Graphene, made of $s{p}^2$ hybridized carbon, is characterized with a Dirac band, representative of its underlying 2D hexagonal lattice. The fundamental understanding of graphene has recently spurred a surge in the search for 2D topological quantum phases in solid-state materials. Here, we propose a new form of 2D material, consisting of $s{d}^2$ hybridized transition metal atoms in hexagonal lattice, called $s{d}^2$ “graphene.” The $s{d}^2$ graphene is characterized by bond-centered electronic hopping, which transforms the apparent atomic hexagonal lattice into the physics of a kagome lattice that may exhibit a wide range of topological quantum phases. Based on first-principles calculations, room-temperature quantum anomalous Hall states with an energy gap of $\sim 0.1\mathrm{eV}$ are demonstrated for one such lattice made of W, which can be epitaxially grown on a semiconductor surface of $1/3$ monolayer Cl-covered Si(111), with high thermodynamic and kinetic stability.

Using time-and angle-resolved photoemission spectroscopy, we determine directly energy-, momentum-, and time-resolved distributions of hot electrons photoinjected into the conduction band of GaAs, a prototypical direct-gap semiconductor. The nascent distributions of photoinjected electrons are captured for different pump photon energies and polarization. The evolutions of hot electron distributions in ultrafast intervalley scattering processes are resolved in momentum space with fs-temporal resolution, revealing an intervalley transition time as short as 20 fs.

We report the formation of a nonmagnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator ${\mathrm{LaTiO}}_3$ and the antiferromagnetic charge transfer insulator ${\mathrm{LaFeO}}_3$. By density-functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the $t_{2g}$ and $e_g$ bands. As a result of these two driving forces, the Fe $3d$ bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe $3d$ bands and reveals an unprecedented charge transfer up to $1.2\pm 0.2e^{-}/\text{interface}$ unit cell in our ${\mathrm{LaTiO}}_3/{\mathrm{LaFeO}}_3$ heterostructures.

The eukaryotic flagellum beats with apparently unfailing periodicity, yet responds rapidly to stimuli. Like the human heartbeat, flagellar oscillations are now known to be noisy. Using the alga C. reinhardtii, we explore three aspects of nonuniform flagellar beating. We report the existence of rhythmicity, waveform noise peaking at transitions between power and recovery strokes, and fluctuations of interbeat intervals that are correlated and even recurrent, with memory extending to hundreds of beats. These features are altered qualitatively by physiological perturbations. Further, we quantify the recovery of periodic breaststroke beating from transient hydrodynamic forcing. These results will help constrain microscopic theories on the origins and regulation of flagellar beating.

We present molecular dynamics simulations on the electrophoresis of a negative colloid grafted with positive polyelectrolytes. Net-neutral colloids show a varying mobility in monovalent salt. For colloids with negative net charge the mobility is negative at low and positive at high salt concentrations. This mobility reversal is an electrokinetic effect, and thus different from that observed in multivalent salt. Our results agree with numerical calculations based on the Darcy-Brinkman formalism, with which we predict the mobility reversal to also occur for experimentally accessible colloids.

The most conspicuous property of a semiflexible polymer is its persistence length, defined as the decay length of tangent correlations along its contour. Using an efficient stochastic growth algorithm to sample polymers embedded in a quenched hard-disk fluid, we find apparent wormlike chain statistics with a renormalized persistence length. We identify a universal form of the disorder renormalization that suggests itself as a quantitative measure of molecular crowding.

We study the starvation of a lattice random walker in which each site initially contains one food unit and the walker can travel $\mathcal{S}$ steps without food before starving. When the walker encounters food, it is completely eaten, and the walker can again travel $\mathcal{S}$ steps without food before starving. When the walker hits an empty site, the time until the walker starves decreases by 1. In spatial dimension $d=1$, the average lifetime of the walker $⟨\tau ⟩\propto \mathcal{S}$, while for $d>2$, $⟨\tau ⟩\simeq \exp ({\mathcal{S}}^{\omega })$, with $\omega \to 1$ as $d\to \infty$; the latter behavior suggests that the upper critical dimension is infinite. In the marginal case of $d=2$, $⟨\tau ⟩\propto {\mathcal{S}}^z$, with $z\approx 2$. Long-lived walks explore a highly ramified region so they always remain close to sources of food and the distribution of distinct sites visited does not obey single-parameter scaling.

We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive nonequilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are: (i) a power law rise of order and correlations after an initial collapse of the equilibrium state and (ii) a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches.

We introduce a superconducting qubit architecture that combines high-coherence qubits and tunable qubit-qubit coupling. With the ability to set the coupling to zero, we demonstrate that this architecture is protected from the frequency crowding problems that arise from fixed coupling. More importantly, the coupling can be tuned dynamically with nanosecond resolution, making this architecture a versatile platform with applications ranging from quantum logic gates to quantum simulation. We illustrate the advantages of dynamical coupling by implementing a novel adiabatic controlled-z gate, with a speed approaching that of single-qubit gates. Integrating coherence and scalable control, the introduced qubit architecture provides a promising path towards large-scale quantum computation and simulation.

We study analytically an intermittent search process in one dimension. There is an immobile target at the origin and a searcher undergoes a discrete time jump process starting at $x_0\ge 0$, where successive jumps are drawn independently from an arbitrary jump distribution $f(\eta )$. In addition, with a probability $0\le r<1$, the position of the searcher is reset to its initial position $x_0$. The efficiency of the search strategy is characterized by the mean time to find the target, i.e., the mean first passage time (MFPT) to the origin. For arbitrary jump distribution $f(\eta )$, initial position $x_0$ and resetting probability $r$, we compute analytically the MFPT. For the heavy-tailed Lévy stable jump distribution characterized by the Lévy index $0<\mu <2$, we show that, for any given $x_0$, the MFPT has a global minimum in the $(\mu ,r)$ plane at $\mathbf{(}{\mu }^{*}(x_0),r^{*}(x_0)\mathbf{)}$. We find a remarkable first-order phase transition as $x_0$ crosses a critical value $x_0^{*}$ at which the optimal parameters change discontinuously. Our analytical results are in good agreement with numerical simulations.

We report the first direct measurement of the overall characteristics of microwave radio emission from extensive air showers. Using a trigger provided by the KASCADE-Grande air shower array, the signals of the microwave antennas of the Cosmic-Ray Observation via Microwave Emission experiment have been read out and searched for signatures of radio emission by high-energy air showers in the GHz frequency range. Microwave signals have been detected for more than 30 showers with energies above $3\times {10}^{16}\mathrm{eV}$. The observations presented in this Letter are consistent with a mainly forward-directed and polarized emission process in the GHz frequency range. The measurements show that microwave radiation offers a new means of studying air showers at $E\ge {10}^{17}\mathrm{eV}$.

We present a measurement of the cosmic ray $(e^{+}+e^{-})$ flux in the range 0.5 GeV to 1 TeV based on the analysis of 10.6 million $(e^{+}+e^{-})$ events collected by AMS. The statistics and the resolution of AMS provide a precision measurement of the flux. The flux is smooth and reveals new and distinct information. Above 30.2 GeV, the flux can be described by a single power law with a spectral index $\gamma =-3.170\pm 0.008(\text{stat}+\text{syst})\pm 0.008(\text{energy}\text{scale})$.

With appropriate interpolating currents the mass spectrum of the $0^{--}$ oddball is obtained in the framework of QCD sum rules. We find there are two stable oddballs with masses of $3.81\pm 0.12$ and $4.33\pm 0.13\mathrm{GeV}$, and analyze their possible production and decay modes in experiments. Noticing that these $0^{--}$ oddballs with an unconventional quantum number are attainable in BESIII, BELLEII, PANDA, Super-B, and LHCb experiments, we believe the long searched for elusive glueball could be measured shortly.

Control of double ionization of He by means of the polarization and carrier-envelope phase (CEP) of an intense, few-cycle extreme ultraviolet (XUV) pulse is demonstrated numerically by solving the six-dimensional two-electron, time-dependent Schrödinger equation for He interacting with an elliptically polarized XUV pulse. Guided by perturbation theory (PT), we predict the existence of a nonlinear dichroic effect ($\propto I^{3/2}$) that is sensitive to the CEP, ellipticity, peak intensity $I$, and temporal duration of the pulse. This dichroic effect (i.e., the difference of the two-electron angular distributions for opposite helicities of the ionizing XUV pulse) originates from interference of first- and second-order PT amplitudes, allowing one to probe and control $S$- and $D$-wave channels of the two-electron continuum. We show that the back-to-back in-plane geometry with unequal energy sharing is an ideal one for observing this dichroic effect that occurs only for an elliptically polarized, few-cycle attosecond pulse.

We investigate the transient coherent transmission of light through an optically thick cold strontium gas. We observe a coherent superflash just after an abrupt probe extinction, with peak intensity more than three times the incident one. We show that this coherent superflash is a direct signature of the cooperative forward emission of the atoms. By engineering fast transient phenomena on the incident field, we give a clear and simple picture of the physical mechanisms at play.

The change of resonance widths in an open system under a perturbation of its interior has been recently introduced by Fyodorov and Savin [Phys. Rev. Lett. 108, 184101 (2012)] as a sensitive indicator of the nonorthogonality of resonance states. We experimentally study universal statistics of this quantity in weakly open two-dimensional microwave cavities and reverberation chambers realizing scalar and electromagnetic vector fields, respectively. We consider global as well as local perturbations, and also extend the theory to treat the latter case. The influence of the perturbation type on the width shift distribution is more pronounced for many-channel systems. We compare the theory to experimental results for one and two attached antennas and to numerical simulations with higher channel numbers, observing a good agreement in all cases.