We study the possibility of realizing topological phases in graphene with randomly distributed adsorbates. When graphene is subjected to periodically distributed adatoms, the enhanced spin-orbit couplings can result in various topological phases. However, at certain adatom coverages, the intervalley scattering renders the system a trivial insulator. By employing a finite-size scaling approach and Landauer-Büttiker formula, we show that the randomization of adatom distribution greatly weakens the intervalley scattering, but plays a negligible role in spin-orbit couplings. Consequently, such a randomization turns graphene from a trivial insulator into a topological state.

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.

We present local probe results on the honeycomb lattice antiferromagnet ${\mathrm{Ba}}_3{\mathrm{CuSb}}_2{\mathrm{O}}_9$. Muon spin relaxation measurements in a zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.

Markov chains provide realistic models of numerous stochastic processes in nature. We demonstrate that in any Markov chain, the change in occupation number in state $A$ is correlated to the change in occupation number in state $B$ if and only if $A$ and $B$ are directly connected. This implies that if we are only interested in state $A$, fluctuations in $B$ may be replaced with their mean if state $B$ is not directly connected to $A$, which shortens computing time considerably. We show the accuracy and efficacy of our approximation theoretically and in simulations of stochastic ion-channel gating in neurons.

We study the structural constraint of random scale-free networks that determines possible combinations of the degree exponent $\gamma$ and the upper cutoff $k_c$ in the thermodynamic limit. We employ the framework of graphicality transitions proposed by Del Genio and co-workers [Phys. Rev. Lett. 107, 178701 (2011)], while making it more rigorous and applicable to general values of $k_c$. Using the graphicality criterion, we show that the upper cutoff must be lower than $k_c\sim N^{1/\gamma }$ for $\gamma <2$, whereas any upper cutoff is allowed for $\gamma >2$. This result is also numerically verified by both the random and deterministic sampling of degree sequences.

Some of the most pivotal moments in intellectual history occur when a new ideology sweeps through a society, supplanting an established system of beliefs in a rapid revolution of thought. Yet in many cases the new ideology is as extreme as the old. Why is it then that moderate positions so rarely prevail? Here, in the context of a simple model of opinion spreading, we test seven plausible strategies for deradicalizing a society and find that only one of them significantly expands the moderate subpopulation without risking its extinction in the process.

We combine the results of searches for the standard model (SM) Higgs boson based on the full CDF Run II data set obtained from $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collisions at the Fermilab Tevatron corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. The searches are conducted for Higgs bosons that are produced in association with a $W$ or $Z$ boson, have masses in the range $90–150\mathrm{GeV}/c^2$, and decay into $b\overline{b}$ pairs. An excess of data is present that is inconsistent with the background prediction at the level of 2.5 standard deviations (the most significant local excess is 2.7 standard deviations).

We present a search for the standard model Higgs boson produced in association with a $Z$ boson in data collected with the CDF II detector at the Tevatron, corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the $Z$ boson to electron or muon pairs, we set 95% credibility level upper limits on the $ZH$ production cross section times the $H\to b\overline{b}$ branching ratio as a function of Higgs boson mass. At a Higgs boson mass of $125\mathrm{GeV}/c^2$, we observe (expect) a limit of 7.1 (3.9) times the standard model value.

We present a search for the standard model Higgs boson produced in association with a $W$ boson in $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the $W$ boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the $WH$ production cross section times the $H\to b\overline{b}$ branching ratio as a function of Higgs boson mass. At a Higgs boson mass of $125\mathrm{GeV}/c^2$, we observe (expect) a limit of 4.9 (2.8) times the standard model value.

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a $b$ quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and $150\mathrm{GeV}/c^2$. For a Higgs boson mass of $125\mathrm{GeV}/c^2$, the observed (expected) limit is 6.7 (3.6) times the standard model prediction.

Exclusive ${\pi }^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and ${\varphi }_{\pi }$, in the $Q^2$ range from 1.0 to $4.6{\mathrm{GeV}}^2$, $-t$ up to $2{\mathrm{GeV}}^2$, and $x_B$ from 0.1 to 0.58. Structure functions ${\sigma }_T+ϵ{\sigma }_L$, ${\sigma }_{TT}$, and ${\sigma }_{LT}$ were extracted as functions of $t$ for each of 17 combinations of $Q^2$ and $x_B$. The data were compared directly with two handbag-based calculations including both longitudinal and transversity generalized parton distributions (GPDs). Inclusion of only longitudinal GPDs very strongly underestimates ${\sigma }_T+ϵ{\sigma }_L$ and fails to account for ${\sigma }_{TT}$ and ${\sigma }_{LT}$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity-flip and helicity nonflip processes. The results confirm that exclusive ${\pi }^0$ electroproduction offers direct experimental access to the transversity GPDs.

We analyzed the electrophysiological response of an isolated rod photoreceptor of Xenopus laevis under stimulation by coherent and pseudothermal light sources. Using the suction-electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim 4\mathrm{\text{−}}\mathrm{kJ}$, 2.5-ns laser pulses focused to an intensity of $\sim {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations.

Evaporation of a sessile droplet is a complex, nonequilibrium phenomenon. Although evaporating droplets upon superhydrophobic surfaces have been known to exhibit distinctive evaporation modes such as a constant contact line (CCL), a constant contact angle (CCA), or both, our fundamental understanding of the effects of surface roughness on the wetting transition remains elusive. We show that the onset time for the CCL-CCA transition and the critical base size at the Cassie-Wenzel transition exhibit remarkable dependence on the surface roughness. Through global interfacial energy analysis we reveal that, when the size of the evaporating droplet becomes comparable to the surface roughness, the line tension at the triple line becomes important in the prediction of the critical base size. Last, we show that both the CCL evaporation mode and the Cassie-Wenzel transition can be effectively inhibited by engineering a surface with hierarchical roughness.

With the advent of scanning probe microscopy techniques that involve a tip and a sample in relative motion in the contact or noncontact regime, the microscopic aspects of friction have become a major branch of research called nanotribology. A significant number of recent studies in this field have concentrated on the distinction between electronic and phononic contributions to friction. Here, we are using the combination of spin-polarized scanning tunneling microscopy and single-atom manipulation in order to move individual magnetic atoms over a magnetic template. By monitoring the spin-resolved manipulation traces and comparing them with results of Monte Carlo simulations, we are able to reveal the characteristic friction force variations resulting from the occurrence of spin friction on the atomic scale.

We present de Haas–van Alphen and resistivity data on single crystals of the delafossite ${\mathrm{PdCoO}}_2$. At 295 K we measure an in-plane resistivity of $2.6\mu \Omega \mathrm{cm}$, making ${\mathrm{PdCoO}}_2$ the most conductive oxide known. The low-temperature in-plane resistivity has an activated rather than the usual $T^5$ temperature dependence, suggesting a gapping of effective scattering that is consistent with phonon drag. Below 10 K, the transport mean free path is $\sim 20\mu \mathrm{m}$, approximately ${10}^5$ lattice spacings and an astoundingly high value for flux-grown crystals. We discuss the origin of these properties in light of our data.

Investigating quasiparticle excitations of molecules on surfaces through photoemission spectroscopy forms a major part of nanotechnology research. Resolving spectral features at these interfaces requires a comprehensive theory of electron removal and addition processes in molecules and solids which captures the complex interplay of image charges, thermal effects, and configurational disorder. Here, we develop such a theory and calculate the quasiparticle energy-level alignment and the valence photoemission spectrum for the prototype biomimetic solar cell interface between anatase ${\mathrm{TiO}}_2$ and the N3 chromophore. By directly matching our calculated photoemission spectrum to experimental data, we clarify the atomistic origin of the chromophore peak at low binding energy. This case study sets a new standard in the interpretation of photoemission spectroscopy at complex chromophore-semiconductor interfaces.

A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. ${}^{57}\mathrm{Fe}$ conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain.

The effects of the lattice strain induced by neutral oxygen vacancies in ferroelectric tetragonal ${\mathrm{BaTiO}}_3$ and ${\mathrm{KNbO}}_3$ are investigated using ab initio simulations. We propose that an oxygen vacancy can transform from its metastable equatorial configuration to the stable axial configuration via either diffusion or rotation of the polar axis near the vacancy site by $90°$. The latter mechanism, predicted to dominate in materials with slow oxygen vacancy diffusion and low formation energy of $90°$ domain walls, can stimulate the formation of domains with their polar axes pinned by the vacancies.

We introduce all-electrical cross-correlation spectroscopy of molecular number fluctuations in nanofluidic channels. Our approach is based on a pair of nanogap electrochemical transducers located downstream from each other in the channel. When liquid is driven through this device, mesoscopic fluctuations in the local density of molecules are transported along the channel. We perform a time-of-flight measurement of these fluctuations by cross-correlating current-time traces obtained at the two detectors. Thereby we are able to detect ultralow liquid flow rates below $10\mathrm{pL}/\min $. This method constitutes the electrical equivalent of fluorescence cross-correlation spectroscopy.