likely example, ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$, was discovered last year, but the search for new materials has so far been hindered by the lack of a guiding principle. Here, we report point-contact spectroscopy experiments suggesting that the low-carrier-density superconductor ${\mathrm{Sn}}_{1-x}{\mathrm{In}}_x\mathrm{Te}$ is accompanied by surface Andreev bound states which, with the help of theoretical analysis, would give evidence for odd-parity pairing and topological superconductivity. The present and previous finding of possible topological superconductivity in ${\mathrm{Sn}}_{1-x}{\mathrm{In}}_x\mathrm{Te}$ and ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$ suggests that odd-parity pairing favored by strong spin-orbit coupling is likely to be a common underlying mechanism for materializing topological superconductivity.

We explore via density functional calculations the magnetic doping of a topological ferroelectric as an unconventional route to multiferroicity. Vanadium doping of the layered perovskite ${\mathrm{La}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ largely preserves electric polarization and produces robust ferromagnetic order and, hence, proper multiferroicity. The marked tendency of dopants to cluster into chains results in an insulating character at generic doping. Ferromagnetism stems from the symmetry breaking of the multiorbital V system via an unusual “antiferro”-orbital order, and from the host’s low-symmetry layered structure.

Pressure-dependent, low-temperature inelastic light (Raman) scattering measurements of ${\mathrm{KCuF}}_3$ show that applied pressure above $P^{*}\sim 7\mathrm{kbar}$ suppresses a previously observed structural phase transition temperature to zero temperature in ${\mathrm{KCuF}}_3$, resulting in the development of a fluctuational (quasielastic) response near $T\sim 0\mathrm{K}$. This pressure-induced fluctuational response—which we associate with slow fluctuations of the ${\mathrm{CuF}}_6$ octahedral orientation—is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, consistent with quantum fluctuations of the ${\mathrm{CuF}}_6$ octahedra. A model of pseudospin-phonon coupling provides a qualitative description of both the temperature- and pressure-dependent evolution of the Raman spectra of ${\mathrm{KCuF}}_3$.

The Lyme disease spirochete, Borrelia burgdorferi, swims by undulating its cell body in the form of a traveling flat wave, a process driven by rotating internal flagella. We study B. burgdorferi’s swimming by treating the cell body and flagella as linearly elastic filaments. The dynamics of the cell are then determined from the balance between elastic and resistive forces and moments. We find that planar, traveling waves only exist when the flagella are effectively anchored at both ends of the bacterium and that these traveling flat waves rotate as they undulate. The model predicts how the undulation frequency is related to the torque from the flagellar motors and how the stiffness of the cell body and flagella affect the undulations and morphology.

We show that hard spheres confined between two parallel hard plates pack denser with periodic adaptive prismatic structures which are composed of alternating prisms of spheres. The internal structure of the prisms adapts to the slit height which results in close packings for a range of plate separations, just above the distance where three intersecting square layers fit exactly between the plates. The adaptive prism phases are also observed in real-space experiments on confined sterically stabilized colloids and in Monte Carlo simulations at finite pressure.

An all-resonant method is proposed to control the quantum state of superconducting resonators. This approach uses a tunable artificial atom linearly coupled to resonators, and allows for efficient routes to Fock state synthesis, qudit logic operations, and synthesis of NOON states. This resonant approach is theoretically analyzed, and found to perform significantly better than existing proposals using the same technology.

A search for direct pair production of supersymmetric top squarks (${\tilde{t}}_1$) is presented, assuming the ${\tilde{t}}_1$ decays into a top quark and the lightest supersymmetric particle, ${\tilde{\chi }}_1^0$, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of ${13.5}_{-3.6}^{+3.7}({4.4}_{-1.3}^{+1.7})$ events in two signal regions based on $\int \mathcal{L}dt=4.7{\mathrm{fb}}^{-1}$ of $pp$ collision data taken at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector at the LHC. An exclusion region in the ${\tilde{t}}_1$ versus ${\tilde{\chi }}_1^0$ mass plane is evaluated: $370<m_{{\tilde{t}}_1}<465\mathrm{GeV}$ is excluded for $m_{{\tilde{\chi }}_1^0}\sim 0\mathrm{GeV}$ while $m_{{\tilde{t}}_1}=445\mathrm{GeV}$ is excluded for $m_{{\tilde{\chi }}_1^0}\le 50\mathrm{GeV}$.

A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$. The measurement is based on $4.7{\mathrm{fb}}^{-1}$ of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.

We introduce the forward-backward asymmetries $A_u$, $A_d$ corresponding to $u\overline{u}$, $d\overline{d}\to t\overline{t}$ production, respectively, at hadron colliders. These are collider and center-of-mass independent observables, directly related to the forward-backward and charge asymmetries measured at the Tevatron and the LHC, respectively. We discuss how to extract these asymmetries from data. Because these asymmetries are collider independent, their measurement at these two colliders could elucidate the nature of the anomalous forward-backward asymmetry measured at the Tevatron. Our framework also shows in a model independent fashion that a positive Tevatron asymmetry exceeding the standard model expectation is compatible with the small asymmetry measured at the LHC.

The mechanism of DNA modification induced by $K$-shell photoabsorption of nitrogen and oxygen atoms was investigated by electron paramagnetic resonance and x-ray absorption near edge structure measurements of calf thymus DNA. A $g$ factor of 2.000 for the unpaired electron species, which only arises during irradiation, was measured. The EPR intensities for DNA zwere twofold times larger than those estimated based on the photoabsorption cross section. This suggests that the DNA film itself forms unpaired electron species through the excitation of enhanced electron recapturing, known as the postcollision interaction process.

A beam of light, reflected at a planar interface, does not follow perfectly the ray optics prediction. Diffractive corrections lead to beam shifts; the reflected beam is displaced (spatial Goos-Hänchen type shifts) and/or travels in a different direction (angular Imbert-Fedorov type shifts), as compared to geometric optics. How does the degree of spatial coherence of light influence these shifts? We investigate this issue first experimentally and find that the degree of spatial coherence influences the angular beam shifts, while the spatial beam shifts are unaffected.